Re: [Kaldi-developers] Fwd: sem_t

[Daniel P. <dp...@gm...>]

Oh OK, maybe the sem_t is more heavyweight than it needs to be because it
is designed to work across processes.
Dan


On Fri, Jan 23, 2015 at 12:47 PM, Nagendra Goel <nag...@go...>
wrote:

> This is from:
> http://www.experts-exchange.com/Programming/System/Linux/Q_20375101.html
>
>
>
> semaphores can be used between different processes to synchronise access
> to some shared object i.e. a file or shared memory.
>
> If you have two processes which require read/write access to some resource
> you need to make sure that both are not trying to change the shared
> resource at the same time.  You can then use a semaphore to protect the
> access to the shared resource i.e each process has to acquire the semaphore
> before being allowed to perform an update on the shared resource.  Once the
> update is complete the process then releases the semaphore to allow another
> process to access/update the shared resource.
>
> pthread_mutex_t is a similar concept but shared between multiple threads
> of a single process.  If for example you have a multithreaded program which
> contains global data accessible/updatable by multiple threads then you
> would a mutex to protect the access in the same way.
>
>
>
> *From:* Daniel Povey [mailto:dp...@gm...]
> *Sent:* Friday, January 23, 2015 12:36 PM
> *To:* kal...@li...
> *Subject:* [Kaldi-developers] Fwd: sem_t
>
>
>
> I'm wondering if there is anyone on the list who is familiar with issues
> such as semaphores?
>
> The semaphore implementation in kaldi-semaphore.h uses two variables:
>
>   pthread_mutex_t mutex_;
>
>   pthread_cond_t cond_;
>
> but I just noticed there is something called sem_t, a semaphore type, from
> the POSIX standard.
>
> Does anyone know what portability issues this would bring, and what the
> reasons might be for
>
> using the two things from pthreads instead?
> Dan
>
>
>
> ---------- Forwarded message ----------
> From: *Karel Veselý* <ive...@fi...>
> Date: Fri, Jan 23, 2015 at 6:27 AM
> Subject: Re: sem_t
> To: dp...@gm...
>
>
> Hi Dan,
> frankly, it is hard for me to answer, years ago we learned how to
> implement semaphore in pthreads, so I used the code I had in a school
> project.
> Perhaps sem_t can do the same job, and perhaps it internally uses same
> functions as my implementation.
> Karel.
>
> Dne 23. 1. 2015 v 4:13 Daniel Povey napsal(a):
>
>
>
> Karel,
> I just found out there is a semaphore type in POSIX, called sem-t.
> Why doesn't your semaphore code use that, do you know?
> Dan
>
>
>
> --
> Karel Vesely, Brno University of Technology
> ive...@fi..., +420-54114-1300
>
>
>