src/runtime/mfinal.go - go - Git at Google

 // 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.

 // Garbage collector: finalizers and block profiling.

 package runtime

 import (
 	"internal/abi"
 	"internal/goarch"
 	"internal/goexperiment"
 	"runtime/internal/atomic"
 	"runtime/internal/sys"
 	"unsafe"
 )

 // finblock is an array of finalizers to be executed. finblocks are
 // arranged in a linked list for the finalizer queue.
 //
 // finblock is allocated from non-GC'd memory, so any heap pointers
 // must be specially handled. GC currently assumes that the finalizer
 // queue does not grow during marking (but it can shrink).
 type finblock struct {
 	_       sys.NotInHeap
 	alllink *finblock
 	next    *finblock
 	cnt     uint32
 	_       int32
 	fin     [(_FinBlockSize - 2*goarch.PtrSize - 2*4) / unsafe.Sizeof(finalizer{})]finalizer
 }

 var fingStatus atomic.Uint32

 // finalizer goroutine status.
 const (
 	fingUninitialized uint32 = iota
 	fingCreated       uint32 = 1 << (iota - 1)
 	fingRunningFinalizer
 	fingWait
 	fingWake
 )

 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 / goarch.PtrSize / 8]byte

 var allfin *finblock // list of all blocks

 // NOTE: Layout known to queuefinalizer.
 type finalizer struct {
 	fn   *funcval       // function to call (may be a heap pointer)
 	arg  unsafe.Pointer // ptr to object (may be a heap pointer)
 	nret uintptr        // bytes of return values from fn
 	fint *_type         // type of first argument of fn
 	ot   *ptrtype       // type of ptr to object (may be a heap pointer)
 }

 var finalizer1 = [...]byte{
 	// Each Finalizer is 5 words, ptr ptr INT ptr ptr (INT = uintptr here)
 	// Each byte describes 8 words.
 	// Need 8 Finalizers described by 5 bytes before pattern repeats:
 	//	ptr ptr INT ptr ptr
 	//	ptr ptr INT ptr ptr
 	//	ptr ptr INT ptr ptr
 	//	ptr ptr INT ptr ptr
 	//	ptr ptr INT ptr ptr
 	//	ptr ptr INT ptr ptr
 	//	ptr ptr INT ptr ptr
 	//	ptr ptr INT ptr ptr
 	// aka
 	//
 	//	ptr ptr INT ptr ptr ptr ptr INT
 	//	ptr ptr ptr ptr INT ptr ptr ptr
 	//	ptr INT ptr ptr ptr ptr INT ptr
 	//	ptr ptr ptr INT ptr ptr ptr ptr
 	//	INT ptr ptr ptr ptr INT ptr ptr
 	//
 	// Assumptions about Finalizer layout checked below.
 	1<<0 | 1<<1 | 0<<2 | 1<<3 | 1<<4 | 1<<5 | 1<<6 | 0<<7,
 	1<<0 | 1<<1 | 1<<2 | 1<<3 | 0<<4 | 1<<5 | 1<<6 | 1<<7,
 	1<<0 | 0<<1 | 1<<2 | 1<<3 | 1<<4 | 1<<5 | 0<<6 | 1<<7,
 	1<<0 | 1<<1 | 1<<2 | 0<<3 | 1<<4 | 1<<5 | 1<<6 | 1<<7,
 	0<<0 | 1<<1 | 1<<2 | 1<<3 | 1<<4 | 0<<5 | 1<<6 | 1<<7,
 }

 // lockRankMayQueueFinalizer records the lock ranking effects of a
 // function that may call queuefinalizer.
 func lockRankMayQueueFinalizer() {
 	lockWithRankMayAcquire(&finlock, getLockRank(&finlock))
 }

 func queuefinalizer(p unsafe.Pointer, fn *funcval, nret uintptr, fint *_type, ot *ptrtype) {
 	if gcphase != _GCoff {
 		// Currently we assume that the finalizer queue won't
 		// grow during marking so we don't have to rescan it
 		// during mark termination. If we ever need to lift
 		// this assumption, we can do it by adding the
 		// necessary barriers to queuefinalizer (which it may
 		// have automatically).
 		throw("queuefinalizer during GC")
 	}

 	lock(&finlock)
 	if finq == nil || finq.cnt == uint32(len(finq.fin)) {
 		if finc == nil {
 			finc = (*finblock)(persistentalloc(_FinBlockSize, 0, &memstats.gcMiscSys))
 			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*goarch.PtrSize ||
 					unsafe.Offsetof(finalizer{}.fn) != 0 ||
 					unsafe.Offsetof(finalizer{}.arg) != goarch.PtrSize ||
 					unsafe.Offsetof(finalizer{}.nret) != 2*goarch.PtrSize ||
 					unsafe.Offsetof(finalizer{}.fint) != 3*goarch.PtrSize ||
 					unsafe.Offsetof(finalizer{}.ot) != 4*goarch.PtrSize) {
 					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]
 	atomic.Xadd(&finq.cnt, +1) // Sync with markroots
 	f.fn = fn
 	f.nret = nret
 	f.fint = fint
 	f.ot = ot
 	f.arg = p
 	unlock(&finlock)
 	fingStatus.Or(fingWake)
 }

