src/runtime/runtime2.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.

 package runtime

 import "unsafe"

 /*
  * defined constants
  */
 const (
 	// G status
 	//
 	// If you add to this list, add to the list
 	// of "okay during garbage collection" status
 	// in mgcmark.go too.
 	_Gidle            = iota // 0
 	_Grunnable               // 1 runnable and on a run queue
 	_Grunning                // 2
 	_Gsyscall                // 3
 	_Gwaiting                // 4
 	_Gmoribund_unused        // 5 currently unused, but hardcoded in gdb scripts
 	_Gdead                   // 6
 	_Genqueue                // 7 Only the Gscanenqueue is used.
 	_Gcopystack              // 8 in this state when newstack is moving the stack
 	// the following encode that the GC is scanning the stack and what to do when it is done
 	_Gscan = 0x1000 // atomicstatus&~Gscan = the non-scan state,
 	// _Gscanidle =     _Gscan + _Gidle,      // Not used. Gidle only used with newly malloced gs
 	_Gscanrunnable = _Gscan + _Grunnable //  0x1001 When scanning complets make Grunnable (it is already on run queue)
 	_Gscanrunning  = _Gscan + _Grunning  //  0x1002 Used to tell preemption newstack routine to scan preempted stack.
 	_Gscansyscall  = _Gscan + _Gsyscall  //  0x1003 When scanning completes make it Gsyscall
 	_Gscanwaiting  = _Gscan + _Gwaiting  //  0x1004 When scanning completes make it Gwaiting
 	// _Gscanmoribund_unused,               //  not possible
 	// _Gscandead,                          //  not possible
 	_Gscanenqueue = _Gscan + _Genqueue //  When scanning completes make it Grunnable and put on runqueue
 )

 const (
 	// P status
 	_Pidle    = iota
 	_Prunning // Only this P is allowed to change from _Prunning.
 	_Psyscall
 	_Pgcstop
 	_Pdead
 )

 // The next line makes 'go generate' write the zgen_*.go files with
 // per-OS and per-arch information, including constants
 // named goos_$GOOS and goarch_$GOARCH for every
 // known GOOS and GOARCH. The constant is 1 on the
 // current system, 0 otherwise; multiplying by them is
 // useful for defining GOOS- or GOARCH-specific constants.
 //go:generate go run gengoos.go

 type mutex struct {
 	// Futex-based impl treats it as uint32 key,
 	// while sema-based impl as M* waitm.
 	// Used to be a union, but unions break precise GC.
 	key uintptr
 }

 type note struct {
 	// Futex-based impl treats it as uint32 key,
 	// while sema-based impl as M* waitm.
 	// Used to be a union, but unions break precise GC.
 	key uintptr
 }

 type _string struct {
 	str *byte
 	len int
 }

 type funcval struct {
 	fn uintptr
 	// variable-size, fn-specific data here
 }

 type iface struct {
 	tab  *itab
 	data unsafe.Pointer
 }

 type eface struct {
 	_type *_type
 	data  unsafe.Pointer
 }

 // The guintptr, muintptr, and puintptr are all used to bypass write barriers.
 // It is particularly important to avoid write barriers when the current P has
 // been released, because the GC thinks the world is stopped, and an
 // unexpected write barrier would not be synchronized with the GC,
 // which can lead to a half-executed write barrier that has marked the object
 // but not queued it. If the GC skips the object and completes before the
 // queuing can occur, it will incorrectly free the object.
 //
 // We tried using special assignment functions invoked only when not
 // holding a running P, but then some updates to a particular memory
 // word went through write barriers and some did not. This breaks the
 // write barrier shadow checking mode, and it is also scary: better to have
 // a word that is completely ignored by the GC than to have one for which
 // only a few updates are ignored.
 //
 // Gs, Ms, and Ps are always reachable via true pointers in the
 // allgs, allm, and allp lists or (during allocation before they reach those lists)
 // from stack variables.

 // A guintptr holds a goroutine pointer, but typed as a uintptr
 // to bypass write barriers. It is used in the Gobuf goroutine state
 // and in scheduling lists that are manipulated without a P.
 //
 // The Gobuf.g goroutine pointer is almost always updated by assembly code.
 // In one of the few places it is updated by Go code - func save - it must be
 // treated as a uintptr to avoid a write barrier being emitted at a bad time.
 // Instead of figuring out how to emit the write barriers missing in the
 // assembly manipulation, we change the type of the field to uintptr,
 // so that it does not require write barriers at all.
 //
 // Goroutine structs are published in the allg list and never freed.
 // That will keep the goroutine structs from being collected.
 // There is never a time that Gobuf.g's contain the only references
 // to a goroutine: the publishing of the goroutine in allg comes first.
 // Goroutine pointers are also kept in non-GC-visible places like TLS,
 // so I can't see them ever moving. If we did want to start moving data
 // in the GC, we'd need to allocate the goroutine structs from an
 // alternate arena. Using guintptr doesn't make that problem any worse.
 type guintptr uintptr

 func (gp guintptr) ptr() *g   { return (*g)(unsafe.Pointer(gp)) }
 func (gp *guintptr) set(g *g) { *gp = guintptr(unsafe.Pointer(g)) }
 func (gp *guintptr) cas(old, new guintptr) bool {
 	return casuintptr((*uintptr)(unsafe.Pointer(gp)), uintptr(old), uintptr(new))
 }

 type puintptr uintptr

 func (pp puintptr) ptr() *p   { return (*p)(unsafe.Pointer(pp)) }
 func (pp *puintptr) set(p *p) { *pp = puintptr(unsafe.Pointer(p)) }

 type muintptr uintptr

 func (mp muintptr) ptr() *m   { return (*m)(unsafe.Pointer(mp)) }
 func (mp *muintptr) set(m *m) { *mp = muintptr(unsafe.Pointer(m)) }

 type gobuf struct {
 	// The offsets of sp, pc, and g are known to (hard-coded in) libmach.
 	sp   uintptr
 	pc   uintptr
 	g    guintptr
 	ctxt unsafe.Pointer // this has to be a pointer so that gc scans it
 	ret  uintreg
 	lr   uintptr
 	bp   uintptr // for GOEXPERIMENT=framepointer
 }

