linux-kernel - Re: [PATCH] V1 1/2] ipc: let message queues use SIGEV_THREAD_ID with mq

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Message-ID: <541ED4C2.2050009@colorfullife.com>
Date:	Sun, 21 Sep 2014 15:38:10 +0200
From:	Manfred Spraul <manfred@...orfullife.com>
To:	Steven Stewart-Gallus <sstewartgallus00@...angara.bc.ca>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	dbueso@...e.de
Subject: Re: [PATCH] V1 1/2] ipc: let message queues use SIGEV_THREAD_ID with
 mq_notify

Hi Steven,

You wrote:
> Currently the only thread-safe way of using mq_notify with message 
> queues is to use the SIGEV_THREAD option.
Could you explain what you mean with "only thread-safe way"?
I'm a bit relunctant to extend mq_notify() without understanding the reason.

What about:
- use sigprocmask()
- create one worker thread
- then in a loop in that worker thread: use sigwaitinfo() or signalfd() 
to collect the signals.


And one point I don't like: Within timer_create():
>  SIGEV_THREAD_ID (Linux-specific)
>  [...]
> The sigev_notify_thread_id field specifies a kernel thread ID, that 
> is, the value returned by clone(2) or gettid(2).
Does that mean that SIGEV_THREAD_ID is guaranteed to remain 
Linux-specific, it's implicitely linked to the Linux clone()/gettid() 
threading model?

> This flag is intended only for use by threading libraries.


--
     Manfred
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