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Date: Wed, 18 Jun 2025 20:31:27 +0900
To: cygwin AT cygwin DOT com
Subject: Re: Calling system() in multi-threads.
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From: Takashi Yano via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>
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On Tue, 17 Jun 2025 15:42:26 -0700
Mark Geisert wrote:
> Hi Takashi,
> 
> On 6/17/2025 5:54 AM, Takashi Yano via Cygwin wrote:
> > Hi,
> > 
> > If system() is called in parallel in threads, system()
> > fails with exit code 127.
> > 
> > Just compile pthread_system.c attached and run.
> > 
> > I believe system() is multi-thread safe so the STC
> > should work.
> 
> I regret to inform that system() is not currently MT-safe.  I discovered 
> this a few years ago when porting YAFU (Yet Another Factoring Utility).
> 
> I ended up supplying a wrapper that serialized the system() call itself 
> but allowed multiple wrappers (and thus child processes) to be running 
> at the same time.  I never got around to supplying a fix for Cygwin. 
> I've attached the code.
> HTH somehow,

Thanks for the information. I guess the cause is that accessing
child_info_spawn NO_COPY ch_spawn;
in spwan.cc conflicts with other threads. I wonder ch_spawn should
be thread-specific. Or should be guarded by lock.

-- 
Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>

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