 // Known to compiler.
 // Changes here must also be made in src/cmd/internal/gc/select.go's selecttype.
 type sudog struct {
 	g           *g
 	selectdone  *uint32
 	next        *sudog
 	prev        *sudog
 	elem        unsafe.Pointer // data element
 	releasetime int64
 	nrelease    int32  // -1 for acquire
 	waitlink    *sudog // g.waiting list
 }

 type gcstats struct {
 	// the struct must consist of only uint64's,
 	// because it is casted to uint64[].
 	nhandoff    uint64
 	nhandoffcnt uint64
 	nprocyield  uint64
 	nosyield    uint64
 	nsleep      uint64
 }

 type libcall struct {
 	fn   uintptr
 	n    uintptr // number of parameters
 	args uintptr // parameters
 	r1   uintptr // return values
 	r2   uintptr
 	err  uintptr // error number
 }

 // describes how to handle callback
 type wincallbackcontext struct {
 	gobody       unsafe.Pointer // go function to call
 	argsize      uintptr        // callback arguments size (in bytes)
 	restorestack uintptr        // adjust stack on return by (in bytes) (386 only)
 	cleanstack   bool
 }

 // Stack describes a Go execution stack.
 // The bounds of the stack are exactly [lo, hi),
 // with no implicit data structures on either side.
 type stack struct {
 	lo uintptr
 	hi uintptr
 }

 type g struct {
 	// Stack parameters.
 	// stack describes the actual stack memory: [stack.lo, stack.hi).
 	// stackguard0 is the stack pointer compared in the Go stack growth prologue.
 	// It is stack.lo+StackGuard normally, but can be StackPreempt to trigger a preemption.
 	// stackguard1 is the stack pointer compared in the C stack growth prologue.
 	// It is stack.lo+StackGuard on g0 and gsignal stacks.
 	// It is ~0 on other goroutine stacks, to trigger a call to morestackc (and crash).
 	stack       stack   // offset known to runtime/cgo
 	stackguard0 uintptr // offset known to liblink
 	stackguard1 uintptr // offset known to liblink

 	_panic       *_panic // innermost panic - offset known to liblink
 	_defer       *_defer // innermost defer
 	sched        gobuf
 	syscallsp    uintptr        // if status==Gsyscall, syscallsp = sched.sp to use during gc
 	syscallpc    uintptr        // if status==Gsyscall, syscallpc = sched.pc to use during gc
 	param        unsafe.Pointer // passed parameter on wakeup
 	atomicstatus uint32
 	goid         int64
 	waitsince    int64  // approx time when the g become blocked
 	waitreason   string // if status==Gwaiting
 	schedlink    guintptr
 	preempt      bool // preemption signal, duplicates stackguard0 = stackpreempt
 	paniconfault bool // panic (instead of crash) on unexpected fault address
 	preemptscan  bool // preempted g does scan for gc
 	gcworkdone   bool // debug: cleared at begining of gc work phase cycle, set by gcphasework, tested at end of cycle
 	gcscanvalid  bool // false at start of gc cycle, true if G has not run since last scan
 	throwsplit   bool // must not split stack
 	raceignore   int8 // ignore race detection events
 	m            *m   // for debuggers, but offset not hard-coded
 	lockedm      *m
 	sig          uint32
 	writebuf     []byte
 	sigcode0     uintptr
 	sigcode1     uintptr
 	sigpc        uintptr
 	gopc         uintptr // pc of go statement that created this goroutine
 	startpc      uintptr // pc of goroutine function
 	racectx      uintptr
 	waiting      *sudog // sudog structures this g is waiting on (that have a valid elem ptr)
 	readyg       *g     // scratch for readyExecute

 	// Per-G gcController state
 	gcalloc    uintptr // bytes allocated during this GC cycle
 	gcscanwork int64   // scan work done (or stolen) this GC cycle
 }

 type mts struct {
 	tv_sec  int64
 	tv_nsec int64
 }

 type mscratch struct {
 	v [6]uintptr
 }

 type m struct {
 	g0      *g    // goroutine with scheduling stack
 	morebuf gobuf // gobuf arg to morestack

