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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
#include "runtime.h"
#include "stack.h"
#include "../../cmd/ld/textflag.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(m->locks++ < 0)
runtime·throw("runtime·lock: lock count");
// Speculative grab for lock.
v = runtime·xchg((uint32*)&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((uint32*)&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((uint32*)&l->key, MUTEX_UNLOCKED, wait))
return;
runtime·osyield();
}
// Sleep.
v = runtime·xchg((uint32*)&l->key, MUTEX_SLEEPING);
if(v == MUTEX_UNLOCKED)
return;
wait = MUTEX_SLEEPING;
runtime·futexsleep((uint32*)&l->key, MUTEX_SLEEPING, -1);
}
}
void
runtime·unlock(Lock *l)
{
uint32 v;
v = runtime·xchg((uint32*)&l->key, MUTEX_UNLOCKED);
if(v == MUTEX_UNLOCKED)
runtime·throw("unlock of unlocked lock");
if(v == MUTEX_SLEEPING)
runtime·futexwakeup((uint32*)&l->key, 1);
if(--m->locks < 0)
runtime·throw("runtime·unlock: lock count");
if(m->locks == 0 && g->preempt) // restore the preemption request in case we've cleared it in newstack
g->stackguard0 = StackPreempt;
}
// One-time notifications.
void
runtime·noteclear(Note *n)
{
n->key = 0;
}
void
runtime·notewakeup(Note *n)
{
uint32 old;
old = runtime·xchg((uint32*)&n->key, 1);
if(old != 0) {
runtime·printf("notewakeup - double wakeup (%d)\n", old);
runtime·throw("notewakeup - double wakeup");
}
runtime·futexwakeup((uint32*)&n->key, 1);
}
void
runtime·notesleep(Note *n)
{
if(g != m->g0)
runtime·throw("notesleep not on g0");
while(runtime·atomicload((uint32*)&n->key) == 0)
runtime·futexsleep((uint32*)&n->key, 0, -1);
}
#pragma textflag NOSPLIT
static bool
notetsleep(Note *n, int64 ns, int64 deadline, int64 now)
{
// Conceptually, deadline and now are local variables.
// They are passed as arguments so that the space for them
// does not count against our nosplit stack sequence.
if(ns < 0) {
while(runtime·atomicload((uint32*)&n->key) == 0)
runtime·futexsleep((uint32*)&n->key, 0, -1);
return true;
}
if(runtime·atomicload((uint32*)&n->key) != 0)
return true;
deadline = runtime·nanotime() + ns;
for(;;) {
runtime·futexsleep((uint32*)&n->key, 0, ns);
if(runtime·atomicload((uint32*)&n->key) != 0)
break;
now = runtime·nanotime();
if(now >= deadline)
break;
ns = deadline - now;
}
return runtime·atomicload((uint32*)&n->key) != 0;
}
bool
runtime·notetsleep(Note *n, int64 ns)
{
bool res;
if(g != m->g0 && !m->gcing)
runtime·throw("notetsleep not on g0");
res = notetsleep(n, ns, 0, 0);
return res;
}
// same as runtime·notetsleep, but called on user g (not g0)
// calls only nosplit functions between entersyscallblock/exitsyscall
bool
runtime·notetsleepg(Note *n, int64 ns)
{
bool res;
if(g == m->g0)
runtime·throw("notetsleepg on g0");
runtime·entersyscallblock();
res = notetsleep(n, ns, 0, 0);
runtime·exitsyscall();
return res;
}
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