Bug when compiled with optimization?

[powfagged]

If you compile thpool.c with optimization it seems to hang.

To see this, edit tests/threadpool and change the line
gcc src/conc_increment.c ../thpool.c -pthread -o test
to
gcc -g -O src/conc_increment.c ../thpool.c -pthread -o test
Then when you run ./threadpool, it hangs at

$ gdb -p 22284 ./test
0x00000000004011c5 in thpool_init (num_threads=4) at ../thpool.c:150
150 while (thpool_p->num_threads_alive != num_threads) {}
(gdb) p thpool_p->num_threads_alive
$1 = 4
(gdb) p num_threads
$2 = 4

This is with gcc-4.8.3.

If I change thpool.c, adding "volatile",

typedef struct thpool_{
    thread**   threads;                  /* pointer to threads        */
    volatile int num_threads_alive;        /* threads currently alive   */
    volatile int num_threads_working;      /* threads currently working */
    pthread_mutex_t  thcount_lock;       /* used for thread count etc */
    jobqueue*  jobqueue_p;               /* pointer to the job queue  */    
} thpool_;

That seems to fix it, though it might be worth compiling the other tests with optimization to see if everything still works ok.

[Pithikos]

Thank you for your input and the fixes! I re-factored the tests now so all tests can be run with or without optimization. You can run all tests with an optimized binary by running ./optimized_compile.sh. I ran the tests and your fix seems to work nice for all test cases.

Thanks again :)