Golang atomic.Loaduintptr函数代码示例

func lock(l *mutex) {
	gp := getg()
	if gp.m.locks < 0 {
		throw("runtime·lock: lock count")
	}
	gp.m.locks++

	// Speculative grab for lock.
	if atomic.Casuintptr(&l.key, 0, locked) {
		return
	}
	semacreate(gp.m)

	// On uniprocessor's, no point spinning.
	// On multiprocessors, spin for ACTIVE_SPIN attempts.
	spin := 0
	if ncpu > 1 {
		spin = active_spin
	}
Loop:
	for i := 0; ; i++ {
		v := atomic.Loaduintptr(&l.key)
		if v&locked == 0 {
			// Unlocked. Try to lock.
			if atomic.Casuintptr(&l.key, v, v|locked) {
				return
			}
			i = 0
		}
		if i < spin {
			procyield(active_spin_cnt)
		} else if i < spin+passive_spin {
			osyield()
		} else {
			// Someone else has it.
			// l->waitm points to a linked list of M's waiting
			// for this lock, chained through m->nextwaitm.
			// Queue this M.
			for {
				gp.m.nextwaitm = v &^ locked
				if atomic.Casuintptr(&l.key, v, uintptr(unsafe.Pointer(gp.m))|locked) {
					break
				}
				v = atomic.Loaduintptr(&l.key)
				if v&locked == 0 {
					continue Loop
				}
			}
			if v&locked != 0 {
				// Queued.  Wait.
				semasleep(-1)
				i = 0
			}
		}
	}
}

// block returns the spans in the i'th block of buffer b. block is
// safe to call concurrently with push.
func (b *gcSweepBuf) block(i int) []*mspan {
	// Perform bounds check before loading spine address since
	// push ensures the allocated length is at least spineLen.
	if i < 0 || uintptr(i) >= atomic.Loaduintptr(&b.spineLen) {
		throw("block index out of range")
	}

	// Get block i.
	spine := atomic.Loadp(unsafe.Pointer(&b.spine))
	blockp := add(spine, sys.PtrSize*uintptr(i))
	block := (*gcSweepBlock)(atomic.Loadp(blockp))

	// Slice the block if necessary.
	cursor := uintptr(atomic.Load(&b.index))
	top, bottom := cursor/gcSweepBlockEntries, cursor%gcSweepBlockEntries
	var spans []*mspan
	if uintptr(i) < top {
		spans = block.spans[:]
	} else {
		spans = block.spans[:bottom]
	}

	// push may have reserved a slot but not filled it yet, so
	// trim away unused entries.
	for len(spans) > 0 && spans[len(spans)-1] == nil {
		spans = spans[:len(spans)-1]
	}
	return spans
}

//go:nowritebarrier
// We might not be holding a p in this code.
func unlock(l *mutex) {
	gp := getg()
	var mp *m
	for {
		v := atomic.Loaduintptr(&l.key)
		if v == locked {
			if atomic.Casuintptr(&l.key, locked, 0) {
				break
			}
		} else {
			// Other M's are waiting for the lock.
			// Dequeue an M.
			mp = (*m)(unsafe.Pointer(v &^ locked))
			if atomic.Casuintptr(&l.key, v, mp.nextwaitm) {
				// Dequeued an M.  Wake it.
				semawakeup(mp)
				break
			}
		}
	}
	gp.m.locks--
	if gp.m.locks < 0 {
		throw("runtime·unlock: lock count")
	}
	if gp.m.locks == 0 && gp.preempt { // restore the preemption request in case we've cleared it in newstack
		gp.stackguard0 = stackPreempt
	}
}

