linux-kernel - Re: Change in functionality of futex() system call.

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Message-ID: <1307597133.3980.65.camel@edumazet-laptop>
Date:	Thu, 09 Jun 2011 07:25:33 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	George Spelvin <linux@...izon.com>
Cc:	luto@....edu, david@...advisors.com, dvhart@...ux.intel.com,
	kyle@...fetthome.net, linux-kernel@...r.kernel.org
Subject: Re: Change in functionality of futex() system call.

Le jeudi 09 juin 2011 à 00:43 -0400, George Spelvin a écrit :

> Just for example, consider a circular buffer that a few (trusted)
> processes can write to, but many (less trusted) can read.  Obviously,
> being able to sleep on the head pointer is useful.


If its useful, then it needs a futex extension (and this must be
emulated on old kernels without this extension)

Remember futex_wake() call would just have to wakeup _all_ threads
instead of one, if kernel lacks this function.

If you dont trust futex_wait() users, just use futex_wake(ALL)

Its should not be a consequence of a previous (unrelated) patch, it
should be an added functionality, dully documented.



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