Source file src/runtime/runtime2.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package runtime
     6  
     7  import (
     8  	"internal/goarch"
     9  	"runtime/internal/atomic"
    10  	"unsafe"
    11  )
    12  
    13  // defined constants
    14  const (
    15  	// G status
    16  	//
    17  	// Beyond indicating the general state of a G, the G status
    18  	// acts like a lock on the goroutine's stack (and hence its
    19  	// ability to execute user code).
    20  	//
    21  	// If you add to this list, add to the list
    22  	// of "okay during garbage collection" status
    23  	// in mgcmark.go too.
    24  	//
    25  	// TODO(austin): The _Gscan bit could be much lighter-weight.
    26  	// For example, we could choose not to run _Gscanrunnable
    27  	// goroutines found in the run queue, rather than CAS-looping
    28  	// until they become _Grunnable. And transitions like
    29  	// _Gscanwaiting -> _Gscanrunnable are actually okay because
    30  	// they don't affect stack ownership.
    31  
    32  	// _Gidle means this goroutine was just allocated and has not
    33  	// yet been initialized.
    34  	_Gidle = iota // 0
    35  
    36  	// _Grunnable means this goroutine is on a run queue. It is
    37  	// not currently executing user code. The stack is not owned.
    38  	_Grunnable // 1
    39  
    40  	// _Grunning means this goroutine may execute user code. The
    41  	// stack is owned by this goroutine. It is not on a run queue.
    42  	// It is assigned an M and a P (g.m and g.m.p are valid).
    43  	_Grunning // 2
    44  
    45  	// _Gsyscall means this goroutine is executing a system call.
    46  	// It is not executing user code. The stack is owned by this
    47  	// goroutine. It is not on a run queue. It is assigned an M.
    48  	_Gsyscall // 3
    49  
    50  	// _Gwaiting means this goroutine is blocked in the runtime.
    51  	// It is not executing user code. It is not on a run queue,
    52  	// but should be recorded somewhere (e.g., a channel wait
    53  	// queue) so it can be ready()d when necessary. The stack is
    54  	// not owned *except* that a channel operation may read or
    55  	// write parts of the stack under the appropriate channel
    56  	// lock. Otherwise, it is not safe to access the stack after a
    57  	// goroutine enters _Gwaiting (e.g., it may get moved).
    58  	_Gwaiting // 4
    59  
    60  	// _Gmoribund_unused is currently unused, but hardcoded in gdb
    61  	// scripts.
    62  	_Gmoribund_unused // 5
    63  
    64  	// _Gdead means this goroutine is currently unused. It may be
    65  	// just exited, on a free list, or just being initialized. It
    66  	// is not executing user code. It may or may not have a stack
    67  	// allocated. The G and its stack (if any) are owned by the M
    68  	// that is exiting the G or that obtained the G from the free
    69  	// list.
    70  	_Gdead // 6
    71  
    72  	// _Genqueue_unused is currently unused.
    73  	_Genqueue_unused // 7
    74  
    75  	// _Gcopystack means this goroutine's stack is being moved. It
    76  	// is not executing user code and is not on a run queue. The
    77  	// stack is owned by the goroutine that put it in _Gcopystack.
    78  	_Gcopystack // 8
    79  
    80  	// _Gpreempted means this goroutine stopped itself for a
    81  	// suspendG preemption. It is like _Gwaiting, but nothing is
    82  	// yet responsible for ready()ing it. Some suspendG must CAS
    83  	// the status to _Gwaiting to take responsibility for
    84  	// ready()ing this G.
    85  	_Gpreempted // 9
    86  
    87  	// _Gscan combined with one of the above states other than
    88  	// _Grunning indicates that GC is scanning the stack. The
    89  	// goroutine is not executing user code and the stack is owned
    90  	// by the goroutine that set the _Gscan bit.
    91  	//
    92  	// _Gscanrunning is different: it is used to briefly block
    93  	// state transitions while GC signals the G to scan its own
    94  	// stack. This is otherwise like _Grunning.
    95  	//
    96  	// atomicstatus&~Gscan gives the state the goroutine will
    97  	// return to when the scan completes.
    98  	_Gscan          = 0x1000
    99  	_Gscanrunnable  = _Gscan + _Grunnable  // 0x1001
   100  	_Gscanrunning   = _Gscan + _Grunning   // 0x1002
   101  	_Gscansyscall   = _Gscan + _Gsyscall   // 0x1003
   102  	_Gscanwaiting   = _Gscan + _Gwaiting   // 0x1004
   103  	_Gscanpreempted = _Gscan + _Gpreempted // 0x1009
   104  )
   105  
   106  const (
   107  	// P status
   108  
   109  	// _Pidle means a P is not being used to run user code or the
   110  	// scheduler. Typically, it's on the idle P list and available
   111  	// to the scheduler, but it may just be transitioning between
   112  	// other states.
   113  	//
   114  	// The P is owned by the idle list or by whatever is
   115  	// transitioning its state. Its run queue is empty.
   116  	_Pidle = iota
   117  
   118  	// _Prunning means a P is owned by an M and is being used to
   119  	// run user code or the scheduler. Only the M that owns this P
   120  	// is allowed to change the P's status from _Prunning. The M
   121  	// may transition the P to _Pidle (if it has no more work to
   122  	// do), _Psyscall (when entering a syscall), or _Pgcstop (to
   123  	// halt for the GC). The M may also hand ownership of the P
   124  	// off directly to another M (e.g., to schedule a locked G).
   125  	_Prunning
   126  
   127  	// _Psyscall means a P is not running user code. It has
   128  	// affinity to an M in a syscall but is not owned by it and
   129  	// may be stolen by another M. This is similar to _Pidle but
   130  	// uses lightweight transitions and maintains M affinity.
   131  	//
   132  	// Leaving _Psyscall must be done with a CAS, either to steal
   133  	// or retake the P. Note that there's an ABA hazard: even if
   134  	// an M successfully CASes its original P back to _Prunning
   135  	// after a syscall, it must understand the P may have been
   136  	// used by another M in the interim.
   137  	_Psyscall
   138  
   139  	// _Pgcstop means a P is halted for STW and owned by the M
   140  	// that stopped the world. The M that stopped the world
   141  	// continues to use its P, even in _Pgcstop. Transitioning
   142  	// from _Prunning to _Pgcstop causes an M to release its P and
   143  	// park.
   144  	//
   145  	// The P retains its run queue and startTheWorld will restart
   146  	// the scheduler on Ps with non-empty run queues.