// lockextra locks the extra list and returns the list head.
// The caller must unlock the list by storing a new list head
// to extram. If nilokay is true, then lockextra will
// return a nil list head if that's what it finds. If nilokay is false,
// lockextra will keep waiting until the list head is no longer nil.
//go:nosplit
func lockextra(nilokay bool) *m {
	const locked = 1

	incr := false
	for {
		old := atomic.Loaduintptr(&extram)
		if old == locked {
			yield := osyield
			yield()
			continue
		}
		if old == 0 && !nilokay {
			if !incr {
				// Add 1 to the number of threads
				// waiting for an M.
				// This is cleared by newextram.
				atomic.Xadd(&extraMWaiters, 1)
				incr = true
			}
			usleep(1)
			continue
		}
		if atomic.Casuintptr(&extram, old, locked) {
			return (*m)(unsafe.Pointer(old))
		}
		yield := osyield
		yield()
		continue
	}
}

// gcMarkRootPrepare queues root scanning jobs (stacks, globals, and
// some miscellany) and initializes scanning-related state.
//
// The caller must have call gcCopySpans().
//
// The world must be stopped.
//
//go:nowritebarrier
func gcMarkRootPrepare() {
	// Compute how many data and BSS root blocks there are.
	nBlocks := func(bytes uintptr) int {
		return int((bytes + rootBlockBytes - 1) / rootBlockBytes)
	}

	work.nDataRoots = 0
	work.nBSSRoots = 0

	// Only scan globals once per cycle; preferably concurrently.
	if !work.markrootDone {
		for datap := &firstmoduledata; datap != nil; datap = datap.next {
			nDataRoots := nBlocks(datap.edata - datap.data)
			if nDataRoots > work.nDataRoots {
				work.nDataRoots = nDataRoots
			}
		}

		for datap := &firstmoduledata; datap != nil; datap = datap.next {
			nBSSRoots := nBlocks(datap.ebss - datap.bss)
			if nBSSRoots > work.nBSSRoots {
				work.nBSSRoots = nBSSRoots
			}
		}
	}

	if !work.markrootDone {
		// On the first markroot, we need to scan span roots.
		// In concurrent GC, this happens during concurrent
		// mark and we depend on addfinalizer to ensure the
		// above invariants for objects that get finalizers
		// after concurrent mark. In STW GC, this will happen
		// during mark termination.
		work.nSpanRoots = (len(work.spans) + rootBlockSpans - 1) / rootBlockSpans

		// On the first markroot, we need to scan all Gs. Gs
		// may be created after this point, but it's okay that
		// we ignore them because they begin life without any
		// roots, so there's nothing to scan, and any roots
		// they create during the concurrent phase will be
		// scanned during mark termination. During mark
		// termination, allglen isn't changing, so we'll scan
		// all Gs.
		work.nStackRoots = int(atomic.Loaduintptr(&allglen))
		work.nRescanRoots = 0
	} else {
		// We've already scanned span roots and kept the scan
		// up-to-date during concurrent mark.
		work.nSpanRoots = 0

		// On the second pass of markroot, we're just scanning
		// dirty stacks. It's safe to access rescan since the
		// world is stopped.
		work.nStackRoots = 0
		work.nRescanRoots = len(work.rescan.list)
	}

	work.markrootNext = 0
	work.markrootJobs = uint32(fixedRootCount + work.nDataRoots + work.nBSSRoots + work.nSpanRoots + work.nStackRoots + work.nRescanRoots)
}

func notewakeup(n *note) {
	var v uintptr
	for {
		v = atomic.Loaduintptr(&n.key)
		if atomic.Casuintptr(&n.key, v, locked) {
			break
		}
	}