 	// Fields not known to debuggers.
 	procid        uint64     // for debuggers, but offset not hard-coded
 	gsignal       *g         // signal-handling g
 	sigmask       [4]uintptr // storage for saved signal mask
 	tls           [4]uintptr // thread-local storage (for x86 extern register)
 	mstartfn      func()
 	curg          *g       // current running goroutine
 	caughtsig     guintptr // goroutine running during fatal signal
 	p             puintptr // attached p for executing go code (nil if not executing go code)
 	nextp         puintptr
 	id            int32
 	mallocing     int32
 	throwing      int32
 	preemptoff    string // if != "", keep curg running on this m
 	locks         int32
 	softfloat     int32
 	dying         int32
 	profilehz     int32
 	helpgc        int32
 	spinning      bool // m is out of work and is actively looking for work
 	blocked       bool // m is blocked on a note
 	inwb          bool // m is executing a write barrier
 	printlock     int8
 	fastrand      uint32
 	ncgocall      uint64 // number of cgo calls in total
 	ncgo          int32  // number of cgo calls currently in progress
 	park          note
 	alllink       *m // on allm
 	schedlink     muintptr
 	machport      uint32 // return address for mach ipc (os x)
 	mcache        *mcache
 	lockedg       *g
 	createstack   [32]uintptr // stack that created this thread.
 	freglo        [16]uint32  // d[i] lsb and f[i]
 	freghi        [16]uint32  // d[i] msb and f[i+16]
 	fflag         uint32      // floating point compare flags
 	locked        uint32      // tracking for lockosthread
 	nextwaitm     uintptr     // next m waiting for lock
 	waitsema      uintptr     // semaphore for parking on locks
 	waitsemacount uint32
 	waitsemalock  uint32
 	gcstats       gcstats
 	needextram    bool
 	traceback     uint8
 	waitunlockf   unsafe.Pointer // todo go func(*g, unsafe.pointer) bool
 	waitlock      unsafe.Pointer
 	waittraceev   byte
 	waittraceskip int
 	syscalltick   uint32
 	//#ifdef GOOS_windows
 	thread uintptr // thread handle
 	// these are here because they are too large to be on the stack
 	// of low-level NOSPLIT functions.
 	libcall   libcall
 	libcallpc uintptr // for cpu profiler
 	libcallsp uintptr
 	libcallg  guintptr
 	//#endif
 	//#ifdef GOOS_solaris
 	perrno *int32 // pointer to tls errno
 	// these are here because they are too large to be on the stack
 	// of low-level NOSPLIT functions.
 	//LibCall	libcall;
 	ts      mts
 	scratch mscratch
 	//#endif
 	//#ifdef GOOS_plan9
 	notesig *int8
 	errstr  *byte
 	//#endif
 }

 type p struct {
 	lock mutex

 	id          int32
 	status      uint32 // one of pidle/prunning/...
 	link        puintptr
 	schedtick   uint32   // incremented on every scheduler call
 	syscalltick uint32   // incremented on every system call
 	m           muintptr // back-link to associated m (nil if idle)
 	mcache      *mcache

 	deferpool    [5][]*_defer // pool of available defer structs of different sizes (see panic.go)
 	deferpoolbuf [5][32]*_defer

 	// Cache of goroutine ids, amortizes accesses to runtime·sched.goidgen.
 	goidcache    uint64
 	goidcacheend uint64

 	// Queue of runnable goroutines. Accessed without lock.
 	runqhead uint32
 	runqtail uint32
 	runq     [256]*g
 	// runnext, if non-nil, is a runnable G that was ready'd by
 	// the current G and should be run next instead of what's in
 	// runq if there's time remaining in the running G's time
 	// slice. It will inherit the time left in the current time
 	// slice. If a set of goroutines is locked in a
 	// communicate-and-wait pattern, this schedules that set as a
 	// unit and eliminates the (potentially large) scheduling
 	// latency that otherwise arises from adding the ready'd
 	// goroutines to the end of the run queue.
 	runnext guintptr

 	// Available G's (status == Gdead)
 	gfree    *g
 	gfreecnt int32

 	sudogcache []*sudog
 	sudogbuf   [128]*sudog

 	tracebuf *traceBuf

 	palloc persistentAlloc // per-P to avoid mutex

 	// Per-P GC state
 	gcAssistTime     int64 // Nanoseconds in assistAlloc
 	gcBgMarkWorker   *g
 	gcMarkWorkerMode gcMarkWorkerMode

 	// gcw is this P's GC work buffer cache. The work buffer is
 	// filled by write barriers, drained by mutator assists, and
 	// disposed on certain GC state transitions.
 	gcw gcWork

 	runSafePointFn uint32 // if 1, run sched.safePointFn at next safe point

 	pad [64]byte
 }

 const (
 	// The max value of GOMAXPROCS.
 	// There are no fundamental restrictions on the value.
 	_MaxGomaxprocs = 1 << 8
 )

 type schedt struct {
 	lock mutex

 	goidgen uint64

 	midle        muintptr // idle m's waiting for work
 	nmidle       int32    // number of idle m's waiting for work
 	nmidlelocked int32    // number of locked m's waiting for work
 	mcount       int32    // number of m's that have been created
 	maxmcount    int32    // maximum number of m's allowed (or die)

 	pidle      puintptr // idle p's
 	npidle     uint32
 	nmspinning uint32

 	// Global runnable queue.
 	runqhead guintptr
 	runqtail guintptr
 	runqsize int32

 	// Global cache of dead G's.
 	gflock mutex
 	gfree  *g
 	ngfree int32

 	// Central cache of sudog structs.
 	sudoglock  mutex
 	sudogcache *sudog

 	// Central pool of available defer structs of different sizes.
 	deferlock mutex
 	deferpool [5]*_defer

 	gcwaiting  uint32 // gc is waiting to run
 	stopwait   int32
 	stopnote   note
 	sysmonwait uint32
 	sysmonnote note
 	lastpoll   uint64

 	// safepointFn should be called on each P at the next GC
 	// safepoint if p.runSafePointFn is set.
 	safePointFn   func(*p)
 	safePointWait int32
 	safePointNote note

 	profilehz int32 // cpu profiling rate

 	procresizetime int64 // nanotime() of last change to gomaxprocs
 	totaltime      int64 // ∫gomaxprocs dt up to procresizetime
 }

 // The m->locked word holds two pieces of state counting active calls to LockOSThread/lockOSThread.
 // The low bit (LockExternal) is a boolean reporting whether any LockOSThread call is active.
 // External locks are not recursive; a second lock is silently ignored.
 // The upper bits of m->lockedcount record the nesting depth of calls to lockOSThread
 // (counting up by LockInternal), popped by unlockOSThread (counting down by LockInternal).
 // Internal locks can be recursive. For instance, a lock for cgo can occur while the main
 // goroutine is holding the lock during the initialization phase.
 const (
 	_LockExternal = 1
 	_LockInternal = 2
 )

 type sigtabtt struct {
 	flags int32
 	name  *int8
 }

 const (
 	_SigNotify   = 1 << iota // let signal.Notify have signal, even if from kernel
 	_SigKill                 // if signal.Notify doesn't take it, exit quietly
 	_SigThrow                // if signal.Notify doesn't take it, exit loudly
 	_SigPanic                // if the signal is from the kernel, panic
 	_SigDefault              // if the signal isn't explicitly requested, don't monitor it
 	_SigHandling             // our signal handler is registered
 	_SigIgnored              // the signal was ignored before we registered for it
 	_SigGoExit               // cause all runtime procs to exit (only used on Plan 9).
 	_SigSetStack             // add SA_ONSTACK to libc handler
 	_SigUnblock              // unblocked in minit
 )

