Golang atomic.Casuintptr函数代码示例

//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
	}
}

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
			}
		}
	}
}

func netpollunblock(pd *pollDesc, mode int32, ioready bool) *g {
	gpp := &pd.rg
	if mode == 'w' {
		gpp = &pd.wg
	}

	for {
		old := *gpp
		if old == pdReady {
			return nil
		}
		if old == 0 && !ioready {
			// Only set READY for ioready. runtime_pollWait
			// will check for timeout/cancel before waiting.
			return nil
		}
		var new uintptr
		if ioready {
			new = pdReady
		}
		if atomic.Casuintptr(gpp, old, new) {
			if old == pdReady || old == pdWait {
				old = 0
			}
			return (*g)(unsafe.Pointer(old))
		}
	}
}

// returns true if IO is ready, or false if timedout or closed
// waitio - wait only for completed IO, ignore errors
func netpollblock(pd *pollDesc, mode int32, waitio bool) bool {
	gpp := &pd.rg
	if mode == 'w' {
		gpp = &pd.wg
	}

	// set the gpp semaphore to WAIT
	for {
		old := *gpp
		if old == pdReady {
			*gpp = 0
			return true
		}
		if old != 0 {
			throw("netpollblock: double wait")
		}
		if atomic.Casuintptr(gpp, 0, pdWait) {
			break
		}
	}

	// need to recheck error states after setting gpp to WAIT
	// this is necessary because runtime_pollUnblock/runtime_pollSetDeadline/deadlineimpl
	// do the opposite: store to closing/rd/wd, membarrier, load of rg/wg
	if waitio || netpollcheckerr(pd, mode) == 0 {
		gopark(netpollblockcommit, unsafe.Pointer(gpp), "IO wait", traceEvGoBlockNet, 5)
	}
	// be careful to not lose concurrent READY notification
	old := atomic.Xchguintptr(gpp, 0)
	if old > pdWait {
		throw("netpollblock: corrupted state")
	}
	return old == pdReady
}

// 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
	}
}

//go:nosplit
func gostringnocopy(str *byte) string {
	ss := stringStruct{str: unsafe.Pointer(str), len: findnull(str)}
	s := *(*string)(unsafe.Pointer(&ss))
	for {
		ms := maxstring
		if uintptr(len(s)) <= ms || atomic.Casuintptr(&maxstring, ms, uintptr(len(s))) {
			break
		}
	}
	return s
}

// rawstring allocates storage for a new string. The returned
// string and byte slice both refer to the same storage.
// The storage is not zeroed. Callers should use
// b to set the string contents and then drop b.
func rawstring(size int) (s string, b []byte) {
	p := mallocgc(uintptr(size), nil, flagNoScan|flagNoZero)

	stringStructOf(&s).str = p
	stringStructOf(&s).len = size

	*(*slice)(unsafe.Pointer(&b)) = slice{p, size, size}

	for {
		ms := maxstring
		if uintptr(size) <= ms || atomic.Casuintptr((*uintptr)(unsafe.Pointer(&maxstring)), ms, uintptr(size)) {
			return
		}
	}
}

func notesleep(n *note) {
	gp := getg()
	if gp != gp.m.g0 {
		throw("notesleep not on g0")
	}
	semacreate(gp.m)
	if !atomic.Casuintptr(&n.key, 0, uintptr(unsafe.Pointer(gp.m))) {
		// Must be locked (got wakeup).
		if n.key != locked {
			throw("notesleep - waitm out of sync")
		}
		return
	}
	// Queued.  Sleep.
	gp.m.blocked = true
	semasleep(-1)
	gp.m.blocked = false
}

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 notesleep(n *note) {
	gp := getg()

	// Currently OK to sleep in non-g0 for gccgo.  It happens in
	// stoptheworld because we have not implemented preemption.
	// if gp != gp.m.g0 {
	//	throw("notesleep not on g0")
	// }

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

//go:nosplit
func (gp *guintptr) cas(old, new guintptr) bool {
	return atomic.Casuintptr((*uintptr)(unsafe.Pointer(gp)), uintptr(old), uintptr(new))
}

func netpollblockcommit(gp *g, gpp unsafe.Pointer) bool {
	return atomic.Casuintptr((*uintptr)(gpp), pdWait, uintptr(unsafe.Pointer(gp)))
}

//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")
		}
	}
}