	// Successfully set waitm to locked.
	// What was it before?
	switch {
	case v == 0:
		// Nothing was waiting. Done.
	case v == locked:
		// Two notewakeups!  Not allowed.
		throw("notewakeup - double wakeup")
	default:
		// Must be the waiting m.  Wake it up.
		semawakeup((*m)(unsafe.Pointer(v)))
	}
}

func profileloop1(param uintptr) uint32 {
	stdcall2(_SetThreadPriority, currentThread, _THREAD_PRIORITY_HIGHEST)

	for {
		stdcall2(_WaitForSingleObject, profiletimer, _INFINITE)
		first := (*m)(atomic.Loadp(unsafe.Pointer(&allm)))
		for mp := first; mp != nil; mp = mp.alllink {
			thread := atomic.Loaduintptr(&mp.thread)
			// Do not profile threads blocked on Notes,
			// this includes idle worker threads,
			// idle timer thread, idle heap scavenger, etc.
			if thread == 0 || mp.profilehz == 0 || mp.blocked {
				continue
			}
			stdcall1(_SuspendThread, thread)
			if mp.profilehz != 0 && !mp.blocked {
				profilem(mp)
			}
			stdcall1(_ResumeThread, thread)
		}
	}
}

// gcMarkRootPrepare queues root scanning jobs (stacks, globals, and
// some miscellany) and initializes scanning-related state.
//
// The caller must have call gcCopySpans().
//
//go:nowritebarrier
func gcMarkRootPrepare() {
	// Compute how many data and BSS root blocks there are.
	nBlocks := func(bytes uintptr) int {
		return int((bytes + rootBlockBytes - 1) / rootBlockBytes)
	}

	work.nDataRoots = 0
	for datap := &firstmoduledata; datap != nil; datap = datap.next {
		nDataRoots := nBlocks(datap.edata - datap.data)
		if nDataRoots > work.nDataRoots {
			work.nDataRoots = nDataRoots
		}
	}

	work.nBSSRoots = 0
	for datap := &firstmoduledata; datap != nil; datap = datap.next {
		nBSSRoots := nBlocks(datap.ebss - datap.bss)
		if nBSSRoots > work.nBSSRoots {
			work.nBSSRoots = nBSSRoots
		}
	}

	// Compute number of span roots.
	work.nSpanRoots = (len(work.spans) + rootBlockSpans - 1) / rootBlockSpans

	// Snapshot of allglen. During concurrent scan, we just need
	// to be consistent about how many markroot jobs we create and
	// how many Gs we check. Gs may be created after this point,
	// but it's okay that we ignore them because they begin life
	// without any roots, so there's nothing to scan, and any
	// roots they create during the concurrent phase will be
	// scanned during mark termination. During mark termination,
	// allglen isn't changing, so we'll scan all Gs.
	work.nStackRoots = int(atomic.Loaduintptr(&allglen))

	work.markrootNext = 0
	work.markrootJobs = uint32(fixedRootCount + work.nDataRoots + work.nBSSRoots + work.nSpanRoots + work.nStackRoots)
}

// gcMarkRootPrepare queues root scanning jobs (stacks, globals, and
// some miscellany) and initializes scanning-related state.
//
// The caller must have call gcCopySpans().
//
// The world must be stopped.
//
//go:nowritebarrier
func gcMarkRootPrepare() {
	if gcphase == _GCmarktermination {
		work.nFlushCacheRoots = int(gomaxprocs)
	} else {
		work.nFlushCacheRoots = 0
	}

	// Compute how many data and BSS root blocks there are.
	nBlocks := func(bytes uintptr) int {
		return int((bytes + rootBlockBytes - 1) / rootBlockBytes)
	}

	work.nDataRoots = 0
	work.nBSSRoots = 0

	// Only scan globals once per cycle; preferably concurrently.
	if !work.markrootDone {
		for _, datap := range activeModules() {
			nDataRoots := nBlocks(datap.edata - datap.data)
			if nDataRoots > work.nDataRoots {
				work.nDataRoots = nDataRoots
			}
		}

		for _, datap := range activeModules() {
			nBSSRoots := nBlocks(datap.ebss - datap.bss)
			if nBSSRoots > work.nBSSRoots {
				work.nBSSRoots = nBSSRoots
			}
		}
	}

	if !work.markrootDone {
		// On the first markroot, we need to scan span roots.
		// In concurrent GC, this happens during concurrent
		// mark and we depend on addfinalizer to ensure the
		// above invariants for objects that get finalizers
		// after concurrent mark. In STW GC, this will happen
		// during mark termination.
		//
		// We're only interested in scanning the in-use spans,
		// which will all be swept at this point. More spans
		// may be added to this list during concurrent GC, but
		// we only care about spans that were allocated before
		// this mark phase.
		work.nSpanRoots = mheap_.sweepSpans[mheap_.sweepgen/2%2].numBlocks()