   147  	_Pgcstop
   148  
   149  	// _Pdead means a P is no longer used (GOMAXPROCS shrank). We
   150  	// reuse Ps if GOMAXPROCS increases. A dead P is mostly
   151  	// stripped of its resources, though a few things remain
   152  	// (e.g., trace buffers).
   153  	_Pdead
   154  )
   155  
   156  // Mutual exclusion locks.  In the uncontended case,
   157  // as fast as spin locks (just a few user-level instructions),
   158  // but on the contention path they sleep in the kernel.
   159  // A zeroed Mutex is unlocked (no need to initialize each lock).
   160  // Initialization is helpful for static lock ranking, but not required.
   161  type mutex struct {
   162  	// Empty struct if lock ranking is disabled, otherwise includes the lock rank
   163  	lockRankStruct
   164  	// Futex-based impl treats it as uint32 key,
   165  	// while sema-based impl as M* waitm.
   166  	// Used to be a union, but unions break precise GC.
   167  	key uintptr
   168  }
   169  
   170  // sleep and wakeup on one-time events.
   171  // before any calls to notesleep or notewakeup,
   172  // must call noteclear to initialize the Note.
   173  // then, exactly one thread can call notesleep
   174  // and exactly one thread can call notewakeup (once).
   175  // once notewakeup has been called, the notesleep
   176  // will return.  future notesleep will return immediately.
   177  // subsequent noteclear must be called only after
   178  // previous notesleep has returned, e.g. it's disallowed
   179  // to call noteclear straight after notewakeup.
   180  //
   181  // notetsleep is like notesleep but wakes up after
   182  // a given number of nanoseconds even if the event
   183  // has not yet happened.  if a goroutine uses notetsleep to
   184  // wake up early, it must wait to call noteclear until it
   185  // can be sure that no other goroutine is calling
   186  // notewakeup.
   187  //
   188  // notesleep/notetsleep are generally called on g0,
   189  // notetsleepg is similar to notetsleep but is called on user g.
   190  type note struct {
   191  	// Futex-based impl treats it as uint32 key,
   192  	// while sema-based impl as M* waitm.
   193  	// Used to be a union, but unions break precise GC.
   194  	key uintptr
   195  }
   196  
   197  type funcval struct {
   198  	fn uintptr
   199  	// variable-size, fn-specific data here
   200  }
   201  
   202  type iface struct {
   203  	tab  *itab
   204  	data unsafe.Pointer
   205  }
   206  
   207  type eface struct {
   208  	_type *_type
   209  	data  unsafe.Pointer
   210  }
   211  
   212  func efaceOf(ep *any) *eface {
   213  	return (*eface)(unsafe.Pointer(ep))
   214  }
   215  
   216  // The guintptr, muintptr, and puintptr are all used to bypass write barriers.
   217  // It is particularly important to avoid write barriers when the current P has
   218  // been released, because the GC thinks the world is stopped, and an
   219  // unexpected write barrier would not be synchronized with the GC,
   220  // which can lead to a half-executed write barrier that has marked the object
   221  // but not queued it. If the GC skips the object and completes before the
   222  // queuing can occur, it will incorrectly free the object.
   223  //
   224  // We tried using special assignment functions invoked only when not
   225  // holding a running P, but then some updates to a particular memory
   226  // word went through write barriers and some did not. This breaks the
   227  // write barrier shadow checking mode, and it is also scary: better to have
   228  // a word that is completely ignored by the GC than to have one for which
   229  // only a few updates are ignored.
   230  //
   231  // Gs and Ps are always reachable via true pointers in the
   232  // allgs and allp lists or (during allocation before they reach those lists)
   233  // from stack variables.
   234  //
   235  // Ms are always reachable via true pointers either from allm or
   236  // freem. Unlike Gs and Ps we do free Ms, so it's important that
   237  // nothing ever hold an muintptr across a safe point.
   238  
   239  // A guintptr holds a goroutine pointer, but typed as a uintptr
   240  // to bypass write barriers. It is used in the Gobuf goroutine state
   241  // and in scheduling lists that are manipulated without a P.
   242  //
   243  // The Gobuf.g goroutine pointer is almost always updated by assembly code.
   244  // In one of the few places it is updated by Go code - func save - it must be
   245  // treated as a uintptr to avoid a write barrier being emitted at a bad time.
   246  // Instead of figuring out how to emit the write barriers missing in the
   247  // assembly manipulation, we change the type of the field to uintptr,
   248  // so that it does not require write barriers at all.
   249  //
   250  // Goroutine structs are published in the allg list and never freed.
   251  // That will keep the goroutine structs from being collected.
   252  // There is never a time that Gobuf.g's contain the only references
   253  // to a goroutine: the publishing of the goroutine in allg comes first.
   254  // Goroutine pointers are also kept in non-GC-visible places like TLS,
   255  // so I can't see them ever moving. If we did want to start moving data
   256  // in the GC, we'd need to allocate the goroutine structs from an
   257  // alternate arena. Using guintptr doesn't make that problem any worse.
   258  // Note that pollDesc.rg, pollDesc.wg also store g in uintptr form,
   259  // so they would need to be updated too if g's start moving.
   260  type guintptr uintptr
   261  
   262  //go:nosplit
   263  func (gp guintptr) ptr() *g { return (*g)(unsafe.Pointer(gp)) }
   264  
   265  //go:nosplit
   266  func (gp *guintptr) set(g *g) { *gp = guintptr(unsafe.Pointer(g)) }
   267  
   268  //go:nosplit
   269  func (gp *guintptr) cas(old, new guintptr) bool {
   270  	return atomic.Casuintptr((*uintptr)(unsafe.Pointer(gp)), uintptr(old), uintptr(new))
   271  }
   272  
   273  // setGNoWB performs *gp = new without a write barrier.
   274  // For times when it's impractical to use a guintptr.
   275  //
   276  //go:nosplit
   277  //go:nowritebarrier
   278  func setGNoWB(gp **g, new *g) {
   279  	(*guintptr)(unsafe.Pointer(gp)).set(new)
   280  }
   281  
   282  type puintptr uintptr
   283  
   284  //go:nosplit
   285  func (pp puintptr) ptr() *p { return (*p)(unsafe.Pointer(pp)) }
   286  
   287  //go:nosplit
   288  func (pp *puintptr) set(p *p) { *pp = puintptr(unsafe.Pointer(p)) }
   289  
   290  // muintptr is a *m that is not tracked by the garbage collector.
   291  //
   292  // Because we do free Ms, there are some additional constrains on
   293  // muintptrs:
   294  //
   295  //  1. Never hold an muintptr locally across a safe point.
