error while using mutex

Question

when I try to make a map that has string as key and pthread_mutex_t as element,

    map<string, pthread_mutex_t> connectedClientsMutexes;

    pthread_mutex_t myMutex;//= PTHREAD_MUTEX_INITIALIZER;
    connectedClientsMutexes.insert(pair<string,pthread_mutex_t>(userName,myMutex));
while (1)
    {

    pthread_mutex_lock(&connectedClientsMutexes[userName]); 
     // do something here 
    }

this generates:

phase3: pthread_mutex_lock.c:312: __pthread_mutex_lock_full: Assertion `(-(e)) != 3 || !robust' failed.

Answer 1

It is undefined to copy a mutex. Try putting a pointer to the mutex in the map.

EDIT That's the nature of undefined behavior. Sometimes you get lucky (or seem to) and sometimes you don't.

Instead of copies of multiple mutexes in the map you put multiple pointers to the mutexes instead. So something like:

map<string, pthread_mutex_t *> connectedClientsMutexes;

connectedClientsMutexes.insert(pair<string,pthread_mutex_t *>(userName, &myMutex));

pthread_mutex_lock(connectedClientsMutexes[userName]);

Presumably you are passing the map around to various threads so it would be wise not to allocate those mutexes on the stack unless you are positive they aren't going to go out of scope. Declare them as globals or dynamically allocate them and initialize them with pthread_mutex_init().