 //go:nowritebarrier
 func iterate_finq(callback func(*funcval, unsafe.Pointer, uintptr, *_type, *ptrtype)) {
 	for fb := allfin; fb != nil; fb = fb.alllink {
 		for i := uint32(0); i < fb.cnt; i++ {
 			f := &fb.fin[i]
 			callback(f.fn, f.arg, f.nret, f.fint, f.ot)
 		}
 	}
 }

 func wakefing() *g {
 	if ok := fingStatus.CompareAndSwap(fingCreated|fingWait|fingWake, fingCreated); ok {
 		return fing
 	}
 	return nil
 }

 func createfing() {
 	// start the finalizer goroutine exactly once
 	if fingStatus.Load() == fingUninitialized && fingStatus.CompareAndSwap(fingUninitialized, fingCreated) {
 		go runfinq()
 	}
 }

 func finalizercommit(gp *g, lock unsafe.Pointer) bool {
 	unlock((*mutex)(lock))
 	// fingStatus should be modified after fing is put into a waiting state
 	// to avoid waking fing in running state, even if it is about to be parked.
 	fingStatus.Or(fingWait)
 	return true
 }

 // This is the goroutine that runs all of the finalizers.
 func runfinq() {
 	var (
 		frame    unsafe.Pointer
 		framecap uintptr
 		argRegs  int
 	)

 	gp := getg()
 	lock(&finlock)
 	fing = gp
 	unlock(&finlock)

 	for {
 		lock(&finlock)
 		fb := finq
 		finq = nil
 		if fb == nil {
 			gopark(finalizercommit, unsafe.Pointer(&finlock), waitReasonFinalizerWait, traceBlockSystemGoroutine, 1)
 			continue
 		}
 		argRegs = intArgRegs
 		unlock(&finlock)
 		if raceenabled {
 			racefingo()
 		}
 		for fb != nil {
 			for i := fb.cnt; i > 0; i-- {
 				f := &fb.fin[i-1]

 				var regs abi.RegArgs
 				// The args may be passed in registers or on stack. Even for
 				// the register case, we still need the spill slots.
 				// TODO: revisit if we remove spill slots.
 				//
 				// Unfortunately because we can have an arbitrary
 				// amount of returns and it would be complex to try and
 				// figure out how many of those can get passed in registers,
 				// just conservatively assume none of them do.
 				framesz := unsafe.Sizeof((any)(nil)) + f.nret
 				if framecap < framesz {
 					// The frame does not contain pointers interesting for GC,
 					// all not yet finalized objects are stored in finq.
 					// If we do not mark it as FlagNoScan,
 					// the last finalized object is not collected.
 					frame = mallocgc(framesz, nil, true)
 					framecap = framesz
 				}

 				if f.fint == nil {
 					throw("missing type in runfinq")
 				}
 				r := frame
 				if argRegs > 0 {
 					r = unsafe.Pointer(&regs.Ints)
 				} else {
 					// frame is effectively uninitialized
 					// memory. That means we have to clear
 					// it before writing to it to avoid
 					// confusing the write barrier.
 					*(*[2]uintptr)(frame) = [2]uintptr{}
 				}
 				switch f.fint.Kind_ & kindMask {
 				case kindPtr:
 					// direct use of pointer
 					*(*unsafe.Pointer)(r) = f.arg
 				case kindInterface:
 					ityp := (*interfacetype)(unsafe.Pointer(f.fint))
 					// set up with empty interface
 					(*eface)(r)._type = &f.ot.Type
 					(*eface)(r).data = f.arg
 					if len(ityp.Methods) != 0 {
 						// convert to interface with methods
 						// this conversion is guaranteed to succeed - we checked in SetFinalizer
 						(*iface)(r).tab = assertE2I(ityp, (*eface)(r)._type)
 					}
 				default:
 					throw("bad kind in runfinq")
 				}
 				fingStatus.Or(fingRunningFinalizer)
 				reflectcall(nil, unsafe.Pointer(f.fn), frame, uint32(framesz), uint32(framesz), uint32(framesz), &regs)
 				fingStatus.And(^fingRunningFinalizer)

 				// Drop finalizer queue heap references
 				// before hiding them from markroot.
 				// This also ensures these will be
 				// clear if we reuse the finalizer.
 				f.fn = nil
 				f.arg = nil
 				f.ot = nil
 				atomic.Store(&fb.cnt, i-1)
 			}
 			next := fb.next
 			lock(&finlock)
 			fb.next = finc
 			finc = fb
 			unlock(&finlock)
 			fb = next
 		}
 	}
 }

 func isGoPointerWithoutSpan(p unsafe.Pointer) bool {
 	// 0-length objects are okay.
 	if p == unsafe.Pointer(&zerobase) {
 		return true
 	}

 	// Global initializers might be linker-allocated.
 	//	var Foo = &Object{}
 	//	func main() {
 	//		runtime.SetFinalizer(Foo, nil)
 	//	}
 	// The relevant segments are: noptrdata, data, bss, noptrbss.
 	// We cannot assume they are in any order or even contiguous,
 	// due to external linking.
 	for datap := &firstmoduledata; datap != nil; datap = datap.next {
 		if datap.noptrdata <= uintptr(p) && uintptr(p) < datap.enoptrdata ||
 			datap.data <= uintptr(p) && uintptr(p) < datap.edata ||
 			datap.bss <= uintptr(p) && uintptr(p) < datap.ebss ||
 			datap.noptrbss <= uintptr(p) && uintptr(p) < datap.enoptrbss {
 			return true
 		}
 	}
 	return false
 }

