src/android/jni/pthread_once.c

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// pthread_once(3C) of Android 2.1 and 2.2 have a bug that it's not recursively-
// callable (nor reentrant).  It hangs when it's recursively called.
// This module provides a replacement of pthread_once() and supposed to be
// linked prior to the default one.
// Once we get rid of Android 2.1 and 2.2, we no longer need this hack.

#ifdef OS_ANDROID

#include <pthread.h>
#include <stddef.h>

static pthread_mutex_t once_lock = PTHREAD_RECURSIVE_MUTEX_INITIALIZER;

// This implementation doesn't support thread-cancelation nor fork during
// the execution of init_routine().
int pthread_once(pthread_once_t  *once_control, void (*init_routine)(void)) {
  // pthread_once always returns 0.

  if (once_control == NULL || init_routine == NULL) {
    return 0;
  }

  // Double-checked locking is not a good solution in general, but it works
  // in this case in C.
  if (*once_control != PTHREAD_ONCE_INIT) {
    return 0;
  }

  pthread_mutex_lock(&once_lock);

  if (*once_control == PTHREAD_ONCE_INIT) {
    init_routine();
    *once_control = PTHREAD_ONCE_INIT + 1;
  }

  pthread_mutex_unlock(&once_lock);

  return 0;
}

#endif