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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// TODO(rsc): The code having to do with the heap bitmap needs very serious cleanup.
// It has gotten completely out of control.
// Garbage collector (GC).
//
// The GC runs concurrently with mutator threads, is type accurate (aka precise), allows multiple
// GC thread to run in parallel. It is a concurrent mark and sweep that uses a write barrier. It is
// non-generational and non-compacting. Allocation is done using size segregated per P allocation
// areas to minimize fragmentation while eliminating locks in the common case.
//
// The algorithm decomposes into several steps.
// This is a high level description of the algorithm being used. For an overview of GC a good
// place to start is Richard Jones' gchandbook.org.
//
// The algorithm's intellectual heritage includes Dijkstra's on-the-fly algorithm, see
// Edsger W. Dijkstra, Leslie Lamport, A. J. Martin, C. S. Scholten, and E. F. M. Steffens. 1978.
// On-the-fly garbage collection: an exercise in cooperation. Commun. ACM 21, 11 (November 1978),
// 966-975.
// For journal quality proofs that these steps are complete, correct, and terminate see
// Hudson, R., and Moss, J.E.B. Copying Garbage Collection without stopping the world.
// Concurrency and Computation: Practice and Experience 15(3-5), 2003.
//
// 0. Set phase = GCscan from GCoff.
// 1. Wait for all P's to acknowledge phase change.
// At this point all goroutines have passed through a GC safepoint and
// know we are in the GCscan phase.
// 2. GC scans all goroutine stacks, mark and enqueues all encountered pointers
// (marking avoids most duplicate enqueuing but races may produce benign duplication).
// Preempted goroutines are scanned before P schedules next goroutine.
// 3. Set phase = GCmark.
// 4. Wait for all P's to acknowledge phase change.
// 5. Now write barrier marks and enqueues black, grey, or white to white pointers.
// Malloc still allocates white (non-marked) objects.
// 6. Meanwhile GC transitively walks the heap marking reachable objects.
// 7. When GC finishes marking heap, it preempts P's one-by-one and
// retakes partial wbufs (filled by write barrier or during a stack scan of the goroutine
// currently scheduled on the P).
// 8. Once the GC has exhausted all available marking work it sets phase = marktermination.
// 9. Wait for all P's to acknowledge phase change.
// 10. Malloc now allocates black objects, so number of unmarked reachable objects
// monotonically decreases.
// 11. GC preempts P's one-by-one taking partial wbufs and marks all unmarked yet
// reachable objects.
// 12. When GC completes a full cycle over P's and discovers no new grey
// objects, (which means all reachable objects are marked) set phase = GCsweep.
// 13. Wait for all P's to acknowledge phase change.
// 14. Now malloc allocates white (but sweeps spans before use).
// Write barrier becomes nop.
// 15. GC does background sweeping, see description below.
// 16. When sweeping is complete set phase to GCoff.
// 17. When sufficient allocation has taken place replay the sequence starting at 0 above,
// see discussion of GC rate below.
// Changing phases.
// Phases are changed by setting the gcphase to the next phase and possibly calling ackgcphase.
// All phase action must be benign in the presence of a change.
// Starting with GCoff
// GCoff to GCscan
// GSscan scans stacks and globals greying them and never marks an object black.
// Once all the P's are aware of the new phase they will scan gs on preemption.
// This means that the scanning of preempted gs can't start until all the Ps
// have acknowledged.
// GCscan to GCmark
// GCMark turns on the write barrier which also only greys objects. No scanning
// of objects (making them black) can happen until all the Ps have acknowledged
// the phase change.
// GCmark to GCmarktermination
// The only change here is that we start allocating black so the Ps must acknowledge
// the change before we begin the termination algorithm
// GCmarktermination to GSsweep
// Object currently on the freelist must be marked black for this to work.
// Are things on the free lists black or white? How does the sweep phase work?
// Concurrent sweep.
// The sweep phase proceeds concurrently with normal program execution.
// The heap is swept span-by-span both lazily (when a goroutine needs another span)
// and concurrently in a background goroutine (this helps programs that are not CPU bound).
// However, at the end of the stop-the-world GC phase we don't know the size of the live heap,
// and so next_gc calculation is tricky and happens as follows.
// At the end of the stop-the-world phase next_gc is conservatively set based on total
// heap size; all spans are marked as "needs sweeping".
// Whenever a span is swept, next_gc is decremented by GOGC*newly_freed_memory.
// The background sweeper goroutine simply sweeps spans one-by-one bringing next_gc
// closer to the target value. However, this is not enough to avoid over-allocating memory.
// Consider that a goroutine wants to allocate a new span for a large object and
// there are no free swept spans, but there are small-object unswept spans.
// If the goroutine naively allocates a new span, it can surpass the yet-unknown
// target next_gc value. In order to prevent such cases (1) when a goroutine needs
// to allocate a new small-object span, it sweeps small-object spans for the same
// object size until it frees at least one object; (2) when a goroutine needs to
// allocate large-object span from heap, it sweeps spans until it frees at least
// that many pages into heap. Together these two measures ensure that we don't surpass
// target next_gc value by a large margin. There is an exception: if a goroutine sweeps
// and frees two nonadjacent one-page spans to the heap, it will allocate a new two-page span,
// but there can still be other one-page unswept spans which could be combined into a
// two-page span.
// It's critical to ensure that no operations proceed on unswept spans (that would corrupt
// mark bits in GC bitmap). During GC all mcaches are flushed into the central cache,
// so they are empty. When a goroutine grabs a new span into mcache, it sweeps it.
// When a goroutine explicitly frees an object or sets a finalizer, it ensures that
// the span is swept (either by sweeping it, or by waiting for the concurrent sweep to finish).
// The finalizer goroutine is kicked off only when all spans are swept.
// When the next GC starts, it sweeps all not-yet-swept spans (if any).
// GC rate.
// Next GC is after we've allocated an extra amount of memory proportional to
// the amount already in use. The proportion is controlled by GOGC environment variable
// (100 by default). If GOGC=100 and we're using 4M, we'll GC again when we get to 8M
// (this mark is tracked in next_gc variable). This keeps the GC cost in linear
// proportion to the allocation cost. Adjusting GOGC just changes the linear constant
// (and also the amount of extra memory used).
package runtime
import "unsafe"
const (
_DebugGC = 0
_DebugGCPtrs = false // if true, print trace of every pointer load during GC
_ConcurrentSweep = true
_WorkbufSize = 4 * 256
_FinBlockSize = 4 * 1024
_RootData = 0
_RootBss = 1
_RootFinalizers = 2
_RootSpans = 3
_RootFlushCaches = 4
_RootCount = 5
)
// ptrmask for an allocation containing a single pointer.
var oneptr = [...]uint8{bitsPointer}
// Initialized from $GOGC. GOGC=off means no GC.
var gcpercent int32
// Holding worldsema grants an M the right to try to stop the world.
// The procedure is:
//
// semacquire(&worldsema);
// m.gcing = 1;
// stoptheworld();
//
// ... do stuff ...
//
// m.gcing = 0;
// semrelease(&worldsema);
// starttheworld();
//
var worldsema uint32 = 1
// It is a bug if bits does not have bitBoundary set but
// there are still some cases where this happens related
// to stack spans.
type markbits struct {
bitp *byte // pointer to the byte holding xbits
shift uintptr // bits xbits needs to be shifted to get bits
xbits byte // byte holding all the bits from *bitp
bits byte // mark and boundary bits relevant to corresponding slot.
tbits byte // pointer||scalar bits relevant to corresponding slot.
}
type workbuf struct {
node lfnode // must be first
nobj uintptr
obj [(_WorkbufSize - unsafe.Sizeof(lfnode{}) - ptrSize) / ptrSize]uintptr
}
var data, edata, bss, ebss, gcdata, gcbss struct{}
var finlock mutex // protects the following variables
var fing *g // goroutine that runs finalizers
var finq *finblock // list of finalizers that are to be executed
var finc *finblock // cache of free blocks
var finptrmask [_FinBlockSize / ptrSize / pointersPerByte]byte
var fingwait bool
var fingwake bool
var allfin *finblock // list of all blocks
var gcdatamask bitvector
var gcbssmask bitvector
var gclock mutex
var badblock [1024]uintptr
var nbadblock int32
type workdata struct {
full uint64 // lock-free list of full blocks workbuf
empty uint64 // lock-free list of empty blocks workbuf
partial uint64 // lock-free list of partially filled blocks workbuf
pad0 [_CacheLineSize]uint8 // prevents false-sharing between full/empty and nproc/nwait
nproc uint32
tstart int64
nwait uint32
ndone uint32
alldone note
markfor *parfor
// Copy of mheap.allspans for marker or sweeper.
spans []*mspan
}
var work workdata
//go:linkname weak_cgo_allocate go.weak.runtime._cgo_allocate_internal
var weak_cgo_allocate byte
// Is _cgo_allocate linked into the binary?
//go:nowritebarrier
func have_cgo_allocate() bool {
return &weak_cgo_allocate != nil
}
// To help debug the concurrent GC we remark with the world
// stopped ensuring that any object encountered has their normal
// mark bit set. To do this we use an orthogonal bit
// pattern to indicate the object is marked. The following pattern
// uses the upper two bits in the object's bounday nibble.
// 01: scalar not marked
// 10: pointer not marked
// 11: pointer marked
// 00: scalar marked
// Xoring with 01 will flip the pattern from marked to unmarked and vica versa.
// The higher bit is 1 for pointers and 0 for scalars, whether the object
// is marked or not.
// The first nibble no longer holds the bitsDead pattern indicating that the
// there are no more pointers in the object. This information is held
// in the second nibble.
// When marking an object if the bool checkmark is true one uses the above
// encoding, otherwise one uses the bitMarked bit in the lower two bits
// of the nibble.
var (
checkmark = false
gccheckmarkenable = true
)
// inheap reports whether b is a pointer into a (potentially dead) heap object.
// It returns false for pointers into stack spans.
//go:nowritebarrier
func inheap(b uintptr) bool {
if b == 0 || b < mheap_.arena_start || b >= mheap_.arena_used {
return false
}
// Not a beginning of a block, consult span table to find the block beginning.
k := b >> _PageShift
x := k
x -= mheap_.arena_start >> _PageShift
s := h_spans[x]
if s == nil || pageID(k) < s.start || b >= s.limit || s.state != mSpanInUse {
return false
}
return true
}
// Given an address in the heap return the relevant byte from the gcmap. This routine
// can be used on addresses to the start of an object or to the interior of the an object.
//go:nowritebarrier
func slottombits(obj uintptr, mbits *markbits) {
off := (obj&^(ptrSize-1) - mheap_.arena_start) / ptrSize
*(*uintptr)(unsafe.Pointer(&mbits.bitp)) = mheap_.arena_start - off/wordsPerBitmapByte - 1
mbits.shift = off % wordsPerBitmapByte * gcBits
mbits.xbits = *mbits.bitp
mbits.bits = (mbits.xbits >> mbits.shift) & bitMask
mbits.tbits = ((mbits.xbits >> mbits.shift) & bitPtrMask) >> 2
}
// b is a pointer into the heap.
// Find the start of the object refered to by b.
// Set mbits to the associated bits from the bit map.
// If b is not a valid heap object return nil and
// undefined values in mbits.
