problem mutex-thread "Unlocking mutex owned by another thread ???"

"NaeiKinDus" <>
14 Apr 2007 10:11:18 -0700
Hello, i'm trying to program a thread that would be locked (by a
mutex) and that would only be unlocked once that a function
(generating data) is done. The purpose is to generate data, and unlock
the mutex in order to activate the thread once the data is generated.
I have to do it this way, i can only call the thread if the data are

step 1: initialize the mutex

mx (the mutex is part of the class "cl")

class Client

        pthread_mutex_t mx;


pthread_mutex_init(&cl->mx, NULL);

step 2:

as i'm calling a thread, i have to pass in param a structure with the
mutex :

struct S_PARAMS

  pthread_mutex_t *mx;

} typedef T_PARAMS;

i create the thread and i copy the mutex in the param structure :

pthread_t thread;
params->mx = &cl->mx;

if ((thId = pthread_create(&thread, NULL, OBody::thFileSender, (void
*)params)) != 0)
   THREAD NOT CREATED ... throw ...

step 3:

i lock my thread :

void *OBody::thFileSender(void *lpParam)
        cout << "locking MUTX*****" << endl;
        cout << pthread_mutex_lock(params->mx) << endl;
        cout << "unlocked MUTX *****" << endl;

        ... (sending data)


step 4:

once i know my functions generating data are done, i call the thread
unlocking function.

cout << "*** before unlock ***" << endl;
cout << "*** after unlock ***" << endl;


Finally i get :



locking MUTX*****
unlocked MUTX *****

.... (generated data)

*** before unlock ***
server: Error detected by libpthread: Unlocking mutex owned by another
Detected by file "/root/netbsd-3.0/src/lib/libpthread/
pthread_mutex.c", line 347, function "pthread_mutex_unlock".
See pthread(3) for information.



What i understand is that the mutex is not locking the thread because
in the step3,
the "cout << "locking MUTX*****" << endl;" is done when is start the

I put a sleep(10) in order to be sure that the thread was still
running without calling thread_unlock.

Moreover, when i try to unlock the thread, i get the error "Unlocking
mutex owned by another thread.".

all the mutex functions (init, lock, unlock) return 0 which mean that
the function are running correctly.

i have been working on this problem for hours and hours, i'm not a
specialist of the mutex/thread.

Thank you for your help.

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