pthread_mutex_lock.c:62: __pthread_mutex_lock: Assertion `mutex->__data.__owner == 0' failed

Question

I received that error:

pthread_mutex_lock.c:62: __pthread_mutex_lock: Assertion `mutex->_data._owner == 0' failed.

And I cannot found any cause of that. However I'm not sure about the following piece of code:

Declarations:

std::mutex lock;
std::condition_variable cond;

Sequence of locks & unlocks:

std::unique_lock<std::mutex> lk(lock);

cond.wait(lk);

lock.unlock();

If I remove this sequence - everything works fine, but without any protection. I'm not sure if I use unique_lock properly.

Solution

std::unique_lock and the other locks acquire a mutex in constructor and releases it in destructor. You called lock.unlock() in your code manually, making it being called effectively twice.

After removing that statement your code should work properly.

Comments

[Mike Seymour]

Alternatively, call lk.unlock(), so the lock knows that the mutex has been unlocked. (And perhaps call the mutex something other than "lock", so you don't confuse it with a lock).