//go:nowritebarrier
func objectstart(b uintptr, mbits *markbits) uintptr {
obj := b &^ (ptrSize - 1)
for {
slottombits(obj, mbits)
if mbits.bits&bitBoundary == bitBoundary {
break
}
// Not a beginning of a block, consult span table to find the block beginning.
k := b >> _PageShift
x := k
x -= mheap_.arena_start >> _PageShift
s := h_spans[x]
if s == nil || pageID(k) < s.start || b >= s.limit || s.state != mSpanInUse {
if s != nil && s.state == _MSpanStack {
return 0 // This is legit.
}
// The following ensures that we are rigorous about what data
// structures hold valid pointers
if false {
// Still happens sometimes. We don't know why.
printlock()
print("runtime:objectstart Span weird: obj=", hex(obj), " k=", hex(k))
if s == nil {
print(" s=nil\n")
} else {
print(" s.start=", hex(s.start<<_PageShift), " s.limit=", hex(s.limit), " s.state=", s.state, "\n")
}
printunlock()
throw("objectstart: bad pointer in unexpected span")
}
return 0
}
p := uintptr(s.start) << _PageShift
if s.sizeclass != 0 {
size := s.elemsize
idx := (obj - p) / size
p = p + idx*size
}
if p == obj {
print("runtime: failed to find block beginning for ", hex(p), " s=", hex(s.start*_PageSize), " s.limit=", hex(s.limit), "\n")
throw("failed to find block beginning")
}
obj = p
}
// if size(obj.firstfield) < PtrSize, the &obj.secondfield could map to the boundary bit
// Clear any low bits to get to the start of the object.
// greyobject depends on this.
return obj
}
// Slow for now as we serialize this, since this is on a debug path
// speed is not critical at this point.
var andlock mutex
//go:nowritebarrier
func atomicand8(src *byte, val byte) {
lock(&andlock)
*src &= val
unlock(&andlock)
}
// Mark using the checkmark scheme.
//go:nowritebarrier
func docheckmark(mbits *markbits) {
// xor 01 moves 01(scalar unmarked) to 00(scalar marked)
// and 10(pointer unmarked) to 11(pointer marked)
if mbits.tbits == _BitsScalar {
atomicand8(mbits.bitp, ^byte(_BitsCheckMarkXor<<mbits.shift<<2))
} else if mbits.tbits == _BitsPointer {
atomicor8(mbits.bitp, byte(_BitsCheckMarkXor<<mbits.shift<<2))
}
// reload bits for ischeckmarked
mbits.xbits = *mbits.bitp
mbits.bits = (mbits.xbits >> mbits.shift) & bitMask
mbits.tbits = ((mbits.xbits >> mbits.shift) & bitPtrMask) >> 2
}
// In the default scheme does mbits refer to a marked object.
//go:nowritebarrier
func ismarked(mbits *markbits) bool {
if mbits.bits&bitBoundary != bitBoundary {
throw("ismarked: bits should have boundary bit set")
}
return mbits.bits&bitMarked == bitMarked
}
// In the checkmark scheme does mbits refer to a marked object.
//go:nowritebarrier
func ischeckmarked(mbits *markbits) bool {
if mbits.bits&bitBoundary != bitBoundary {
throw("ischeckmarked: bits should have boundary bit set")
}
return mbits.tbits == _BitsScalarMarked || mbits.tbits == _BitsPointerMarked
}
// When in GCmarkterminate phase we allocate black.
//go:nowritebarrier
func gcmarknewobject_m(obj uintptr) {
if gcphase != _GCmarktermination {
throw("marking new object while not in mark termination phase")
}
if checkmark { // The world should be stopped so this should not happen.
throw("gcmarknewobject called while doing checkmark")
}
var mbits markbits
slottombits(obj, &mbits)
if mbits.bits&bitMarked != 0 {
return
}
// Each byte of GC bitmap holds info for two words.
// If the current object is larger than two words, or if the object is one word
// but the object it shares the byte with is already marked,
// then all the possible concurrent updates are trying to set the same bit,
// so we can use a non-atomic update.
if mbits.xbits&(bitMask|(bitMask<<gcBits)) != bitBoundary|bitBoundary<<gcBits || work.nproc == 1 {
*mbits.bitp = mbits.xbits | bitMarked<<mbits.shift
} else {
atomicor8(mbits.bitp, bitMarked<<mbits.shift)
}
}
// obj is the start of an object with mark mbits.
// If it isn't already marked, mark it and enqueue into workbuf.
// Return possibly new workbuf to use.
// base and off are for debugging only and could be removed.
//go:nowritebarrier
func greyobject(obj uintptr, base, off uintptr, mbits *markbits, wbuf *workbuf) *workbuf {
// obj should be start of allocation, and so must be at least pointer-aligned.
if obj&(ptrSize-1) != 0 {
throw("greyobject: obj not pointer-aligned")
}
if checkmark {
if !ismarked(mbits) {
print("runtime:greyobject: checkmarks finds unexpected unmarked object obj=", hex(obj), ", mbits->bits=", hex(mbits.bits), " *mbits->bitp=", hex(*mbits.bitp), "\n")
print("runtime: found obj at *(", hex(base), "+", hex(off), ")\n")
k := obj >> _PageShift
x := k
x -= mheap_.arena_start >> _PageShift
s := h_spans[x]
printlock()
print("runtime:greyobject Span: obj=", hex(obj), " k=", hex(k))
if s == nil {
print(" s=nil\n")
} else {
print(" s.start=", hex(s.start*_PageSize), " s.limit=", hex(s.limit), " s.sizeclass=", s.sizeclass, " s.elemsize=", s.elemsize, "\n")
// NOTE(rsc): This code is using s.sizeclass as an approximation of the
// number of pointer-sized words in an object. Perhaps not what was intended.
for i := 0; i < int(s.sizeclass); i++ {
print(" *(obj+", i*ptrSize, ") = ", hex(*(*uintptr)(unsafe.Pointer(obj + uintptr(i)*ptrSize))), "\n")
}
}
throw("checkmark found unmarked object")
}
if ischeckmarked(mbits) {
return wbuf
}
docheckmark(mbits)
if !ischeckmarked(mbits) {
print("mbits xbits=", hex(mbits.xbits), " bits=", hex(mbits.bits), " tbits=", hex(mbits.tbits), " shift=", mbits.shift, "\n")
throw("docheckmark and ischeckmarked disagree")
}
} else {
// If marked we have nothing to do.
if mbits.bits&bitMarked != 0 {
return wbuf
}
// Each byte of GC bitmap holds info for two words.
// If the current object is larger than two words, or if the object is one word
// but the object it shares the byte with is already marked,
// then all the possible concurrent updates are trying to set the same bit,
// so we can use a non-atomic update.
if mbits.xbits&(bitMask|bitMask<<gcBits) != bitBoundary|bitBoundary<<gcBits || work.nproc == 1 {
*mbits.bitp = mbits.xbits | bitMarked<<mbits.shift
} else {
atomicor8(mbits.bitp, bitMarked<<mbits.shift)
}
}
if !checkmark && (mbits.xbits>>(mbits.shift+2))&_BitsMask == _BitsDead {
return wbuf // noscan object
}
// Queue the obj for scanning. The PREFETCH(obj) logic has been removed but
// seems like a nice optimization that can be added back in.
// There needs to be time between the PREFETCH and the use.
// Previously we put the obj in an 8 element buffer that is drained at a rate
// to give the PREFETCH time to do its work.
// Use of PREFETCHNTA might be more appropriate than PREFETCH
// If workbuf is full, obtain an empty one.
if wbuf.nobj >= uintptr(len(wbuf.obj)) {
wbuf = getempty(wbuf)
}
wbuf.obj[wbuf.nobj] = obj
wbuf.nobj++
return wbuf
}
// Scan the object b of size n, adding pointers to wbuf.
// Return possibly new wbuf to use.
// If ptrmask != nil, it specifies where pointers are in b.
// If ptrmask == nil, the GC bitmap should be consulted.
// In this case, n may be an overestimate of the size; the GC bitmap
// must also be used to make sure the scan stops at the end of b.
//go:nowritebarrier
func scanobject(b, n uintptr, ptrmask *uint8, wbuf *workbuf) *workbuf {
arena_start := mheap_.arena_start
arena_used := mheap_.arena_used
// Find bits of the beginning of the object.
var ptrbitp unsafe.Pointer
var mbits markbits
if ptrmask == nil {
b = objectstart(b, &mbits)
if b == 0 {
return wbuf
}
ptrbitp = unsafe.Pointer(mbits.bitp)
}
for i := uintptr(0); i < n; i += ptrSize {
// Find bits for this word.
var bits uintptr
if ptrmask != nil {
// dense mask (stack or data)
bits = (uintptr(*(*byte)(add(unsafe.Pointer(ptrmask), (i/ptrSize)/4))) >> (((i / ptrSize) % 4) * bitsPerPointer)) & bitsMask
} else {
// Check if we have reached end of span.
// n is an overestimate of the size of the object.
if (b+i)%_PageSize == 0 && h_spans[(b-arena_start)>>_PageShift] != h_spans[(b+i-arena_start)>>_PageShift] {
break
}
// Consult GC bitmap.
bits = uintptr(*(*byte)(ptrbitp))
if wordsPerBitmapByte != 2 {
throw("alg doesn't work for wordsPerBitmapByte != 2")
}
j := (uintptr(b) + i) / ptrSize & 1 // j indicates upper nibble or lower nibble
bits >>= gcBits * j
if i == 0 {
bits &^= bitBoundary
}
ptrbitp = add(ptrbitp, -j)
if bits&bitBoundary != 0 && i != 0 {
break // reached beginning of the next object
}
bits = (bits & bitPtrMask) >> 2 // bits refer to the type bits.
if i != 0 && bits == bitsDead { // BitsDead in first nibble not valid during checkmark
break // reached no-scan part of the object
}
}
if bits <= _BitsScalar { // _BitsScalar, _BitsDead, _BitsScalarMarked
continue
}
if bits&_BitsPointer != _BitsPointer {
print("gc checkmark=", checkmark, " b=", hex(b), " ptrmask=", ptrmask, " mbits.bitp=", mbits.bitp, " mbits.xbits=", hex(mbits.xbits), " bits=", hex(bits), "\n")
throw("unexpected garbage collection bits")
}
obj := *(*uintptr)(unsafe.Pointer(b + i))
// At this point we have extracted the next potential pointer.
// Check if it points into heap.
if obj == 0 || obj < arena_start || obj >= arena_used {
continue
}
if mheap_.shadow_enabled && debug.wbshadow >= 2 && gccheckmarkenable && checkmark {
checkwbshadow((*uintptr)(unsafe.Pointer(b + i)))
}
// Mark the object. return some important bits.
// We we combine the following two rotines we don't have to pass mbits or obj around.
var mbits markbits
obj = objectstart(obj, &mbits)
if obj == 0 {
continue
}
wbuf = greyobject(obj, b, i, &mbits, wbuf)
}
return wbuf
}
// scanblock starts by scanning b as scanobject would.
// If the gcphase is GCscan, that's all scanblock does.
// Otherwise it traverses some fraction of the pointers it found in b, recursively.
// As a special case, scanblock(nil, 0, nil) means to scan previously queued work,
// stopping only when no work is left in the system.
