Intel FPGA SDK for OpenCL: Issue while launching same opencl kernel multiple times

Hi,

I am using Intel FPGA SDK for OpenCL to perform matrix multiplication on DE1-SoC board. As per my requirement I have to perform this multiplication multiple times and hence iterating over a loop to enqueue the kernel. The first kernel successfully completes however the second kernel stuck in CL_RUNNING state indefinitely. I tried simplifying my code to narrow down the problem and removed all computatons from the kernel as below-

__kernel void multiplication()
{

//Empty kernel
}

instead of loop I am equeueing my kernel 2 times as below-

cl_int err;

size_t global_work_size[] = {static_cast<size_t>(1)};
size_t local_work_size[] = {static_cast<size_t>(1)};

cl_event kernel_event1;

// Enqueue the kernel for execution
std::cout << "started enqueue" << std::endl;
err = clEnqueueNDRangeKernel(queue, kernel, 1, NULL, global_work_size, local_work_size, 0, NULL, &kernel_event1);

if (err != CL_SUCCESS)

{

std::cout << "Failed to enqueue"<< std::endl;

}
else{

std::cout << "Done enqueue"<< std::endl;

}

err = clWaitForEvents(1, &kernel_event1);
if (err != CL_SUCCESS) {
std::cerr << "Error waiting for kernel event." << std::endl;
}else{
std::cout << "done executing the kernel" << std::endl;
clReleaseEvent(kernel_event1);
}

//Second kernel execution

cl_event kernel_event2;

// Enqueue the kernel for execution
std::cout << "started enqueue" << std::endl;
err = clEnqueueNDRangeKernel(queue, kernel, 1, NULL, global_work_size, local_work_size, 0, NULL, &kernel_event2);

if (err != CL_SUCCESS)

{

std::cout << "Failed to enqueue"<< std::endl;

}
else{

std::cout << "Done enqueue"<< std::endl;

}

cl_int event_status;
clGetEventInfo(kernel_event2, CL_EVENT_COMMAND_EXECUTION_STATUS, sizeof(event_status), &event_status, NULL);
if(event_status == CL_QUEUED){
printf("Kernel is queued.\n");
}else if(event_status == CL_SUBMITTED){
printf("Kernel is submitted.\n");
}else if(event_status == CL_RUNNING){
printf("Kernel is running.\n");
}else if(event_status == CL_COMPLETE){
printf("Kernel has completed.\n");
}else{
printf("Unknown status.\n");
}

err = clWaitForEvents(1, &kernel_event2);
if (err != CL_SUCCESS) {
std::cerr << "Error waiting for kernel event." << std::endl;
}else{
std::cout << "done executing the kernel" << std::endl;
clReleaseEvent(kernel_event2);
}

In the above simplified code, my kernel is not performing any computations and just trying to launch same kernel second time after successful completion of first one. During the execution, I can see the debug statements printed that first execution is completed and second execution is successfully enqueued but status gets printed as CL_RUNNING and waits indefinitely at clWaitForEvents and not even returning an error message for the wait status.

I'd highly appreciate if someone assist me to understand this issue.

Thank you.