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Date: Sat, 29 Jun 2024 00:32:09 +0900
To: cygwin AT cygwin DOT com
Subject: Re: cygwin application hangs on closing console
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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 Fri, 28 Jun 2024 21:17:26 +0900
Takashi Yano wrote:
> Sorry for very late replay.
> 
> On Mon, 3 Jun 2024 15:20:32 +0200
> Johannes Khoshnazar-Thoma wrote:
> > We did more testing and it looks like the name of the event
> > that signals console master thread start and end is shared between
> > unrelated processes (it uses the console minor which is always (?)
> > 0 when running from a powershell).
> > 
> > So since it is a two-state event (as opposed to a semaphore)
> > in theory the following can happen:
> > 
> > Process A	Process B
> > SetEvent(e)
> > 		SetEvent(e)
> > Waitforevent(e)
> > 		Waitforevent(e)
> 
> This should not happen. Master thread is unique to console.
> get_minor() number is always 0 for the first opened console.
> If you open another powershell window and start cygwin process
> while the first cygwin process is still active, the get_minor()
> returns 1.
> 
> Waiting for thread_sync_event is executed only
>   if (shared_console_info[unit] && con.owner == myself->pid)
> con.owner is in the shared memory which is shared among all
> processes started in the same console. Therefore, only the
> one process start to wait the event.
> 
> > The second SetEvent does nothing. As a result the
> > later Waitforevent is stuck (which is what we observe).
> > 
> > So the question is: why should this event be used in
> > unrelated cygwin processes? Is there a technical reason
> > we don't understand (yet) for doing that (sharing the event).
> > 
> > We patched cygwin to use pseudo random event names (the
> > tm_usec field of gettimeofday()) and the stuckness vanished.
> > So unless there is a reason for sharing the event between
> > cygwin processes this patch should work:
> 
> Do you really confirm that your patch resolves the issue?
> If so, the cause might be some kind of race issue.

There was similar bug in cygwin 3.5.1, however, it has been
already fixed in 3.5.3.
https://cygwin.com/git/?p=newlib-cygwin.git;a=commitdiff;h=fc5e9525453fea7c27b0e13635ae54abaa0db69d

I believe your problem is reproducible with 3.5.3. Right?

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

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