Hi~
I would be appreciate it if you could provide your lthread code for me. And
I found that DPDK lthreads does not provide lthread_cond_timedwait API which I
am looking for.
Thanks.
________________________________
Regards,
Wubenqing
From: Wiles, Keith<mailto:keith.wi...@intel.com>
Date: 2018-07-19 13:21
To: 吴本卿(研五 福州)<mailto:wubenq...@ruijie.com.cn>
CC: dev@dpdk.org<mailto:dev@dpdk.org>
Subject: Re: [dpdk-dev] Does lthread_cond_wait need a mutex?
> On Jul 18, 2018, at 7:34 PM, wubenq...@ruijie.com.cn wrote:
>
> Hi~
>
> If the lthreads run on different lcores, a race condition with lthread_mutex
> may occur.
> Like this:
> lthread1 run on lcore=1
> lthread2 run on lcore=2
> If the mutex is owned by lthread2, lthread1 try to lock the mutex that will
> block thread1. lthread_sched on lcore1 will insert lthread1 to the blocked
> queue of the mutex. lthread1 blocks until lthread2 unlock the mutex.
> Is that right?
>
> Let's go back to the previous question.
>
> Refer to
> http://pubs.opengroup.org/onlinepubs/7908799/xsh/pthread_cond_wait.html
> "The pthread_cond_wait() and pthread_cond_timedwait() functions are used to
> block on a condition variable. They are called with mutex locked by the
> calling thread or undefined behaviour will result.
> These functions atomically release mutex and cause the calling thread to
> block on the condition variable cond; atomically here means "atomically with
> respect to access by another thread to the mutex and then the condition
> variable”."
Yes, I believe you are correct. I was able to look at my version of lthreads
and I had changed lthread_cond_wait() to have a mutex argument and removed the
reserved variable. The same was done for timed wait function. As I remember I
found a couple minor problems in lthreads, which I fixed. The problem is my
lthread code is somewhat different then the code in DPDK and my changes would
not apply to DPDK lthreads.
>
> So I think there is a problem with pthread_cond_wait implemented by lthread.
> If that is the case, could lthread fix this problem?
>
> Regards,
> Wubenqing
>
>
> From: Wiles, Keith
> Date: 2018-07-18 23:01
> To: 吴本卿(研五 福州)
> CC: dev@dpdk.org
> Subject: Re: [dpdk-dev] Does lthread_cond_wait need a mutex?
>
>
> > On Jul 17, 2018, at 10:43 PM, wubenq...@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
Regards,
Keith
