linux-kernel - Re: [patch 14/22] pollfs: pollable futex

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Message-ID: <4638C37D.7050503@haxent.com.br>
Date:	Wed, 02 May 2007 13:59:41 -0300
From:	Davi Arnaut <davi@...ent.com.br>
To:	Ulrich Drepper <drepper@...il.com>
Cc:	Eric Dumazet <dada1@...mosbay.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Davide Libenzi <davidel@...ilserver.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [patch 14/22] pollfs: pollable futex

Ulrich Drepper wrote:
> On 5/2/07, Eric Dumazet <dada1@...mosbay.com> wrote:
>> I understand your concerns, but *this* patch bundle extends 
>> poll()/select()/epoll, and is not an alternative to kevent or other 
>> work in progress, (and linux centered)
>
> It is adding huge amounts of complexity and at the same time is not
> future-safe.  I consider this enough reason to reject this approach.
Huge amounts of complexity? It just _moves_ some futex code around!
The intended use is not for locking, but for event signaling. Why can't
it be future-safe? It just needs a address and a value! Pseudocode:

thread A:
    int fd = plfutex(addr, 0);
    do
        poll(fdset+fd);
        process network events
        queue obj to thread B
        if fd:
            job processed

thread B:
    wait_job();
    process_job();
    raise_event(addr);
> You never can get rid of the interface.  It's much cleaner and safer
> to do it right instead of piling on more and more workarounds for
> special situations.
It simple as is, there is no need to overdesign.

--
Davi Arnaut
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