等待内核完成OpenCL

Question

My OpenCL program doesn't always finish before further host (c++) code is executed. The OpenCL code is only executed up to a certain point (which apperears to be random). The code is shortened a bit, so there may be a few things missing.

cl::Program::Sources sources;
string code = ResourceLoader::loadFile(filename);
sources.push_back({ code.c_str(),code.length() });

program = cl::Program(OpenCL::context, sources);

if (program.build({ OpenCL::default_device }) != CL_SUCCESS)
{
    exit(-1);
}
queue = CommandQueue(OpenCL::context, OpenCL::default_device);
kernel = Kernel(program, "main");
Buffer b(OpenCL::context, CL_MEM_READ_WRITE, size);
queue.enqueueWriteBuffer(b, CL_TRUE, 0, size, arg);
buffers.push_back(b);
kernel.setArg(0, this->buffers[0]);

vector<Event> wait{ Event() };

Version 1:

queue.enqueueNDRangeKernel(kernel, NDRange(), range, NullRange, NULL, &wait[0]);

Version 2:

queue.enqueueNDRangeKernel(kernel, NDRange(), range, NullRange, &wait, NULL);

.

wait[0].wait();

queue.finish();

Version 1 just does not wait for the OpenCL program. Version 2 crashes the program (at queue.enqueueNDRangeKernel):

Exception thrown at 0x51D99D09 (nvopencl.dll) in foo.exe: 0xC0000005: Access violation reading location 0x0000002C.

How would one make the host wait for the GPU to finish here?

EDIT: queue.enqueueNDRangeKernel returns -1000. While it returns 0 on a rather small kernel

Answer 1

Version 1 says to signal wait[0] when the kernel is finished - which is the right thing to do.

Version 2 is asking your clEnqueueNDRangeKernel() to wait for the events in wait before it starts that kernel [which clearly won't work].

On it's own, queue.finish() [or clFinish() ] should be enough to ensure that your kernel has completed.

Since you haven'd done clCreateUserEvent , and you haven't passed it into anything else that initializes the event, the second variant doesn't work.

It is rather bad that it crashes [it should return "invalid event" or some such - but presumably the driver you are using doesn't have a way to check that the event hasn't been initialized]. I'm reasonably sure the driver I work with will issue an error for this case - but I try to avoid getting it wrong...

I have no idea where -1000 comes from - it is neither a valid error code, nor a reasonable return value from the CL C++ wrappers. Whether the kernel is small or large [and/or completes in short or long time] shouldn't affect the return value from the enqueue, since all that SHOULD do is to enqueue the work [with no guarantee that it starts until a queue.flush() or clFlush is performed]. Waiting for it to finish should happen elsewhere.

I do most of my work via the raw OpenCL API, not the C++ wrappers, which is why I'm referring to what they do, rather than the C++ wrappers.

Answer 2

I faced a similar problem with OpenCL that some packages of a data stream we're not processed by OpenCL.

I realized it just happens while the notebook is plugged into a docking station.

Maybe this helps so (No clFlush or clFinish calls)