[SOLVED] Terminated pthreads decreasing memory, until Seg Fault

truboy · 12-21-2010, 03:22 AM

Hi all,

I'm currently developping an app in C++ that has to transmit over CAN bus.
It runs on a SBC9261 board, under Linux 2.6.24.

Two pthreads are working for this : the first checks whether a CAN-frame was received. If so, it launches a second thread that has to handle the frame. This way, I'm able to receive frames while handling others (this is sometimes necessary, as some frame-processing needs informations from other CAN-devices).

Here is the code (a bit simplified) of the first thread's routine (the one which receive the frames) :

Code:

void *canRead(void *arg) {

    struct can_frame frameRecv;
    unsigned int i;
    pthread_attr_t attr;
    pthread_t threadHandler;

    // P. thread attribute
    pthread_attr_init(&attr);
    pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM);

    while(1) {

        // Init frame
        memset(&frameRecv, 0, sizeof(struct can_frame));

        // Read from CAN
        read(canDevice, &frameRecv, sizeof(struct can_frame));

        // Threading to be able to receive while handling requests
        // pthread_create() prototype : int pthread_create(pthread *thread, const pthread_attr_t *attr, void *(*start_routine)(void*), void *arg_of_routine);
	if (pthread_create(&threadHandler, &attr, canHandler, &frameRecv)) {
            perror("pthread_create");
            exit(-1);
        }

        // Sleep for a while
        usleep(50*1000);
    }
}

canHandler is the routine that handles the CAN-frame. There is no infinite loop in it, and it could take like 3 secs to end, in the worst case.

This works fine, at least the first 15 minutes, because here is the problem :
The canHandler threads seem to remain in memory after they terminate, as it decreases until the program crashes, throwing a Segmentation Fault.

I spotted this behavior with the top command. If I remove the pthread_create line, the app can run all night without exceeding 17% of memory.

I took a look at the pthread_create manual and one gives a usage example where freeing memory is done.

The interessant part is :

Code:

void *res;

/*Creating different threads, doing stuff here...*/

pthread_join(<whatever_thread>, &res);

free(res);      /* Free memory allocated by thread */

But I can't use it that way, as I have no thread to join...

But does someone know how I could initialize that res pointer or use that free() function to stop those memory leaks ?

Thank you for your help or suggestions !

truboy · 01-04-2011, 08:17 AM

I submitted my problem to a french forum and got this answer.

For those who don't speak French, here is the solution :

My threads were staying in memory because they were default joinable threads, which free the memory only when pthread_join() is executed.
What I needed were detached threads which release memory automatically after they terminate :

Code:

pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);

It works all right now !

I hope it can help !