[dpdk-dev] Does lthread_cond_wait need a mutex?

[Wiles, Keith]

> On Jul 17, 2018, at 10:43 PM, wubenqing at ruijie.com.cn wrote:
> 
> Hi~
>    Reference: http://doc.dpdk.org/guides-18.05/sample_app_ug/performance_thread.html?highlight=lthread
>    The L-thread subsystem provides a set of functions that are logically equivalent to the corresponding functions offered by the POSIX pthread library.
>    I think there is a bug with pthread_cond_wait of lthread implement.
>    Look at this code, there are two lthread:
> 
> lthread1:
>    pthread_mutex_lock(mutex);                 //a1
>    if (predicate == FALSE) {                        //a2
>        pthread_cond_wait(cond, mutex)        //a3
>    }
>    pthread_mutex_unlock(mutex);            //a4
> 
> int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex)
> {
> if (override) {
> pthread_mutex_unlock(mutex); //a31
> int rv = lthread_cond_wait(*(struct lthread_cond **)cond, 0); //a32
> 
> pthread_mutex_lock(mutex); //a33
> return rv;
> }
> return _sys_pthread_funcs.f_pthread_cond_wait(cond, mutex);
> }
> 
> lthread2:
>    pthread_mutex_lock(mutex);                //b1
>    predicate = TRUE;                                //b2
>    pthread_mutex_unlock(mutex);            //b3
>    pthread_cond_signal(cond);                //b4
> 
> 
>    If the sequence is:
>    a1->a2->a31->b1->b2->b3->b4->a32
>    Will lthread1 sleep forever?

Maybe is it possible, my brain is not working this morning. Please remember that lthreads must give up control or lthread will continue to and can not be preempted.

Does that fix the problem?

> 
> ________________________________
> 吴本卿(研五 福州)

Regards,
Keith