//go:nowritebarrier
func scanblock(b0, n0 uintptr, ptrmask *uint8) {
// Use local copies of original parameters, so that a stack trace
// due to one of the throws below shows the original block
// base and extent.
b := b0
n := n0
// ptrmask can have 2 possible values:
// 1. nil - obtain pointer mask from GC bitmap.
// 2. pointer to a compact mask (for stacks and data).
wbuf := getpartialorempty()
if b != 0 {
wbuf = scanobject(b, n, ptrmask, wbuf)
if gcphase == _GCscan {
if inheap(b) && ptrmask == nil {
// b is in heap, we are in GCscan so there should be a ptrmask.
throw("scanblock: In GCscan phase and inheap is true.")
}
// GCscan only goes one level deep since mark wb not turned on.
putpartial(wbuf)
return
}
}
drainallwbufs := b == 0
drainworkbuf(wbuf, drainallwbufs)
}
// Scan objects in wbuf until wbuf is empty.
// If drainallwbufs is true find all other available workbufs and repeat the process.
//go:nowritebarrier
func drainworkbuf(wbuf *workbuf, drainallwbufs bool) {
if gcphase != _GCmark && gcphase != _GCmarktermination {
println("gcphase", gcphase)
throw("scanblock phase")
}
for {
if wbuf.nobj == 0 {
if !drainallwbufs {
putempty(wbuf)
return
}
// Refill workbuf from global queue.
wbuf = getfull(wbuf)
if wbuf == nil { // nil means out of work barrier reached
return
}
if wbuf.nobj <= 0 {
throw("runtime:scanblock getfull returns empty buffer")
}
}
// If another proc wants a pointer, give it some.
if work.nwait > 0 && wbuf.nobj > 4 && work.full == 0 {
wbuf = handoff(wbuf)
}
// This might be a good place to add prefetch code...
// if(wbuf->nobj > 4) {
// PREFETCH(wbuf->obj[wbuf->nobj - 3];
// }
wbuf.nobj--
b := wbuf.obj[wbuf.nobj]
wbuf = scanobject(b, mheap_.arena_used-b, nil, wbuf)
}
}
// Scan at most count objects in the wbuf.
//go:nowritebarrier
func drainobjects(wbuf *workbuf, count uintptr) {
for i := uintptr(0); i < count; i++ {
if wbuf.nobj == 0 {
putempty(wbuf)
return
}
// This might be a good place to add prefetch code...
// if(wbuf->nobj > 4) {
// PREFETCH(wbuf->obj[wbuf->nobj - 3];
// }
wbuf.nobj--
b := wbuf.obj[wbuf.nobj]
wbuf = scanobject(b, mheap_.arena_used-b, nil, wbuf)
}
putpartial(wbuf)
return
}
//go:nowritebarrier
func markroot(desc *parfor, i uint32) {
// Note: if you add a case here, please also update heapdump.c:dumproots.
switch i {
case _RootData:
scanblock(uintptr(unsafe.Pointer(&data)), uintptr(unsafe.Pointer(&edata))-uintptr(unsafe.Pointer(&data)), gcdatamask.bytedata)
case _RootBss:
scanblock(uintptr(unsafe.Pointer(&bss)), uintptr(unsafe.Pointer(&ebss))-uintptr(unsafe.Pointer(&bss)), gcbssmask.bytedata)
case _RootFinalizers:
for fb := allfin; fb != nil; fb = fb.alllink {
scanblock(uintptr(unsafe.Pointer(&fb.fin[0])), uintptr(fb.cnt)*unsafe.Sizeof(fb.fin[0]), &finptrmask[0])
}
case _RootSpans:
// mark MSpan.specials
sg := mheap_.sweepgen
for spanidx := uint32(0); spanidx < uint32(len(work.spans)); spanidx++ {
s := work.spans[spanidx]
if s.state != mSpanInUse {
continue
}
if !checkmark && s.sweepgen != sg {
// sweepgen was updated (+2) during non-checkmark GC pass
print("sweep ", s.sweepgen, " ", sg, "\n")
throw("gc: unswept span")
}
for sp := s.specials; sp != nil; sp = sp.next {
if sp.kind != _KindSpecialFinalizer {
continue
}
// don't mark finalized object, but scan it so we
// retain everything it points to.
spf := (*specialfinalizer)(unsafe.Pointer(sp))
// A finalizer can be set for an inner byte of an object, find object beginning.
p := uintptr(s.start<<_PageShift) + uintptr(spf.special.offset)/s.elemsize*s.elemsize
if gcphase != _GCscan {
scanblock(p, s.elemsize, nil) // scanned during mark phase
}
scanblock(uintptr(unsafe.Pointer(&spf.fn)), ptrSize, &oneptr[0])
}
}
case _RootFlushCaches:
if gcphase != _GCscan { // Do not flush mcaches during GCscan phase.
flushallmcaches()
}
default:
// the rest is scanning goroutine stacks
if uintptr(i-_RootCount) >= allglen {
throw("markroot: bad index")
}
gp := allgs[i-_RootCount]
// remember when we've first observed the G blocked
// needed only to output in traceback
status := readgstatus(gp) // We are not in a scan state
if (status == _Gwaiting || status == _Gsyscall) && gp.waitsince == 0 {
gp.waitsince = work.tstart
}
// Shrink a stack if not much of it is being used but not in the scan phase.
if gcphase != _GCscan { // Do not shrink during GCscan phase.
shrinkstack(gp)
}
if readgstatus(gp) == _Gdead {
gp.gcworkdone = true
} else {
gp.gcworkdone = false
}
restart := stopg(gp)
// goroutine will scan its own stack when it stops running.
// Wait until it has.
for readgstatus(gp) == _Grunning && !gp.gcworkdone {
}
// scanstack(gp) is done as part of gcphasework
// But to make sure we finished we need to make sure that
// the stack traps have all responded so drop into
// this while loop until they respond.
for !gp.gcworkdone {
status = readgstatus(gp)
if status == _Gdead {
gp.gcworkdone = true // scan is a noop
break
}
if status == _Gwaiting || status == _Grunnable {
restart = stopg(gp)
}
}
if restart {
restartg(gp)
}
}
}
// Get an empty work buffer off the work.empty list,
// allocating new buffers as needed.
//go:nowritebarrier
func getempty(b *workbuf) *workbuf {
if b != nil {
putfull(b)
b = nil
}
if work.empty != 0 {
b = (*workbuf)(lfstackpop(&work.empty))
}
if b != nil && b.nobj != 0 {
_g_ := getg()
print("m", _g_.m.id, ": getempty: popped b=", b, " with non-zero b.nobj=", b.nobj, "\n")
throw("getempty: workbuffer not empty, b->nobj not 0")
}
if b == nil {
b = (*workbuf)(persistentalloc(unsafe.Sizeof(*b), _CacheLineSize, &memstats.gc_sys))
b.nobj = 0
}
return b
}
//go:nowritebarrier
func putempty(b *workbuf) {
if b.nobj != 0 {
throw("putempty: b->nobj not 0")
}
lfstackpush(&work.empty, &b.node)
}
//go:nowritebarrier
func putfull(b *workbuf) {
if b.nobj <= 0 {
throw("putfull: b->nobj <= 0")
}
lfstackpush(&work.full, &b.node)
}
// Get an partially empty work buffer
// if none are available get an empty one.
//go:nowritebarrier
func getpartialorempty() *workbuf {
b := (*workbuf)(lfstackpop(&work.partial))
if b == nil {
b = getempty(nil)
}
return b
}
//go:nowritebarrier
func putpartial(b *workbuf) {
if b.nobj == 0 {
lfstackpush(&work.empty, &b.node)
} else if b.nobj < uintptr(len(b.obj)) {
lfstackpush(&work.partial, &b.node)
} else if b.nobj == uintptr(len(b.obj)) {
lfstackpush(&work.full, &b.node)
} else {
print("b=", b, " b.nobj=", b.nobj, " len(b.obj)=", len(b.obj), "\n")
throw("putpartial: bad Workbuf b.nobj")
}
}
// trygetfull tries to get a full or partially empty workbuffer.
// if one is not immediately available return nil
//go:nowritebarrier
func trygetfull() *workbuf {
wbuf := (*workbuf)(lfstackpop(&work.full))
if wbuf == nil {
wbuf = (*workbuf)(lfstackpop(&work.partial))
}
return wbuf
}
// Get a full work buffer off the work.full or a partially
// filled one off the work.partial list. If nothing is available
// wait until all the other gc helpers have finished and then
// return nil.
// getfull acts as a barrier for work.nproc helpers. As long as one
// gchelper is actively marking objects it
// may create a workbuffer that the other helpers can work on.
// The for loop either exits when a work buffer is found
// or when _all_ of the work.nproc GC helpers are in the loop
// looking for work and thus not capable of creating new work.
// This is in fact the termination condition for the STW mark
// phase.
//go:nowritebarrier
func getfull(b *workbuf) *workbuf {
if b != nil {
putempty(b)
}
b = (*workbuf)(lfstackpop(&work.full))
if b == nil {
b = (*workbuf)(lfstackpop(&work.partial))
}
if b != nil || work.nproc == 1 {
return b
}
xadd(&work.nwait, +1)
for i := 0; ; i++ {
if work.full != 0 {
xadd(&work.nwait, -1)
b = (*workbuf)(lfstackpop(&work.full))
if b == nil {
b = (*workbuf)(lfstackpop(&work.partial))
}
if b != nil {
return b
}
xadd(&work.nwait, +1)
}
if work.nwait == work.nproc {
return nil
}
_g_ := getg()
if i < 10 {
_g_.m.gcstats.nprocyield++
procyield(20)
} else if i < 20 {
_g_.m.gcstats.nosyield++
osyield()
} else {
_g_.m.gcstats.nsleep++
usleep(100)
}
}
}
//go:nowritebarrier
func handoff(b *workbuf) *workbuf {
// Make new buffer with half of b's pointers.
b1 := getempty(nil)
n := b.nobj / 2
b.nobj -= n
b1.nobj = n
memmove(unsafe.Pointer(&b1.obj[0]), unsafe.Pointer(&b.obj[b.nobj]), n*unsafe.Sizeof(b1.obj[0]))
_g_ := getg()
_g_.m.gcstats.nhandoff++
_g_.m.gcstats.nhandoffcnt += uint64(n)
// Put b on full list - let first half of b get stolen.
lfstackpush(&work.full, &b.node)
return b1
}
//go:nowritebarrier
func stackmapdata(stkmap *stackmap, n int32) bitvector {
if n < 0 || n >= stkmap.n {
throw("stackmapdata: index out of range")
}
return bitvector{stkmap.nbit, (*byte)(add(unsafe.Pointer(&stkmap.bytedata), uintptr(n*((stkmap.nbit+31)/32*4))))}
}
// Scan a stack frame: local variables and function arguments/results.