 // Layout of in-memory per-function information prepared by linker
 // See http://golang.org/s/go12symtab.
 // Keep in sync with linker
 // and with package debug/gosym and with symtab.go in package runtime.
 type _func struct {
 	entry   uintptr // start pc
 	nameoff int32   // function name

 	args  int32 // in/out args size
 	frame int32 // legacy frame size; use pcsp if possible

 	pcsp      int32
 	pcfile    int32
 	pcln      int32
 	npcdata   int32
 	nfuncdata int32
 }

 // layout of Itab known to compilers
 // allocated in non-garbage-collected memory
 type itab struct {
 	inter  *interfacetype
 	_type  *_type
 	link   *itab
 	bad    int32
 	unused int32
 	fun    [1]uintptr // variable sized
 }

 // Lock-free stack node.
 // // Also known to export_test.go.
 type lfnode struct {
 	next    uint64
 	pushcnt uintptr
 }

 type forcegcstate struct {
 	lock mutex
 	g    *g
 	idle uint32
 }

 /*
  * known to compiler
  */
 const (
 	_Structrnd = regSize
 )

 // startup_random_data holds random bytes initialized at startup.  These come from
 // the ELF AT_RANDOM auxiliary vector (vdso_linux_amd64.go or os_linux_386.go).
 var startupRandomData []byte

 // extendRandom extends the random numbers in r[:n] to the whole slice r.
 // Treats n<0 as n==0.
 func extendRandom(r []byte, n int) {
 	if n < 0 {
 		n = 0
 	}
 	for n < len(r) {
 		// Extend random bits using hash function & time seed
 		w := n
 		if w > 16 {
 			w = 16
 		}
 		h := memhash(unsafe.Pointer(&r[n-w]), uintptr(nanotime()), uintptr(w))
 		for i := 0; i < ptrSize && n < len(r); i++ {
 			r[n] = byte(h)
 			n++
 			h >>= 8
 		}
 	}
 }

 /*
  * deferred subroutine calls
  */
 type _defer struct {
 	siz     int32
 	started bool
 	sp      uintptr // sp at time of defer
 	pc      uintptr
 	fn      *funcval
 	_panic  *_panic // panic that is running defer
 	link    *_defer
 }

 /*
  * panics
  */
 type _panic struct {
 	argp      unsafe.Pointer // pointer to arguments of deferred call run during panic; cannot move - known to liblink
 	arg       interface{}    // argument to panic
 	link      *_panic        // link to earlier panic
 	recovered bool           // whether this panic is over
 	aborted   bool           // the panic was aborted
 }

 /*
  * stack traces
  */

 type stkframe struct {
 	fn       *_func     // function being run
 	pc       uintptr    // program counter within fn
 	continpc uintptr    // program counter where execution can continue, or 0 if not
 	lr       uintptr    // program counter at caller aka link register
 	sp       uintptr    // stack pointer at pc
 	fp       uintptr    // stack pointer at caller aka frame pointer
 	varp     uintptr    // top of local variables
 	argp     uintptr    // pointer to function arguments
 	arglen   uintptr    // number of bytes at argp
 	argmap   *bitvector // force use of this argmap
 }

 const (
 	_TraceRuntimeFrames = 1 << iota // include frames for internal runtime functions.
 	_TraceTrap                      // the initial PC, SP are from a trap, not a return PC from a call
 	_TraceJumpStack                 // if traceback is on a systemstack, resume trace at g that called into it
 )

 const (
 	// The maximum number of frames we print for a traceback
 	_TracebackMaxFrames = 100
 )

 var (
 	emptystring string
 	allg        **g
 	allglen     uintptr
 	lastg       *g
 	allm        *m
 	allp        [_MaxGomaxprocs + 1]*p
 	gomaxprocs  int32
 	panicking   uint32
 	goos        *int8
 	ncpu        int32
 	signote     note
 	forcegc     forcegcstate
 	sched       schedt
 	newprocs    int32

 	// Information about what cpu features are available.
 	// Set on startup in asm_{x86,amd64}.s.
 	cpuid_ecx         uint32
 	cpuid_edx         uint32
 	lfenceBeforeRdtsc bool
 )

 // Set by the linker so the runtime can determine the buildmode.
 var (
 	islibrary bool // -buildmode=c-shared
 	isarchive bool // -buildmode=c-archive
 )

 /*
  * mutual exclusion locks.  in the uncontended case,
  * as fast as spin locks (just a few user-level instructions),
  * but on the contention path they sleep in the kernel.
  * a zeroed Mutex is unlocked (no need to initialize each lock).
  */

 /*
  * sleep and wakeup on one-time events.
  * before any calls to notesleep or notewakeup,
  * must call noteclear to initialize the Note.
  * then, exactly one thread can call notesleep
  * and exactly one thread can call notewakeup (once).
  * once notewakeup has been called, the notesleep
  * will return.  future notesleep will return immediately.
  * subsequent noteclear must be called only after
  * previous notesleep has returned, e.g. it's disallowed
  * to call noteclear straight after notewakeup.
  *
  * notetsleep is like notesleep but wakes up after
  * a given number of nanoseconds even if the event
  * has not yet happened.  if a goroutine uses notetsleep to
  * wake up early, it must wait to call noteclear until it
  * can be sure that no other goroutine is calling
  * notewakeup.
  *
  * notesleep/notetsleep are generally called on g0,
  * notetsleepg is similar to notetsleep but is called on user g.
  */
 // bool	runtime·notetsleep(Note*, int64);  // false - timeout
 // bool	runtime·notetsleepg(Note*, int64);  // false - timeout

