1 files changed, 270 insertions, 0 deletions
diff --git a/src/runtime/lock_sema.go b/src/runtime/lock_sema.go
new file mode 100644
index 000000000..d136b8280
--- /dev/null
+++ b/src/runtime/lock_sema.go
@@ -0,0 +1,270 @@
+// Copyright 2011 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.
+
+// +build darwin nacl netbsd openbsd plan9 solaris windows
+
+package runtime
+
+import "unsafe"
+
+// This implementation depends on OS-specific implementations of
+//
+//	uintptr runtime·semacreate(void)
+//		Create a semaphore, which will be assigned to m->waitsema.
+//		The zero value is treated as absence of any semaphore,
+//		so be sure to return a non-zero value.
+//
+//	int32 runtime·semasleep(int64 ns)
+//		If ns < 0, acquire m->waitsema and return 0.
+//		If ns >= 0, try to acquire m->waitsema for at most ns nanoseconds.
+//		Return 0 if the semaphore was acquired, -1 if interrupted or timed out.
+//
+//	int32 runtime·semawakeup(M *mp)
+//		Wake up mp, which is or will soon be sleeping on mp->waitsema.
+//
+const (
+	locked uintptr = 1
+
+	active_spin     = 4
+	active_spin_cnt = 30
+	passive_spin    = 1
+)
+
+func semacreate() uintptr
+func semasleep(int64) int32
+func semawakeup(mp *m)
+
+func lock(l *mutex) {
+	gp := getg()
+	if gp.m.locks < 0 {
+		gothrow("runtime·lock: lock count")
+	}
+	gp.m.locks++
+
+	// Speculative grab for lock.
+	if casuintptr(&l.key, 0, locked) {
+		return
+	}
+	if gp.m.waitsema == 0 {
+		gp.m.waitsema = semacreate()
+	}
+
+	// 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 := atomicloaduintptr(&l.key)
+		if v&locked == 0 {
+			// Unlocked. Try to lock.
+			if 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 = (*m)((unsafe.Pointer)(v &^ locked))
+				if casuintptr(&l.key, v, uintptr(unsafe.Pointer(gp.m))|locked) {
+					break
+				}
+				v = atomicloaduintptr(&l.key)
+				if v&locked == 0 {
+					continue Loop
+				}
+			}
+			if v&locked != 0 {
+				// Queued.  Wait.
+				semasleep(-1)
+				i = 0
+			}
+		}
+	}
+}
+
+func unlock(l *mutex) {
+	gp := getg()
+	var mp *m
+	for {
+		v := atomicloaduintptr(&l.key)
+		if v == locked {
+			if 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 casuintptr(&l.key, v, uintptr(unsafe.Pointer(mp.nextwaitm))) {
+				// Dequeued an M.  Wake it.
+				semawakeup(mp)
+				break
+			}
+		}
+	}
+	gp.m.locks--
+	if gp.m.locks < 0 {
+		gothrow("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
+	}
+}
+
+// One-time notifications.
+func noteclear(n *note) {
+	n.key = 0
+}
+
+func notewakeup(n *note) {
+	var v uintptr
+	for {
+		v = atomicloaduintptr(&n.key)
+		if 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.
+		gothrow("notewakeup - double wakeup")
+	default:
+		// Must be the waiting m.  Wake it up.
+		semawakeup((*m)(unsafe.Pointer(v)))
+	}
+}
+
+func notesleep(n *note) {
+	gp := getg()
+	if gp != gp.m.g0 {
+		gothrow("notesleep not on g0")
+	}
+	if gp.m.waitsema == 0 {
+		gp.m.waitsema = semacreate()
+	}
+	if !casuintptr(&n.key, 0, uintptr(unsafe.Pointer(gp.m))) {
+		// Must be locked (got wakeup).
+		if n.key != locked {
+			gothrow("notesleep - waitm out of sync")
+		}
+		return
+	}
+	// Queued.  Sleep.
+	gp.m.blocked = true
+	semasleep(-1)
+	gp.m.blocked = false
+}
+
+//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 !casuintptr(&n.key, 0, uintptr(unsafe.Pointer(gp.m))) {
+		// Must be locked (got wakeup).
+		if n.key != locked {
+			gothrow("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 := atomicloaduintptr(&n.key)
+		switch v {
+		case uintptr(unsafe.Pointer(gp.m)):
+			// No wakeup yet; unregister if possible.
+			if 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 {
+				gothrow("runtime: unable to acquire - semaphore out of sync")
+			}
+			gp.m.blocked = false
+			return true
+		default:
+			gothrow("runtime: unexpected waitm - semaphore out of sync")
+		}
+	}
+}
+
+func notetsleep(n *note, ns int64) bool {
+	gp := getg()
+	if gp != gp.m.g0 && gp.m.gcing == 0 {
+		gothrow("notetsleep not on g0")
+	}
+	if gp.m.waitsema == 0 {
+		gp.m.waitsema = semacreate()
+	}
+	return notetsleep_internal(n, ns, nil, 0)
+}
+
+// same as runtime·notetsleep, but called on user g (not g0)
+// calls only nosplit functions between entersyscallblock/exitsyscall
+func notetsleepg(n *note, ns int64) bool {
+	gp := getg()
+	if gp == gp.m.g0 {
+		gothrow("notetsleepg on g0")
+	}
+	if gp.m.waitsema == 0 {
+		gp.m.waitsema = semacreate()
+	}
+	entersyscallblock()
+	ok := notetsleep_internal(n, ns, nil, 0)
+	exitsyscall()
+	return ok
+}