6. Exercises

See the book for exercises using helgrind, i.e. valgrind --tool=helgrind

Example: Q1,2 main-race.c

     1	#include <stdio.h>
     2
     3	#include "common_threads.h"
     4
     5	int balance = 0;
     6
     7	void* worker(void* arg) {
     8	    balance++; // unprotected access
     9	    return NULL;
    10	}
    11
    12	int main(int argc, char *argv[]) {
    13	    pthread_t p;
    14	    Pthread_create(&p, NULL, worker, NULL);
    15	    balance++; // unprotected access
    16	    Pthread_join(p, NULL);
    17	    return 0;
    18	}

$ valgrind --tool=helgrind ./main-race
...
==25147== Possible data race during read of size 4 at 0x30A040 by thread #1
==25147== Locks held: none
...
==25147== This conflicts with a previous write of size 4 by thread #2
==25147== Locks held: none
...

Fix using a lock.