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Subject: Re: Change in functionality of futex() system call.
From: Eric Dumazet <eric.dumazet@gmail.com>
To: George Spelvin <linux@horizon.com>
Cc: luto@mit.edu, david@rgmadvisors.com, dvhart@linux.intel.com,
        kyle@moffetthome.net, linux-kernel@vger.kernel.org
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References: <20110609044354.1171.qmail@science.horizon.com>
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Date: Thu, 09 Jun 2011 07:25:33 +0200
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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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