   296  //
   297  //  2. Any muintptr in the heap must be owned by the M itself so it can
   298  //     ensure it is not in use when the last true *m is released.
   299  type muintptr uintptr
   300  
   301  //go:nosplit
   302  func (mp muintptr) ptr() *m { return (*m)(unsafe.Pointer(mp)) }
   303  
   304  //go:nosplit
   305  func (mp *muintptr) set(m *m) { *mp = muintptr(unsafe.Pointer(m)) }
   306  
   307  // setMNoWB performs *mp = new without a write barrier.
   308  // For times when it's impractical to use an muintptr.
   309  //
   310  //go:nosplit
   311  //go:nowritebarrier
   312  func setMNoWB(mp **m, new *m) {
   313  	(*muintptr)(unsafe.Pointer(mp)).set(new)
   314  }
   315  
   316  type gobuf struct {
   317  	// The offsets of sp, pc, and g are known to (hard-coded in) libmach.
   318  	//
   319  	// ctxt is unusual with respect to GC: it may be a
   320  	// heap-allocated funcval, so GC needs to track it, but it
   321  	// needs to be set and cleared from assembly, where it's
   322  	// difficult to have write barriers. However, ctxt is really a
   323  	// saved, live register, and we only ever exchange it between
   324  	// the real register and the gobuf. Hence, we treat it as a
   325  	// root during stack scanning, which means assembly that saves
   326  	// and restores it doesn't need write barriers. It's still
   327  	// typed as a pointer so that any other writes from Go get
   328  	// write barriers.
   329  	sp   uintptr
   330  	pc   uintptr
   331  	g    guintptr
   332  	ctxt unsafe.Pointer
   333  	ret  uintptr
   334  	lr   uintptr
   335  	bp   uintptr // for framepointer-enabled architectures
   336  }
   337  
   338  // sudog represents a g in a wait list, such as for sending/receiving
   339  // on a channel.
   340  //
   341  // sudog is necessary because the g ↔ synchronization object relation
   342  // is many-to-many. A g can be on many wait lists, so there may be
   343  // many sudogs for one g; and many gs may be waiting on the same
   344  // synchronization object, so there may be many sudogs for one object.
   345  //
   346  // sudogs are allocated from a special pool. Use acquireSudog and
   347  // releaseSudog to allocate and free them.
   348  type sudog struct {
   349  	// The following fields are protected by the hchan.lock of the
   350  	// channel this sudog is blocking on. shrinkstack depends on
   351  	// this for sudogs involved in channel ops.
   352  
   353  	g *g
   354  
   355  	next *sudog
   356  	prev *sudog
   357  	elem unsafe.Pointer // data element (may point to stack)
   358  
   359  	// The following fields are never accessed concurrently.
   360  	// For channels, waitlink is only accessed by g.
   361  	// For semaphores, all fields (including the ones above)
   362  	// are only accessed when holding a semaRoot lock.
   363  
   364  	acquiretime int64
   365  	releasetime int64
   366  	ticket      uint32
   367  
   368  	// isSelect indicates g is participating in a select, so
   369  	// g.selectDone must be CAS'd to win the wake-up race.
   370  	isSelect bool
   371  
   372  	// success indicates whether communication over channel c
   373  	// succeeded. It is true if the goroutine was awoken because a
   374  	// value was delivered over channel c, and false if awoken
   375  	// because c was closed.
   376  	success bool
   377  
   378  	parent   *sudog // semaRoot binary tree
   379  	waitlink *sudog // g.waiting list or semaRoot
   380  	waittail *sudog // semaRoot
   381  	c        *hchan // channel
   382  }
   383  
   384  type libcall struct {
   385  	fn   uintptr
   386  	n    uintptr // number of parameters
   387  	args uintptr // parameters
   388  	r1   uintptr // return values
   389  	r2   uintptr
   390  	err  uintptr // error number
   391  }
   392  
   393  // Stack describes a Go execution stack.
   394  // The bounds of the stack are exactly [lo, hi),
   395  // with no implicit data structures on either side.
   396  type stack struct {
   397  	lo uintptr
   398  	hi uintptr
   399  }
   400  
   401  // heldLockInfo gives info on a held lock and the rank of that lock
   402  type heldLockInfo struct {
   403  	lockAddr uintptr
   404  	rank     lockRank
   405  }
   406  
   407  type g struct {
   408  	// Stack parameters.
   409  	// stack describes the actual stack memory: [stack.lo, stack.hi).
   410  	// stackguard0 is the stack pointer compared in the Go stack growth prologue.
   411  	// It is stack.lo+StackGuard normally, but can be StackPreempt to trigger a preemption.
   412  	// stackguard1 is the stack pointer compared in the C stack growth prologue.
   413  	// It is stack.lo+StackGuard on g0 and gsignal stacks.
   414  	// It is ~0 on other goroutine stacks, to trigger a call to morestackc (and crash).
   415  	stack       stack   // offset known to runtime/cgo
   416  	stackguard0 uintptr // offset known to liblink
   417  	stackguard1 uintptr // offset known to liblink
   418  
   419  	_panic    *_panic // innermost panic - offset known to liblink
   420  	_defer    *_defer // innermost defer
   421  	m         *m      // current m; offset known to arm liblink
   422  	sched     gobuf
   423  	syscallsp uintptr // if status==Gsyscall, syscallsp = sched.sp to use during gc
   424  	syscallpc uintptr // if status==Gsyscall, syscallpc = sched.pc to use during gc
   425  	stktopsp  uintptr // expected sp at top of stack, to check in traceback
   426  	// param is a generic pointer parameter field used to pass
   427  	// values in particular contexts where other storage for the
   428  	// parameter would be difficult to find. It is currently used
   429  	// in three ways:
   430  	// 1. When a channel operation wakes up a blocked goroutine, it sets param to
   431  	//    point to the sudog of the completed blocking operation.
   432  	// 2. By gcAssistAlloc1 to signal back to its caller that the goroutine completed
   433  	//    the GC cycle. It is unsafe to do so in any other way, because the goroutine's
   434  	//    stack may have moved in the meantime.
   435  	// 3. By debugCallWrap to pass parameters to a new goroutine because allocating a
   436  	//    closure in the runtime is forbidden.
   437  	param        unsafe.Pointer
   438  	atomicstatus uint32
   439  	stackLock    uint32 // sigprof/scang lock; TODO: fold in to atomicstatus
   440  	goid         int64
   441  	schedlink    guintptr
   442  	waitsince    int64      // approx time when the g become blocked
   443  	waitreason   waitReason // if status==Gwaiting
   444  
   445  	preempt       bool // preemption signal, duplicates stackguard0 = stackpreempt
   446  	preemptStop   bool // transition to _Gpreempted on preemption; otherwise, just deschedule
   447  	preemptShrink bool // shrink stack at synchronous safe point
   448  
   449  	// asyncSafePoint is set if g is stopped at an asynchronous
   450  	// safe point. This means there are frames on the stack
   451  	// without precise pointer information.
