It's not a good idea to pass a stack temporary variable(structure) to thread routine: 1. we don't know the execution sequence of created threads 2. the temporary variable(structure) may get cleared before the sub threads access it

test_pool.c

/* definition of thread argument passed to pool wrapper*/
typedef struct {
    thread_pool *pool;
    uint64_t     id;
} thread_argument;

//////////////////////////////////////////////////////////////
// thread_pool_wrapper: thread start routine waiting for tasks
// to execute
/////////////////////////////////////////////////////////////

/* version 1: use temporary variable in main thread stack */
void *thread_pool_wrapper(void *arg)
{
    thread_argument *ta   = (thread_argument *)arg;
    thread_pool     *pool = ta->pool;
    uint64_t        id    = ta->id;
}

/* version 2: use global counter `nthread' and `xadd' instruction */
void *thread_pool_wrapper(void *arg)
{
    uint64_t id = __sync_fetch_and_add(&nthread, 1);
}

//////////////////////////////////////////////////////////////
// thread_pool_init: create workers with thread_pool_wrapper
// with thread info stored in array
/////////////////////////////////////////////////////////////

void thread_pool_init(thread_pool *pool)
{
    uint64_t i;

    pool->bitmap = 0L;
    pool->tear_down = 0;
    pthread_mutex_init(&mutex, NULL);
    pthread_mutex_init(&pool_mutex, NULL);
    pthread_mutex_init(&io_mutex, NULL);
    pthread_cond_init(&cond, NULL);
    pthread_mutex_lock(&mutex);
    memset(&pool->tasks, 0, MAX_WORKER * sizeof(worker_task));

    for (i = 0; i < WORKER_ENABLE; ++i)
    {
        /* version 1: pass a stack structure to wapper */
        thread_argument ta = {
            .pool = pool,
            .id = i
        };
        pthread_create(&(pool->tasks[i].tid), NULL, thread_pool_wrapper, &ta);

        /* version 2: pass only pool argument (actually can be nothing)
           and leave id to be determined by `xadd' */
        pthread_create(&(pool->tasks[i].tid), NULL, thread_pool_wrapper, pool);
        dprintf(INFO, "pthread_create: %x\n", pool->tasks[i].tid);
    }

    pthread_mutex_unlock(&mutex);
}