147 lines
3.2 KiB
C
147 lines
3.2 KiB
C
// 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.
|
|
|
|
#include "runtime.h"
|
|
|
|
// 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.
|
|
|
|
enum
|
|
{
|
|
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.
|
|
void
|
|
runtime_lock(Lock *l)
|
|
{
|
|
uint32 i, v, wait, spin;
|
|
|
|
if(runtime_m()->locks++ < 0)
|
|
runtime_throw("runtime_lock: lock count");
|
|
|
|
// Speculative grab for lock.
|
|
v = runtime_xchg(&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 uniprocessor's, no point spinning.
|
|
// On multiprocessors, spin for ACTIVE_SPIN attempts.
|
|
spin = 0;
|
|
if(runtime_ncpu > 1)
|
|
spin = ACTIVE_SPIN;
|
|
|
|
for(;;) {
|
|
// Try for lock, spinning.
|
|
for(i = 0; i < spin; i++) {
|
|
while(l->key == MUTEX_UNLOCKED)
|
|
if(runtime_cas(&l->key, MUTEX_UNLOCKED, wait))
|
|
return;
|
|
runtime_procyield(ACTIVE_SPIN_CNT);
|
|
}
|
|
|
|
// Try for lock, rescheduling.
|
|
for(i=0; i < PASSIVE_SPIN; i++) {
|
|
while(l->key == MUTEX_UNLOCKED)
|
|
if(runtime_cas(&l->key, MUTEX_UNLOCKED, wait))
|
|
return;
|
|
runtime_osyield();
|
|
}
|
|
|
|
// Sleep.
|
|
v = runtime_xchg(&l->key, MUTEX_SLEEPING);
|
|
if(v == MUTEX_UNLOCKED)
|
|
return;
|
|
wait = MUTEX_SLEEPING;
|
|
runtime_futexsleep(&l->key, MUTEX_SLEEPING, -1);
|
|
}
|
|
}
|
|
|
|
void
|
|
runtime_unlock(Lock *l)
|
|
{
|
|
uint32 v;
|
|
|
|
if(--runtime_m()->locks < 0)
|
|
runtime_throw("runtime_unlock: lock count");
|
|
|
|
v = runtime_xchg(&l->key, MUTEX_UNLOCKED);
|
|
if(v == MUTEX_UNLOCKED)
|
|
runtime_throw("unlock of unlocked lock");
|
|
if(v == MUTEX_SLEEPING)
|
|
runtime_futexwakeup(&l->key, 1);
|
|
}
|
|
|
|
// One-time notifications.
|
|
void
|
|
runtime_noteclear(Note *n)
|
|
{
|
|
n->key = 0;
|
|
}
|
|
|
|
void
|
|
runtime_notewakeup(Note *n)
|
|
{
|
|
runtime_xchg(&n->key, 1);
|
|
runtime_futexwakeup(&n->key, 1);
|
|
}
|
|
|
|
void
|
|
runtime_notesleep(Note *n)
|
|
{
|
|
while(runtime_atomicload(&n->key) == 0)
|
|
runtime_futexsleep(&n->key, 0, -1);
|
|
}
|
|
|
|
void
|
|
runtime_notetsleep(Note *n, int64 ns)
|
|
{
|
|
int64 deadline, now;
|
|
|
|
if(ns < 0) {
|
|
runtime_notesleep(n);
|
|
return;
|
|
}
|
|
|
|
if(runtime_atomicload(&n->key) != 0)
|
|
return;
|
|
|
|
deadline = runtime_nanotime() + ns;
|
|
for(;;) {
|
|
runtime_futexsleep(&n->key, 0, ns);
|
|
if(runtime_atomicload(&n->key) != 0)
|
|
return;
|
|
now = runtime_nanotime();
|
|
if(now >= deadline)
|
|
return;
|
|
ns = deadline - now;
|
|
}
|
|
}
|