 // blockUntilEmptyFinalizerQueue blocks until either the finalizer
 // queue is emptied (and the finalizers have executed) or the timeout
 // is reached. Returns true if the finalizer queue was emptied.
 // This is used by the runtime and sync tests.
 func blockUntilEmptyFinalizerQueue(timeout int64) bool {
 	start := nanotime()
 	for nanotime()-start < timeout {
 		lock(&finlock)
 		// We know the queue has been drained when both finq is nil
 		// and the finalizer g has stopped executing.
 		empty := finq == nil
 		empty = empty && readgstatus(fing) == _Gwaiting && fing.waitreason == waitReasonFinalizerWait
 		unlock(&finlock)
 		if empty {
 			return true
 		}
 		Gosched()
 	}
 	return false
 }

 // SetFinalizer sets the finalizer associated with obj to the provided
 // finalizer function. When the garbage collector finds an unreachable block
 // with an associated finalizer, it clears the association and runs
 // finalizer(obj) in a separate goroutine. This makes obj reachable again,
 // but now without an associated finalizer. Assuming that SetFinalizer
 // is not called again, the next time the garbage collector sees
 // that obj is unreachable, it will free obj.
 //
 // SetFinalizer(obj, nil) clears any finalizer associated with obj.
 //
 // The argument obj must be a pointer to an object allocated by calling
 // new, by taking the address of a composite literal, or by taking the
 // address of a local variable.
 // The argument finalizer must be a function that takes a single argument
 // to which obj's type can be assigned, and can have arbitrary ignored return
 // values. If either of these is not true, SetFinalizer may abort the
 // program.
 //
 // Finalizers are run in dependency order: if A points at B, both have
 // finalizers, and they are otherwise unreachable, only the finalizer
 // for A runs; once A is freed, the finalizer for B can run.
 // If a cyclic structure includes a block with a finalizer, that
 // cycle is not guaranteed to be garbage collected and the finalizer
 // is not guaranteed to run, because there is no ordering that
 // respects the dependencies.
 //
 // The finalizer is scheduled to run at some arbitrary time after the
 // program can no longer reach the object to which obj points.
 // There is no guarantee that finalizers will run before a program exits,
 // so typically they are useful only for releasing non-memory resources
 // associated with an object during a long-running program.
 // For example, an [os.File] object could use a finalizer to close the
 // associated operating system file descriptor when a program discards
 // an os.File without calling Close, but it would be a mistake
 // to depend on a finalizer to flush an in-memory I/O buffer such as a
 // [bufio.Writer], because the buffer would not be flushed at program exit.
 //
 // It is not guaranteed that a finalizer will run if the size of *obj is
 // zero bytes, because it may share same address with other zero-size
 // objects in memory. See https://go.dev/ref/spec#Size_and_alignment_guarantees.
 //
 // It is not guaranteed that a finalizer will run for objects allocated
 // in initializers for package-level variables. Such objects may be
 // linker-allocated, not heap-allocated.
 //
 // Note that because finalizers may execute arbitrarily far into the future
 // after an object is no longer referenced, the runtime is allowed to perform
 // a space-saving optimization that batches objects together in a single
 // allocation slot. The finalizer for an unreferenced object in such an
 // allocation may never run if it always exists in the same batch as a
 // referenced object. Typically, this batching only happens for tiny
 // (on the order of 16 bytes or less) and pointer-free objects.
 //
 // A finalizer may run as soon as an object becomes unreachable.
 // In order to use finalizers correctly, the program must ensure that
 // the object is reachable until it is no longer required.
 // Objects stored in global variables, or that can be found by tracing
 // pointers from a global variable, are reachable. For other objects,
 // pass the object to a call of the [KeepAlive] function to mark the
 // last point in the function where the object must be reachable.
 //
 // For example, if p points to a struct, such as os.File, that contains
 // a file descriptor d, and p has a finalizer that closes that file
 // descriptor, and if the last use of p in a function is a call to
 // syscall.Write(p.d, buf, size), then p may be unreachable as soon as
 // the program enters [syscall.Write]. The finalizer may run at that moment,
 // closing p.d, causing syscall.Write to fail because it is writing to
 // a closed file descriptor (or, worse, to an entirely different
 // file descriptor opened by a different goroutine). To avoid this problem,
 // call KeepAlive(p) after the call to syscall.Write.
 //
 // A single goroutine runs all finalizers for a program, sequentially.
 // If a finalizer must run for a long time, it should do so by starting
 // a new goroutine.
 //
 // In the terminology of the Go memory model, a call
 // SetFinalizer(x, f) “synchronizes before” the finalization call f(x).
 // However, there is no guarantee that KeepAlive(x) or any other use of x
 // “synchronizes before” f(x), so in general a finalizer should use a mutex
 // or other synchronization mechanism if it needs to access mutable state in x.
 // For example, consider a finalizer that inspects a mutable field in x
 // that is modified from time to time in the main program before x
 // becomes unreachable and the finalizer is invoked.
 // The modifications in the main program and the inspection in the finalizer
 // need to use appropriate synchronization, such as mutexes or atomic updates,
 // to avoid read-write races.
 func SetFinalizer(obj any, finalizer any) {
 	if debug.sbrk != 0 {
 		// debug.sbrk never frees memory, so no finalizers run
 		// (and we don't have the data structures to record them).
 		return
 	}
 	e := efaceOf(&obj)
 	etyp := e._type
 	if etyp == nil {
 		throw("runtime.SetFinalizer: first argument is nil")
 	}
 	if etyp.Kind_&kindMask != kindPtr {
 		throw("runtime.SetFinalizer: first argument is " + toRType(etyp).string() + ", not pointer")
 	}
 	ot := (*ptrtype)(unsafe.Pointer(etyp))
 	if ot.Elem == nil {
 		throw("nil elem type!")
 	}

