linux-kernel - RE: [RFC PATCH v2 00/13] Add futex2 syscall

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Message-ID: <f594f043f5c7440d8e3534e9a14c97c4@AcuMS.aculab.com>
Date:   Mon, 8 Mar 2021 11:11:13 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Stefan Metzmacher' <metze@...ba.org>,
        André Almeida <andrealmeid@...labora.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Darren Hart" <dvhart@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
CC:     "kernel@...labora.com" <kernel@...labora.com>,
        "krisman@...labora.com" <krisman@...labora.com>,
        "pgriffais@...vesoftware.com" <pgriffais@...vesoftware.com>,
        "z.figura12@...il.com" <z.figura12@...il.com>,
        "joel@...lfernandes.org" <joel@...lfernandes.org>,
        "malteskarupke@...tmail.fm" <malteskarupke@...tmail.fm>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "fweimer@...hat.com" <fweimer@...hat.com>,
        "libc-alpha@...rceware.org" <libc-alpha@...rceware.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "shuah@...nel.org" <shuah@...nel.org>,
        "acme@...nel.org" <acme@...nel.org>,
        "corbet@....net" <corbet@....net>,
        io-uring <io-uring@...r.kernel.org>
Subject: RE: [RFC PATCH v2 00/13] Add futex2 syscall

From: Stefan Metzmacher
> Sent: 07 March 2021 11:35
> 
> Hi André,
> >  ** The wait on multiple problem
> >
> >  The use case lies in the Wine implementation of the Windows NT interface
> >  WaitMultipleObjects. This Windows API function allows a thread to sleep
> >  waiting on the first of a set of event sources (mutexes, timers, signal,
> >  console input, etc) to signal.

They are all events.
You can only wait on either events or sockets (using select).
There is a socket api to signal an event when data arrives (etc).
There is also the insane (these days) restriction of 64 events.

> With that in mind would it be good to have some interaction with epoll (and similar calls)?

Or hook something up so that pollwakeup can kick a futex as well
as waking up poll() and adding an event to epoll().

	David

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