[nanomsg] Re: signal mask in posix threads
- From: Paul Colomiets <paul@xxxxxxxxxxxxxx>
- To: "nanomsg@xxxxxxxxxxxxx" <nanomsg@xxxxxxxxxxxxx>
- Date: Wed, 28 May 2014 13:08:21 +0300
Hi Martin,
On Wed, May 28, 2014 at 11:10 AM, Martin Sustrik <sustrik@xxxxxxxxxx> wrote:
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> On 28/05/14 03:44, Achille Roussel wrote:
>> Hi everyone, I have a question on nanomsg implementation, I think
>> there may be a race conditions in the code.
>>
>> In src/utils/thread_posix.inc, pthread_sigmask is called at the
>> beginning of the thread routine (nn_thread_main_routine), this
>> means there’s a small amount of instructions where the thread could
>> potentially be interrupted by an asynchronous signal… if the
>> program isn’t expecting this to happen that could lead it to miss
>> some signals, or worse, get killed if some default signal handlers
>> get called by the worker thread instead of being handled in another
>> way by the program itself (epoll / kevent / sigwait… ). A way to
>> solve that would be to move the call to pthread_sigmask in before
>> pthread_create, because the new thread inherits a the signal mask
>> of its parent, then restore the previous signal mask after the
>> call, please let me know what you think about this.
>
> Wouln't that just trade one synchronisation issue for another? I.e.
> the main thread could lose some signals while it has signals disabled?
>
I think they are not lost:
A signal may be blocked, which means that it will not be delivered
until it is later unblocked. Between the time when it is generated
and when it is delivered a signal is said to be pending.
--
Paul
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