linux-kernel - Re: I disabled more compiler warnings..

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Message-ID: <5cb62c1a8ca38a3eceb37f7d236828761cad07ce.camel@gnu.org>
Date:   Wed, 13 May 2020 12:06:45 -0400
From:   Paul Smith <psmith@....org>
To:     David Laight <David.Laight@...LAB.COM>,
        'Linus Torvalds' <torvalds@...ux-foundation.org>
Cc:     'Arnd Bergmann' <arnd@...db.de>,
        'Masahiro Yamada' <yamada.masahiro@...ionext.com>,
        'Linux Kernel Mailing List' <linux-kernel@...r.kernel.org>
Subject: Re: I disabled more compiler warnings..

On Wed, 2020-05-13 at 15:53 +0000, David Laight wrote:
> > If we don't have pselect() we use the close() in the signal
> > handler. In that case we're just waiting in the read(), we're not
> > using select() or poll() or whatever.  It's definitely the case
> > that if we're waiting in read() and someone closes the FD, we'll
> > wake up! :)
> 
> Ugg, that is relying on getting either EINTR or EBADFD.

Yes, exactly.

> I can't remember if Posix allows SIGCHLD to be delivered
> in a different thread.

It does: all you have to do is ensure that all threads other than the
one you want block the signal.

However, GNU make is not multithreaded so this is moot.

> Windows definitely likes delivering signals that way :-)

In Windows IIRC GNU make doesn't use this method at all; Windows has
some kind of process shared semaphore that is used instead.  I didn't
write that code so I can't really describe it in detail :)