 	if inUserArenaChunk(uintptr(e.data)) {
 		// Arena-allocated objects are not eligible for finalizers.
 		throw("runtime.SetFinalizer: first argument was allocated into an arena")
 	}

 	// find the containing object
 	base, span, _ := findObject(uintptr(e.data), 0, 0)

 	if base == 0 {
 		if isGoPointerWithoutSpan(e.data) {
 			return
 		}
 		throw("runtime.SetFinalizer: pointer not in allocated block")
 	}

 	// Move base forward if we've got an allocation header.
 	if goexperiment.AllocHeaders && !span.spanclass.noscan() && !heapBitsInSpan(span.elemsize) && span.spanclass.sizeclass() != 0 {
 		base += mallocHeaderSize
 	}

 	if uintptr(e.data) != base {
 		// As an implementation detail we allow to set finalizers for an inner byte
 		// of an object if it could come from tiny alloc (see mallocgc for details).
 		if ot.Elem == nil || ot.Elem.PtrBytes != 0 || ot.Elem.Size_ >= maxTinySize {
 			throw("runtime.SetFinalizer: pointer not at beginning of allocated block")
 		}
 	}

 	f := efaceOf(&finalizer)
 	ftyp := f._type
 	if ftyp == nil {
 		// switch to system stack and remove finalizer
 		systemstack(func() {
 			removefinalizer(e.data)
 		})
 		return
 	}

 	if ftyp.Kind_&kindMask != kindFunc {
 		throw("runtime.SetFinalizer: second argument is " + toRType(ftyp).string() + ", not a function")
 	}
 	ft := (*functype)(unsafe.Pointer(ftyp))
 	if ft.IsVariadic() {
 		throw("runtime.SetFinalizer: cannot pass " + toRType(etyp).string() + " to finalizer " + toRType(ftyp).string() + " because dotdotdot")
 	}
 	if ft.InCount != 1 {
 		throw("runtime.SetFinalizer: cannot pass " + toRType(etyp).string() + " to finalizer " + toRType(ftyp).string())
 	}
 	fint := ft.InSlice()[0]
 	switch {
 	case fint == etyp:
 		// ok - same type
 		goto okarg
 	case fint.Kind_&kindMask == kindPtr:
 		if (fint.Uncommon() == nil || etyp.Uncommon() == nil) && (*ptrtype)(unsafe.Pointer(fint)).Elem == ot.Elem {
 			// ok - not same type, but both pointers,
 			// one or the other is unnamed, and same element type, so assignable.
 			goto okarg
 		}
 	case fint.Kind_&kindMask == kindInterface:
 		ityp := (*interfacetype)(unsafe.Pointer(fint))
 		if len(ityp.Methods) == 0 {
 			// ok - satisfies empty interface
 			goto okarg
 		}
 		if itab := assertE2I2(ityp, efaceOf(&obj)._type); itab != nil {
 			goto okarg
 		}
 	}
 	throw("runtime.SetFinalizer: cannot pass " + toRType(etyp).string() + " to finalizer " + toRType(ftyp).string())
 okarg:
 	// compute size needed for return parameters
 	nret := uintptr(0)
 	for _, t := range ft.OutSlice() {
 		nret = alignUp(nret, uintptr(t.Align_)) + t.Size_
 	}
 	nret = alignUp(nret, goarch.PtrSize)

 	// make sure we have a finalizer goroutine
 	createfing()

 	systemstack(func() {
 		if !addfinalizer(e.data, (*funcval)(f.data), nret, fint, ot) {
 			throw("runtime.SetFinalizer: finalizer already set")
 		}
 	})
 }

 // Mark KeepAlive as noinline so that it is easily detectable as an intrinsic.
 //
 //go:noinline

 // KeepAlive marks its argument as currently reachable.
 // This ensures that the object is not freed, and its finalizer is not run,
 // before the point in the program where KeepAlive is called.
 //
 // A very simplified example showing where KeepAlive is required:
 //
 //	type File struct { d int }
 //	d, err := syscall.Open("/file/path", syscall.O_RDONLY, 0)
 //	// ... do something if err != nil ...
 //	p := &File{d}
 //	runtime.SetFinalizer(p, func(p *File) { syscall.Close(p.d) })
 //	var buf [10]byte
 //	n, err := syscall.Read(p.d, buf[:])
 //	// Ensure p is not finalized until Read returns.
 //	runtime.KeepAlive(p)
 //	// No more uses of p after this point.
 //
 // Without the KeepAlive call, the finalizer could run at the start of
 // [syscall.Read], closing the file descriptor before syscall.Read makes
 // the actual system call.
 //
 // Note: KeepAlive should only be used to prevent finalizers from
 // running prematurely. In particular, when used with [unsafe.Pointer],
 // the rules for valid uses of unsafe.Pointer still apply.
 func KeepAlive(x any) {
 	// Introduce a use of x that the compiler can't eliminate.
 	// This makes sure x is alive on entry. We need x to be alive
 	// on entry for "defer runtime.KeepAlive(x)"; see issue 21402.
 	if cgoAlwaysFalse {
 		println(x)
 	}
 }
	// 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.