//go:nowritebarrier
func scanframe(frame *stkframe, unused unsafe.Pointer) bool {
f := frame.fn
targetpc := frame.continpc
if targetpc == 0 {
// Frame is dead.
return true
}
if _DebugGC > 1 {
print("scanframe ", funcname(f), "\n")
}
if targetpc != f.entry {
targetpc--
}
pcdata := pcdatavalue(f, _PCDATA_StackMapIndex, targetpc)
if pcdata == -1 {
// We do not have a valid pcdata value but there might be a
// stackmap for this function. It is likely that we are looking
// at the function prologue, assume so and hope for the best.
pcdata = 0
}
// Scan local variables if stack frame has been allocated.
size := frame.varp - frame.sp
var minsize uintptr
if thechar != '6' && thechar != '8' {
minsize = ptrSize
} else {
minsize = 0
}
if size > minsize {
stkmap := (*stackmap)(funcdata(f, _FUNCDATA_LocalsPointerMaps))
if stkmap == nil || stkmap.n <= 0 {
print("runtime: frame ", funcname(f), " untyped locals ", hex(frame.varp-size), "+", hex(size), "\n")
throw("missing stackmap")
}
// Locals bitmap information, scan just the pointers in locals.
if pcdata < 0 || pcdata >= stkmap.n {
// don't know where we are
print("runtime: pcdata is ", pcdata, " and ", stkmap.n, " locals stack map entries for ", funcname(f), " (targetpc=", targetpc, ")\n")
throw("scanframe: bad symbol table")
}
bv := stackmapdata(stkmap, pcdata)
size = (uintptr(bv.n) * ptrSize) / bitsPerPointer
scanblock(frame.varp-size, uintptr(bv.n)/bitsPerPointer*ptrSize, bv.bytedata)
}
// Scan arguments.
if frame.arglen > 0 {
var bv bitvector
if frame.argmap != nil {
bv = *frame.argmap
} else {
stkmap := (*stackmap)(funcdata(f, _FUNCDATA_ArgsPointerMaps))
if stkmap == nil || stkmap.n <= 0 {
print("runtime: frame ", funcname(f), " untyped args ", hex(frame.argp), "+", hex(frame.arglen), "\n")
throw("missing stackmap")
}
if pcdata < 0 || pcdata >= stkmap.n {
// don't know where we are
print("runtime: pcdata is ", pcdata, " and ", stkmap.n, " args stack map entries for ", funcname(f), " (targetpc=", targetpc, ")\n")
throw("scanframe: bad symbol table")
}
bv = stackmapdata(stkmap, pcdata)
}
scanblock(frame.argp, uintptr(bv.n)/bitsPerPointer*ptrSize, bv.bytedata)
}
return true
}
//go:nowritebarrier
func scanstack(gp *g) {
if readgstatus(gp)&_Gscan == 0 {
print("runtime:scanstack: gp=", gp, ", goid=", gp.goid, ", gp->atomicstatus=", hex(readgstatus(gp)), "\n")
throw("scanstack - bad status")
}
switch readgstatus(gp) &^ _Gscan {
default:
print("runtime: gp=", gp, ", goid=", gp.goid, ", gp->atomicstatus=", readgstatus(gp), "\n")
throw("mark - bad status")
case _Gdead:
return
case _Grunning:
print("runtime: gp=", gp, ", goid=", gp.goid, ", gp->atomicstatus=", readgstatus(gp), "\n")
throw("scanstack: goroutine not stopped")
case _Grunnable, _Gsyscall, _Gwaiting:
// ok
}
if gp == getg() {
throw("can't scan our own stack")
}
mp := gp.m
if mp != nil && mp.helpgc != 0 {
throw("can't scan gchelper stack")
}
gentraceback(^uintptr(0), ^uintptr(0), 0, gp, 0, nil, 0x7fffffff, scanframe, nil, 0)
tracebackdefers(gp, scanframe, nil)
}
// If the slot is grey or black return true, if white return false.
// If the slot is not in the known heap and thus does not have a valid GC bitmap then
// it is considered grey. Globals and stacks can hold such slots.
// The slot is grey if its mark bit is set and it is enqueued to be scanned.
// The slot is black if it has already been scanned.
// It is white if it has a valid mark bit and the bit is not set.
//go:nowritebarrier
func shaded(slot uintptr) bool {
if !inheap(slot) { // non-heap slots considered grey
return true
}
var mbits markbits
valid := objectstart(slot, &mbits)
if valid == 0 {
return true
}
if checkmark {
return ischeckmarked(&mbits)
}
return mbits.bits&bitMarked != 0
}
// Shade the object if it isn't already.
// The object is not nil and known to be in the heap.
//go:nowritebarrier
func shade(b uintptr) {
if !inheap(b) {
throw("shade: passed an address not in the heap")
}
wbuf := getpartialorempty()
// Mark the object, return some important bits.
// If we combine the following two rotines we don't have to pass mbits or obj around.
var mbits markbits
obj := objectstart(b, &mbits)
if obj != 0 {
wbuf = greyobject(obj, 0, 0, &mbits, wbuf) // augments the wbuf
}
putpartial(wbuf)
}
// This is the Dijkstra barrier coarsened to always shade the ptr (dst) object.
// The original Dijkstra barrier only shaded ptrs being placed in black slots.
//
// Shade indicates that it has seen a white pointer by adding the referent
// to wbuf as well as marking it.
//
// slot is the destination (dst) in go code
// ptr is the value that goes into the slot (src) in the go code
//
// Dijkstra pointed out that maintaining the no black to white
// pointers means that white to white pointers not need
// to be noted by the write barrier. Furthermore if either
// white object dies before it is reached by the
// GC then the object can be collected during this GC cycle
// instead of waiting for the next cycle. Unfortunately the cost of
// ensure that the object holding the slot doesn't concurrently
// change to black without the mutator noticing seems prohibitive.
//
// Consider the following example where the mutator writes into
// a slot and then loads the slot's mark bit while the GC thread
// writes to the slot's mark bit and then as part of scanning reads
// the slot.
//
// Initially both [slot] and [slotmark] are 0 (nil)
// Mutator thread GC thread
// st [slot], ptr st [slotmark], 1
//
// ld r1, [slotmark] ld r2, [slot]
//
// This is a classic example of independent reads of independent writes,
// aka IRIW. The question is if r1==r2==0 is allowed and for most HW the
// answer is yes without inserting a memory barriers between the st and the ld.
// These barriers are expensive so we have decided that we will
// always grey the ptr object regardless of the slot's color.
//go:nowritebarrier
func gcmarkwb_m(slot *uintptr, ptr uintptr) {
switch gcphase {
default:
throw("gcphasework in bad gcphase")
case _GCoff, _GCquiesce, _GCstw, _GCsweep, _GCscan:
// ok
case _GCmark, _GCmarktermination:
if ptr != 0 && inheap(ptr) {
shade(ptr)
}
}
}
// gchelpwork does a small bounded amount of gc work. The purpose is to
// shorten the time (as measured by allocations) spent doing a concurrent GC.
// The number of mutator calls is roughly propotional to the number of allocations
// made by that mutator. This slows down the allocation while speeding up the GC.
//go:nowritebarrier
func gchelpwork() {
switch gcphase {
default:
throw("gcphasework in bad gcphase")
case _GCoff, _GCquiesce, _GCstw:
// No work.
case _GCsweep:
// We could help by calling sweepone to sweep a single span.
// _ = sweepone()
case _GCscan:
// scan the stack, mark the objects, put pointers in work buffers
// hanging off the P where this is being run.
// scanstack(gp)
case _GCmark:
// Get a full work buffer and empty it.
var wbuf *workbuf
wbuf = trygetfull()
if wbuf != nil {
drainobjects(wbuf, uintptr(len(wbuf.obj))) // drain upto one buffer's worth of objects
}
case _GCmarktermination:
// We should never be here since the world is stopped.
// All available mark work will be emptied before returning.
throw("gcphasework in bad gcphase")
}
}
// The gp has been moved to a GC safepoint. GC phase specific
// work is done here.
//go:nowritebarrier
func gcphasework(gp *g) {
switch gcphase {
default:
throw("gcphasework in bad gcphase")
case _GCoff, _GCquiesce, _GCstw, _GCsweep:
// No work.
case _GCscan:
// scan the stack, mark the objects, put pointers in work buffers
// hanging off the P where this is being run.
scanstack(gp)
case _GCmark:
// No work.
case _GCmarktermination:
scanstack(gp)
// All available mark work will be emptied before returning.
}
gp.gcworkdone = true
}
var finalizer1 = [...]byte{
// Each Finalizer is 5 words, ptr ptr uintptr ptr ptr.
// Each byte describes 4 words.
// Need 4 Finalizers described by 5 bytes before pattern repeats:
// ptr ptr uintptr ptr ptr
// ptr ptr uintptr ptr ptr
// ptr ptr uintptr ptr ptr
// ptr ptr uintptr ptr ptr
// aka
// ptr ptr uintptr ptr
// ptr ptr ptr uintptr
// ptr ptr ptr ptr
// uintptr ptr ptr ptr
// ptr uintptr ptr ptr
// Assumptions about Finalizer layout checked below.
bitsPointer | bitsPointer<<2 | bitsScalar<<4 | bitsPointer<<6,
bitsPointer | bitsPointer<<2 | bitsPointer<<4 | bitsScalar<<6,
bitsPointer | bitsPointer<<2 | bitsPointer<<4 | bitsPointer<<6,
bitsScalar | bitsPointer<<2 | bitsPointer<<4 | bitsPointer<<6,
bitsPointer | bitsScalar<<2 | bitsPointer<<4 | bitsPointer<<6,
}
func queuefinalizer(p unsafe.Pointer, fn *funcval, nret uintptr, fint *_type, ot *ptrtype) {
lock(&finlock)
if finq == nil || finq.cnt == int32(len(finq.fin)) {
if finc == nil {
// Note: write barrier here, assigning to finc, but should be okay.
finc = (*finblock)(persistentalloc(_FinBlockSize, 0, &memstats.gc_sys))
finc.alllink = allfin
allfin = finc
if finptrmask[0] == 0 {
// Build pointer mask for Finalizer array in block.
// Check assumptions made in finalizer1 array above.
if (unsafe.Sizeof(finalizer{}) != 5*ptrSize ||
unsafe.Offsetof(finalizer{}.fn) != 0 ||
unsafe.Offsetof(finalizer{}.arg) != ptrSize ||
unsafe.Offsetof(finalizer{}.nret) != 2*ptrSize ||
unsafe.Offsetof(finalizer{}.fint) != 3*ptrSize ||
unsafe.Offsetof(finalizer{}.ot) != 4*ptrSize ||
bitsPerPointer != 2) {
throw("finalizer out of sync")
}
for i := range finptrmask {
finptrmask[i] = finalizer1[i%len(finalizer1)]
}
}
}
block := finc
finc = block.next
block.next = finq
finq = block
}
f := &finq.fin[finq.cnt]
finq.cnt++
f.fn = fn
f.nret = nret
f.fint = fint
f.ot = ot
f.arg = p
fingwake = true
unlock(&finlock)
}
//go:nowritebarrier
func iterate_finq(callback func(*funcval, unsafe.Pointer, uintptr, *_type, *ptrtype)) {
for fb := allfin; fb != nil; fb = fb.alllink {
for i := int32(0); i < fb.cnt; i++ {
f := &fb.fin[i]
callback(f.fn, f.arg, f.nret, f.fint, f.ot)
}
}
}
// Returns only when span s has been swept.
//go:nowritebarrier
func mSpan_EnsureSwept(s *mspan) {
// Caller must disable preemption.
// Otherwise when this function returns the span can become unswept again
// (if GC is triggered on another goroutine).
