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

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Date:   Wed, 13 May 2020 15:53:43 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'psmith@....org'" <psmith@....org>,
        '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..

From: Paul Smith
> Sent: 13 May 2020 16:33
> On Wed, 2020-05-13 at 08:21 +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.
I can't remember if Posix allows SIGCHLD to be delivered
in a different thread.
Windows definitely likes delivering signals that way :-)

> > > Having the parent not acquire a token at all won't work; without
> > > limiting sub-makes it means you might have 100's of them running at
> > > the same time, even with -j2 or whatever.
> >
> > Hmmm...
> > That means the sub-make must always hold one token.
> > Otherwise the parent-make could use it to create a new sub-make.
> 
> Right, my first idea has this same problem so it won't work.
> 
> > Actually the token pipe can be opened NON_BLOCK because poll()
> > can/will be used to wait for a token.
> 
> Again, that only works on systems where pselect() is available.
> 
> > So you always try to read a token - even when you have one 'in your
> > hand' (either entry or because a job just finished).  If it isn't the
> > 'abort' one, put it back.
> 
> Something like that would be needed, yes.
> 
> Note this is only needed in a rare situation where you're running with
> parallelism enabled BUT you have a makefile which never actually tries
> to run two or more jobs at the same time for some reason.

I did have to recirculate the tokens.
Can't exactly remember why.

	David

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