 /*
  * Lock-free stack.
  * Initialize uint64 head to 0, compare with 0 to test for emptiness.
  * The stack does not keep pointers to nodes,
  * so they can be garbage collected if there are no other pointers to nodes.
  */

 // for mmap, we only pass the lower 32 bits of file offset to the
 // assembly routine; the higher bits (if required), should be provided
 // by the assembly routine as 0.
	// 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.

	package runtime

	import "unsafe"

	/*
	* defined constants
	*/
	const (
	// G status
	//
	// If you add to this list, add to the list
	// of "okay during garbage collection" status
	// in mgcmark.go too.
	_Gidle = iota // 0
	_Grunnable // 1 runnable and on a run queue
	_Grunning // 2
	_Gsyscall // 3
	_Gwaiting // 4
	_Gmoribund_unused // 5 currently unused, but hardcoded in gdb scripts
	_Gdead // 6
	_Genqueue // 7 Only the Gscanenqueue is used.
	_Gcopystack // 8 in this state when newstack is moving the stack
	// the following encode that the GC is scanning the stack and what to do when it is done
	_Gscan = 0x1000 // atomicstatus&~Gscan = the non-scan state,
	// _Gscanidle = _Gscan + _Gidle, // Not used. Gidle only used with newly malloced gs
	_Gscanrunnable = _Gscan + _Grunnable // 0x1001 When scanning complets make Grunnable (it is already on run queue)
	_Gscanrunning = _Gscan + _Grunning // 0x1002 Used to tell preemption newstack routine to scan preempted stack.
	_Gscansyscall = _Gscan + _Gsyscall // 0x1003 When scanning completes make it Gsyscall
	_Gscanwaiting = _Gscan + _Gwaiting // 0x1004 When scanning completes make it Gwaiting
	// _Gscanmoribund_unused, // not possible
	// _Gscandead, // not possible
	_Gscanenqueue = _Gscan + _Genqueue // When scanning completes make it Grunnable and put on runqueue
	)

	const (
	// P status
	_Pidle = iota
	_Prunning // Only this P is allowed to change from _Prunning.
	_Psyscall
	_Pgcstop
	_Pdead
	)

	// The next line makes 'go generate' write the zgen_*.go files with
	// per-OS and per-arch information, including constants
	// named goos_$GOOS and goarch_$GOARCH for every
	// known GOOS and GOARCH. The constant is 1 on the
	// current system, 0 otherwise; multiplying by them is
	// useful for defining GOOS- or GOARCH-specific constants.
	//go:generate go run gengoos.go

	type mutex struct {
	// Futex-based impl treats it as uint32 key,
	// while sema-based impl as M* waitm.
	// Used to be a union, but unions break precise GC.
	key uintptr
	}

	type note struct {
	// Futex-based impl treats it as uint32 key,
	// while sema-based impl as M* waitm.
	// Used to be a union, but unions break precise GC.
	key uintptr
	}

	type _string struct {
	str *byte
	len int
	}

	type funcval struct {
	fn uintptr
	// variable-size, fn-specific data here
	}

	type iface struct {
	tab *itab
	data unsafe.Pointer
	}

	type eface struct {
	_type *_type
	data unsafe.Pointer
	}

	// The guintptr, muintptr, and puintptr are all used to bypass write barriers.
	// It is particularly important to avoid write barriers when the current P has
	// been released, because the GC thinks the world is stopped, and an
	// unexpected write barrier would not be synchronized with the GC,
	// which can lead to a half-executed write barrier that has marked the object
	// but not queued it. If the GC skips the object and completes before the
	// queuing can occur, it will incorrectly free the object.
	//
	// We tried using special assignment functions invoked only when not
	// holding a running P, but then some updates to a particular memory
	// word went through write barriers and some did not. This breaks the
	// write barrier shadow checking mode, and it is also scary: better to have
	// a word that is completely ignored by the GC than to have one for which
	// only a few updates are ignored.
	//
	// Gs, Ms, and Ps are always reachable via true pointers in the
	// allgs, allm, and allp lists or (during allocation before they reach those lists)
	// from stack variables.

	// A guintptr holds a goroutine pointer, but typed as a uintptr
	// to bypass write barriers. It is used in the Gobuf goroutine state
	// and in scheduling lists that are manipulated without a P.
	//
	// The Gobuf.g goroutine pointer is almost always updated by assembly code.
	// In one of the few places it is updated by Go code - func save - it must be
	// treated as a uintptr to avoid a write barrier being emitted at a bad time.
	// Instead of figuring out how to emit the write barriers missing in the
	// assembly manipulation, we change the type of the field to uintptr,
	// so that it does not require write barriers at all.
	//
	// Goroutine structs are published in the allg list and never freed.
	// That will keep the goroutine structs from being collected.
	// There is never a time that Gobuf.g's contain the only references
	// to a goroutine: the publishing of the goroutine in allg comes first.
	// Goroutine pointers are also kept in non-GC-visible places like TLS,
	// so I can't see them ever moving. If we did want to start moving data
	// in the GC, we'd need to allocate the goroutine structs from an
	// alternate arena. Using guintptr doesn't make that problem any worse.
	type guintptr uintptr

	func (gp guintptr) ptr() g { return (g)(unsafe.Pointer(gp)) }
	func (gp guintptr) set(g g) { *gp = guintptr(unsafe.Pointer(g)) }
	func (gp *guintptr) cas(old, new guintptr) bool {
	return casuintptr((*uintptr)(unsafe.Pointer(gp)), uintptr(old), uintptr(new))
	}