   452  	asyncSafePoint bool
   453  
   454  	paniconfault bool // panic (instead of crash) on unexpected fault address
   455  	gcscandone   bool // g has scanned stack; protected by _Gscan bit in status
   456  	throwsplit   bool // must not split stack
   457  	// activeStackChans indicates that there are unlocked channels
   458  	// pointing into this goroutine's stack. If true, stack
   459  	// copying needs to acquire channel locks to protect these
   460  	// areas of the stack.
   461  	activeStackChans bool
   462  	// parkingOnChan indicates that the goroutine is about to
   463  	// park on a chansend or chanrecv. Used to signal an unsafe point
   464  	// for stack shrinking. It's a boolean value, but is updated atomically.
   465  	parkingOnChan uint8
   466  
   467  	raceignore     int8     // ignore race detection events
   468  	sysblocktraced bool     // StartTrace has emitted EvGoInSyscall about this goroutine
   469  	tracking       bool     // whether we're tracking this G for sched latency statistics
   470  	trackingSeq    uint8    // used to decide whether to track this G
   471  	runnableStamp  int64    // timestamp of when the G last became runnable, only used when tracking
   472  	runnableTime   int64    // the amount of time spent runnable, cleared when running, only used when tracking
   473  	sysexitticks   int64    // cputicks when syscall has returned (for tracing)
   474  	traceseq       uint64   // trace event sequencer
   475  	tracelastp     puintptr // last P emitted an event for this goroutine
   476  	lockedm        muintptr
   477  	sig            uint32
   478  	writebuf       []byte
   479  	sigcode0       uintptr
   480  	sigcode1       uintptr
   481  	sigpc          uintptr
   482  	gopc           uintptr         // pc of go statement that created this goroutine
   483  	ancestors      *[]ancestorInfo // ancestor information goroutine(s) that created this goroutine (only used if debug.tracebackancestors)
   484  	startpc        uintptr         // pc of goroutine function
   485  	racectx        uintptr
   486  	waiting        *sudog         // sudog structures this g is waiting on (that have a valid elem ptr); in lock order
   487  	cgoCtxt        []uintptr      // cgo traceback context
   488  	labels         unsafe.Pointer // profiler labels
   489  	timer          *timer         // cached timer for time.Sleep
   490  	selectDone     uint32         // are we participating in a select and did someone win the race?
   491  
   492  	// goroutineProfiled indicates the status of this goroutine's stack for the
   493  	// current in-progress goroutine profile
   494  	goroutineProfiled goroutineProfileStateHolder
   495  
   496  	// Per-G GC state
   497  
   498  	// gcAssistBytes is this G's GC assist credit in terms of
   499  	// bytes allocated. If this is positive, then the G has credit
   500  	// to allocate gcAssistBytes bytes without assisting. If this
   501  	// is negative, then the G must correct this by performing
   502  	// scan work. We track this in bytes to make it fast to update
   503  	// and check for debt in the malloc hot path. The assist ratio
   504  	// determines how this corresponds to scan work debt.
   505  	gcAssistBytes int64
   506  }
   507  
   508  // gTrackingPeriod is the number of transitions out of _Grunning between
   509  // latency tracking runs.
   510  const gTrackingPeriod = 8
   511  
   512  const (
   513  	// tlsSlots is the number of pointer-sized slots reserved for TLS on some platforms,
   514  	// like Windows.
   515  	tlsSlots = 6
   516  	tlsSize  = tlsSlots * goarch.PtrSize
   517  )
   518  
   519  // Values for m.freeWait.
   520  const (
   521  	freeMStack = 0  // M done, free stack and reference.
   522  	freeMRef   = 1  // M done, free reference.
   523  	freeMWait  = 2  // M still in use.
   524  )
   525  
   526  type m struct {
   527  	g0      *g     // goroutine with scheduling stack
   528  	morebuf gobuf  // gobuf arg to morestack
   529  	divmod  uint32 // div/mod denominator for arm - known to liblink
   530  	_       uint32 // align next field to 8 bytes
   531  
   532  	// Fields not known to debuggers.
   533  	procid        uint64            // for debuggers, but offset not hard-coded
   534  	gsignal       *g                // signal-handling g
   535  	goSigStack    gsignalStack      // Go-allocated signal handling stack
   536  	sigmask       sigset            // storage for saved signal mask
   537  	tls           [tlsSlots]uintptr // thread-local storage (for x86 extern register)
   538  	mstartfn      func()
   539  	curg          *g       // current running goroutine
   540  	caughtsig     guintptr // goroutine running during fatal signal
   541  	p             puintptr // attached p for executing go code (nil if not executing go code)
   542  	nextp         puintptr
   543  	oldp          puintptr // the p that was attached before executing a syscall
   544  	id            int64
   545  	mallocing     int32
   546  	throwing      throwType
   547  	preemptoff    string // if != "", keep curg running on this m
   548  	locks         int32
   549  	dying         int32
   550  	profilehz     int32
   551  	spinning      bool // m is out of work and is actively looking for work
   552  	blocked       bool // m is blocked on a note
   553  	newSigstack   bool // minit on C thread called sigaltstack
   554  	printlock     int8
   555  	incgo         bool   // m is executing a cgo call
   556  	freeWait      atomic.Uint32 // Whether it is safe to free g0 and delete m (one of freeMRef, freeMStack, freeMWait)
   557  	fastrand      uint64
   558  	needextram    bool
   559  	traceback     uint8
   560  	ncgocall      uint64      // number of cgo calls in total
   561  	ncgo          int32       // number of cgo calls currently in progress
   562  	cgoCallersUse uint32      // if non-zero, cgoCallers in use temporarily
   563  	cgoCallers    *cgoCallers // cgo traceback if crashing in cgo call
   564  	park          note
   565  	alllink       *m // on allm
   566  	schedlink     muintptr
   567  	lockedg       guintptr
   568  	createstack   [32]uintptr // stack that created this thread.
