mirror of
https://github.com/jart/cosmopolitan.git
synced 2025-02-07 23:13:34 +00:00
7ff0ea8c13
pthread_mutex_lock() now uses a better algorithm which goes much faster in multithreaded environments that have lock contention. This comes at the cost of adding some fixed-cost overhead to mutex invocations. That doesn't matter for Cosmopolitan because our core libraries all encode locking operations as NOP instructions when in single-threaded mode. Overhead only applies starting the moment you first call clone().
68 lines
3.3 KiB
C
68 lines
3.3 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2022 Justine Alexandra Roberts Tunney │
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│ │
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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/assert.h"
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#include "libc/calls/calls.h"
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#include "libc/errno.h"
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#include "libc/intrin/atomic.h"
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#include "libc/intrin/pthread.h"
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/**
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* Locks mutex if it isn't locked already.
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*
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* Unlike pthread_mutex_lock() this function won't block and instead
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* returns an error immediately if the lock couldn't be acquired.
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*
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* @return 0 on success, or errno on error
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* @raise EBUSY if lock is already held
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* @raise ENOTRECOVERABLE if `mutex` is corrupted
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*/
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int pthread_mutex_trylock(pthread_mutex_t *mutex) {
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int c, me, owner;
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switch (mutex->attr) {
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case PTHREAD_MUTEX_NORMAL:
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c = 0;
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if (atomic_compare_exchange_strong_explicit(&mutex->lock, &c, 1,
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memory_order_acquire,
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memory_order_relaxed)) {
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return 0;
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} else {
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return EBUSY;
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}
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case PTHREAD_MUTEX_RECURSIVE:
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case PTHREAD_MUTEX_ERRORCHECK:
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owner = 0;
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me = gettid();
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if (!atomic_compare_exchange_strong_explicit(&mutex->lock, &owner, me,
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memory_order_acquire,
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memory_order_relaxed)) {
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if (owner == me) {
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if (mutex->attr == PTHREAD_MUTEX_ERRORCHECK) {
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return EBUSY;
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}
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} else {
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return EBUSY;
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}
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}
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++mutex->reent;
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return 0;
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default:
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assert(!"badlock");
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return ENOTRECOVERABLE;
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}
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}
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