| // 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. |
| |
| //go:build (dragonfly || freebsd || linux) && !goexperiment.spinbitmutex |
| |
| package runtime |
| |
| import ( |
| "internal/runtime/atomic" |
| ) |
| |
| // This implementation depends on OS-specific implementations of |
| // |
| // futexsleep(addr *uint32, val uint32, ns int64) |
| // Atomically, |
| // if *addr == val { sleep } |
| // Might be woken up spuriously; that's allowed. |
| // Don't sleep longer than ns; ns < 0 means forever. |
| // |
| // futexwakeup(addr *uint32, cnt uint32) |
| // 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. |
| |
| type mWaitList struct{} |
| |
| func lockVerifyMSize() {} |
| |
| func mutexContended(l *mutex) bool { |
| return atomic.Load(key32(&l.key)) > mutex_locked |
| } |
| |
| func lock(l *mutex) { |
| lockWithRank(l, getLockRank(l)) |
| } |
| |
| func lock2(l *mutex) { |
| gp := getg() |
| |
| if gp.m.locks < 0 { |
| throw("runtimeĀ·lock: lock count") |
| } |
| gp.m.locks++ |
| |
| // Speculative grab for lock. |
| v := atomic.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 |
| |
| timer := &lockTimer{lock: l} |
| timer.begin() |
| // 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 atomic.Cas(key32(&l.key), mutex_unlocked, wait) { |
| timer.end() |
| return |
| } |
| } |
| procyield(active_spin_cnt) |
| } |
| |
| // Try for lock, rescheduling. |
| for i := 0; i < passive_spin; i++ { |
| for l.key == mutex_unlocked { |
| if atomic.Cas(key32(&l.key), mutex_unlocked, wait) { |
| timer.end() |
| return |
| } |
| } |
| osyield() |
| } |
| |
| // Sleep. |
| v = atomic.Xchg(key32(&l.key), mutex_sleeping) |
| if v == mutex_unlocked { |
| timer.end() |
| return |
| } |
| wait = mutex_sleeping |
| futexsleep(key32(&l.key), mutex_sleeping, -1) |
| } |
| } |
| |
| func unlock(l *mutex) { |
| unlockWithRank(l) |
| } |
| |
| func unlock2(l *mutex) { |
| v := atomic.Xchg(key32(&l.key), mutex_unlocked) |
| if v == mutex_unlocked { |
| throw("unlock of unlocked lock") |
| } |
| if v == mutex_sleeping { |
| futexwakeup(key32(&l.key), 1) |
| } |
| |
| gp := getg() |
| gp.m.mLockProfile.recordUnlock(l) |
| gp.m.locks-- |
| if gp.m.locks < 0 { |
| throw("runtimeĀ·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 |
| } |
| } |