147 lines
3.2 KiB
C
147 lines
3.2 KiB
C
// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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#include "runtime.h"
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// This implementation depends on OS-specific implementations of
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//
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// runtime.futexsleep(uint32 *addr, uint32 val, int64 ns)
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// Atomically,
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// if(*addr == val) sleep
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// Might be woken up spuriously; that's allowed.
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// Don't sleep longer than ns; ns < 0 means forever.
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//
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// runtime.futexwakeup(uint32 *addr, uint32 cnt)
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// If any procs are sleeping on addr, wake up at most cnt.
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enum
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{
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MUTEX_UNLOCKED = 0,
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MUTEX_LOCKED = 1,
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MUTEX_SLEEPING = 2,
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ACTIVE_SPIN = 4,
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ACTIVE_SPIN_CNT = 30,
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PASSIVE_SPIN = 1,
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};
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// Possible lock states are MUTEX_UNLOCKED, MUTEX_LOCKED and MUTEX_SLEEPING.
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// MUTEX_SLEEPING means that there is presumably at least one sleeping thread.
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// Note that there can be spinning threads during all states - they do not
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// affect mutex's state.
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void
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runtime_lock(Lock *l)
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{
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uint32 i, v, wait, spin;
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if(m->locks++ < 0)
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runtime_throw("runtime_lock: lock count");
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// Speculative grab for lock.
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v = runtime_xchg(&l->key, MUTEX_LOCKED);
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if(v == MUTEX_UNLOCKED)
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return;
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// wait is either MUTEX_LOCKED or MUTEX_SLEEPING
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// depending on whether there is a thread sleeping
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// on this mutex. If we ever change l->key from
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// MUTEX_SLEEPING to some other value, we must be
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// careful to change it back to MUTEX_SLEEPING before
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// returning, to ensure that the sleeping thread gets
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// its wakeup call.
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wait = v;
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// On uniprocessor's, no point spinning.
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// On multiprocessors, spin for ACTIVE_SPIN attempts.
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spin = 0;
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if(runtime_ncpu > 1)
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spin = ACTIVE_SPIN;
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for(;;) {
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// Try for lock, spinning.
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for(i = 0; i < spin; i++) {
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while(l->key == MUTEX_UNLOCKED)
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if(runtime_cas(&l->key, MUTEX_UNLOCKED, wait))
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return;
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runtime_procyield(ACTIVE_SPIN_CNT);
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}
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// Try for lock, rescheduling.
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for(i=0; i < PASSIVE_SPIN; i++) {
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while(l->key == MUTEX_UNLOCKED)
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if(runtime_cas(&l->key, MUTEX_UNLOCKED, wait))
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return;
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runtime_osyield();
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}
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// Sleep.
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v = runtime_xchg(&l->key, MUTEX_SLEEPING);
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if(v == MUTEX_UNLOCKED)
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return;
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wait = MUTEX_SLEEPING;
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runtime_futexsleep(&l->key, MUTEX_SLEEPING, -1);
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}
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}
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void
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runtime_unlock(Lock *l)
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{
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uint32 v;
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if(--m->locks < 0)
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runtime_throw("runtime_unlock: lock count");
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v = runtime_xchg(&l->key, MUTEX_UNLOCKED);
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if(v == MUTEX_UNLOCKED)
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runtime_throw("unlock of unlocked lock");
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if(v == MUTEX_SLEEPING)
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runtime_futexwakeup(&l->key, 1);
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}
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// One-time notifications.
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void
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runtime_noteclear(Note *n)
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{
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n->key = 0;
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}
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void
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runtime_notewakeup(Note *n)
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{
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runtime_xchg(&n->key, 1);
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runtime_futexwakeup(&n->key, 1);
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}
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void
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runtime_notesleep(Note *n)
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{
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while(runtime_atomicload(&n->key) == 0)
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runtime_futexsleep(&n->key, 0, -1);
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}
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void
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runtime_notetsleep(Note *n, int64 ns)
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{
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int64 deadline, now;
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if(ns < 0) {
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runtime_notesleep(n);
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return;
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}
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if(runtime_atomicload(&n->key) != 0)
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return;
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deadline = runtime_nanotime() + ns;
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for(;;) {
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runtime_futexsleep(&n->key, 0, ns);
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if(runtime_atomicload(&n->key) != 0)
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return;
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now = runtime_nanotime();
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if(now >= deadline)
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return;
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ns = deadline - now;
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}
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}
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