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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"
// 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((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(--runtime_m()->locks < 0)
runtime_throw("runtime_unlock: lock count");
}
// 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)
{
/* For gccgo it's OK to sleep in non-g0, and it happens in
stoptheworld because we have not implemented preemption.
if(runtime_g() != runtime_m()->g0)
runtime_throw("notesleep not on g0");
*/
while(runtime_atomicload((uint32*)&n->key) == 0)
runtime_futexsleep((uint32*)&n->key, 0, -1);
}
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(runtime_g() != runtime_m()->g0 && !runtime_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(runtime_g() == runtime_m()->g0)
runtime_throw("notetsleepg on g0");
runtime_entersyscallblock();
res = notetsleep(n, ns, 0, 0);
runtime_exitsyscall();
return res;
}
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