Re: Official Linux system wrapper library?

From: Adam Borowski <kilobyte@angband.pl>
To: Florian Weimer <fweimer@redhat.com>
Cc: Willy Tarreau <w@1wt.eu>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
	Daniel Colascione <dancol@google.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Joel Fernandes <joelaf@google.com>,
	Linux API <linux-api@vger.kernel.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	Carlos O'Donell <carlos@redhat.com>,
	"libc-alpha@sourceware.org" <libc-alpha@sourceware.org>
Subject: Re: Official Linux system wrapper library?
Date: Wed, 14 Nov 2018 13:03:48 +0100	[thread overview]
Message-ID: <20181114120348.or5id3hzrmltkyvb@angband.pl> (raw)
In-Reply-To: <87zhufvntw.fsf@oldenburg.str.redhat.com>

On Sun, Nov 11, 2018 at 12:46:35PM +0100, Florian Weimer wrote:
> A lot of multi-threaded applications assume that most high-level
> functionality remains usable even after fork in a multi-threaded
> process.

How would this be even possible?  Currently fork kills all threads
(save for the caller).

Glibc's manpage also warns:

# After a fork() in a multithreaded program, the child can safely call only
# async-signal-safe functions (see signal-safety(7)) until such time as it
# calls execve(2).

Which makes sense as its malloc uses a mutex, and you can't take a breath
without a library call using malloc somewhere (or in C++, the language
itself).

So any functionality remaining usable after fork is pretty strictly
limited...

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