	type puintptr uintptr

	func (pp puintptr) ptr() p { return (p)(unsafe.Pointer(pp)) }
	func (pp puintptr) set(p p) { *pp = puintptr(unsafe.Pointer(p)) }

	type muintptr uintptr

	func (mp muintptr) ptr() m { return (m)(unsafe.Pointer(mp)) }
	func (mp muintptr) set(m m) { *mp = muintptr(unsafe.Pointer(m)) }

	type gobuf struct {
	// The offsets of sp, pc, and g are known to (hard-coded in) libmach.
	sp uintptr
	pc uintptr
	g guintptr
	ctxt unsafe.Pointer // this has to be a pointer so that gc scans it
	ret uintreg
	lr uintptr
	bp uintptr // for GOEXPERIMENT=framepointer
	}

	// Known to compiler.
	// Changes here must also be made in src/cmd/internal/gc/select.go's selecttype.
	type sudog struct {
	g *g
	selectdone *uint32
	next *sudog
	prev *sudog
	elem unsafe.Pointer // data element
	releasetime int64
	nrelease int32 // -1 for acquire
	waitlink *sudog // g.waiting list
	}

	type gcstats struct {
	// the struct must consist of only uint64's,
	// because it is casted to uint64[].
	nhandoff uint64
	nhandoffcnt uint64
	nprocyield uint64
	nosyield uint64
	nsleep uint64
	}

	type libcall struct {
	fn uintptr
	n uintptr // number of parameters
	args uintptr // parameters
	r1 uintptr // return values
	r2 uintptr
	err uintptr // error number
	}

	// describes how to handle callback
	type wincallbackcontext struct {
	gobody unsafe.Pointer // go function to call
	argsize uintptr // callback arguments size (in bytes)
	restorestack uintptr // adjust stack on return by (in bytes) (386 only)
	cleanstack bool
	}

	// Stack describes a Go execution stack.
	// The bounds of the stack are exactly [lo, hi),
	// with no implicit data structures on either side.
	type stack struct {
	lo uintptr
	hi uintptr
	}

	type g struct {
	// Stack parameters.
	// stack describes the actual stack memory: [stack.lo, stack.hi).
	// stackguard0 is the stack pointer compared in the Go stack growth prologue.
	// It is stack.lo+StackGuard normally, but can be StackPreempt to trigger a preemption.
	// stackguard1 is the stack pointer compared in the C stack growth prologue.
	// It is stack.lo+StackGuard on g0 and gsignal stacks.
	// It is ~0 on other goroutine stacks, to trigger a call to morestackc (and crash).
	stack stack // offset known to runtime/cgo
	stackguard0 uintptr // offset known to liblink
	stackguard1 uintptr // offset known to liblink

	_panic *_panic // innermost panic - offset known to liblink
	_defer *_defer // innermost defer
	sched gobuf
	syscallsp uintptr // if status==Gsyscall, syscallsp = sched.sp to use during gc
	syscallpc uintptr // if status==Gsyscall, syscallpc = sched.pc to use during gc
	param unsafe.Pointer // passed parameter on wakeup
	atomicstatus uint32
	goid int64
	waitsince int64 // approx time when the g become blocked
	waitreason string // if status==Gwaiting
	schedlink guintptr
	preempt bool // preemption signal, duplicates stackguard0 = stackpreempt
	paniconfault bool // panic (instead of crash) on unexpected fault address
	preemptscan bool // preempted g does scan for gc
	gcworkdone bool // debug: cleared at begining of gc work phase cycle, set by gcphasework, tested at end of cycle
	gcscanvalid bool // false at start of gc cycle, true if G has not run since last scan
	throwsplit bool // must not split stack
	raceignore int8 // ignore race detection events
	m *m // for debuggers, but offset not hard-coded
	lockedm *m
	sig uint32
	writebuf []byte
	sigcode0 uintptr
	sigcode1 uintptr
	sigpc uintptr
	gopc uintptr // pc of go statement that created this goroutine
	startpc uintptr // pc of goroutine function
	racectx uintptr
	waiting *sudog // sudog structures this g is waiting on (that have a valid elem ptr)
	readyg *g // scratch for readyExecute

	// Per-G gcController state
	gcalloc uintptr // bytes allocated during this GC cycle
	gcscanwork int64 // scan work done (or stolen) this GC cycle
	}

	type mts struct {
	tv_sec int64
	tv_nsec int64
	}

	type mscratch struct {
	v [6]uintptr
	}

	type m struct {
	g0 *g // goroutine with scheduling stack
	morebuf gobuf // gobuf arg to morestack

