pthread_mutex_lock() returns zero after completing successfully. Any other return value indicates that an error occurred. When any of the following conditions occurs, the function fails and returns the corresponding value.
The mutex could not be acquired because the maximum number of recursive locks for mutex has been exceeded.
The current thread already owns the mutex.
If the mutex was initialized with the PTHREAD_MUTEX_ROBUST_NProbustness attribute, pthread_mutex_lock() may return one of the following values:
The last owner of this mutex terminated while holding the mutex. This mutex is now owned by the caller. The caller must attempt to make the state protected by the mutex consistent.
If the caller is able to make the state consistent, call pthread_mutex_consistent_np() for the mutex and unlock the mutex. Subsequent calls to pthread_mutex_lock() behave normally.
If the caller is unable to make the state consistent, do not call pthread_mutex_init() for the mutex. Unlock the mutex instead. Subsequent calls to pthread_mutex_lock() fail to acquire the mutex and return an ENOTRECOVERABLE error code.
If the owner that acquired the lock with EOWNERDEAD terminates while holding the mutex, the next owner acquires the lock with EOWNERDEAD.
The mutex you are trying to acquire was protecting state left irrecoverable by the mutex's previous owner. The mutex has not been acquired. This irrecoverable condition can occur when:
The lock was previously acquired with EOWNERDEAD
The owner was unable to cleanup the state
The owner unlocked the mutex without making the mutex state consistent
The limit on the number of simultaneously held mutexes has been exceeded.