cosmopolitan/libc/intrin/spinlock.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/assert.h"
#include "libc/calls/calls.h"
#include "libc/calls/strace.internal.h"
#include "libc/intrin/lockcmpxchg.h"
#include "libc/intrin/spinlock.h"

/**
 * Acquires spinlock.
 */
void cthread_spinlock(cthread_spinlock_t *lock) {
#if 0
  // TODO(jart): possibly reenable for !NDEBUG when we have TLS
  int me = gettid();
  if (lock->x && lock->owner == me) {
    assert(!"cosmo spinlock not intended to be reentrant");
    return;
  }
#endif
  do
    while (lock->x) asm("pause");
  while (!_lockcmpxchg(&lock->x, false, true));
#if 0
  lock->owner = me;
#endif
}

/**
 * Releases spinlock.
 */
void cthread_spunlock(cthread_spinlock_t *lock) {
  lock->x = false;
}