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

static void sem_delay(int n) {
  volatile int i;
  for (i = 0; i != 1 << n; i++) donothing;
}

static void sem_timedwait_cleanup(void *arg) {
  sem_t *sem = arg;
  _unassert(atomic_fetch_add_explicit(&sem->sem_waiters, -1,
                                      memory_order_acq_rel) > 0);
}

/**
 * Locks semaphore w/ deadline.
 *
 * @param abstime is absolute deadline or null to wait forever
 * @return 0 on success, or -1 w/ errno
 * @raise ECANCELED if calling thread was cancelled in masked mode
 * @raise EINTR if signal was delivered instead
 * @raise EDEADLK if deadlock was detected
 * @raise ETIMEDOUT if deadline expired
 * @raise EINVAL if `sem` is invalid
 * @cancellationpoint
 */
int sem_timedwait(sem_t *sem, const struct timespec *abstime) {
  int e, i, v, rc;
  struct timespec ts;

  e = errno;
  for (i = 0; i < 7; ++i) {
    rc = sem_trywait(sem);
    if (!rc) {
      return rc;
    } else if (errno == EAGAIN) {
      errno = e;
      sem_delay(i);
    } else {
      return rc;
    }
  }

  BEGIN_CANCELLATION_POINT;
  _unassert(atomic_fetch_add_explicit(&sem->sem_waiters, +1,
                                      memory_order_acq_rel) >= 0);
  pthread_cleanup_push(sem_timedwait_cleanup, sem);

  do {
    if (!(v = atomic_load_explicit(&sem->sem_value, memory_order_relaxed))) {
      rc = nsync_futex_wait_(&sem->sem_value, v, true, abstime);
      if (rc == -EINTR || rc == -ECANCELED) {
        errno = -rc;
        rc = -1;
      } else if (rc == -EAGAIN || rc == -EWOULDBLOCK) {
        rc = 0;
      } else if (rc == -ETIMEDOUT) {
        _npassert(abstime);
        if (timespec_cmp(*abstime, timespec_real()) <= 0) {
          rc = etimedout();
        } else {
          rc = 0;
        }
      } else {
        _npassert(!rc);
        rc = 0;
      }
    } else if (v > 0) {
      rc = 0;
    } else {
      _unassert(v > INT_MIN);
      rc = einval();
    }
  } while (!rc && (!v || !atomic_compare_exchange_weak_explicit(
                             &sem->sem_value, &v, v - 1, memory_order_acquire,
                             memory_order_relaxed)));

  pthread_cleanup_pop(1);
  END_CANCELLATION_POINT;

  return rc;
}
