[parsec-users] About VIPS's synchronization

jzz jzz at mit.edu
Thu Mar 7 06:56:05 EST 2013


Hi John,

Thanks a lot!

Cheers,
Justin

Sent from my iPhone

On Mar 7, 2013, at 4:10 AM, jcupitt at gmail.com wrote:

> Hi Justin,
> 
> On 7 March 2013 05:20, Zhunping Zhang <jzz at mit.edu> wrote:
>> Wonder if anyone can enlighten me how VIPS handles input synchronization. As I
>> understand, an operation in VIPS read inputs from several images and outputs to
>> one. The output images is shredded into blocks to be processed in parallel.
>> Evaluating two different blocks might depend on the same pixel in the input
>> images, and some synchronization method is needed to avoid races. May I know
>> how VIPs implement this? (Pointing to line numbers would be really helpful.)
> 
> I wrote a post about this:
> 
> http://libvips.blogspot.co.uk/2012/06/how-libvips-opens-file.html
> 
> The PARSEC benchmark uses direct access (the first method described in that post).
> 
> I don't know which version of vips is bundled in current PARSEC, but looking at libvips git master, the methods you need are vips_region_image(), which selects a rectangular area of a memory-mapped file:
> 
> https://github.com/jcupitt/libvips/blob/master/libvips/iofuncs/region.c#L579
> 
> Which in turn calls vips_window_ref() to get a reference to a chunk of a file:
> 
> https://github.com/jcupitt/libvips/blob/master/libvips/iofuncs/window.c#L349
> 
> John
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