Re: [boost] [compute] Review period starts today December 15, 2014, ends on December 24, 2014

Subject: Re: [boost] [compute] Review period starts today December 15, 2014, ends on December 24, 2014
From: Sebastian Schaetz (seb.schaetz_at_[hidden])
Date: 2014-12-21 18:01:04

Asbjørn <lordcrc <at> gmail.com> writes:

> In my "just for fun" Delphi.Compute library (written in Delphi, inspired by 
> Boost.Compute) I made Copy() and Transform() return futures of the output 
> buffers, as well as accept futures as parameters. Note, Delphi doesn't have 
> iterators like C++ so my routines operate directly on buffers.
> 
> So when Transform() say got a Future<Buffer> instead of a Buffer for a 
> parameter, it would add the future's associated event to the wait list
passed to 
> clEnqueueNDRangeKernel (technically the Buffer type has an implicit
conversion 
> operator to an "immediate" Future<Buffer>).
> 
> This made it pretty seamless to queue up everything and then just wait for
the 
> final read (the default "copy device buffer to host array and return it"
call is 
> blocking). The code looks sequential but would only block on that last read.

This idea is pretty nifty and I've been pondering this exact way of
implementing asynchrony as well in my library. 

Another method that I also like would be to just let the buffer store the
futures. This is how Joel's/Numscale's NT2 works [0], he gave an awesome
talk about it at this years Meeting C++ [1]. But this might just be a
higher-level interface more applicable to expression trees as opposed to STL
like functions.

A third way would be to return a future<void> from all meta-functions and
allow meta-functions to take a future<void> - this would directly map to the
stream/command_queue but the interface is maybe not that meaningful any more.

Does your implementation implicitly synchronize two command_queues if you 
issue a binary function with two different futures?

Sebastian

[0] https://github.com/MetaScale/nt2
[1]
http://www.slideshare.net/joelfalcou/automatic-taskbased-code-generation-for-high-performance-dsel