_g_ := getg()
if _g_.m.locks == 0 && _g_.m.mallocing == 0 && _g_ != _g_.m.g0 {
throw("MSpan_EnsureSwept: m is not locked")
}
sg := mheap_.sweepgen
if atomicload(&s.sweepgen) == sg {
return
}
// The caller must be sure that the span is a MSpanInUse span.
if cas(&s.sweepgen, sg-2, sg-1) {
mSpan_Sweep(s, false)
return
}
// unfortunate condition, and we don't have efficient means to wait
for atomicload(&s.sweepgen) != sg {
osyield()
}
}
// Sweep frees or collects finalizers for blocks not marked in the mark phase.
// It clears the mark bits in preparation for the next GC round.
// Returns true if the span was returned to heap.
// If preserve=true, don't return it to heap nor relink in MCentral lists;
// caller takes care of it.
//TODO go:nowritebarrier
func mSpan_Sweep(s *mspan, preserve bool) bool {
if checkmark {
throw("MSpan_Sweep: checkmark only runs in STW and after the sweep")
}
// It's critical that we enter this function with preemption disabled,
// GC must not start while we are in the middle of this function.
_g_ := getg()
if _g_.m.locks == 0 && _g_.m.mallocing == 0 && _g_ != _g_.m.g0 {
throw("MSpan_Sweep: m is not locked")
}
sweepgen := mheap_.sweepgen
if s.state != mSpanInUse || s.sweepgen != sweepgen-1 {
print("MSpan_Sweep: state=", s.state, " sweepgen=", s.sweepgen, " mheap.sweepgen=", sweepgen, "\n")
throw("MSpan_Sweep: bad span state")
}
arena_start := mheap_.arena_start
cl := s.sizeclass
size := s.elemsize
var n int32
var npages int32
if cl == 0 {
n = 1
} else {
// Chunk full of small blocks.
npages = class_to_allocnpages[cl]
n = (npages << _PageShift) / int32(size)
}
res := false
nfree := 0
var head, end gclinkptr
c := _g_.m.mcache
sweepgenset := false
// Mark any free objects in this span so we don't collect them.
for link := s.freelist; link.ptr() != nil; link = link.ptr().next {
off := (uintptr(unsafe.Pointer(link)) - arena_start) / ptrSize
bitp := arena_start - off/wordsPerBitmapByte - 1
shift := (off % wordsPerBitmapByte) * gcBits
*(*byte)(unsafe.Pointer(bitp)) |= bitMarked << shift
}
// Unlink & free special records for any objects we're about to free.
specialp := &s.specials
special := *specialp
for special != nil {
// A finalizer can be set for an inner byte of an object, find object beginning.
p := uintptr(s.start<<_PageShift) + uintptr(special.offset)/size*size
off := (p - arena_start) / ptrSize
bitp := arena_start - off/wordsPerBitmapByte - 1
shift := (off % wordsPerBitmapByte) * gcBits
bits := (*(*byte)(unsafe.Pointer(bitp)) >> shift) & bitMask
if bits&bitMarked == 0 {
// Find the exact byte for which the special was setup
// (as opposed to object beginning).
p := uintptr(s.start<<_PageShift) + uintptr(special.offset)
// about to free object: splice out special record
y := special
special = special.next
*specialp = special
if !freespecial(y, unsafe.Pointer(p), size, false) {
// stop freeing of object if it has a finalizer
*(*byte)(unsafe.Pointer(bitp)) |= bitMarked << shift
}
} else {
// object is still live: keep special record
specialp = &special.next
special = *specialp
}
}
// Sweep through n objects of given size starting at p.
// This thread owns the span now, so it can manipulate
// the block bitmap without atomic operations.
p := uintptr(s.start << _PageShift)
off := (p - arena_start) / ptrSize
bitp := arena_start - off/wordsPerBitmapByte - 1
shift := uint(0)
step := size / (ptrSize * wordsPerBitmapByte)
// Rewind to the previous quadruple as we move to the next
// in the beginning of the loop.
bitp += step
if step == 0 {
// 8-byte objects.
bitp++
shift = gcBits
}
for ; n > 0; n, p = n-1, p+size {
bitp -= step
if step == 0 {
if shift != 0 {
bitp--
}
shift = gcBits - shift
}
xbits := *(*byte)(unsafe.Pointer(bitp))
bits := (xbits >> shift) & bitMask
// Allocated and marked object, reset bits to allocated.
if bits&bitMarked != 0 {
*(*byte)(unsafe.Pointer(bitp)) &^= bitMarked << shift
continue
}
// At this point we know that we are looking at garbage object
// that needs to be collected.
if debug.allocfreetrace != 0 {
tracefree(unsafe.Pointer(p), size)
}
// Reset to allocated+noscan.
*(*byte)(unsafe.Pointer(bitp)) = uint8(uintptr(xbits&^((bitMarked|bitsMask<<2)<<shift)) | uintptr(bitsDead)<<(shift+2))
if cl == 0 {
// Free large span.
if preserve {
throw("can't preserve large span")
}
unmarkspan(p, s.npages<<_PageShift)
s.needzero = 1
// important to set sweepgen before returning it to heap
atomicstore(&s.sweepgen, sweepgen)
sweepgenset = true
// NOTE(rsc,dvyukov): The original implementation of efence
// in CL 22060046 used SysFree instead of SysFault, so that
// the operating system would eventually give the memory
// back to us again, so that an efence program could run
// longer without running out of memory. Unfortunately,
// calling SysFree here without any kind of adjustment of the
// heap data structures means that when the memory does
// come back to us, we have the wrong metadata for it, either in
// the MSpan structures or in the garbage collection bitmap.
// Using SysFault here means that the program will run out of
// memory fairly quickly in efence mode, but at least it won't
// have mysterious crashes due to confused memory reuse.
// It should be possible to switch back to SysFree if we also
// implement and then call some kind of MHeap_DeleteSpan.
if debug.efence > 0 {
s.limit = 0 // prevent mlookup from finding this span
sysFault(unsafe.Pointer(p), size)
} else {
mHeap_Free(&mheap_, s, 1)
}
c.local_nlargefree++
c.local_largefree += size
xadd64(&memstats.next_gc, -int64(size)*int64(gcpercent+100)/100)
res = true
} else {
// Free small object.
if size > 2*ptrSize {
*(*uintptr)(unsafe.Pointer(p + ptrSize)) = uintptrMask & 0xdeaddeaddeaddead // mark as "needs to be zeroed"
} else if size > ptrSize {
*(*uintptr)(unsafe.Pointer(p + ptrSize)) = 0
}
if head.ptr() == nil {
head = gclinkptr(p)
} else {
end.ptr().next = gclinkptr(p)
}
end = gclinkptr(p)
end.ptr().next = gclinkptr(0x0bade5)
nfree++
}
}
// We need to set s.sweepgen = h.sweepgen only when all blocks are swept,
// because of the potential for a concurrent free/SetFinalizer.
// But we need to set it before we make the span available for allocation
// (return it to heap or mcentral), because allocation code assumes that a
// span is already swept if available for allocation.
if !sweepgenset && nfree == 0 {
// The span must be in our exclusive ownership until we update sweepgen,
// check for potential races.
if s.state != mSpanInUse || s.sweepgen != sweepgen-1 {
print("MSpan_Sweep: state=", s.state, " sweepgen=", s.sweepgen, " mheap.sweepgen=", sweepgen, "\n")
throw("MSpan_Sweep: bad span state after sweep")
}
atomicstore(&s.sweepgen, sweepgen)
}
if nfree > 0 {
c.local_nsmallfree[cl] += uintptr(nfree)
c.local_cachealloc -= intptr(uintptr(nfree) * size)
xadd64(&memstats.next_gc, -int64(nfree)*int64(size)*int64(gcpercent+100)/100)
res = mCentral_FreeSpan(&mheap_.central[cl].mcentral, s, int32(nfree), head, end, preserve)
// MCentral_FreeSpan updates sweepgen
}
return res
}
// State of background sweep.
// Protected by gclock.
type sweepdata struct {
g *g
parked bool
started bool
spanidx uint32 // background sweeper position
nbgsweep uint32
npausesweep uint32
}
var sweep sweepdata
// State of the background concurrent GC goroutine.
var bggc struct {
lock mutex
g *g
working uint
started bool
}
// sweeps one span
// returns number of pages returned to heap, or ^uintptr(0) if there is nothing to sweep
//go:nowritebarrier
func sweepone() uintptr {
_g_ := getg()
// increment locks to ensure that the goroutine is not preempted
// in the middle of sweep thus leaving the span in an inconsistent state for next GC
_g_.m.locks++
sg := mheap_.sweepgen
for {
idx := xadd(&sweep.spanidx, 1) - 1
if idx >= uint32(len(work.spans)) {
mheap_.sweepdone = 1
_g_.m.locks--
return ^uintptr(0)
}
s := work.spans[idx]
if s.state != mSpanInUse {
s.sweepgen = sg
continue
}
if s.sweepgen != sg-2 || !cas(&s.sweepgen, sg-2, sg-1) {
continue
}
npages := s.npages
if !mSpan_Sweep(s, false) {
npages = 0
}
_g_.m.locks--
return npages
}
}
//go:nowritebarrier
func gosweepone() uintptr {
var ret uintptr
systemstack(func() {
ret = sweepone()
})
return ret
}
//go:nowritebarrier
func gosweepdone() bool {
return mheap_.sweepdone != 0
}
//go:nowritebarrier
func gchelper() {
_g_ := getg()
_g_.m.traceback = 2
gchelperstart()
// parallel mark for over GC roots
parfordo(work.markfor)
if gcphase != _GCscan {
scanblock(0, 0, nil) // blocks in getfull
}
nproc := work.nproc // work.nproc can change right after we increment work.ndone
if xadd(&work.ndone, +1) == nproc-1 {
notewakeup(&work.alldone)
}
_g_.m.traceback = 0
}
//go:nowritebarrier
func cachestats() {
for i := 0; ; i++ {
p := allp[i]
if p == nil {
break
}
c := p.mcache
if c == nil {
continue
}
purgecachedstats(c)
}
}
//go:nowritebarrier
func flushallmcaches() {
for i := 0; ; i++ {
p := allp[i]
if p == nil {
break
}
c := p.mcache
if c == nil {
continue
}
mCache_ReleaseAll(c)
stackcache_clear(c)
}
}
//go:nowritebarrier
func updatememstats(stats *gcstats) {
if stats != nil {
*stats = gcstats{}
}
for mp := allm; mp != nil; mp = mp.alllink {
if stats != nil {
src := (*[unsafe.Sizeof(gcstats{}) / 8]uint64)(unsafe.Pointer(&mp.gcstats))
dst := (*[unsafe.Sizeof(gcstats{}) / 8]uint64)(unsafe.Pointer(stats))
for i, v := range src {
dst[i] += v
}
mp.gcstats = gcstats{}
}
}
memstats.mcache_inuse = uint64(mheap_.cachealloc.inuse)
memstats.mspan_inuse = uint64(mheap_.spanalloc.inuse)
memstats.sys = memstats.heap_sys + memstats.stacks_sys + memstats.mspan_sys +
memstats.mcache_sys + memstats.buckhash_sys + memstats.gc_sys + memstats.other_sys
// Calculate memory allocator stats.
// During program execution we only count number of frees and amount of freed memory.
// Current number of alive object in the heap and amount of alive heap memory
// are calculated by scanning all spans.
// Total number of mallocs is calculated as number of frees plus number of alive objects.