   569  	lockedExt     uint32      // tracking for external LockOSThread
   570  	lockedInt     uint32      // tracking for internal lockOSThread
   571  	nextwaitm     muintptr    // next m waiting for lock
   572  	waitunlockf   func(*g, unsafe.Pointer) bool
   573  	waitlock      unsafe.Pointer
   574  	waittraceev   byte
   575  	waittraceskip int
   576  	startingtrace bool
   577  	syscalltick   uint32
   578  	freelink      *m // on sched.freem
   579  
   580  	// these are here because they are too large to be on the stack
   581  	// of low-level NOSPLIT functions.
   582  	libcall   libcall
   583  	libcallpc uintptr // for cpu profiler
   584  	libcallsp uintptr
   585  	libcallg  guintptr
   586  	syscall   libcall // stores syscall parameters on windows
   587  
   588  	vdsoSP uintptr // SP for traceback while in VDSO call (0 if not in call)
   589  	vdsoPC uintptr // PC for traceback while in VDSO call
   590  
   591  	// preemptGen counts the number of completed preemption
   592  	// signals. This is used to detect when a preemption is
   593  	// requested, but fails. Accessed atomically.
   594  	preemptGen uint32
   595  
   596  	// Whether this is a pending preemption signal on this M.
   597  	// Accessed atomically.
   598  	signalPending uint32
   599  
   600  	dlogPerM
   601  
   602  	mOS
   603  
   604  	// Up to 10 locks held by this m, maintained by the lock ranking code.
   605  	locksHeldLen int
   606  	locksHeld    [10]heldLockInfo
   607  }
   608  
   609  type p struct {
   610  	id          int32
   611  	status      uint32 // one of pidle/prunning/...
   612  	link        puintptr
   613  	schedtick   uint32     // incremented on every scheduler call
   614  	syscalltick uint32     // incremented on every system call
   615  	sysmontick  sysmontick // last tick observed by sysmon
   616  	m           muintptr   // back-link to associated m (nil if idle)
   617  	mcache      *mcache
   618  	pcache      pageCache
   619  	raceprocctx uintptr
   620  
   621  	deferpool    []*_defer // pool of available defer structs (see panic.go)
   622  	deferpoolbuf [32]*_defer
   623  
   624  	// Cache of goroutine ids, amortizes accesses to runtime·sched.goidgen.
   625  	goidcache    uint64
   626  	goidcacheend uint64
   627  
   628  	// Queue of runnable goroutines. Accessed without lock.
   629  	runqhead uint32
   630  	runqtail uint32
   631  	runq     [256]guintptr
   632  	// runnext, if non-nil, is a runnable G that was ready'd by
   633  	// the current G and should be run next instead of what's in
   634  	// runq if there's time remaining in the running G's time
   635  	// slice. It will inherit the time left in the current time
   636  	// slice. If a set of goroutines is locked in a
   637  	// communicate-and-wait pattern, this schedules that set as a
   638  	// unit and eliminates the (potentially large) scheduling
   639  	// latency that otherwise arises from adding the ready'd
   640  	// goroutines to the end of the run queue.
   641  	//
   642  	// Note that while other P's may atomically CAS this to zero,
   643  	// only the owner P can CAS it to a valid G.
   644  	runnext guintptr
   645  
   646  	// Available G's (status == Gdead)
   647  	gFree struct {
   648  		gList
   649  		n int32
   650  	}
   651  
   652  	sudogcache []*sudog
   653  	sudogbuf   [128]*sudog
   654  
   655  	// Cache of mspan objects from the heap.
   656  	mspancache struct {
   657  		// We need an explicit length here because this field is used
   658  		// in allocation codepaths where write barriers are not allowed,
   659  		// and eliminating the write barrier/keeping it eliminated from
   660  		// slice updates is tricky, moreso than just managing the length
   661  		// ourselves.
   662  		len int
   663  		buf [128]*mspan
   664  	}
   665  
   666  	tracebuf traceBufPtr
   667  
   668  	// traceSweep indicates the sweep events should be traced.
   669  	// This is used to defer the sweep start event until a span
   670  	// has actually been swept.
   671  	traceSweep bool
   672  	// traceSwept and traceReclaimed track the number of bytes
   673  	// swept and reclaimed by sweeping in the current sweep loop.
   674  	traceSwept, traceReclaimed uintptr
   675  
   676  	palloc persistentAlloc // per-P to avoid mutex
   677  
   678  	_ uint32 // Alignment for atomic fields below
   679  
   680  	// The when field of the first entry on the timer heap.
   681  	// This is updated using atomic functions.
   682  	// This is 0 if the timer heap is empty.
   683  	timer0When uint64
   684  
   685  	// The earliest known nextwhen field of a timer with
   686  	// timerModifiedEarlier status. Because the timer may have been
   687  	// modified again, there need not be any timer with this value.
   688  	// This is updated using atomic functions.
   689  	// This is 0 if there are no timerModifiedEarlier timers.
   690  	timerModifiedEarliest uint64
   691  
   692  	// Per-P GC state
   693  	gcAssistTime         int64 // Nanoseconds in assistAlloc
   694  	gcFractionalMarkTime int64 // Nanoseconds in fractional mark worker (atomic)
   695  
   696  	// limiterEvent tracks events for the GC CPU limiter.
   697  	limiterEvent limiterEvent
   698  
   699  	// gcMarkWorkerMode is the mode for the next mark worker to run in.
   700  	// That is, this is used to communicate with the worker goroutine
   701  	// selected for immediate execution by
   702  	// gcController.findRunnableGCWorker. When scheduling other goroutines,
   703  	// this field must be set to gcMarkWorkerNotWorker.
   704  	gcMarkWorkerMode gcMarkWorkerMode
   705  	// gcMarkWorkerStartTime is the nanotime() at which the most recent
   706  	// mark worker started.
   707  	gcMarkWorkerStartTime int64
   708  
   709  	// gcw is this P's GC work buffer cache. The work buffer is
   710  	// filled by write barriers, drained by mutator assists, and
   711  	// disposed on certain GC state transitions.
   712  	gcw gcWork
   713  
   714  	// wbBuf is this P's GC write barrier buffer.
   715  	//
   716  	// TODO: Consider caching this in the running G.
   717  	wbBuf wbBuf
   718  
   719  	runSafePointFn uint32 // if 1, run sched.safePointFn at next safe point
   720  
   721  	// statsSeq is a counter indicating whether this P is currently
   722  	// writing any stats. Its value is even when not, odd when it is.
   723  	statsSeq uint32
   724  
   725  	// Lock for timers. We normally access the timers while running
   726  	// on this P, but the scheduler can also do it from a different P.
   727  	timersLock mutex
   728  
   729  	// Actions to take at some time. This is used to implement the
   730  	// standard library's time package.
   731  	// Must hold timersLock to access.
