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Date: Fri, 10 Mar 2017 21:10:36 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: fork() fails if it is called recursively from a child thread.
Message-ID: <20170310201036.GA18927@calimero.vinschen.de>
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Hi,

On Mar  9 20:39, Takashi Yano wrote:
> Hello,
>=20
> I found fork() fails if it is called recursively from a child thread.
>=20
> Simple test case, attached (fk.c), reproduces this problem.
>=20
> Expected result:
> Parent 0 [22034] exit.
> Child 0 [22036] works.
> Parent 1 [22036] exit.
> Child 1 [22038] works.
> Parent 2 [22038] exit.
> Child 2 [22039] works.
> Parent 3 [22039] exit.
> Child 3 [22040] works.
> Parent 4 [22040] exit.
> Child 4 [22041] works.
>=20
> Result in cygwin 2.7.0:
> Child 0 [4668] works.
> Parent 0 [7188] exit.
>       0 [main] a 4668 fork: child -1 - forked process 8456 died unexpecte=
dly, retry 0, exit code 0xC0000142, errno 11
> fork(): Resource temporarily unavailable
>=20
> Strictly speaking, the test case is not safe because it calls functions
> which are not async-signal-safe from forked child process, i.e. printf()
> and perror(), in spite of multi-thread. However the same happens even
> without printf() and perror().
>=20
> This is the cause of which iperf 2.0.5 with option -s -D fails to start
> as daemon.

Thanks for the report and especially the testcase.

It was a tricky problem to debug so it took me a while, but I think
I got it now.

I uploaded new developer snapshots to https://cygwin.com/snapshots/

Please give them a try.  I'd be also interested if that fixes the iperf
problem.  Can you check?  There's always a chance that this uncovers
another problem hidden under this one...


Thanks,
Corinna

--=20
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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