// Similarly, total amount of allocated memory is calculated as amount of freed memory
// plus amount of alive heap memory.
memstats.alloc = 0
memstats.total_alloc = 0
memstats.nmalloc = 0
memstats.nfree = 0
for i := 0; i < len(memstats.by_size); i++ {
memstats.by_size[i].nmalloc = 0
memstats.by_size[i].nfree = 0
}
// Flush MCache's to MCentral.
systemstack(flushallmcaches)
// Aggregate local stats.
cachestats()
// Scan all spans and count number of alive objects.
lock(&mheap_.lock)
for i := uint32(0); i < mheap_.nspan; i++ {
s := h_allspans[i]
if s.state != mSpanInUse {
continue
}
if s.sizeclass == 0 {
memstats.nmalloc++
memstats.alloc += uint64(s.elemsize)
} else {
memstats.nmalloc += uint64(s.ref)
memstats.by_size[s.sizeclass].nmalloc += uint64(s.ref)
memstats.alloc += uint64(s.ref) * uint64(s.elemsize)
}
}
unlock(&mheap_.lock)
// Aggregate by size class.
smallfree := uint64(0)
memstats.nfree = mheap_.nlargefree
for i := 0; i < len(memstats.by_size); i++ {
memstats.nfree += mheap_.nsmallfree[i]
memstats.by_size[i].nfree = mheap_.nsmallfree[i]
memstats.by_size[i].nmalloc += mheap_.nsmallfree[i]
smallfree += uint64(mheap_.nsmallfree[i]) * uint64(class_to_size[i])
}
memstats.nfree += memstats.tinyallocs
memstats.nmalloc += memstats.nfree
// Calculate derived stats.
memstats.total_alloc = uint64(memstats.alloc) + uint64(mheap_.largefree) + smallfree
memstats.heap_alloc = memstats.alloc
memstats.heap_objects = memstats.nmalloc - memstats.nfree
}
func gcinit() {
if unsafe.Sizeof(workbuf{}) != _WorkbufSize {
throw("runtime: size of Workbuf is suboptimal")
}
work.markfor = parforalloc(_MaxGcproc)
gcpercent = readgogc()
gcdatamask = unrollglobgcprog((*byte)(unsafe.Pointer(&gcdata)), uintptr(unsafe.Pointer(&edata))-uintptr(unsafe.Pointer(&data)))
gcbssmask = unrollglobgcprog((*byte)(unsafe.Pointer(&gcbss)), uintptr(unsafe.Pointer(&ebss))-uintptr(unsafe.Pointer(&bss)))
}
// Called from malloc.go using onM, stopping and starting the world handled in caller.
//go:nowritebarrier
func gc_m(start_time int64, eagersweep bool) {
_g_ := getg()
gp := _g_.m.curg
casgstatus(gp, _Grunning, _Gwaiting)
gp.waitreason = "garbage collection"
gc(start_time, eagersweep)
casgstatus(gp, _Gwaiting, _Grunning)
}
// Similar to clearcheckmarkbits but works on a single span.
// It preforms two tasks.
// 1. When used before the checkmark phase it converts BitsDead (00) to bitsScalar (01)
// for nibbles with the BoundaryBit set.
// 2. When used after the checkmark phase it converts BitsPointerMark (11) to BitsPointer 10 and
// BitsScalarMark (00) to BitsScalar (01), thus clearing the checkmark mark encoding.
// For the second case it is possible to restore the BitsDead pattern but since
// clearmark is a debug tool performance has a lower priority than simplicity.
// The span is MSpanInUse and the world is stopped.
//go:nowritebarrier
func clearcheckmarkbitsspan(s *mspan) {
if s.state != _MSpanInUse {
print("runtime:clearcheckmarkbitsspan: state=", s.state, "\n")
throw("clearcheckmarkbitsspan: bad span state")
}
arena_start := mheap_.arena_start
cl := s.sizeclass
size := s.elemsize
var n int32
if cl == 0 {
n = 1
} else {
// Chunk full of small blocks
npages := class_to_allocnpages[cl]
n = npages << _PageShift / int32(size)
}
// MSpan_Sweep has similar code but instead of overloading and
// complicating that routine we do a simpler walk here.
// Sweep through n objects of given size starting at p.
// This thread owns the span now, so it can manipulate
// the block bitmap without atomic operations.
p := uintptr(s.start) << _PageShift
// Find bits for the beginning of the span.
off := (p - arena_start) / ptrSize
bitp := (*byte)(unsafe.Pointer(arena_start - off/wordsPerBitmapByte - 1))
step := size / (ptrSize * wordsPerBitmapByte)
// The type bit values are:
// 00 - BitsDead, for us BitsScalarMarked
// 01 - BitsScalar
// 10 - BitsPointer
// 11 - unused, for us BitsPointerMarked
//
// When called to prepare for the checkmark phase (checkmark==1),
// we change BitsDead to BitsScalar, so that there are no BitsScalarMarked
// type bits anywhere.
//
// The checkmark phase marks by changing BitsScalar to BitsScalarMarked
// and BitsPointer to BitsPointerMarked.
//
// When called to clean up after the checkmark phase (checkmark==0),
// we unmark by changing BitsScalarMarked back to BitsScalar and
// BitsPointerMarked back to BitsPointer.
//
// There are two problems with the scheme as just described.
// First, the setup rewrites BitsDead to BitsScalar, but the type bits
// following a BitsDead are uninitialized and must not be used.
// Second, objects that are free are expected to have their type
// bits zeroed (BitsDead), so in the cleanup we need to restore
// any BitsDeads that were there originally.
//
// In a one-word object (8-byte allocation on 64-bit system),
// there is no difference between BitsScalar and BitsDead, because
// neither is a pointer and there are no more words in the object,
// so using BitsScalar during the checkmark is safe and mapping
// both back to BitsDead during cleanup is also safe.
//
// In a larger object, we need to be more careful. During setup,
// if the type of the first word is BitsDead, we change it to BitsScalar
// (as we must) but also initialize the type of the second
// word to BitsDead, so that a scan during the checkmark phase
// will still stop before seeing the uninitialized type bits in the
// rest of the object. The sequence 'BitsScalar BitsDead' never
// happens in real type bitmaps - BitsDead is always as early
// as possible, so immediately after the last BitsPointer.
// During cleanup, if we see a BitsScalar, we can check to see if it
// is followed by BitsDead. If so, it was originally BitsDead and
// we can change it back.
if step == 0 {
// updating top and bottom nibbles, all boundaries
for i := int32(0); i < n/2; i, bitp = i+1, addb(bitp, uintptrMask&-1) {
if *bitp&bitBoundary == 0 {
throw("missing bitBoundary")
}
b := (*bitp & bitPtrMask) >> 2
if !checkmark && (b == _BitsScalar || b == _BitsScalarMarked) {
*bitp &^= 0x0c // convert to _BitsDead
} else if b == _BitsScalarMarked || b == _BitsPointerMarked {
*bitp &^= _BitsCheckMarkXor << 2
}
if (*bitp>>gcBits)&bitBoundary == 0 {
throw("missing bitBoundary")
}
b = ((*bitp >> gcBits) & bitPtrMask) >> 2
if !checkmark && (b == _BitsScalar || b == _BitsScalarMarked) {
*bitp &^= 0xc0 // convert to _BitsDead
} else if b == _BitsScalarMarked || b == _BitsPointerMarked {
*bitp &^= _BitsCheckMarkXor << (2 + gcBits)
}
}
} else {
// updating bottom nibble for first word of each object
for i := int32(0); i < n; i, bitp = i+1, addb(bitp, -step) {
if *bitp&bitBoundary == 0 {
throw("missing bitBoundary")
}
b := (*bitp & bitPtrMask) >> 2
if checkmark && b == _BitsDead {
// move BitsDead into second word.
// set bits to BitsScalar in preparation for checkmark phase.
*bitp &^= 0xc0
*bitp |= _BitsScalar << 2
} else if !checkmark && (b == _BitsScalar || b == _BitsScalarMarked) && *bitp&0xc0 == 0 {
// Cleaning up after checkmark phase.
// First word is scalar or dead (we forgot)
// and second word is dead.
// First word might as well be dead too.
*bitp &^= 0x0c
} else if b == _BitsScalarMarked || b == _BitsPointerMarked {
*bitp ^= _BitsCheckMarkXor << 2
}
}
}
}
// clearcheckmarkbits preforms two tasks.
// 1. When used before the checkmark phase it converts BitsDead (00) to bitsScalar (01)
// for nibbles with the BoundaryBit set.
// 2. When used after the checkmark phase it converts BitsPointerMark (11) to BitsPointer 10 and
// BitsScalarMark (00) to BitsScalar (01), thus clearing the checkmark mark encoding.
// This is a bit expensive but preserves the BitsDead encoding during the normal marking.
// BitsDead remains valid for every nibble except the ones with BitsBoundary set.
//go:nowritebarrier
func clearcheckmarkbits() {
for _, s := range work.spans {
if s.state == _MSpanInUse {
clearcheckmarkbitsspan(s)
}
}
}
// Called from malloc.go using onM.
// The world is stopped. Rerun the scan and mark phases
// using the bitMarkedCheck bit instead of the
// bitMarked bit. If the marking encounters an
// bitMarked bit that is not set then we throw.
//go:nowritebarrier
func gccheckmark_m(startTime int64, eagersweep bool) {
if !gccheckmarkenable {
return
}
if checkmark {
throw("gccheckmark_m, entered with checkmark already true")
}
checkmark = true
clearcheckmarkbits() // Converts BitsDead to BitsScalar.
gc_m(startTime, eagersweep) // turns off checkmark + calls clearcheckmarkbits
}
//go:nowritebarrier
func gccheckmarkenable_m() {
gccheckmarkenable = true
}
//go:nowritebarrier
func gccheckmarkdisable_m() {
gccheckmarkenable = false
}
//go:nowritebarrier
func finishsweep_m() {
// The world is stopped so we should be able to complete the sweeps
// quickly.
for sweepone() != ^uintptr(0) {
sweep.npausesweep++
}
// There may be some other spans being swept concurrently that
// we need to wait for. If finishsweep_m is done with the world stopped
// this code is not required.
sg := mheap_.sweepgen
for _, s := range work.spans {
if s.sweepgen != sg && s.state == _MSpanInUse {
mSpan_EnsureSwept(s)
}
}
}
// Scan all of the stacks, greying (or graying if in America) the referents
// but not blackening them since the mark write barrier isn't installed.
//go:nowritebarrier
func gcscan_m() {
_g_ := getg()
// Grab the g that called us and potentially allow rescheduling.
// This allows it to be scanned like other goroutines.
mastergp := _g_.m.curg
casgstatus(mastergp, _Grunning, _Gwaiting)
mastergp.waitreason = "garbage collection scan"
// Span sweeping has been done by finishsweep_m.
// Long term we will want to make this goroutine runnable
// by placing it onto a scanenqueue state and then calling
// runtime·restartg(mastergp) to make it Grunnable.
// At the bottom we will want to return this p back to the scheduler.
// Prepare flag indicating that the scan has not been completed.
lock(&allglock)
local_allglen := allglen
for i := uintptr(0); i < local_allglen; i++ {
gp := allgs[i]
gp.gcworkdone = false // set to true in gcphasework
}
unlock(&allglock)
work.nwait = 0
work.ndone = 0
work.nproc = 1 // For now do not do this in parallel.