   732  	timers []*timer
   733  
   734  	// Number of timers in P's heap.
   735  	// Modified using atomic instructions.
   736  	numTimers uint32
   737  
   738  	// Number of timerDeleted timers in P's heap.
   739  	// Modified using atomic instructions.
   740  	deletedTimers uint32
   741  
   742  	// Race context used while executing timer functions.
   743  	timerRaceCtx uintptr
   744  
   745  	// maxStackScanDelta accumulates the amount of stack space held by
   746  	// live goroutines (i.e. those eligible for stack scanning).
   747  	// Flushed to gcController.maxStackScan once maxStackScanSlack
   748  	// or -maxStackScanSlack is reached.
   749  	maxStackScanDelta int64
   750  
   751  	// gc-time statistics about current goroutines
   752  	// Note that this differs from maxStackScan in that this
   753  	// accumulates the actual stack observed to be used at GC time (hi - sp),
   754  	// not an instantaneous measure of the total stack size that might need
   755  	// to be scanned (hi - lo).
   756  	scannedStackSize uint64 // stack size of goroutines scanned by this P
   757  	scannedStacks    uint64 // number of goroutines scanned by this P
   758  
   759  	// preempt is set to indicate that this P should be enter the
   760  	// scheduler ASAP (regardless of what G is running on it).
   761  	preempt bool
   762  
   763  	// Padding is no longer needed. False sharing is now not a worry because p is large enough
   764  	// that its size class is an integer multiple of the cache line size (for any of our architectures).
   765  }
   766  
   767  type schedt struct {
   768  	// accessed atomically. keep at top to ensure alignment on 32-bit systems.
   769  	goidgen   uint64
   770  	lastpoll  uint64 // time of last network poll, 0 if currently polling
   771  	pollUntil uint64 // time to which current poll is sleeping
   772  
   773  	lock mutex
   774  
   775  	// When increasing nmidle, nmidlelocked, nmsys, or nmfreed, be
   776  	// sure to call checkdead().
   777  
   778  	midle        muintptr // idle m's waiting for work
   779  	nmidle       int32    // number of idle m's waiting for work
   780  	nmidlelocked int32    // number of locked m's waiting for work
   781  	mnext        int64    // number of m's that have been created and next M ID
   782  	maxmcount    int32    // maximum number of m's allowed (or die)
   783  	nmsys        int32    // number of system m's not counted for deadlock
   784  	nmfreed      int64    // cumulative number of freed m's
   785  
   786  	ngsys uint32 // number of system goroutines; updated atomically
   787  
   788  	pidle      puintptr // idle p's
   789  	npidle     uint32
   790  	nmspinning uint32 // See "Worker thread parking/unparking" comment in proc.go.
   791  
   792  	// Global runnable queue.
   793  	runq     gQueue
   794  	runqsize int32
   795  
   796  	// disable controls selective disabling of the scheduler.
   797  	//
   798  	// Use schedEnableUser to control this.
   799  	//
   800  	// disable is protected by sched.lock.
   801  	disable struct {
   802  		// user disables scheduling of user goroutines.
   803  		user     bool
   804  		runnable gQueue // pending runnable Gs
   805  		n        int32  // length of runnable
   806  	}
   807  
   808  	// Global cache of dead G's.
   809  	gFree struct {
   810  		lock    mutex
   811  		stack   gList // Gs with stacks
   812  		noStack gList // Gs without stacks
   813  		n       int32
   814  	}
   815  
   816  	// Central cache of sudog structs.
   817  	sudoglock  mutex
   818  	sudogcache *sudog
   819  
   820  	// Central pool of available defer structs.
   821  	deferlock mutex
   822  	deferpool *_defer
   823  
   824  	// freem is the list of m's waiting to be freed when their
   825  	// m.exited is set. Linked through m.freelink.
   826  	freem *m
   827  
   828  	gcwaiting  uint32 // gc is waiting to run
   829  	stopwait   int32
   830  	stopnote   note
   831  	sysmonwait uint32
   832  	sysmonnote note
   833  
   834  	// safepointFn should be called on each P at the next GC
   835  	// safepoint if p.runSafePointFn is set.
   836  	safePointFn   func(*p)
   837  	safePointWait int32
   838  	safePointNote note
   839  
   840  	profilehz int32 // cpu profiling rate
   841  
   842  	procresizetime int64 // nanotime() of last change to gomaxprocs
   843  	totaltime      int64 // ∫gomaxprocs dt up to procresizetime
   844  
   845  	// sysmonlock protects sysmon's actions on the runtime.
   846  	//
   847  	// Acquire and hold this mutex to block sysmon from interacting
   848  	// with the rest of the runtime.
   849  	sysmonlock mutex
   850  
   851  	// timeToRun is a distribution of scheduling latencies, defined
   852  	// as the sum of time a G spends in the _Grunnable state before
   853  	// it transitions to _Grunning.
   854  	//
   855  	// timeToRun is protected by sched.lock.
   856  	timeToRun timeHistogram
   857  }
   858  
   859  // Values for the flags field of a sigTabT.
   860  const (
   861  	_SigNotify   = 1 << iota // let signal.Notify have signal, even if from kernel
   862  	_SigKill                 // if signal.Notify doesn't take it, exit quietly
   863  	_SigThrow                // if signal.Notify doesn't take it, exit loudly
   864  	_SigPanic                // if the signal is from the kernel, panic
   865  	_SigDefault              // if the signal isn't explicitly requested, don't monitor it
   866  	_SigGoExit               // cause all runtime procs to exit (only used on Plan 9).
   867  	_SigSetStack             // Don't explicitly install handler, but add SA_ONSTACK to existing libc handler
   868  	_SigUnblock              // always unblock; see blockableSig
   869  	_SigIgn                  // _SIG_DFL action is to ignore the signal
   870  )
   871  
   872  // Layout of in-memory per-function information prepared by linker
   873  // See https://golang.org/s/go12symtab.
   874  // Keep in sync with linker (../cmd/link/internal/ld/pcln.go:/pclntab)
   875  // and with package debug/gosym and with symtab.go in package runtime.
   876  type _func struct {
   877  	entryoff uint32 // start pc, as offset from moduledata.text/pcHeader.textStart
   878  	nameoff  int32  // function name
   879  
   880  	args        int32  // in/out args size
   881  	deferreturn uint32 // offset of start of a deferreturn call instruction from entry, if any.
