mutex and pthread

[kenrus]

Platform: AIX

I am new to using mutex'es and pthreads so I have been writing some very simple test programs to just understand the concept and the syntax.

Well, my first non-threaded app seemed to work just fine with mutex'es (the function calls did not return any errors), but now that I have introduced pthreads and some of the mutex functions are now returning errors.

Here is the code:

#include <pthread.h>
#include <stdio.h>

//GLOBAL MUTEX
pthread_mutex_t gMutex;

void* mutex_test(void*);

int main(int argc, char** argv)
{
int rv_init = 0;
int rv_destroy = 0;
int rv_thread = 0;

int i = 0;

pthread_t threads[10];

char thread_ids[10][2] ={"A", "B", "C", "D", "E", "F", "G", "H", "I", "J"};

//INITIALIZE MUTEX
rv_init = pthread_mutex_init(&gMutex, 0);

printf("\nMutex Initialization Status: %i", rv_init);

//LAUNCHING THREADS
for(i = 0; i < 2; i++)
{
rv_thread = pthread_create(&threads[i], 0, mutex_test, (void*)(&thread_ids[i]));
}


//DESTROY MUTEX
rv_destroy = pthread_mutex_destroy(&gMutex);

printf("\nMutex Destruction Status: %i", rv_destroy);

pthread_exit(0);

return 0;
}

void* mutex_test(void* pszThreadId)
{
char* pszId = (char*)pszThreadId;

unsigned int i = 0;
int rv_lock = 0;
int rv_unlock = 0;
time_t start_t = 0;
time_t now_t = 0;

for(i = 0; i < 4; i++)
{
printf("\n[%s]: Starting...", pszId);
printf("\n[%s]: Attempting to lock mutex...", pszId);

rv_lock = pthread_mutex_lock(&gMutex);

printf("\n[%s]: mutex locked - rv_lock == %i", pszId, rv_lock);
printf("\n[%s]: holding for a sec ...", pszId);

time(&start_t);

while((start_t + 3) > now_t)
time(&now_t);

printf("\n[%s]: unlocking the mutex now", pszId);

rv_unlock = pthread_mutex_unlock(&gMutex);

printf("\n[%s]: mutex has been unlocked - rv_unlock == %i", pszId, rv_unlock);
}


}



The functions in main both return 0 - success:
pthread_mutex_init()
pthread_mutex_destroy()

The function in the thread (mutex_test) both return 22
pthread_mutex_lock()
pthread_mutex_unlock()

My first, non-threaded, attempt just had all the code in main(), now I have moved the mutex (gMutex) to being a global variable and it is being initialized in main, but used in the thread function (mutex_test)

Any help would be appreciated.

Thanks

[kenrus]

Sorry, I noticed my problem right when I posted the question.

I was destroying the mutex before the threads were done.

[ka3ak]

you can call pthread_join(...) to wait for the threads to finish before destroying the mutex. (http://www.opengroup.org/onlinepubs/007908799/xsh/pthread_join.html)

[NoHero]

[ Moved ]