	// Fields not known to debuggers.
	procid uint64 // for debuggers, but offset not hard-coded
	gsignal *g // signal-handling g
	sigmask [4]uintptr // storage for saved signal mask
	tls [4]uintptr // thread-local storage (for x86 extern register)
	mstartfn func()
	curg *g // current running goroutine
	caughtsig guintptr // goroutine running during fatal signal
	p puintptr // attached p for executing go code (nil if not executing go code)
	nextp puintptr
	id int32
	mallocing int32
	throwing int32
	preemptoff string // if != "", keep curg running on this m
	locks int32
	softfloat int32
	dying int32
	profilehz int32
	helpgc int32
	spinning bool // m is out of work and is actively looking for work
	blocked bool // m is blocked on a note
	inwb bool // m is executing a write barrier
	printlock int8
	fastrand uint32
	ncgocall uint64 // number of cgo calls in total
	ncgo int32 // number of cgo calls currently in progress
	park note
	alllink *m // on allm
	schedlink muintptr
	machport uint32 // return address for mach ipc (os x)
	mcache *mcache
	lockedg *g
	createstack [32]uintptr // stack that created this thread.
	freglo [16]uint32 // d[i] lsb and f[i]
	freghi [16]uint32 // d[i] msb and f[i+16]
	fflag uint32 // floating point compare flags
	locked uint32 // tracking for lockosthread
	nextwaitm uintptr // next m waiting for lock
	waitsema uintptr // semaphore for parking on locks
	waitsemacount uint32
	waitsemalock uint32
	gcstats gcstats
	needextram bool
	traceback uint8
	waitunlockf unsafe.Pointer // todo go func(*g, unsafe.pointer) bool
	waitlock unsafe.Pointer
	waittraceev byte
	waittraceskip int
	syscalltick uint32
	//#ifdef GOOS_windows
	thread uintptr // thread handle
	// these are here because they are too large to be on the stack
	// of low-level NOSPLIT functions.
	libcall libcall
	libcallpc uintptr // for cpu profiler
	libcallsp uintptr
	libcallg guintptr
	//#endif
	//#ifdef GOOS_solaris
	perrno *int32 // pointer to tls errno
	// these are here because they are too large to be on the stack
	// of low-level NOSPLIT functions.
	//LibCall libcall;
	ts mts
	scratch mscratch
	//#endif
	//#ifdef GOOS_plan9
	notesig *int8
	errstr *byte
	//#endif
	}

	type p struct {
	lock mutex

	id int32
	status uint32 // one of pidle/prunning/...
	link puintptr
	schedtick uint32 // incremented on every scheduler call
	syscalltick uint32 // incremented on every system call
	m muintptr // back-link to associated m (nil if idle)
	mcache *mcache

	deferpool [5][]*_defer // pool of available defer structs of different sizes (see panic.go)
	deferpoolbuf [5][32]*_defer

	// Cache of goroutine ids, amortizes accesses to runtime·sched.goidgen.
	goidcache uint64
	goidcacheend uint64

	// Queue of runnable goroutines. Accessed without lock.
	runqhead uint32
	runqtail uint32
	runq [256]*g
	// runnext, if non-nil, is a runnable G that was ready'd by
	// the current G and should be run next instead of what's in
	// runq if there's time remaining in the running G's time
	// slice. It will inherit the time left in the current time
	// slice. If a set of goroutines is locked in a
	// communicate-and-wait pattern, this schedules that set as a
	// unit and eliminates the (potentially large) scheduling
	// latency that otherwise arises from adding the ready'd
	// goroutines to the end of the run queue.
	runnext guintptr

	// Available G's (status == Gdead)
	gfree *g
	gfreecnt int32

	sudogcache []*sudog
	sudogbuf [128]*sudog

	tracebuf *traceBuf

	palloc persistentAlloc // per-P to avoid mutex

	// Per-P GC state
	gcAssistTime int64 // Nanoseconds in assistAlloc
	gcBgMarkWorker *g
	gcMarkWorkerMode gcMarkWorkerMode

	// gcw is this P's GC work buffer cache. The work buffer is
	// filled by write barriers, drained by mutator assists, and
	// disposed on certain GC state transitions.
	gcw gcWork

	runSafePointFn uint32 // if 1, run sched.safePointFn at next safe point

	pad [64]byte
	}

	const (
	// The max value of GOMAXPROCS.
	// There are no fundamental restrictions on the value.
	_MaxGomaxprocs = 1 << 8
	)

	type schedt struct {
	lock mutex

	goidgen uint64

	midle muintptr // idle m's waiting for work
	nmidle int32 // number of idle m's waiting for work
	nmidlelocked int32 // number of locked m's waiting for work
	mcount int32 // number of m's that have been created
	maxmcount int32 // maximum number of m's allowed (or die)

	pidle puintptr // idle p's
	npidle uint32
	nmspinning uint32

	// Global runnable queue.
	runqhead guintptr
	runqtail guintptr
	runqsize int32

	// Global cache of dead G's.
	gflock mutex
	gfree *g
	ngfree int32

	// Central cache of sudog structs.
	sudoglock mutex
	sudogcache *sudog

	// Central pool of available defer structs of different sizes.
	deferlock mutex
	deferpool [5]*_defer

	gcwaiting uint32 // gc is waiting to run
	stopwait int32
	stopnote note
	sysmonwait uint32
	sysmonnote note
	lastpoll uint64

	// safepointFn should be called on each P at the next GC
	// safepoint if p.runSafePointFn is set.
	safePointFn func(*p)
	safePointWait int32
	safePointNote note

	profilehz int32 // cpu profiling rate

	procresizetime int64 // nanotime() of last change to gomaxprocs
	totaltime int64 // ∫gomaxprocs dt up to procresizetime
	}

	// The m->locked word holds two pieces of state counting active calls to LockOSThread/lockOSThread.
	// The low bit (LockExternal) is a boolean reporting whether any LockOSThread call is active.
	// External locks are not recursive; a second lock is silently ignored.
	// The upper bits of m->lockedcount record the nesting depth of calls to lockOSThread
	// (counting up by LockInternal), popped by unlockOSThread (counting down by LockInternal).
	// Internal locks can be recursive. For instance, a lock for cgo can occur while the main
	// goroutine is holding the lock during the initialization phase.
	const (
	_LockExternal = 1
	_LockInternal = 2
	)

	type sigtabtt struct {
	flags int32
	name *int8
	}

	const (
	_SigNotify = 1 << iota // let signal.Notify have signal, even if from kernel
	_SigKill // if signal.Notify doesn't take it, exit quietly
	_SigThrow // if signal.Notify doesn't take it, exit loudly
	_SigPanic // if the signal is from the kernel, panic
	_SigDefault // if the signal isn't explicitly requested, don't monitor it
	_SigHandling // our signal handler is registered
	_SigIgnored // the signal was ignored before we registered for it
	_SigGoExit // cause all runtime procs to exit (only used on Plan 9).
	_SigSetStack // add SA_ONSTACK to libc handler
	_SigUnblock // unblocked in minit
	)

