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// 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 dragonfly freebsd linux
package runtime
import "unsafe"
// This implementation depends on OS-specific implementations of
//
// runtime·futexsleep(uint32 *addr, uint32 val, int64 ns)
// Atomically,
// if(*addr == val) sleep
// Might be woken up spuriously; that's allowed.
// Don't sleep longer than ns; ns < 0 means forever.
//
// runtime·futexwakeup(uint32 *addr, uint32 cnt)
// If any procs are sleeping on addr, wake up at most cnt.
const (
mutex_unlocked = 0
mutex_locked = 1
mutex_sleeping = 2
active_spin = 4
active_spin_cnt = 30
passive_spin = 1
)
// Possible lock states are mutex_unlocked, mutex_locked and mutex_sleeping.
// mutex_sleeping means that there is presumably at least one sleeping thread.
// Note that there can be spinning threads during all states - they do not
// affect mutex's state.
// We use the uintptr mutex.key and note.key as a uint32.
func key32(p *uintptr) *uint32 {
return (*uint32)(unsafe.Pointer(p))
}
func lock(l *mutex) {
gp := getg()
if gp.m.locks < 0 {
gothrow("runtime·lock: lock count")
}
gp.m.locks++
// Speculative grab for lock.
v := xchg(key32(&l.key), mutex_locked)
if v == mutex_unlocked {
return
}
// wait is either MUTEX_LOCKED or MUTEX_SLEEPING
// depending on whether there is a thread sleeping
// on this mutex. If we ever change l->key from
// MUTEX_SLEEPING to some other value, we must be
// careful to change it back to MUTEX_SLEEPING before
// returning, to ensure that the sleeping thread gets
// its wakeup call.
wait := v
// On uniprocessors, no point spinning.
// On multiprocessors, spin for ACTIVE_SPIN attempts.
spin := 0
if ncpu > 1 {
spin = active_spin
}
for {
// Try for lock, spinning.
for i := 0; i < spin; i++ {
for l.key == mutex_unlocked {
if cas(key32(&l.key), mutex_unlocked, wait) {
return
}
}
procyield(active_spin_cnt)
}
// Try for lock, rescheduling.
for i := 0; i < passive_spin; i++ {
for l.key == mutex_unlocked {
if cas(key32(&l.key), mutex_unlocked, wait) {
return
}
}
osyield()
}
// Sleep.
v = xchg(key32(&l.key), mutex_sleeping)
if v == mutex_unlocked {
return
}
wait = mutex_sleeping
futexsleep(key32(&l.key), mutex_sleeping, -1)
}
}
func unlock(l *mutex) {
v := xchg(key32(&l.key), mutex_unlocked)
if v == mutex_unlocked {
gothrow("unlock of unlocked lock")
}
if v == mutex_sleeping {
futexwakeup(key32(&l.key), 1)
}
gp := getg()
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) {
old := xchg(key32(&n.key), 1)
if old != 0 {
print("notewakeup - double wakeup (", old, ")\n")
gothrow("notewakeup - double wakeup")
}
futexwakeup(key32(&n.key), 1)
}
func notesleep(n *note) {
gp := getg()
if gp != gp.m.g0 {
gothrow("notesleep not on g0")
}
for atomicload(key32(&n.key)) == 0 {
gp.m.blocked = true
futexsleep(key32(&n.key), 0, -1)
gp.m.blocked = false
}
}
//go:nosplit
func notetsleep_internal(n *note, ns int64) bool {
gp := getg()
if ns < 0 {
for atomicload(key32(&n.key)) == 0 {
gp.m.blocked = true
futexsleep(key32(&n.key), 0, -1)
gp.m.blocked = false
}
return true
}
if atomicload(key32(&n.key)) != 0 {
return true
}
deadline := nanotime() + ns
for {
gp.m.blocked = true
futexsleep(key32(&n.key), 0, ns)
gp.m.blocked = false
if atomicload(key32(&n.key)) != 0 {
break
}
now := nanotime()
if now >= deadline {
break
}
ns = deadline - now
}
return atomicload(key32(&n.key)) != 0
}
func notetsleep(n *note, ns int64) bool {
gp := getg()
if gp != gp.m.g0 && gp.m.gcing == 0 {
gothrow("notetsleep not on g0")
}
return notetsleep_internal(n, ns)
}
// 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")
}
entersyscallblock(0)
ok := notetsleep_internal(n, ns)
exitsyscall(0)
return ok
}
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