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Date: Sun, 16 Aug 2020 19:11:37 +0200
From: Florian Weimer <>
To: Rich Felker <>
Subject: Re: Restrictions on child context after multithreaded fork

* Rich Felker:

> On Sun, Aug 16, 2020 at 11:10:37AM +0200, Florian Weimer wrote:
>> * Rich Felker:
>> > On some inspection, glibc does not actually attempt to make the child
>> > environment unrestricted. The only things it does around fork are:
>> I think pthread_once initializers that have partially executed are
>> also executed from the start in the child if initialization is
>> requested again.
> I don't follow how pthread_once is related. The vast majority of the
> things I found glibc doing no specific handling for are actual mutable
> state not just on-demand initialization.

If a fork happens during a pthread_once initialization, the subsystem
related to that becomes unavailable after fork.  The pthread_once_t
reinitialization logic intends to avoid that.  Like resetting locks
after fork in the new process, it is rather questionable.

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