CODEWITHSUNDEEP
opencl
daniel
daniel

Reputation: 107

Is it possibile in OpenCL to wait for an event that has not been returned by clEnqueueNDRangeKernel yet?

Let's say there are two Command Queues and I want to synchronize them using events. It can be done like this:

cl_event event1;
clEnqueueNDRangeKernel(queue1, <..params..>, 0, NULL, &event1);
cl_event event2;
clEnqueueNDRangeKernel(queue2, <..params..>, 0, NULL, &event2);

clEnqueueNDRangeKernel(queue1, <..params..>, 1, &event2, NULL);
clEnqueueNDRangeKernel(queue2, <..params..>, 1, &event1, NULL);

Is there a possibility to achive similar results but with a different order of clEnqueueNDRangeKernel calls? For example:

cl_event event1;
cl_event event2;

clEnqueueNDRangeKernel(queue1, <..params..>, 0, NULL, &event1);
clEnqueueNDRangeKernel(queue1, <..params..>, 1, &event2, NULL); //it fails here because event2 does not exist

clEnqueueNDRangeKernel(queue2, <..params..>, 0, NULL, &event2);
clEnqueueNDRangeKernel(queue2, <..params..>, 1, &event1, NULL);

Upvotes: 0

Views: 297

Answers (1)

mogu
mogu

Reputation: 1119

Is it possibile in OpenCL to wait for an event that has not been returned by clEnqueueNDRangeKernel yet?

Not really, but there's a different approach possible.

You could create a user event (clCreateUserEvent) and use the returned userEvent instead of event2 argument in the enqueue call. Then, after enqueueing a kernel that creates event2, you add a callback (clSetEventCallback) on event2, and from that callback you call clSetUserEventStatus(userEvent, CL_COMPLETE).

There are only two problems with this, 1) even if the most common OpenCL implementations weren't horrible WRT user events, you're introducing unnecessary userspace trips (= slowdown), 2) they are horrible WRT user events. By which i mean, the callback will be called... at some point. It's not unusual to see it called with 10-200ms delay after the event has actually finished.

You could get more useful answers if you said what is the problem you're trying to solve.

Upvotes: 1

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