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Diffstat (limited to 'libgo/go/runtime/lock_sema.go')
| -rw-r--r-- | libgo/go/runtime/lock_sema.go | 281 |
1 files changed, 281 insertions, 0 deletions
diff --git a/libgo/go/runtime/lock_sema.go b/libgo/go/runtime/lock_sema.go new file mode 100644 index 0000000..eaf938a --- /dev/null +++ b/libgo/go/runtime/lock_sema.go @@ -0,0 +1,281 @@ +// 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 ( + "runtime/internal/atomic" + "unsafe" +) + +// For gccgo, while we still have C runtime code, use go:linkname to +// rename some functions to themselves, so that the compiler will +// export them. +// +//go:linkname lock runtime.lock +//go:linkname unlock runtime.unlock +//go:linkname noteclear runtime.noteclear +//go:linkname notewakeup runtime.notewakeup +//go:linkname notesleep runtime.notesleep +//go:linkname notetsleep runtime.notetsleep +//go:linkname notetsleepg runtime.notetsleepg + +// This implementation depends on OS-specific implementations of +// +// func semacreate(mp *m) +// Create a semaphore for mp, if it does not already have one. +// +// func semasleep(ns int64) int32 +// If ns < 0, acquire m's semaphore and return 0. +// If ns >= 0, try to acquire m's semaphore for at most ns nanoseconds. +// Return 0 if the semaphore was acquired, -1 if interrupted or timed out. +// +// func semawakeup(mp *m) +// Wake up mp, which is or will soon be sleeping on its semaphore. +// +const ( + mutex_locked uintptr = 1 + + active_spin = 4 + active_spin_cnt = 30 + passive_spin = 1 +) + +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, mutex_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&mutex_locked == 0 { + // Unlocked. Try to lock. + if atomic.Casuintptr(&l.key, v, v|mutex_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 &^ mutex_locked + if atomic.Casuintptr(&l.key, v, uintptr(unsafe.Pointer(gp.m))|mutex_locked) { + break + } + v = atomic.Loaduintptr(&l.key) + if v&mutex_locked == 0 { + continue Loop + } + } + if v&mutex_locked != 0 { + // Queued. Wait. + semasleep(-1) + i = 0 + } + } + } +} + +//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 == mutex_locked { + if atomic.Casuintptr(&l.key, mutex_locked, 0) { + break + } + } else { + // Other M's are waiting for the lock. + // Dequeue an M. + mp = (*m)(unsafe.Pointer(v &^ mutex_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 + // } +} + +// One-time notifications. +func noteclear(n *note) { + n.key = 0 +} + +func notewakeup(n *note) { + var v uintptr + for { + v = atomic.Loaduintptr(&n.key) + if atomic.Casuintptr(&n.key, v, mutex_locked) { + break + } + } + + // Successfully set waitm to locked. + // What was it before? + switch { + case v == 0: + // Nothing was waiting. Done. + case v == mutex_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 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 != mutex_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 mutex_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") + } + } +} + +func notetsleep(n *note, ns int64) bool { + 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 && gp.m.preemptoff != "" { + // throw("notetsleep not on g0") + // } + + semacreate(gp.m) + 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 { + throw("notetsleepg on g0") + } + semacreate(gp.m) + entersyscallblock(0) + ok := notetsleep_internal(n, ns, nil, 0) + exitsyscall(0) + return ok +} |