cosmopolitan/libc/intrin/pthread_mutex_lock.c

/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2022 Justine Alexandra Roberts Tunney                              │
│                                                                              │
│ Permission to use, copy, modify, and/or distribute this software for         │
│ any purpose with or without fee is hereby granted, provided that the         │
│ above copyright notice and this permission notice appear in all copies.      │
│                                                                              │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
│ PERFORMANCE OF THIS SOFTWARE.                                                │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/bits/atomic.h"
#include "libc/calls/calls.h"
#include "libc/dce.h"
#include "libc/errno.h"
#include "libc/intrin/pthread.h"
#include "libc/linux/futex.h"
#include "libc/nexgen32e/threaded.h"

/**
 * Locks mutex.
 * @return 0 on success, or error number on failure
 */
int pthread_mutex_lock(pthread_mutex_t *mutex) {
  int i, me, owner, tries;
  for (tries = 0, me = gettid();;) {
    owner = atomic_load_explicit(&mutex->lock, memory_order_relaxed);
    if (!owner && atomic_compare_exchange_weak_explicit(
                      &mutex->lock, &owner, me, memory_order_acquire,
                      memory_order_relaxed)) {
      break;
    } else if (owner == me) {
      if (mutex->attr != PTHREAD_MUTEX_ERRORCHECK) {
        break;
      } else {
        return EDEADLK;
      }
    }
    if (tries < 7) {
      for (i = 0; i != 1 << tries; i++) {
      }
      tries++;
    } else if (IsLinux()) {
      atomic_fetch_add(&mutex->waits, 1);
      LinuxFutexWait(&mutex->lock, owner, 0);
      atomic_fetch_sub(&mutex->waits, 1);
    } else {
      sched_yield();
    }
  }
  ++mutex->reent;
  return 0;
}