/*-*- 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/errno.h"
#include "libc/intrin/atomic.h"
#include "libc/thread/thread.h"

/**
 * Locks mutex if it isn't locked already.
 *
 * Unlike pthread_mutex_lock() this function won't block and instead
 * returns an error immediately if the lock couldn't be acquired.
 *
 * @return 0 on success, or errno on error
 * @raise EBUSY if lock is already held
 * @raise ENOTRECOVERABLE if `mutex` is corrupted
 */
int pthread_mutex_trylock(pthread_mutex_t *mutex) {
  int c, me, owner;
  switch (mutex->type) {
    case PTHREAD_MUTEX_NORMAL:
      c = 0;
      if (atomic_compare_exchange_strong_explicit(&mutex->lock, &c, 1,
                                                  memory_order_acquire,
                                                  memory_order_relaxed)) {
        return 0;
      } else {
        return EBUSY;
      }
    case PTHREAD_MUTEX_RECURSIVE:
    case PTHREAD_MUTEX_ERRORCHECK:
      owner = 0;
      me = gettid();
      if (!atomic_compare_exchange_strong_explicit(&mutex->lock, &owner, me,
                                                   memory_order_acquire,
                                                   memory_order_relaxed)) {
        if (owner == me) {
          if (mutex->type == PTHREAD_MUTEX_ERRORCHECK) {
            return EBUSY;
          }
        } else {
          return EBUSY;
        }
      }
      ++mutex->reent;
      return 0;
    default:
      assert(!"badlock");
      return ENOTRECOVERABLE;
  }
}