	// Garbage collector: finalizers and block profiling.

	package runtime

	import (
	"internal/abi"
	"internal/goarch"
	"internal/goexperiment"
	"runtime/internal/atomic"
	"runtime/internal/sys"
	"unsafe"
	)

	// finblock is an array of finalizers to be executed. finblocks are
	// arranged in a linked list for the finalizer queue.
	//
	// finblock is allocated from non-GC'd memory, so any heap pointers
	// must be specially handled. GC currently assumes that the finalizer
	// queue does not grow during marking (but it can shrink).
	type finblock struct {
	_ sys.NotInHeap
	alllink *finblock
	next *finblock
	cnt uint32
	_ int32
	fin [(_FinBlockSize - 2goarch.PtrSize - 24) / unsafe.Sizeof(finalizer{})]finalizer
	}

	var fingStatus atomic.Uint32

	// finalizer goroutine status.
	const (
	fingUninitialized uint32 = iota
	fingCreated uint32 = 1 << (iota - 1)
	fingRunningFinalizer
	fingWait
	fingWake
	)

	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 / goarch.PtrSize / 8]byte

	var allfin *finblock // list of all blocks

	// NOTE: Layout known to queuefinalizer.
	type finalizer struct {
	fn *funcval // function to call (may be a heap pointer)
	arg unsafe.Pointer // ptr to object (may be a heap pointer)
	nret uintptr // bytes of return values from fn
	fint *_type // type of first argument of fn
	ot *ptrtype // type of ptr to object (may be a heap pointer)
	}

	var finalizer1 = [...]byte{
	// Each Finalizer is 5 words, ptr ptr INT ptr ptr (INT = uintptr here)
	// Each byte describes 8 words.
	// Need 8 Finalizers described by 5 bytes before pattern repeats:
	// ptr ptr INT ptr ptr
	// ptr ptr INT ptr ptr
	// ptr ptr INT ptr ptr
	// ptr ptr INT ptr ptr
	// ptr ptr INT ptr ptr
	// ptr ptr INT ptr ptr
	// ptr ptr INT ptr ptr
	// ptr ptr INT ptr ptr
	// aka
	//
	// ptr ptr INT ptr ptr ptr ptr INT
	// ptr ptr ptr ptr INT ptr ptr ptr
	// ptr INT ptr ptr ptr ptr INT ptr
	// ptr ptr ptr INT ptr ptr ptr ptr
	// INT ptr ptr ptr ptr INT ptr ptr
	//
	// Assumptions about Finalizer layout checked below.
	1<<0 \| 1<<1 \| 0<<2 \| 1<<3 \| 1<<4 \| 1<<5 \| 1<<6 \| 0<<7,
	1<<0 \| 1<<1 \| 1<<2 \| 1<<3 \| 0<<4 \| 1<<5 \| 1<<6 \| 1<<7,
	1<<0 \| 0<<1 \| 1<<2 \| 1<<3 \| 1<<4 \| 1<<5 \| 0<<6 \| 1<<7,
	1<<0 \| 1<<1 \| 1<<2 \| 0<<3 \| 1<<4 \| 1<<5 \| 1<<6 \| 1<<7,
	0<<0 \| 1<<1 \| 1<<2 \| 1<<3 \| 1<<4 \| 0<<5 \| 1<<6 \| 1<<7,
	}

	// lockRankMayQueueFinalizer records the lock ranking effects of a
	// function that may call queuefinalizer.
	func lockRankMayQueueFinalizer() {
	lockWithRankMayAcquire(&finlock, getLockRank(&finlock))
	}

	func queuefinalizer(p unsafe.Pointer, fn funcval, nret uintptr, fint _type, ot *ptrtype) {
	if gcphase != _GCoff {
	// Currently we assume that the finalizer queue won't
	// grow during marking so we don't have to rescan it
	// during mark termination. If we ever need to lift
	// this assumption, we can do it by adding the
	// necessary barriers to queuefinalizer (which it may
	// have automatically).
	throw("queuefinalizer during GC")
	}

	lock(&finlock)
	if finq == nil \|\| finq.cnt == uint32(len(finq.fin)) {
	if finc == nil {
	finc = (*finblock)(persistentalloc(_FinBlockSize, 0, &memstats.gcMiscSys))
	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*goarch.PtrSize \|\|
	unsafe.Offsetof(finalizer{}.fn) != 0 \|\|
	unsafe.Offsetof(finalizer{}.arg) != goarch.PtrSize \|\|
	unsafe.Offsetof(finalizer{}.nret) != 2*goarch.PtrSize \|\|
	unsafe.Offsetof(finalizer{}.fint) != 3*goarch.PtrSize \|\|
	unsafe.Offsetof(finalizer{}.ot) != 4*goarch.PtrSize) {
	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]
	atomic.Xadd(&finq.cnt, +1) // Sync with markroots
	f.fn = fn
	f.nret = nret
	f.fint = fint
	f.ot = ot
	f.arg = p
	unlock(&finlock)
	fingStatus.Or(fingWake)
	}