		// On the first markroot, we need to scan all Gs. Gs
		// may be created after this point, but it's okay that
		// we ignore them because they begin life without any
		// roots, so there's nothing to scan, and any roots
		// they create during the concurrent phase will be
		// scanned during mark termination. During mark
		// termination, allglen isn't changing, so we'll scan
		// all Gs.
		work.nStackRoots = int(atomic.Loaduintptr(&allglen))
		work.nRescanRoots = 0
	} else {
		// We've already scanned span roots and kept the scan
		// up-to-date during concurrent mark.
		work.nSpanRoots = 0

		// On the second pass of markroot, we're just scanning
		// dirty stacks. It's safe to access rescan since the
		// world is stopped.
		work.nStackRoots = 0
		work.nRescanRoots = len(work.rescan.list)
	}

	work.markrootNext = 0
	work.markrootJobs = uint32(fixedRootCount + work.nFlushCacheRoots + work.nDataRoots + work.nBSSRoots + work.nSpanRoots + work.nStackRoots + work.nRescanRoots)
}

// push adds span s to buffer b. push is safe to call concurrently
// with other push operations, but NOT to call concurrently with pop.
func (b *gcSweepBuf) push(s *mspan) {
	// Obtain our slot.
	cursor := uintptr(atomic.Xadd(&b.index, +1) - 1)
	top, bottom := cursor/gcSweepBlockEntries, cursor%gcSweepBlockEntries

	// Do we need to add a block?
	spineLen := atomic.Loaduintptr(&b.spineLen)
	var block *gcSweepBlock
retry:
	if top < spineLen {
		spine := atomic.Loadp(unsafe.Pointer(&b.spine))
		blockp := add(spine, sys.PtrSize*top)
		block = (*gcSweepBlock)(atomic.Loadp(blockp))
	} else {
		// Add a new block to the spine, potentially growing
		// the spine.
		lock(&b.spineLock)
		// spineLen cannot change until we release the lock,
		// but may have changed while we were waiting.
		spineLen = atomic.Loaduintptr(&b.spineLen)
		if top < spineLen {
			unlock(&b.spineLock)
			goto retry
		}

		if spineLen == b.spineCap {
			// Grow the spine.
			newCap := b.spineCap * 2
			if newCap == 0 {
				newCap = gcSweepBufInitSpineCap
			}
			newSpine := persistentalloc(newCap*sys.PtrSize, sys.CacheLineSize, &memstats.gc_sys)
			if b.spineCap != 0 {
				// Blocks are allocated off-heap, so
				// no write barriers.
				memmove(newSpine, b.spine, b.spineCap*sys.PtrSize)
			}
			// Spine is allocated off-heap, so no write barrier.
			atomic.StorepNoWB(unsafe.Pointer(&b.spine), newSpine)
			b.spineCap = newCap
			// We can't immediately free the old spine
			// since a concurrent push with a lower index
			// could still be reading from it. We let it
			// leak because even a 1TB heap would waste
			// less than 2MB of memory on old spines. If
			// this is a problem, we could free old spines
			// during STW.
		}

		// Allocate a new block and add it to the spine.
		block = (*gcSweepBlock)(persistentalloc(unsafe.Sizeof(gcSweepBlock{}), sys.CacheLineSize, &memstats.gc_sys))
		blockp := add(b.spine, sys.PtrSize*top)
		// Blocks are allocated off-heap, so no write barrier.
		atomic.StorepNoWB(blockp, unsafe.Pointer(block))
		atomic.Storeuintptr(&b.spineLen, spineLen+1)
		unlock(&b.spineLock)
	}

