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Subject: Re: buflib handling in picture flow plugin

Re: buflib handling in picture flow plugin

From: Thomas Martitz <>
Date: Sun, 22 Feb 2015 21:31:14 +0100

Am 22.02.2015 um 21:15 schrieb Thomas Jarosch:
> Hi Thomas (kugel),
> Am Sonntag, 15. Februar 2015, 23:45:48 schrieb Thomas Martitz:
>> The below commit isn't necessary.
>> buflib buffers can be passed to yielding functions just fine. Problems
>> only arise if the are concurrent allocations, for example if two threads
>> allocate from the same context simultaneously or if the callee does it's
>> own allocations. This can't happen in the pictureflow case, it has it's
>> own context and a single thread allocating from it.
>> Therefore the problem isn't yield() itself, but possible concurrent
>> buflib_alloc() calls that result from the thread switch. This is because
>> compaction only ever happens on allocation (and not in a backgroud
>> thread or so).
>> Best regards.
>> commit 9076b433d18b5db1a1987fe99ca7c70808f22b0e
>> Author: Thomas Jarosch <>
>> Date: Thu Jan 1 23:45:24 2015 +0100
>> PictureFlow: Add move callback for buflib allocations
>> If we don't provide a callback to buflib_alloc(),
>> the buffer is always movable (to reduce fragmentation).
>> Since we pass our buffer to functions that call yield(),
>> this could lead to memory corruption on buflib compaction.
>> Change-Id: Id1fad1822479d692551c55cb8bc87cea7b78f759
> thanks for the review. I noticed the same thing a few days after
> committing it. It occupied my mind why it wasn't crashing before ;)
> Do you think we should revert it or keep it? It won't hurt I guess.
> Did you have a chance to look at the other buflib changes I did?
> They should be correct IMHO.

IMO, yes, it should be reverted, because adds unecessary overhead and
gives the false impression that callbacks are always required.

I didn't notice other problems with your buflib related commits but I
maybe missed some. Do you want me to look at a particular change?

Best regards.
Received on 2015-02-22

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