Memory leak on pthread_create?

This is a discussion on Memory leak on pthread_create? within the C Programming forums, part of the General Programming Boards category; Whenever I run valgrind on my program, it is telling that I have possibly lost memory wherever I call pthread_create. ...

  1. #1
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    Memory leak on pthread_create?

    Whenever I run valgrind on my program, it is telling that I have possibly lost memory wherever I call pthread_create. I have been trying to follow the guidance on

    valgrind memory leak errors when using pthread_create pthread_create valgrind memory leak solved Gelorakan …

    and other various websites google gave me, but nothing has worked. So far I have tried joining the threads, setting an pthread_attr_t to DETACHED, calling pthread_detach on each thread, and calling pthread_exit().

    trying PTHREAD_CREATE_DETACHED -

    Code:
    pthread_attr_t attr;
    pthread_attr_init(&attr);
    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
    
    pthread_create(&c_udp_comm, &attr, udp_comm_thread, (void*)this);
    pthread_create(&drive, &attr, driving_thread, (void*)this);
    pthread_create(&update, &attr, update_server_thread(void*)this);

    I think I may have coded this next one with joining wrong...I am going by https://computing.llnl.gov/tutorials/pthreads/ and they have all their threads in an array so they just for loop. But I don't have them all in an array so I tried to just change it to work. Please tell me if I did it wrong.

    Code:
    void* status;
    pthread_attr_t attr;
    pthread_attr_init(&attr);
    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
    
    pthread_create(&c_udp_comm, &attr, udp_comm_thread, (void*)this);
    pthread_create(&drive, &attr, driving_thread, (void*)this);
    pthread_create(&update, &attr, update_server_thread(void*)this);
    
    pthread_join(c_udp_comm, &status);
    pthread_join(drive, &status);
    pthread_join(update, &status);

    trying pthread_detach -


    Code:
    pthread_create(&c_udp_comm, NULL, udp_comm_thread, (void*)this);
    pthread_create(&drive, NULL, driving_thread, (void*)this);
    pthread_create(&update, NULL, update_server_thread(void*)this);
    
    pthread_detach(c_udp_comm);
    pthread_detach(drive);
    pthread_detach(update);

    trying pthread_exit -

    Code:
    pthread_create(&c_udp_comm, NULL, udp_comm_thread, (void*)this);
    pthread_create(&drive, NULL, driving_thread, (void*)this);
    pthread_create(&update, NULL, update_server_thread(void*)this);
    
    pthread_exit(NULL);
    If anyone can help me figure out why none of this is working I would be very grateful.

  2. #2
    Registered User Codeplug's Avatar
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    Memory leak on pthread_create - CodeGuru Forums

    If you write a simple, complete program and post it, we'll tell you if it contains any memory leaks - then compare that to what Valgrind says and go from there.

    gg

  3. #3
    and the hat of wrongness Salem's Avatar
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    Read the examples here -> https://computing.llnl.gov/tutorials...reatingThreads
    main() ends by calling pthread_exit().

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include <errno.h>
    #include <unistd.h>
    #include <pthread.h>
    
    void* process( void* data ) {
      printf( "hello world\n" );
    }
    
    int main() {
      pthread_t th;
      pthread_attr_t attr;
      pthread_attr_init(&attr);
      pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
      pthread_create( &th, &attr, process, NULL );
      pthread_attr_destroy(&attr);
      //pthread_exit(0);  // no leak when this is in the code.
      // dummy
      return 0;
    }
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  4. #4
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    Whenever I run that code, with or without the explicit pthread_exit, I still get a possible memory loss of 144 bytes each time. So I should just regard that as wrong?

  5. #5
    spurious conceit MK27's Avatar
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    Quote Originally Posted by SterlingM View Post
    Whenever I run that code, with or without the explicit pthread_exit, I still get a possible memory loss of 144 bytes each time. So I should just regard that as wrong?
    Maybe. When I run that code with pthread_exit(), I get a leak of 272 bytes in one block allocated by pthread_create(). Without pthread_exit(), there is no leak.

    But pthread_exit() is pretty vital if you have detached threads and main() ends. Try this one:

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <unistd.h>
    #include <pthread.h>
    
    void* process( void* data ) {
      printf("%ld hello world\n", (long int)data);
      return NULL;
    }
    
    int main() {
    	pthread_t th[3];
    	long int i;
    	for (i = 0; i < 3; i++) {
    		pthread_create(&th[i], NULL, process, (void*)i);
    		pthread_detach(th[i]);
    	}
    
    	pthread_exit(0);
    	return 0;
    }
    I get "All heap blocks were freed -- no leaks are possible" for that with or without pthread_exit (but without pthread_exit not all threads complete). Note that that pthread_exit() terminates main, ie, the return statement is not executed.

    Quote Originally Posted by http://cursuri.cs.pub.ro/~apc/2003/resources/pthreads/uguide/users-18.htm#285690
    Termination of the initial thread via pthread_exit() or any thread termination mechanism terminates the entire process.
    Just returning from main only ends that thread and I believe condemns any incomplete threads spawned in main to some kind of weird oblivion.
    Last edited by MK27; 09-05-2011 at 11:05 AM.
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  6. #6
    and the hat of wrongness Salem's Avatar
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    It's always possible that there is a bug in your library implementation of pthread, or even a bug in valgrind.

    If you demonstrate that you have the problem in a really simple test case (as above), and your main code has no other issues, then I think you should be able to claim success.

    BTW, I have
    $ valgrind --version
    valgrind-3.6.0.SVN-Debian
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

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