Function mutex_lock

examples/stdlib.c:1551–1570

* NOTE: mutex_lock() is marked with the __warn_unused_result__ attribute. * This is because this function can fail with EDEADLOCK in normal use * cases, so the return value should always be checked. */

 *       cases, so the return value should always be checked.
 */
static __attribute__((__noinline__, __warn_unused_result__))
    int mutex_lock(mutex_t *m)
{
    if (mutex_disabled)
        return 0;
    pid_t *x = mutex_get_ptr(m);
    pid_t self = mutex_gettid();
    if (mutex_fast_lock(self, x))
        return 0;
    if (syscall(SYS_futex, x, FUTEX_LOCK_PI, 0, NULL, NULL, 0) != 0)
        return -1;
    if (*x & FUTEX_OWNER_DIED)
    {
        // This can occur if a thread dies while holding a lock.
        *x &= ~FUTEX_OWNER_DIED;
        errno = EOWNERDEAD;
        return -1;
    }
    return 0;                       // acquired
}

static __attribute__((__noinline__)) int mutex_trylock(mutex_t *m)
{