| // 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 || fuchsia || linux |
| |
| package runtime |
| |
| import ( |
| "runtime/internal/atomic" |
| "unsafe" |
| ) |
| |
| // 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. |
| |
| // We use the uintptr mutex.key and note.key as a uint32. |
| // |
| //go:nosplit |
| func key32(p *uintptr) *uint32 { |
| return (*uint32)(unsafe.Pointer(p)) |
| } |
| |
| func lock(l *mutex) { |
| lockWithRank(l, getLockRank(l)) |
| } |
| |
| func lock2(l *mutex) { |
| gp := getg() |
| |
| if gp.m.locks < 0 { |
| throw("runtime·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 |
| |
| // 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) { |
| 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) { |
| return |
| } |
| } |
| osyield() |
| } |
| |
| // Sleep. |
| v = atomic.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) { |
| 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.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) { |
| old := atomic.Xchg(key32(&n.key), 1) |
| if old != 0 { |
| print("notewakeup - double wakeup (", old, ")\n") |
| throw("notewakeup - double wakeup") |
| } |
| futexwakeup(key32(&n.key), 1) |
| } |
| |
| func notesleep(n *note) { |
| gp := getg() |
| if gp != gp.m.g0 { |
| throw("notesleep not on g0") |
| } |
| ns := int64(-1) |
| if *cgo_yield != nil { |
| // Sleep for an arbitrary-but-moderate interval to poll libc interceptors. |
| ns = 10e6 |
| } |
| for atomic.Load(key32(&n.key)) == 0 { |
| gp.m.blocked = true |
| futexsleep(key32(&n.key), 0, ns) |
| if *cgo_yield != nil { |
| asmcgocall(*cgo_yield, nil) |
| } |
| gp.m.blocked = false |
| } |
| } |
| |
| // May run with m.p==nil if called from notetsleep, so write barriers |
| // are not allowed. |
| // |
| //go:nosplit |
| //go:nowritebarrier |
| func notetsleep_internal(n *note, ns int64) bool { |
| gp := getg() |
| |
| if ns < 0 { |
| if *cgo_yield != nil { |
| // Sleep for an arbitrary-but-moderate interval to poll libc interceptors. |
| ns = 10e6 |
| } |
| for atomic.Load(key32(&n.key)) == 0 { |
| gp.m.blocked = true |
| futexsleep(key32(&n.key), 0, ns) |
| if *cgo_yield != nil { |
| asmcgocall(*cgo_yield, nil) |
| } |
| gp.m.blocked = false |
| } |
| return true |
| } |
| |
| if atomic.Load(key32(&n.key)) != 0 { |
| return true |
| } |
| |
| deadline := nanotime() + ns |
| for { |
| if *cgo_yield != nil && ns > 10e6 { |
| ns = 10e6 |
| } |
| gp.m.blocked = true |
| futexsleep(key32(&n.key), 0, ns) |
| if *cgo_yield != nil { |
| asmcgocall(*cgo_yield, nil) |
| } |
| gp.m.blocked = false |
| if atomic.Load(key32(&n.key)) != 0 { |
| break |
| } |
| now := nanotime() |
| if now >= deadline { |
| break |
| } |
| ns = deadline - now |
| } |
| return atomic.Load(key32(&n.key)) != 0 |
| } |
| |
| func notetsleep(n *note, ns int64) bool { |
| gp := getg() |
| if gp != gp.m.g0 && gp.m.preemptoff != "" { |
| throw("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 { |
| throw("notetsleepg on g0") |
| } |
| |
| entersyscallblock() |
| ok := notetsleep_internal(n, ns) |
| exitsyscall() |
| return ok |
| } |
| |
| func beforeIdle(int64, int64) (*g, bool) { |
| return nil, false |
| } |
| |
| func checkTimeouts() {} |