   882  
   883  	pcsp      uint32
   884  	pcfile    uint32
   885  	pcln      uint32
   886  	npcdata   uint32
   887  	cuOffset  uint32 // runtime.cutab offset of this function's CU
   888  	funcID    funcID // set for certain special runtime functions
   889  	flag      funcFlag
   890  	_         [1]byte // pad
   891  	nfuncdata uint8   // must be last, must end on a uint32-aligned boundary
   892  }
   893  
   894  // Pseudo-Func that is returned for PCs that occur in inlined code.
   895  // A *Func can be either a *_func or a *funcinl, and they are distinguished
   896  // by the first uintptr.
   897  type funcinl struct {
   898  	ones  uint32  // set to ^0 to distinguish from _func
   899  	entry uintptr // entry of the real (the "outermost") frame
   900  	name  string
   901  	file  string
   902  	line  int
   903  }
   904  
   905  // layout of Itab known to compilers
   906  // allocated in non-garbage-collected memory
   907  // Needs to be in sync with
   908  // ../cmd/compile/internal/reflectdata/reflect.go:/^func.WriteTabs.
   909  type itab struct {
   910  	inter *interfacetype
   911  	_type *_type
   912  	hash  uint32 // copy of _type.hash. Used for type switches.
   913  	_     [4]byte
   914  	fun   [1]uintptr // variable sized. fun[0]==0 means _type does not implement inter.
   915  }
   916  
   917  // Lock-free stack node.
   918  // Also known to export_test.go.
   919  type lfnode struct {
   920  	next    uint64
   921  	pushcnt uintptr
   922  }
   923  
   924  type forcegcstate struct {
   925  	lock mutex
   926  	g    *g
   927  	idle uint32
   928  }
   929  
   930  // extendRandom extends the random numbers in r[:n] to the whole slice r.
   931  // Treats n<0 as n==0.
   932  func extendRandom(r []byte, n int) {
   933  	if n < 0 {
   934  		n = 0
   935  	}
   936  	for n < len(r) {
   937  		// Extend random bits using hash function & time seed
   938  		w := n
   939  		if w > 16 {
   940  			w = 16
   941  		}
   942  		h := memhash(unsafe.Pointer(&r[n-w]), uintptr(nanotime()), uintptr(w))
   943  		for i := 0; i < goarch.PtrSize && n < len(r); i++ {
   944  			r[n] = byte(h)
   945  			n++
   946  			h >>= 8
   947  		}
   948  	}
   949  }
   950  
   951  // A _defer holds an entry on the list of deferred calls.
   952  // If you add a field here, add code to clear it in deferProcStack.
   953  // This struct must match the code in cmd/compile/internal/ssagen/ssa.go:deferstruct
   954  // and cmd/compile/internal/ssagen/ssa.go:(*state).call.
   955  // Some defers will be allocated on the stack and some on the heap.
   956  // All defers are logically part of the stack, so write barriers to
   957  // initialize them are not required. All defers must be manually scanned,
   958  // and for heap defers, marked.
   959  type _defer struct {
   960  	started bool
   961  	heap    bool
   962  	// openDefer indicates that this _defer is for a frame with open-coded
   963  	// defers. We have only one defer record for the entire frame (which may
   964  	// currently have 0, 1, or more defers active).
   965  	openDefer bool
   966  	sp        uintptr // sp at time of defer
   967  	pc        uintptr // pc at time of defer
   968  	fn        func()  // can be nil for open-coded defers
   969  	_panic    *_panic // panic that is running defer
   970  	link      *_defer // next defer on G; can point to either heap or stack!
   971  
   972  	// If openDefer is true, the fields below record values about the stack
   973  	// frame and associated function that has the open-coded defer(s). sp
   974  	// above will be the sp for the frame, and pc will be address of the
   975  	// deferreturn call in the function.
   976  	fd   unsafe.Pointer // funcdata for the function associated with the frame
   977  	varp uintptr        // value of varp for the stack frame
   978  	// framepc is the current pc associated with the stack frame. Together,
   979  	// with sp above (which is the sp associated with the stack frame),
   980  	// framepc/sp can be used as pc/sp pair to continue a stack trace via
   981  	// gentraceback().
   982  	framepc uintptr
   983  }
   984  
   985  // A _panic holds information about an active panic.
   986  //
   987  // A _panic value must only ever live on the stack.
   988  //
   989  // The argp and link fields are stack pointers, but don't need special
   990  // handling during stack growth: because they are pointer-typed and
   991  // _panic values only live on the stack, regular stack pointer
   992  // adjustment takes care of them.
   993  type _panic struct {
   994  	argp      unsafe.Pointer // pointer to arguments of deferred call run during panic; cannot move - known to liblink
   995  	arg       any            // argument to panic
   996  	link      *_panic        // link to earlier panic
   997  	pc        uintptr        // where to return to in runtime if this panic is bypassed
   998  	sp        unsafe.Pointer // where to return to in runtime if this panic is bypassed
   999  	recovered bool           // whether this panic is over
  1000  	aborted   bool           // the panic was aborted
  1001  	goexit    bool
  1002  }
  1003  
  1004  // stack traces
  1005  type stkframe struct {
  1006  	fn       funcInfo   // function being run
  1007  	pc       uintptr    // program counter within fn
  1008  	continpc uintptr    // program counter where execution can continue, or 0 if not
  1009  	lr       uintptr    // program counter at caller aka link register
  1010  	sp       uintptr    // stack pointer at pc
  1011  	fp       uintptr    // stack pointer at caller aka frame pointer
  1012  	varp     uintptr    // top of local variables
  1013  	argp     uintptr    // pointer to function arguments
  1014  	arglen   uintptr    // number of bytes at argp
  1015  	argmap   *bitvector // force use of this argmap
  1016  }
  1017  
  1018  // ancestorInfo records details of where a goroutine was started.
  1019  type ancestorInfo struct {
  1020  	pcs  []uintptr // pcs from the stack of this goroutine
  1021  	goid int64     // goroutine id of this goroutine; original goroutine possibly dead
  1022  	gopc uintptr   // pc of go statement that created this goroutine
  1023  }
  1024  
  1025  const (
  1026  	_TraceRuntimeFrames = 1 << iota // include frames for internal runtime functions.
  1027  	_TraceTrap                      // the initial PC, SP are from a trap, not a return PC from a call
  1028  	_TraceJumpStack                 // if traceback is on a systemstack, resume trace at g that called into it
  1029  )
  1030  
  1031  // The maximum number of frames we print for a traceback
  1032  const _TracebackMaxFrames = 100
  1033  
  1034  // A waitReason explains why a goroutine has been stopped.
  1035  // See gopark. Do not re-use waitReasons, add new ones.