// ackgcphase is not needed since we are not scanning running goroutines.
parforsetup(work.markfor, work.nproc, uint32(_RootCount+local_allglen), nil, false, markroot)
parfordo(work.markfor)
lock(&allglock)
// Check that gc work is done.
for i := uintptr(0); i < local_allglen; i++ {
gp := allgs[i]
if !gp.gcworkdone {
throw("scan missed a g")
}
}
unlock(&allglock)
casgstatus(mastergp, _Gwaiting, _Grunning)
// Let the g that called us continue to run.
}
// Mark all objects that are known about.
//go:nowritebarrier
func gcmark_m() {
scanblock(0, 0, nil)
}
// For now this must be bracketed with a stoptheworld and a starttheworld to ensure
// all go routines see the new barrier.
//go:nowritebarrier
func gcinstallmarkwb_m() {
gcphase = _GCmark
}
// For now this must be bracketed with a stoptheworld and a starttheworld to ensure
// all go routines see the new barrier.
//go:nowritebarrier
func gcinstalloffwb_m() {
gcphase = _GCoff
}
//TODO go:nowritebarrier
func gc(start_time int64, eagersweep bool) {
if _DebugGCPtrs {
print("GC start\n")
}
if debug.allocfreetrace > 0 {
tracegc()
}
_g_ := getg()
_g_.m.traceback = 2
t0 := start_time
work.tstart = start_time
var t1 int64
if debug.gctrace > 0 {
t1 = nanotime()
}
if !checkmark {
finishsweep_m() // skip during checkmark debug phase.
}
// Cache runtime.mheap_.allspans in work.spans to avoid conflicts with
// resizing/freeing allspans.
// New spans can be created while GC progresses, but they are not garbage for
// this round:
// - new stack spans can be created even while the world is stopped.
// - new malloc spans can be created during the concurrent sweep
// Even if this is stop-the-world, a concurrent exitsyscall can allocate a stack from heap.
lock(&mheap_.lock)
// Free the old cached sweep array if necessary.
if work.spans != nil && &work.spans[0] != &h_allspans[0] {
sysFree(unsafe.Pointer(&work.spans[0]), uintptr(len(work.spans))*unsafe.Sizeof(work.spans[0]), &memstats.other_sys)
}
// Cache the current array for marking.
mheap_.gcspans = mheap_.allspans
work.spans = h_allspans
unlock(&mheap_.lock)
oldphase := gcphase
work.nwait = 0
work.ndone = 0
work.nproc = uint32(gcprocs())
gcphase = _GCmarktermination
// World is stopped so allglen will not change.
for i := uintptr(0); i < allglen; i++ {
gp := allgs[i]
gp.gcworkdone = false // set to true in gcphasework
}
parforsetup(work.markfor, work.nproc, uint32(_RootCount+allglen), nil, false, markroot)
if work.nproc > 1 {
noteclear(&work.alldone)
helpgc(int32(work.nproc))
}
var t2 int64
if debug.gctrace > 0 {
t2 = nanotime()
}
gchelperstart()
parfordo(work.markfor)
scanblock(0, 0, nil)
if work.full != 0 {
throw("work.full != 0")
}
if work.partial != 0 {
throw("work.partial != 0")
}
gcphase = oldphase
var t3 int64
if debug.gctrace > 0 {
t3 = nanotime()
}
if work.nproc > 1 {
notesleep(&work.alldone)
}
shrinkfinish()
cachestats()
// next_gc calculation is tricky with concurrent sweep since we don't know size of live heap
// estimate what was live heap size after previous GC (for printing only)
heap0 := memstats.next_gc * 100 / (uint64(gcpercent) + 100)
// conservatively set next_gc to high value assuming that everything is live
// concurrent/lazy sweep will reduce this number while discovering new garbage
memstats.next_gc = memstats.heap_alloc + memstats.heap_alloc*uint64(gcpercent)/100
t4 := nanotime()
atomicstore64(&memstats.last_gc, uint64(unixnanotime())) // must be Unix time to make sense to user
memstats.pause_ns[memstats.numgc%uint32(len(memstats.pause_ns))] = uint64(t4 - t0)
memstats.pause_end[memstats.numgc%uint32(len(memstats.pause_end))] = uint64(t4)
memstats.pause_total_ns += uint64(t4 - t0)
memstats.numgc++
if memstats.debuggc {
print("pause ", t4-t0, "\n")
}
if debug.gctrace > 0 {
heap1 := memstats.heap_alloc
var stats gcstats
updatememstats(&stats)
if heap1 != memstats.heap_alloc {
print("runtime: mstats skew: heap=", heap1, "/", memstats.heap_alloc, "\n")
throw("mstats skew")
}
obj := memstats.nmalloc - memstats.nfree
stats.nprocyield += work.markfor.nprocyield
stats.nosyield += work.markfor.nosyield
stats.nsleep += work.markfor.nsleep
print("gc", memstats.numgc, "(", work.nproc, "): ",
(t1-t0)/1000, "+", (t2-t1)/1000, "+", (t3-t2)/1000, "+", (t4-t3)/1000, " us, ",
heap0>>20, " -> ", heap1>>20, " MB, ",
obj, " (", memstats.nmalloc, "-", memstats.nfree, ") objects, ",
gcount(), " goroutines, ",
len(work.spans), "/", sweep.nbgsweep, "/", sweep.npausesweep, " sweeps, ",
stats.nhandoff, "(", stats.nhandoffcnt, ") handoff, ",
work.markfor.nsteal, "(", work.markfor.nstealcnt, ") steal, ",
stats.nprocyield, "/", stats.nosyield, "/", stats.nsleep, " yields\n")
sweep.nbgsweep = 0
sweep.npausesweep = 0
}
// See the comment in the beginning of this function as to why we need the following.
// Even if this is still stop-the-world, a concurrent exitsyscall can allocate a stack from heap.
lock(&mheap_.lock)
// Free the old cached mark array if necessary.
if work.spans != nil && &work.spans[0] != &h_allspans[0] {
sysFree(unsafe.Pointer(&work.spans[0]), uintptr(len(work.spans))*unsafe.Sizeof(work.spans[0]), &memstats.other_sys)
}
if gccheckmarkenable {
if !checkmark {
// first half of two-pass; don't set up sweep
unlock(&mheap_.lock)
return
}
checkmark = false // done checking marks
clearcheckmarkbits()
}
// Cache the current array for sweeping.
mheap_.gcspans = mheap_.allspans
mheap_.sweepgen += 2
mheap_.sweepdone = 0
work.spans = h_allspans
sweep.spanidx = 0
unlock(&mheap_.lock)
if _ConcurrentSweep && !eagersweep {
lock(&gclock)
if !sweep.started {
go bgsweep()
sweep.started = true
} else if sweep.parked {
sweep.parked = false
ready(sweep.g)
}
unlock(&gclock)
} else {
// Sweep all spans eagerly.
for sweepone() != ^uintptr(0) {
sweep.npausesweep++
}
// Do an additional mProf_GC, because all 'free' events are now real as well.
mProf_GC()
}
mProf_GC()
_g_.m.traceback = 0
if _DebugGCPtrs {
print("GC end\n")
}
}
func readmemstats_m(stats *MemStats) {
updatememstats(nil)
// Size of the trailing by_size array differs between Go and C,
// NumSizeClasses was changed, but we can not change Go struct because of backward compatibility.
memmove(unsafe.Pointer(stats), unsafe.Pointer(&memstats), sizeof_C_MStats)
// Stack numbers are part of the heap numbers, separate those out for user consumption
stats.StackSys = stats.StackInuse
stats.HeapInuse -= stats.StackInuse
stats.HeapSys -= stats.StackInuse
}
//go:linkname readGCStats runtime/debug.readGCStats
func readGCStats(pauses *[]uint64) {
systemstack(func() {
readGCStats_m(pauses)
})
}
func readGCStats_m(pauses *[]uint64) {
p := *pauses
// Calling code in runtime/debug should make the slice large enough.
if cap(p) < len(memstats.pause_ns)+3 {
throw("runtime: short slice passed to readGCStats")
}
// Pass back: pauses, pause ends, last gc (absolute time), number of gc, total pause ns.
lock(&mheap_.lock)
n := memstats.numgc
if n > uint32(len(memstats.pause_ns)) {
n = uint32(len(memstats.pause_ns))
}
// The pause buffer is circular. The most recent pause is at
// pause_ns[(numgc-1)%len(pause_ns)], and then backward
// from there to go back farther in time. We deliver the times
// most recent first (in p[0]).
p = p[:cap(p)]
for i := uint32(0); i < n; i++ {
j := (memstats.numgc - 1 - i) % uint32(len(memstats.pause_ns))
p[i] = memstats.pause_ns[j]
p[n+i] = memstats.pause_end[j]
}
p[n+n] = memstats.last_gc
p[n+n+1] = uint64(memstats.numgc)
p[n+n+2] = memstats.pause_total_ns
unlock(&mheap_.lock)
*pauses = p[:n+n+3]
}
func setGCPercent(in int32) (out int32) {
lock(&mheap_.lock)
out = gcpercent
if in < 0 {
in = -1
}
gcpercent = in
unlock(&mheap_.lock)
return out
}
func gchelperstart() {
_g_ := getg()
if _g_.m.helpgc < 0 || _g_.m.helpgc >= _MaxGcproc {
throw("gchelperstart: bad m->helpgc")
}
if _g_ != _g_.m.g0 {
throw("gchelper not running on g0 stack")
}
}
func wakefing() *g {
var res *g
lock(&finlock)
if fingwait && fingwake {
fingwait = false
fingwake = false
res = fing
}
unlock(&finlock)
return res
}
//go:nowritebarrier
func addb(p *byte, n uintptr) *byte {
return (*byte)(add(unsafe.Pointer(p), n))
}
// Recursively unrolls GC program in prog.
// mask is where to store the result.
// ppos is a pointer to position in mask, in bits.
// sparse says to generate 4-bits per word mask for heap (2-bits for data/bss otherwise).
