Opencl atomic_add() function returns wrong value

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Have a good time

i have a problem in OpenCL 1.2.
Look, i have an array as global in the kernel and the group size is 1000.
The problem is that the atomic_add() function doesn't work correctly.

My kernel code is :

C++

buffer[3] = 100;
atomic_add(&buffer[3], 1);

if i create 1000 threads, i expect the value of buffer[3] will be 1100, am i right?
but the behavior of the program is undefined.
sometime it will be 1100, sometimes 1064, sometimes 1093 and ...

What I have tried:

i also enable the opencl extension like below :

#pragma OPENCL EXTENSION cl_khr_global_int32_base_atomics : enable

but the problem is still exists.
in the another project i'de create a simple opencl project and the atomic_add works currectly, and i've checked almost the entire of project configuraton but i don't know the problem where is.

can you help me?
thanks

Posted 26-Mar-17 1:13am

Mahdi Nejadsahebi

Updated 14-May-17 21:18pm

v2

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Richard MacCutchan · Answer 1 · 2017-03-26T01:45:00

Solution 1

See OpenCL 2.0 Atomics Overview[^].

Posted 26-Mar-17 1:45am

Richard MacCutchan

Updated 26-Mar-17 1:46am

v2

Comments

Mahdi Nejadsahebi 26-Mar-17 8:04am

Excuse me my friend
i can't findout my problem when i read the link that you've sent.
can you explain for me?
although i'm working with opencl 1.2.
thanks

Richard MacCutchan 26-Mar-17 12:45pm

Sorry, I have never worked with OpenCL, but the chances are quite high that there is something in your code that is not correct.

Richard MacCutchan 26-Mar-17 12:47pm

Where is buffer defined, and what type is it? Has it been initialised correctly as described in the documentation?

[no name] 26-Mar-17 14:12pm

No vote from my side. But this is not an answer! Googled, choosed one of the first best hits, copied as answer, nothing more!

Richard MacCutchan 27-Mar-17 3:46am

Please go away, you are being a child.

Mahdi Nejadsahebi 28-Mar-17 2:17am

Dear Richard i respect to you for spending your time to ans me.
Let me test and then i'll tell you the result.

Mahdi Nejadsahebi 28-Mar-17 2:15am

I've no idea about you dear frined (0x01AA) ... but thanks for your comment.

tugrulGtx · Answer 2 · 2017-05-14T21:18:00

Solution 2

```
buffer[3] = 100;
```

is a race condition. Do it from CPU host side or another kernel.

Posted 14-May-17 21:18pm

tugrulGtx