	//go:nowritebarrier
	func iterate_finq(callback func(funcval, unsafe.Pointer, uintptr, _type, *ptrtype)) {
	for fb := allfin; fb != nil; fb = fb.alllink {
	for i := uint32(0); i < fb.cnt; i++ {
	f := &fb.fin[i]
	callback(f.fn, f.arg, f.nret, f.fint, f.ot)
	}
	}
	}

	func wakefing() *g {
	if ok := fingStatus.CompareAndSwap(fingCreated\|fingWait\|fingWake, fingCreated); ok {
	return fing
	}
	return nil
	}

	func createfing() {
	// start the finalizer goroutine exactly once
	if fingStatus.Load() == fingUninitialized && fingStatus.CompareAndSwap(fingUninitialized, fingCreated) {
	go runfinq()
	}
	}

	func finalizercommit(gp *g, lock unsafe.Pointer) bool {
	unlock((*mutex)(lock))
	// fingStatus should be modified after fing is put into a waiting state
	// to avoid waking fing in running state, even if it is about to be parked.
	fingStatus.Or(fingWait)
	return true
	}

	// This is the goroutine that runs all of the finalizers.
	func runfinq() {
	var (
	frame unsafe.Pointer
	framecap uintptr
	argRegs int
	)

	gp := getg()
	lock(&finlock)
	fing = gp
	unlock(&finlock)

	for {
	lock(&finlock)
	fb := finq
	finq = nil
	if fb == nil {
	gopark(finalizercommit, unsafe.Pointer(&finlock), waitReasonFinalizerWait, traceBlockSystemGoroutine, 1)
	continue
	}
	argRegs = intArgRegs
	unlock(&finlock)
	if raceenabled {
	racefingo()
	}
	for fb != nil {
	for i := fb.cnt; i > 0; i-- {
	f := &fb.fin[i-1]

	var regs abi.RegArgs
	// The args may be passed in registers or on stack. Even for
	// the register case, we still need the spill slots.
	// TODO: revisit if we remove spill slots.
	//
	// Unfortunately because we can have an arbitrary
	// amount of returns and it would be complex to try and
	// figure out how many of those can get passed in registers,
	// just conservatively assume none of them do.
	framesz := unsafe.Sizeof((any)(nil)) + f.nret
	if framecap < framesz {
	// The frame does not contain pointers interesting for GC,
	// all not yet finalized objects are stored in finq.
	// If we do not mark it as FlagNoScan,
	// the last finalized object is not collected.
	frame = mallocgc(framesz, nil, true)
	framecap = framesz
	}

	if f.fint == nil {
	throw("missing type in runfinq")
	}
	r := frame
	if argRegs > 0 {
	r = unsafe.Pointer(&regs.Ints)
	} else {
	// frame is effectively uninitialized
	// memory. That means we have to clear
	// it before writing to it to avoid
	// confusing the write barrier.
	([2]uintptr)(frame) = [2]uintptr{}
	}
	switch f.fint.Kind_ & kindMask {
	case kindPtr:
	// direct use of pointer
	(unsafe.Pointer)(r) = f.arg
	case kindInterface:
	ityp := (*interfacetype)(unsafe.Pointer(f.fint))
	// set up with empty interface
	(*eface)(r)._type = &f.ot.Type
	(*eface)(r).data = f.arg
	if len(ityp.Methods) != 0 {
	// convert to interface with methods
	// this conversion is guaranteed to succeed - we checked in SetFinalizer
	(iface)(r).tab = assertE2I(ityp, (eface)(r)._type)
	}
	default:
	throw("bad kind in runfinq")
	}
	fingStatus.Or(fingRunningFinalizer)
	reflectcall(nil, unsafe.Pointer(f.fn), frame, uint32(framesz), uint32(framesz), uint32(framesz), &regs)
	fingStatus.And(^fingRunningFinalizer)

	// Drop finalizer queue heap references
	// before hiding them from markroot.
	// This also ensures these will be
	// clear if we reuse the finalizer.
	f.fn = nil
	f.arg = nil
	f.ot = nil
	atomic.Store(&fb.cnt, i-1)
	}
	next := fb.next
	lock(&finlock)
	fb.next = finc
	finc = fb
	unlock(&finlock)
	fb = next
	}
	}
	}

	func isGoPointerWithoutSpan(p unsafe.Pointer) bool {
	// 0-length objects are okay.
	if p == unsafe.Pointer(&zerobase) {
	return true
	}

	// Global initializers might be linker-allocated.
	// var Foo = &Object{}
	// func main() {
	// runtime.SetFinalizer(Foo, nil)
	// }
	// The relevant segments are: noptrdata, data, bss, noptrbss.
	// We cannot assume they are in any order or even contiguous,
	// due to external linking.
	for datap := &firstmoduledata; datap != nil; datap = datap.next {
	if datap.noptrdata <= uintptr(p) && uintptr(p) < datap.enoptrdata \|\|
	datap.data <= uintptr(p) && uintptr(p) < datap.edata \|\|
	datap.bss <= uintptr(p) && uintptr(p) < datap.ebss \|\|
	datap.noptrbss <= uintptr(p) && uintptr(p) < datap.enoptrbss {
	return true
	}
	}
	return false
	}