	// We have a block. Insert the span.
	block.spans[bottom] = s
}

// Called from runtime·morestack when more stack is needed.
// Allocate larger stack and relocate to new stack.
// Stack growth is multiplicative, for constant amortized cost.
//
// g->atomicstatus will be Grunning or Gscanrunning upon entry.
// If the GC is trying to stop this g then it will set preemptscan to true.
func newstack() {
	thisg := getg()
	// TODO: double check all gp. shouldn't be getg().
	if thisg.m.morebuf.g.ptr().stackguard0 == stackFork {
		throw("stack growth after fork")
	}
	if thisg.m.morebuf.g.ptr() != thisg.m.curg {
		print("runtime: newstack called from g=", hex(thisg.m.morebuf.g), "\n"+"\tm=", thisg.m, " m->curg=", thisg.m.curg, " m->g0=", thisg.m.g0, " m->gsignal=", thisg.m.gsignal, "\n")
		morebuf := thisg.m.morebuf
		traceback(morebuf.pc, morebuf.sp, morebuf.lr, morebuf.g.ptr())
		throw("runtime: wrong goroutine in newstack")
	}
	if thisg.m.curg.throwsplit {
		gp := thisg.m.curg
		// Update syscallsp, syscallpc in case traceback uses them.
		morebuf := thisg.m.morebuf
		gp.syscallsp = morebuf.sp
		gp.syscallpc = morebuf.pc
		print("runtime: newstack sp=", hex(gp.sched.sp), " stack=[", hex(gp.stack.lo), ", ", hex(gp.stack.hi), "]\n",
			"\tmorebuf={pc:", hex(morebuf.pc), " sp:", hex(morebuf.sp), " lr:", hex(morebuf.lr), "}\n",
			"\tsched={pc:", hex(gp.sched.pc), " sp:", hex(gp.sched.sp), " lr:", hex(gp.sched.lr), " ctxt:", gp.sched.ctxt, "}\n")

		traceback(morebuf.pc, morebuf.sp, morebuf.lr, gp)
		throw("runtime: stack split at bad time")
	}

	gp := thisg.m.curg
	morebuf := thisg.m.morebuf
	thisg.m.morebuf.pc = 0
	thisg.m.morebuf.lr = 0
	thisg.m.morebuf.sp = 0
	thisg.m.morebuf.g = 0
	rewindmorestack(&gp.sched)

	// NOTE: stackguard0 may change underfoot, if another thread
	// is about to try to preempt gp. Read it just once and use that same
	// value now and below.
	preempt := atomic.Loaduintptr(&gp.stackguard0) == stackPreempt

	// Be conservative about where we preempt.
	// We are interested in preempting user Go code, not runtime code.
	// If we're holding locks, mallocing, or preemption is disabled, don't
	// preempt.
	// This check is very early in newstack so that even the status change
	// from Grunning to Gwaiting and back doesn't happen in this case.
	// That status change by itself can be viewed as a small preemption,
	// because the GC might change Gwaiting to Gscanwaiting, and then
	// this goroutine has to wait for the GC to finish before continuing.
	// If the GC is in some way dependent on this goroutine (for example,
	// it needs a lock held by the goroutine), that small preemption turns
	// into a real deadlock.
	if preempt {
		if thisg.m.locks != 0 || thisg.m.mallocing != 0 || thisg.m.preemptoff != "" || thisg.m.p.ptr().status != _Prunning {
			// Let the goroutine keep running for now.
			// gp->preempt is set, so it will be preempted next time.
			gp.stackguard0 = gp.stack.lo + _StackGuard
			gogo(&gp.sched) // never return
		}
	}

