Is Thrust synchronous or asynchronous?

Question

I'm new to using Thrust and there is one thing I don't understand. Is Thrust asynchronous or synchronous?

If I write the following code, the time taken isn't 0. But in the other tags, other users report a result of 0. What is the truth?

clock_t start,end;

start=clock(); 
thrust::sort_by_key(vettore.begin(), vettore.end(), counter.begin()); 

end=clock();

double time=((double)(end-start))/CLOCKS_PER_SEC; 

cout<<"execution time"<<time<<endl;// the result is 0.327

Note: related question on the NVIDIA forum [here](https://devtalk.nvidia.com/default/topic/864759/is-thrust-copy-synchrous-or-asynchronus-/). — BenC, Sep 07 '15 at 04:38

score 3 · Answer 1 · answered Jun 21 '12 at 03:04

3

Kernel launches have always been asynchronous - even in CUDA 1.0 - so any Thrust call that results only in a kernel launch will be asynchronous.

Any Thrust code that implicitly triggers memcpy's will be synchronous due to the lack of stream support, as alluded to by marina.k.

answered Jun 21 '12 at 03:04

ArchaeaSoftware

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For example, thrust::reduce() is definitely synchronous since it reads back the result and returns it to the calling thread via the return value. I make some comments about these limitations in my recent blog post on Thrust: http://developer.nvidia.com/content/expressive-algorithmic-programming-thrust – harrism Jun 21 '12 at 04:24

score 0 · Answer 2 · edited May 23 '17 at 12:10

clock() function's granularity is not good as you think in Windows. And in Windows XP its granularity is as high as 16msec.

Instead of using clock() use a high resolution timer or Cutil library's timing functions (which is generally preferred).

Discussion about High resolution timer in Windows: C++ high precision time measurement in Windows

Discussion about CUtil library's usage for timing: CUDA: CUtil timer - confusion on elapsed time

score 0 · Answer 3 · answered Apr 23 '13 at 03:20

0

you can do it manually add the time.h to the indexer, go to Preferences -> C/C++ -> Indexer and put it in front of the existing "Files to be indexed up-front" like this:

time.h, cstdarg, stdarg.h, .....

it going to work

answered Apr 23 '13 at 03:20

Alamin

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1
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Is Thrust synchronous or asynchronous?

3 Answers3