  1036  type waitReason uint8
  1037  
  1038  const (
  1039  	waitReasonZero                  waitReason = iota // ""
  1040  	waitReasonGCAssistMarking                         // "GC assist marking"
  1041  	waitReasonIOWait                                  // "IO wait"
  1042  	waitReasonChanReceiveNilChan                      // "chan receive (nil chan)"
  1043  	waitReasonChanSendNilChan                         // "chan send (nil chan)"
  1044  	waitReasonDumpingHeap                             // "dumping heap"
  1045  	waitReasonGarbageCollection                       // "garbage collection"
  1046  	waitReasonGarbageCollectionScan                   // "garbage collection scan"
  1047  	waitReasonPanicWait                               // "panicwait"
  1048  	waitReasonSelect                                  // "select"
  1049  	waitReasonSelectNoCases                           // "select (no cases)"
  1050  	waitReasonGCAssistWait                            // "GC assist wait"
  1051  	waitReasonGCSweepWait                             // "GC sweep wait"
  1052  	waitReasonGCScavengeWait                          // "GC scavenge wait"
  1053  	waitReasonChanReceive                             // "chan receive"
  1054  	waitReasonChanSend                                // "chan send"
  1055  	waitReasonFinalizerWait                           // "finalizer wait"
  1056  	waitReasonForceGCIdle                             // "force gc (idle)"
  1057  	waitReasonSemacquire                              // "semacquire"
  1058  	waitReasonSleep                                   // "sleep"
  1059  	waitReasonSyncCondWait                            // "sync.Cond.Wait"
  1060  	waitReasonTimerGoroutineIdle                      // "timer goroutine (idle)"
  1061  	waitReasonTraceReaderBlocked                      // "trace reader (blocked)"
  1062  	waitReasonWaitForGCCycle                          // "wait for GC cycle"
  1063  	waitReasonGCWorkerIdle                            // "GC worker (idle)"
  1064  	waitReasonPreempted                               // "preempted"
  1065  	waitReasonDebugCall                               // "debug call"
  1066  )
  1067  
  1068  var waitReasonStrings = [...]string{
  1069  	waitReasonZero:                  "",
  1070  	waitReasonGCAssistMarking:       "GC assist marking",
  1071  	waitReasonIOWait:                "IO wait",
  1072  	waitReasonChanReceiveNilChan:    "chan receive (nil chan)",
  1073  	waitReasonChanSendNilChan:       "chan send (nil chan)",
  1074  	waitReasonDumpingHeap:           "dumping heap",
  1075  	waitReasonGarbageCollection:     "garbage collection",
  1076  	waitReasonGarbageCollectionScan: "garbage collection scan",
  1077  	waitReasonPanicWait:             "panicwait",
  1078  	waitReasonSelect:                "select",
  1079  	waitReasonSelectNoCases:         "select (no cases)",
  1080  	waitReasonGCAssistWait:          "GC assist wait",
  1081  	waitReasonGCSweepWait:           "GC sweep wait",
  1082  	waitReasonGCScavengeWait:        "GC scavenge wait",
  1083  	waitReasonChanReceive:           "chan receive",
  1084  	waitReasonChanSend:              "chan send",
  1085  	waitReasonFinalizerWait:         "finalizer wait",
  1086  	waitReasonForceGCIdle:           "force gc (idle)",
  1087  	waitReasonSemacquire:            "semacquire",
  1088  	waitReasonSleep:                 "sleep",
  1089  	waitReasonSyncCondWait:          "sync.Cond.Wait",
  1090  	waitReasonTimerGoroutineIdle:    "timer goroutine (idle)",
  1091  	waitReasonTraceReaderBlocked:    "trace reader (blocked)",
  1092  	waitReasonWaitForGCCycle:        "wait for GC cycle",
  1093  	waitReasonGCWorkerIdle:          "GC worker (idle)",
  1094  	waitReasonPreempted:             "preempted",
  1095  	waitReasonDebugCall:             "debug call",
  1096  }
  1097  
  1098  func (w waitReason) String() string {
  1099  	if w < 0 || w >= waitReason(len(waitReasonStrings)) {
  1100  		return "unknown wait reason"
  1101  	}
  1102  	return waitReasonStrings[w]
  1103  }
  1104  
  1105  var (
  1106  	allm       *m
  1107  	gomaxprocs int32
  1108  	ncpu       int32
  1109  	forcegc    forcegcstate
  1110  	sched      schedt
  1111  	newprocs   int32
  1112  
  1113  	// allpLock protects P-less reads and size changes of allp, idlepMask,
  1114  	// and timerpMask, and all writes to allp.
  1115  	allpLock mutex
  1116  	// len(allp) == gomaxprocs; may change at safe points, otherwise
  1117  	// immutable.
  1118  	allp []*p
  1119  	// Bitmask of Ps in _Pidle list, one bit per P. Reads and writes must
  1120  	// be atomic. Length may change at safe points.
  1121  	//
  1122  	// Each P must update only its own bit. In order to maintain
  1123  	// consistency, a P going idle must the idle mask simultaneously with
  1124  	// updates to the idle P list under the sched.lock, otherwise a racing
  1125  	// pidleget may clear the mask before pidleput sets the mask,
  1126  	// corrupting the bitmap.
  1127  	//
  1128  	// N.B., procresize takes ownership of all Ps in stopTheWorldWithSema.
  1129  	idlepMask pMask
  1130  	// Bitmask of Ps that may have a timer, one bit per P. Reads and writes
  1131  	// must be atomic. Length may change at safe points.
  1132  	timerpMask pMask
  1133  
  1134  	// Pool of GC parked background workers. Entries are type
  1135  	// *gcBgMarkWorkerNode.
  1136  	gcBgMarkWorkerPool lfstack
  1137  
  1138  	// Total number of gcBgMarkWorker goroutines. Protected by worldsema.
  1139  	gcBgMarkWorkerCount int32
  1140  
  1141  	// Information about what cpu features are available.
  1142  	// Packages outside the runtime should not use these
  1143  	// as they are not an external api.
  1144  	// Set on startup in asm_{386,amd64}.s
  1145  	processorVersionInfo uint32
  1146  	isIntel              bool
  1147  
  1148  	goarm uint8 // set by cmd/link on arm systems
  1149  )
  1150  
  1151  // Set by the linker so the runtime can determine the buildmode.
  1152  var (
  1153  	islibrary bool // -buildmode=c-shared
  1154  	isarchive bool // -buildmode=c-archive
  1155  )
  1156  
  1157  // Must agree with internal/buildcfg.FramePointerEnabled.
  1158  const framepointer_enabled = GOARCH == "amd64" || GOARCH == "arm64"
  1159  

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