	// blockUntilEmptyFinalizerQueue blocks until either the finalizer
	// queue is emptied (and the finalizers have executed) or the timeout
	// is reached. Returns true if the finalizer queue was emptied.
	// This is used by the runtime and sync tests.
	func blockUntilEmptyFinalizerQueue(timeout int64) bool {
	start := nanotime()
	for nanotime()-start < timeout {
	lock(&finlock)
	// We know the queue has been drained when both finq is nil
	// and the finalizer g has stopped executing.
	empty := finq == nil
	empty = empty && readgstatus(fing) == _Gwaiting && fing.waitreason == waitReasonFinalizerWait
	unlock(&finlock)
	if empty {
	return true
	}
	Gosched()
	}
	return false
	}

	// SetFinalizer sets the finalizer associated with obj to the provided
	// finalizer function. When the garbage collector finds an unreachable block
	// with an associated finalizer, it clears the association and runs
	// finalizer(obj) in a separate goroutine. This makes obj reachable again,
	// but now without an associated finalizer. Assuming that SetFinalizer
	// is not called again, the next time the garbage collector sees
	// that obj is unreachable, it will free obj.
	//
	// SetFinalizer(obj, nil) clears any finalizer associated with obj.
	//
	// The argument obj must be a pointer to an object allocated by calling
	// new, by taking the address of a composite literal, or by taking the
	// address of a local variable.
	// The argument finalizer must be a function that takes a single argument
	// to which obj's type can be assigned, and can have arbitrary ignored return
	// values. If either of these is not true, SetFinalizer may abort the
	// program.
	//
	// Finalizers are run in dependency order: if A points at B, both have
	// finalizers, and they are otherwise unreachable, only the finalizer
	// for A runs; once A is freed, the finalizer for B can run.
	// If a cyclic structure includes a block with a finalizer, that
	// cycle is not guaranteed to be garbage collected and the finalizer
	// is not guaranteed to run, because there is no ordering that
	// respects the dependencies.
	//
	// The finalizer is scheduled to run at some arbitrary time after the
	// program can no longer reach the object to which obj points.
	// There is no guarantee that finalizers will run before a program exits,
	// so typically they are useful only for releasing non-memory resources
	// associated with an object during a long-running program.
	// For example, an [os.File] object could use a finalizer to close the
	// associated operating system file descriptor when a program discards
	// an os.File without calling Close, but it would be a mistake
	// to depend on a finalizer to flush an in-memory I/O buffer such as a
	// [bufio.Writer], because the buffer would not be flushed at program exit.
	//
	// It is not guaranteed that a finalizer will run if the size of *obj is
	// zero bytes, because it may share same address with other zero-size
	// objects in memory. See https://go.dev/ref/spec#Size_and_alignment_guarantees.
	//
	// It is not guaranteed that a finalizer will run for objects allocated
	// in initializers for package-level variables. Such objects may be
	// linker-allocated, not heap-allocated.
	//
	// Note that because finalizers may execute arbitrarily far into the future
	// after an object is no longer referenced, the runtime is allowed to perform
	// a space-saving optimization that batches objects together in a single
	// allocation slot. The finalizer for an unreferenced object in such an
	// allocation may never run if it always exists in the same batch as a
	// referenced object. Typically, this batching only happens for tiny
	// (on the order of 16 bytes or less) and pointer-free objects.
	//
	// A finalizer may run as soon as an object becomes unreachable.
	// In order to use finalizers correctly, the program must ensure that
	// the object is reachable until it is no longer required.
	// Objects stored in global variables, or that can be found by tracing
	// pointers from a global variable, are reachable. For other objects,
	// pass the object to a call of the [KeepAlive] function to mark the
	// last point in the function where the object must be reachable.
	//
	// For example, if p points to a struct, such as os.File, that contains
	// a file descriptor d, and p has a finalizer that closes that file
	// descriptor, and if the last use of p in a function is a call to
	// syscall.Write(p.d, buf, size), then p may be unreachable as soon as
	// the program enters [syscall.Write]. The finalizer may run at that moment,
	// closing p.d, causing syscall.Write to fail because it is writing to
	// a closed file descriptor (or, worse, to an entirely different
	// file descriptor opened by a different goroutine). To avoid this problem,
	// call KeepAlive(p) after the call to syscall.Write.
	//
	// A single goroutine runs all finalizers for a program, sequentially.
	// If a finalizer must run for a long time, it should do so by starting
	// a new goroutine.
	//
	// In the terminology of the Go memory model, a call
	// SetFinalizer(x, f) “synchronizes before” the finalization call f(x).
	// However, there is no guarantee that KeepAlive(x) or any other use of x
	// “synchronizes before” f(x), so in general a finalizer should use a mutex
	// or other synchronization mechanism if it needs to access mutable state in x.
	// For example, consider a finalizer that inspects a mutable field in x
	// that is modified from time to time in the main program before x
	// becomes unreachable and the finalizer is invoked.
	// The modifications in the main program and the inspection in the finalizer
	// need to use appropriate synchronization, such as mutexes or atomic updates,
	// to avoid read-write races.
	func SetFinalizer(obj any, finalizer any) {
	if debug.sbrk != 0 {
	// debug.sbrk never frees memory, so no finalizers run
	// (and we don't have the data structures to record them).
	return
	}
	e := efaceOf(&obj)
	etyp := e._type
	if etyp == nil {
	throw("runtime.SetFinalizer: first argument is nil")
	}
	if etyp.Kind_&kindMask != kindPtr {
	throw("runtime.SetFinalizer: first argument is " + toRType(etyp).string() + ", not pointer")
	}
	ot := (*ptrtype)(unsafe.Pointer(etyp))
	if ot.Elem == nil {
	throw("nil elem type!")
	}

	if inUserArenaChunk(uintptr(e.data)) {
	// Arena-allocated objects are not eligible for finalizers.
	throw("runtime.SetFinalizer: first argument was allocated into an arena")
	}

