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Message-ID: <20261105185412.GX23438@brightrain.aerifal.cx>
Date: Thu, 5 Nov 2026 13:54:13 -0500
From: Rich Felker <dalias@...c.org>
To: Luca Kellermann <mailto.luca.kellermann@...il.com>
Cc: musl@...ts.openwall.com
Subject: Re: [PATCH] thrd_create: inherit signal mask from creating
thread
On Thu, Nov 05, 2026 at 03:39:51PM +0100, Luca Kellermann wrote:
> POSIX.1-2024 requires that the new thread created by thrd_create()
> inherits the signal mask from the creating thread, just like the new
> thread created by pthread_create().
>
> it seems like this was initially the case when thrd_create() was
> implemented in commit 23614b0fcb4cd4d7b2e4148d3b1887b642169765. commit
> 04335d9260c076cf4d9264bd93dd3b06c237a639 then changed pthread_create()
> to always block signals before starting new threads but restoring the
> signal mask was only done for new threads started by pthread_create()
> (start()), not for new threads started by thrd_create() (start_c11()).
> this was before POSIX included threads.h, so it didn't violate any
> specification back then (the C standard doesn't know signal masks).
Hm, I thought this was intentional. Threads created by library code to
be transparent to the calling application need to be created with all
signals masked. Since ISO C has no way to mask signals, the
thrd_create interface should just do that itself.
If POSIX now requires them to inherit, we should probably change that,
but it might be worth opening a defect report. Inheriting signal mask
was really a bug in pthreads, and imposing the same on C11 threads
where the library code creating the may be POSIX-unaware seems like a
bad thing.
Rich
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