c - pthread_mutex_lock returns invalid argument

Question

I am working on some C code and am having a problem with locking a mutex. The code does a call to a function and this function locks a mutex to ensure a file pointer doesn't get overwritten, this works fine for several instances, probably about 10-20 separate calls of the function being called, but on the next call, pthread_mutex_lock will return with a result of 22. I've then put this result into strerror(); and got back invalid argument.

What does invalid argument means, thanks for any help you can provide.

Answer 1

22 is ENVAL error code which means invlalid argument. Make sure that you have initilized you mutex, or if at some point you have unitilized it somewhere.

Also man pthread_mutex_lock says:

EINVAL

The mutex was created with the protocol attribute having the value PTHREAD_PRIO_PROTECT and the calling thread's priority is higher than the mutex's current priority ceiling.

I don't quite understand this but it probably means that you need to change thread's priority. I am not sure. Maybe someone else can shine light on it.