	// find the containing object
	base, span, _ := findObject(uintptr(e.data), 0, 0)

	if base == 0 {
	if isGoPointerWithoutSpan(e.data) {
	return
	}
	throw("runtime.SetFinalizer: pointer not in allocated block")
	}

	// Move base forward if we've got an allocation header.
	if goexperiment.AllocHeaders && !span.spanclass.noscan() && !heapBitsInSpan(span.elemsize) && span.spanclass.sizeclass() != 0 {
	base += mallocHeaderSize
	}

	if uintptr(e.data) != base {
	// As an implementation detail we allow to set finalizers for an inner byte
	// of an object if it could come from tiny alloc (see mallocgc for details).
	if ot.Elem == nil \|\| ot.Elem.PtrBytes != 0 \|\| ot.Elem.Size_ >= maxTinySize {
	throw("runtime.SetFinalizer: pointer not at beginning of allocated block")
	}
	}

	f := efaceOf(&finalizer)
	ftyp := f._type
	if ftyp == nil {
	// switch to system stack and remove finalizer
	systemstack(func() {
	removefinalizer(e.data)
	})
	return
	}

	if ftyp.Kind_&kindMask != kindFunc {
	throw("runtime.SetFinalizer: second argument is " + toRType(ftyp).string() + ", not a function")
	}
	ft := (*functype)(unsafe.Pointer(ftyp))
	if ft.IsVariadic() {
	throw("runtime.SetFinalizer: cannot pass " + toRType(etyp).string() + " to finalizer " + toRType(ftyp).string() + " because dotdotdot")
	}
	if ft.InCount != 1 {
	throw("runtime.SetFinalizer: cannot pass " + toRType(etyp).string() + " to finalizer " + toRType(ftyp).string())
	}
	fint := ft.InSlice()[0]
	switch {
	case fint == etyp:
	// ok - same type
	goto okarg
	case fint.Kind_&kindMask == kindPtr:
	if (fint.Uncommon() == nil \|\| etyp.Uncommon() == nil) && (*ptrtype)(unsafe.Pointer(fint)).Elem == ot.Elem {
	// ok - not same type, but both pointers,
	// one or the other is unnamed, and same element type, so assignable.
	goto okarg
	}
	case fint.Kind_&kindMask == kindInterface:
	ityp := (*interfacetype)(unsafe.Pointer(fint))
	if len(ityp.Methods) == 0 {
	// ok - satisfies empty interface
	goto okarg
	}
	if itab := assertE2I2(ityp, efaceOf(&obj)._type); itab != nil {
	goto okarg
	}
	}
	throw("runtime.SetFinalizer: cannot pass " + toRType(etyp).string() + " to finalizer " + toRType(ftyp).string())
	okarg:
	// compute size needed for return parameters
	nret := uintptr(0)
	for _, t := range ft.OutSlice() {
	nret = alignUp(nret, uintptr(t.Align_)) + t.Size_
	}
	nret = alignUp(nret, goarch.PtrSize)

	// make sure we have a finalizer goroutine
	createfing()

	systemstack(func() {
	if !addfinalizer(e.data, (*funcval)(f.data), nret, fint, ot) {
	throw("runtime.SetFinalizer: finalizer already set")
	}
	})
	}

	// Mark KeepAlive as noinline so that it is easily detectable as an intrinsic.
	//
	//go:noinline

	// KeepAlive marks its argument as currently reachable.
	// This ensures that the object is not freed, and its finalizer is not run,
	// before the point in the program where KeepAlive is called.
	//
	// A very simplified example showing where KeepAlive is required:
	//
	// type File struct { d int }
	// d, err := syscall.Open("/file/path", syscall.O_RDONLY, 0)
	// // ... do something if err != nil ...
	// p := &File{d}
	// runtime.SetFinalizer(p, func(p *File) { syscall.Close(p.d) })
	// var buf [10]byte
	// n, err := syscall.Read(p.d, buf[:])
	// // Ensure p is not finalized until Read returns.
	// runtime.KeepAlive(p)
	// // No more uses of p after this point.
	//
	// Without the KeepAlive call, the finalizer could run at the start of
	// [syscall.Read], closing the file descriptor before syscall.Read makes
	// the actual system call.
	//
	// Note: KeepAlive should only be used to prevent finalizers from
	// running prematurely. In particular, when used with [unsafe.Pointer],
	// the rules for valid uses of unsafe.Pointer still apply.
	func KeepAlive(x any) {
	// Introduce a use of x that the compiler can't eliminate.
	// This makes sure x is alive on entry. We need x to be alive
	// on entry for "defer runtime.KeepAlive(x)"; see issue 21402.
	if cgoAlwaysFalse {
	println(x)
	}
	}