	if gp.stack.lo == 0 {
		throw("missing stack in newstack")
	}
	sp := gp.sched.sp
	if sys.ArchFamily == sys.AMD64 || sys.ArchFamily == sys.I386 {
		// The call to morestack cost a word.
		sp -= sys.PtrSize
	}
	if stackDebug >= 1 || sp < gp.stack.lo {
		print("runtime: newstack sp=", hex(sp), " stack=[", hex(gp.stack.lo), ", ", hex(gp.stack.hi), "]\n",
			"\tmorebuf={pc:", hex(morebuf.pc), " sp:", hex(morebuf.sp), " lr:", hex(morebuf.lr), "}\n",
			"\tsched={pc:", hex(gp.sched.pc), " sp:", hex(gp.sched.sp), " lr:", hex(gp.sched.lr), " ctxt:", gp.sched.ctxt, "}\n")
	}
	if sp < gp.stack.lo {
		print("runtime: gp=", gp, ", gp->status=", hex(readgstatus(gp)), "\n ")
		print("runtime: split stack overflow: ", hex(sp), " < ", hex(gp.stack.lo), "\n")
		throw("runtime: split stack overflow")
	}

	if gp.sched.ctxt != nil {
		// morestack wrote sched.ctxt on its way in here,
		// without a write barrier. Run the write barrier now.
		// It is not possible to be preempted between then
		// and now, so it's okay.
		writebarrierptr_nostore((*uintptr)(unsafe.Pointer(&gp.sched.ctxt)), uintptr(gp.sched.ctxt))
	}

	if preempt {
		if gp == thisg.m.g0 {
			throw("runtime: preempt g0")
		}
		if thisg.m.p == 0 && thisg.m.locks == 0 {
			throw("runtime: g is running but p is not")
		}
//.........这里部分代码省略.........

//go:nosplit
func notetsleep_internal(n *note, ns int64, gp *g, deadline int64) bool {
	// gp and deadline are logically local variables, but they are written
	// as parameters so that the stack space they require is charged
	// to the caller.
	// This reduces the nosplit footprint of notetsleep_internal.
	gp = getg()

	// Register for wakeup on n->waitm.
	if !atomic.Casuintptr(&n.key, 0, uintptr(unsafe.Pointer(gp.m))) {
		// Must be locked (got wakeup).
		if n.key != locked {
			throw("notetsleep - waitm out of sync")
		}
		return true
	}
	if ns < 0 {
		// Queued.  Sleep.
		gp.m.blocked = true
		semasleep(-1)
		gp.m.blocked = false
		return true
	}

	deadline = nanotime() + ns
	for {
		// Registered.  Sleep.
		gp.m.blocked = true
		if semasleep(ns) >= 0 {
			gp.m.blocked = false
			// Acquired semaphore, semawakeup unregistered us.
			// Done.
			return true
		}
		gp.m.blocked = false
		// Interrupted or timed out.  Still registered.  Semaphore not acquired.
		ns = deadline - nanotime()
		if ns <= 0 {
			break
		}
		// Deadline hasn't arrived.  Keep sleeping.
	}

	// Deadline arrived.  Still registered.  Semaphore not acquired.
	// Want to give up and return, but have to unregister first,
	// so that any notewakeup racing with the return does not
	// try to grant us the semaphore when we don't expect it.
	for {
		v := atomic.Loaduintptr(&n.key)
		switch v {
		case uintptr(unsafe.Pointer(gp.m)):
			// No wakeup yet; unregister if possible.
			if atomic.Casuintptr(&n.key, v, 0) {
				return false
			}
		case locked:
			// Wakeup happened so semaphore is available.
			// Grab it to avoid getting out of sync.
			gp.m.blocked = true
			if semasleep(-1) < 0 {
				throw("runtime: unable to acquire - semaphore out of sync")
			}
			gp.m.blocked = false
			return true
		default:
			throw("runtime: unexpected waitm - semaphore out of sync")
		}
	}
}