4. Locks

pthread_mutex_init(), pthread_mutex_lock() (and unlock)

  int pthread_mutex_init(pthread_mutex_t *restrict mutex, const pthread_mutexattr_t *restrict attr);
  pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
  int pthread_mutex_lock(pthread_mutex_t *mutex);
  int pthread_mutex_unlock(pthread_mutex_t *mutex);

Example:

  pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
 // or: pthread_mutex_t lock; assert( pthread_mutex_init(&lock,NULL) == 0);
  ...
  pthread_mutex_lock(&lock);
    x = x + 1; // or whatever your critical section is
    ...
  pthread_mutex_unlock(&lock);