//go:nowritebarrier
func unrollgcprog1(maskp *byte, prog *byte, ppos *uintptr, inplace, sparse bool) *byte {
arena_start := mheap_.arena_start
pos := *ppos
mask := (*[1 << 30]byte)(unsafe.Pointer(maskp))
for {
switch *prog {
default:
throw("unrollgcprog: unknown instruction")
case insData:
prog = addb(prog, 1)
siz := int(*prog)
prog = addb(prog, 1)
p := (*[1 << 30]byte)(unsafe.Pointer(prog))
for i := 0; i < siz; i++ {
v := p[i/_PointersPerByte]
v >>= (uint(i) % _PointersPerByte) * _BitsPerPointer
v &= _BitsMask
if inplace {
// Store directly into GC bitmap.
off := (uintptr(unsafe.Pointer(&mask[pos])) - arena_start) / ptrSize
bitp := (*byte)(unsafe.Pointer(arena_start - off/wordsPerBitmapByte - 1))
shift := (off % wordsPerBitmapByte) * gcBits
if shift == 0 {
*bitp = 0
}
*bitp |= v << (shift + 2)
pos += ptrSize
} else if sparse {
// 4-bits per word
v <<= (pos % 8) + 2
mask[pos/8] |= v
pos += gcBits
} else {
// 2-bits per word
v <<= pos % 8
mask[pos/8] |= v
pos += _BitsPerPointer
}
}
prog = addb(prog, round(uintptr(siz)*_BitsPerPointer, 8)/8)
case insArray:
prog = (*byte)(add(unsafe.Pointer(prog), 1))
siz := uintptr(0)
for i := uintptr(0); i < ptrSize; i++ {
siz = (siz << 8) + uintptr(*(*byte)(add(unsafe.Pointer(prog), ptrSize-i-1)))
}
prog = (*byte)(add(unsafe.Pointer(prog), ptrSize))
var prog1 *byte
for i := uintptr(0); i < siz; i++ {
prog1 = unrollgcprog1(&mask[0], prog, &pos, inplace, sparse)
}
if *prog1 != insArrayEnd {
throw("unrollgcprog: array does not end with insArrayEnd")
}
prog = (*byte)(add(unsafe.Pointer(prog1), 1))
case insArrayEnd, insEnd:
*ppos = pos
return prog
}
}
}
// Unrolls GC program prog for data/bss, returns dense GC mask.
func unrollglobgcprog(prog *byte, size uintptr) bitvector {
masksize := round(round(size, ptrSize)/ptrSize*bitsPerPointer, 8) / 8
mask := (*[1 << 30]byte)(persistentalloc(masksize+1, 0, &memstats.gc_sys))
mask[masksize] = 0xa1
pos := uintptr(0)
prog = unrollgcprog1(&mask[0], prog, &pos, false, false)
if pos != size/ptrSize*bitsPerPointer {
print("unrollglobgcprog: bad program size, got ", pos, ", expect ", size/ptrSize*bitsPerPointer, "\n")
throw("unrollglobgcprog: bad program size")
}
if *prog != insEnd {
throw("unrollglobgcprog: program does not end with insEnd")
}
if mask[masksize] != 0xa1 {
throw("unrollglobgcprog: overflow")
}
return bitvector{int32(masksize * 8), &mask[0]}
}
func unrollgcproginplace_m(v unsafe.Pointer, typ *_type, size, size0 uintptr) {
pos := uintptr(0)
prog := (*byte)(unsafe.Pointer(uintptr(typ.gc[1])))
for pos != size0 {
unrollgcprog1((*byte)(v), prog, &pos, true, true)
}
// Mark first word as bitAllocated.
arena_start := mheap_.arena_start
off := (uintptr(v) - arena_start) / ptrSize
bitp := (*byte)(unsafe.Pointer(arena_start - off/wordsPerBitmapByte - 1))
shift := (off % wordsPerBitmapByte) * gcBits
*bitp |= bitBoundary << shift
// Mark word after last as BitsDead.
if size0 < size {
off := (uintptr(v) + size0 - arena_start) / ptrSize
bitp := (*byte)(unsafe.Pointer(arena_start - off/wordsPerBitmapByte - 1))
shift := (off % wordsPerBitmapByte) * gcBits
*bitp &= uint8(^(bitPtrMask << shift) | uintptr(bitsDead)<<(shift+2))
}
}
var unroll mutex
// Unrolls GC program in typ.gc[1] into typ.gc[0]
//go:nowritebarrier
func unrollgcprog_m(typ *_type) {
lock(&unroll)
mask := (*byte)(unsafe.Pointer(uintptr(typ.gc[0])))
if *mask == 0 {
pos := uintptr(8) // skip the unroll flag
prog := (*byte)(unsafe.Pointer(uintptr(typ.gc[1])))
prog = unrollgcprog1(mask, prog, &pos, false, true)
if *prog != insEnd {
throw("unrollgcprog: program does not end with insEnd")
}
if typ.size/ptrSize%2 != 0 {
// repeat the program
prog := (*byte)(unsafe.Pointer(uintptr(typ.gc[1])))
unrollgcprog1(mask, prog, &pos, false, true)
}
// atomic way to say mask[0] = 1
atomicor8(mask, 1)
}
unlock(&unroll)
}
// mark the span of memory at v as having n blocks of the given size.
// if leftover is true, there is left over space at the end of the span.
//go:nowritebarrier
func markspan(v unsafe.Pointer, size uintptr, n uintptr, leftover bool) {
if uintptr(v)+size*n > mheap_.arena_used || uintptr(v) < mheap_.arena_start {
throw("markspan: bad pointer")
}
// Find bits of the beginning of the span.
off := (uintptr(v) - uintptr(mheap_.arena_start)) / ptrSize
if off%wordsPerBitmapByte != 0 {
throw("markspan: unaligned length")
}
b := mheap_.arena_start - off/wordsPerBitmapByte - 1
// Okay to use non-atomic ops here, because we control
// the entire span, and each bitmap byte has bits for only
// one span, so no other goroutines are changing these bitmap words.
if size == ptrSize {
// Possible only on 64-bits (minimal size class is 8 bytes).
// Set memory to 0x11.
if (bitBoundary|bitsDead)<<gcBits|bitBoundary|bitsDead != 0x11 {
throw("markspan: bad bits")
}
if n%(wordsPerBitmapByte*ptrSize) != 0 {
throw("markspan: unaligned length")
}
b = b - n/wordsPerBitmapByte + 1 // find first byte
if b%ptrSize != 0 {
throw("markspan: unaligned pointer")
}
for i := uintptr(0); i < n; i, b = i+wordsPerBitmapByte*ptrSize, b+ptrSize {
*(*uintptr)(unsafe.Pointer(b)) = uintptrMask & 0x1111111111111111 // bitBoundary | bitsDead, repeated
}
return
}
if leftover {
n++ // mark a boundary just past end of last block too
}
step := size / (ptrSize * wordsPerBitmapByte)
for i := uintptr(0); i < n; i, b = i+1, b-step {
*(*byte)(unsafe.Pointer(b)) = bitBoundary | bitsDead<<2
}
}
// unmark the span of memory at v of length n bytes.
//go:nowritebarrier
func unmarkspan(v, n uintptr) {
if v+n > mheap_.arena_used || v < mheap_.arena_start {
throw("markspan: bad pointer")
}
off := (v - mheap_.arena_start) / ptrSize // word offset
if off%(ptrSize*wordsPerBitmapByte) != 0 {
throw("markspan: unaligned pointer")
}
b := mheap_.arena_start - off/wordsPerBitmapByte - 1
n /= ptrSize
if n%(ptrSize*wordsPerBitmapByte) != 0 {
throw("unmarkspan: unaligned length")
}
// Okay to use non-atomic ops here, because we control
// the entire span, and each bitmap word has bits for only
// one span, so no other goroutines are changing these
// bitmap words.
n /= wordsPerBitmapByte
memclr(unsafe.Pointer(b-n+1), n)
}
//go:nowritebarrier
func mHeap_MapBits(h *mheap) {
// Caller has added extra mappings to the arena.
// Add extra mappings of bitmap words as needed.
// We allocate extra bitmap pieces in chunks of bitmapChunk.
const bitmapChunk = 8192
n := (h.arena_used - h.arena_start) / (ptrSize * wordsPerBitmapByte)
n = round(n, bitmapChunk)
n = round(n, _PhysPageSize)
if h.bitmap_mapped >= n {
return
}
sysMap(unsafe.Pointer(h.arena_start-n), n-h.bitmap_mapped, h.arena_reserved, &memstats.gc_sys)
h.bitmap_mapped = n
}
func getgcmaskcb(frame *stkframe, ctxt unsafe.Pointer) bool {
target := (*stkframe)(ctxt)
if frame.sp <= target.sp && target.sp < frame.varp {
*target = *frame
return false
}
return true
}
// Returns GC type info for object p for testing.
func getgcmask(p unsafe.Pointer, t *_type, mask **byte, len *uintptr) {
*mask = nil
*len = 0
// data
if uintptr(unsafe.Pointer(&data)) <= uintptr(p) && uintptr(p) < uintptr(unsafe.Pointer(&edata)) {
n := (*ptrtype)(unsafe.Pointer(t)).elem.size
*len = n / ptrSize
*mask = &make([]byte, *len)[0]
for i := uintptr(0); i < n; i += ptrSize {
off := (uintptr(p) + i - uintptr(unsafe.Pointer(&data))) / ptrSize
bits := (*(*byte)(add(unsafe.Pointer(gcdatamask.bytedata), off/pointersPerByte)) >> ((off % pointersPerByte) * bitsPerPointer)) & bitsMask
*(*byte)(add(unsafe.Pointer(*mask), i/ptrSize)) = bits
}
return
}
// bss
if uintptr(unsafe.Pointer(&bss)) <= uintptr(p) && uintptr(p) < uintptr(unsafe.Pointer(&ebss)) {
n := (*ptrtype)(unsafe.Pointer(t)).elem.size
*len = n / ptrSize
*mask = &make([]byte, *len)[0]
for i := uintptr(0); i < n; i += ptrSize {
off := (uintptr(p) + i - uintptr(unsafe.Pointer(&bss))) / ptrSize
bits := (*(*byte)(add(unsafe.Pointer(gcbssmask.bytedata), off/pointersPerByte)) >> ((off % pointersPerByte) * bitsPerPointer)) & bitsMask
*(*byte)(add(unsafe.Pointer(*mask), i/ptrSize)) = bits
}
return
}
// heap
var n uintptr
var base uintptr
if mlookup(uintptr(p), &base, &n, nil) != 0 {
*len = n / ptrSize
*mask = &make([]byte, *len)[0]
for i := uintptr(0); i < n; i += ptrSize {
off := (uintptr(base) + i - mheap_.arena_start) / ptrSize
b := mheap_.arena_start - off/wordsPerBitmapByte - 1
shift := (off % wordsPerBitmapByte) * gcBits
bits := (*(*byte)(unsafe.Pointer(b)) >> (shift + 2)) & bitsMask
*(*byte)(add(unsafe.Pointer(*mask), i/ptrSize)) = bits
}
return
}
// stack
var frame stkframe
frame.sp = uintptr(p)
_g_ := getg()
gentraceback(_g_.m.curg.sched.pc, _g_.m.curg.sched.sp, 0, _g_.m.curg, 0, nil, 1000, getgcmaskcb, noescape(unsafe.Pointer(&frame)), 0)
if frame.fn != nil {
f := frame.fn
targetpc := frame.continpc
if targetpc == 0 {
return
}
if targetpc != f.entry {
targetpc--
}
pcdata := pcdatavalue(f, _PCDATA_StackMapIndex, targetpc)
if pcdata == -1 {
return
}
stkmap := (*stackmap)(funcdata(f, _FUNCDATA_LocalsPointerMaps))
if stkmap == nil || stkmap.n <= 0 {
return
}
bv := stackmapdata(stkmap, pcdata)
size := uintptr(bv.n) / bitsPerPointer * ptrSize
n := (*ptrtype)(unsafe.Pointer(t)).elem.size
*len = n / ptrSize
*mask = &make([]byte, *len)[0]
for i := uintptr(0); i < n; i += ptrSize {
off := (uintptr(p) + i - frame.varp + size) / ptrSize
bits := ((*(*byte)(add(unsafe.Pointer(bv.bytedata), off*bitsPerPointer/8))) >> ((off * bitsPerPointer) % 8)) & bitsMask
*(*byte)(add(unsafe.Pointer(*mask), i/ptrSize)) = bits
}
}
}
func unixnanotime() int64 {
var now int64
gc_unixnanotime(&now)
return now
}