	// Layout of in-memory per-function information prepared by linker
	// See http://golang.org/s/go12symtab.
	// Keep in sync with linker
	// and with package debug/gosym and with symtab.go in package runtime.
	type _func struct {
	entry uintptr // start pc
	nameoff int32 // function name

	args int32 // in/out args size
	frame int32 // legacy frame size; use pcsp if possible

	pcsp int32
	pcfile int32
	pcln int32
	npcdata int32
	nfuncdata int32
	}

	// layout of Itab known to compilers
	// allocated in non-garbage-collected memory
	type itab struct {
	inter *interfacetype
	_type *_type
	link *itab
	bad int32
	unused int32
	fun [1]uintptr // variable sized
	}

	// Lock-free stack node.
	// // Also known to export_test.go.
	type lfnode struct {
	next uint64
	pushcnt uintptr
	}

	type forcegcstate struct {
	lock mutex
	g *g
	idle uint32
	}

	/*
	* known to compiler
	*/
	const (
	_Structrnd = regSize
	)

	// startup_random_data holds random bytes initialized at startup. These come from
	// the ELF AT_RANDOM auxiliary vector (vdso_linux_amd64.go or os_linux_386.go).
	var startupRandomData []byte

	// extendRandom extends the random numbers in r[:n] to the whole slice r.
	// Treats n<0 as n==0.
	func extendRandom(r []byte, n int) {
	if n < 0 {
	n = 0
	}
	for n < len(r) {
	// Extend random bits using hash function & time seed
	w := n
	if w > 16 {
	w = 16
	}
	h := memhash(unsafe.Pointer(&r[n-w]), uintptr(nanotime()), uintptr(w))
	for i := 0; i < ptrSize && n < len(r); i++ {
	r[n] = byte(h)
	n++
	h >>= 8
	}
	}
	}

	/*
	* deferred subroutine calls
	*/
	type _defer struct {
	siz int32
	started bool
	sp uintptr // sp at time of defer
	pc uintptr
	fn *funcval
	_panic *_panic // panic that is running defer
	link *_defer
	}

	/*
	* panics
	*/
	type _panic struct {
	argp unsafe.Pointer // pointer to arguments of deferred call run during panic; cannot move - known to liblink
	arg interface{} // argument to panic
	link *_panic // link to earlier panic
	recovered bool // whether this panic is over
	aborted bool // the panic was aborted
	}

	/*
	* stack traces
	*/

	type stkframe struct {
	fn *_func // function being run
	pc uintptr // program counter within fn
	continpc uintptr // program counter where execution can continue, or 0 if not
	lr uintptr // program counter at caller aka link register
	sp uintptr // stack pointer at pc
	fp uintptr // stack pointer at caller aka frame pointer
	varp uintptr // top of local variables
	argp uintptr // pointer to function arguments
	arglen uintptr // number of bytes at argp
	argmap *bitvector // force use of this argmap
	}

	const (
	_TraceRuntimeFrames = 1 << iota // include frames for internal runtime functions.
	_TraceTrap // the initial PC, SP are from a trap, not a return PC from a call
	_TraceJumpStack // if traceback is on a systemstack, resume trace at g that called into it
	)

	const (
	// The maximum number of frames we print for a traceback
	_TracebackMaxFrames = 100
	)

	var (
	emptystring string
	allg **g
	allglen uintptr
	lastg *g
	allm *m
	allp [_MaxGomaxprocs + 1]*p
	gomaxprocs int32
	panicking uint32
	goos *int8
	ncpu int32
	signote note
	forcegc forcegcstate
	sched schedt
	newprocs int32

	// Information about what cpu features are available.
	// Set on startup in asm_{x86,amd64}.s.
	cpuid_ecx uint32
	cpuid_edx uint32
	lfenceBeforeRdtsc bool
	)

	// Set by the linker so the runtime can determine the buildmode.
	var (
	islibrary bool // -buildmode=c-shared
	isarchive bool // -buildmode=c-archive
	)

	/*
	* mutual exclusion locks. in the uncontended case,
	* as fast as spin locks (just a few user-level instructions),
	* but on the contention path they sleep in the kernel.
	* a zeroed Mutex is unlocked (no need to initialize each lock).
	*/

	/*
	* sleep and wakeup on one-time events.
	* before any calls to notesleep or notewakeup,
	* must call noteclear to initialize the Note.
	* then, exactly one thread can call notesleep
	* and exactly one thread can call notewakeup (once).
	* once notewakeup has been called, the notesleep
	* will return. future notesleep will return immediately.
	* subsequent noteclear must be called only after
	* previous notesleep has returned, e.g. it's disallowed
	* to call noteclear straight after notewakeup.
	*
	* notetsleep is like notesleep but wakes up after
	* a given number of nanoseconds even if the event
	* has not yet happened. if a goroutine uses notetsleep to
	* wake up early, it must wait to call noteclear until it
	* can be sure that no other goroutine is calling
	* notewakeup.
	*
	* notesleep/notetsleep are generally called on g0,
	* notetsleepg is similar to notetsleep but is called on user g.
	*/
	// bool runtime·notetsleep(Note*, int64); // false - timeout
	// bool runtime·notetsleepg(Note*, int64); // false - timeout

	/*
	* Lock-free stack.
	* Initialize uint64 head to 0, compare with 0 to test for emptiness.
	* The stack does not keep pointers to nodes,
	* so they can be garbage collected if there are no other pointers to nodes.
	*/

	// for mmap, we only pass the lower 32 bits of file offset to the
	// assembly routine; the higher bits (if required), should be provided
	// by the assembly routine as 0.