OpenCL clFinish never returns - opencl

Question

I'm looking to start learning OpenCL. I was looking for a "hello world" example in order to first verify that everything behaves as expected on my system. After trying multiple such examples, I'm unable to find (or to make) one that works.
The code below is blocking on the call to clFinish and appears to never return.
#include <math.h>
#ifdef __APPLE__
#include <OpenCL/opencl.h>
#else
#include <CL/cl.h>
#endif
const char *KernelSource = "\n" \
"__kernel void hello( \n" \
" __global char* a, \n" \
" __global char* b, \n" \
" __global char* c, \n" \
" const unsigned int count) \n" \
"{ \n" \
" int i = get_global_id(0); \n" \
" if(i < count) \n" \
" c[i] = a[i] + b[i]; \n" \
"} \n" \
"\n";
#define DATA_SIZE (16)
int main(int argc, char** argv)
{
int err; // error code returned from api calls
cl_device_id device_id; // compute device id
cl_context context; // compute context
cl_command_queue commands; // compute command queue
cl_program program; // compute program
cl_kernel kernel; // compute kernel
cl_mem input; // device memory used for the input array
cl_mem input2; // device memory used for the input array
cl_mem output; // device memory used for the output array
size_t global; // global domain size for our calculation
size_t local; // local domain size for our calculation
int i;
unsigned int count = DATA_SIZE;
// Input data
char a[DATA_SIZE] = "Hello \0\0\0\0\0\0";
char b[DATA_SIZE] = {15, 10, 6, 0, -11, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
// Output data
char c[DATA_SIZE];
cl_platform_id platform;
unsigned int no_plat;
err = clGetPlatformIDs(1,&platform,&no_plat);
// Where to run
err = clGetDeviceIDs(platform, CL_DEVICE_TYPE_GPU, 1, &device_id, NULL);
if (err != CL_SUCCESS) return -1;
context = clCreateContext(0, 1, &device_id, NULL, NULL, &err);
if (!context) return -1;
commands = clCreateCommandQueue(context, device_id, 0, &err);
if (!commands) return -1;
// What to run
program = clCreateProgramWithSource(context, 1, (const char **) & KernelSource, NULL, &err);
if (!program) return -1;
err = clBuildProgram(program, 0, NULL, NULL, NULL, NULL);
if (err != CL_SUCCESS) return -1;
kernel = clCreateKernel(program, "hello", &err);
if (!kernel || err != CL_SUCCESS) return -1;
// Create space for data and copy a and b to device (note that we could also use clEnqueueWriteBuffer to upload)
input = clCreateBuffer(context, CL_MEM_READ_ONLY | CL_MEM_USE_HOST_PTR, sizeof(char) * DATA_SIZE, a, NULL);
input2 = clCreateBuffer(context, CL_MEM_READ_ONLY | CL_MEM_USE_HOST_PTR, sizeof(char) * DATA_SIZE, b, NULL);
output = clCreateBuffer(context, CL_MEM_WRITE_ONLY, sizeof(char) * DATA_SIZE, NULL, NULL);
if (!input || !output) return -1;
// Send data
err = clSetKernelArg(kernel, 0, sizeof(cl_mem), &input);
err |= clSetKernelArg(kernel, 1, sizeof(cl_mem), &input2);
err |= clSetKernelArg(kernel, 2, sizeof(cl_mem), &output);
err |= clSetKernelArg(kernel, 3, sizeof(unsigned int), &count);
if (err != CL_SUCCESS) return -1;
local = DATA_SIZE;
// Run kernel!
global = DATA_SIZE; // count;
err = clEnqueueNDRangeKernel(commands, kernel, 1, NULL, &global, &local, 0, NULL, NULL);
if (err != CL_SUCCESS) return -1;
clFinish(commands);
// Read result
err = clEnqueueReadBuffer( commands, output, CL_TRUE, 0, sizeof(char) * count, c, 0, NULL, NULL );
if (err != CL_SUCCESS) return -1;
printf("%s\n", c);
// Clean up
clReleaseMemObject(input);
clReleaseMemObject(output);
clReleaseProgram(program);
clReleaseKernel(kernel);
clReleaseCommandQueue(commands);
clReleaseContext(context);
sleep(1); // Leopard pty bug workaround.
return 0;
}
I have a Ryzen 5 3400G and I'm using Linux.
gcc (Debian 10.2.1-6) 10.2.1 20210110
During compilation I see a couple of warnings (I couldn't find an example that gives no warnings).
from world.c:11:
/usr/include/CL/cl_version.h:22:9: note: ‘#pragma message: cl_version.h: CL_TARGET_OPENCL_VERSION is not defined. Defaulting to 300 (OpenCL 3.0)’
22 | #pragma message("cl_version.h: CL_TARGET_OPENCL_VERSION is not defined. Defaulting to 300 (OpenCL 3.0)")
| ^~~~~~~
world.c: In function ‘main’:
world.c:61:2: warning: ‘clCreateCommandQueue’ is deprecated [-Wdeprecated-declarations]
61 | commands = clCreateCommandQueue(context, device_id, 0, &err);
| ^~~~~~~~
In file included from world.c:11:
/usr/include/CL/cl.h:1906:1: note: declared here
1906 | clCreateCommandQueue(cl_context context,
| ^~~~~~~~~~~~~~~~~~~~
Am I doing something wrong or is the example wrong? In the latter case, where can I find a simple opencl program that works?
EDIT
I happened to restart the computer and clinfo works after the restart:
Number of platforms 1
Platform Name Clover
Platform Vendor Mesa
Platform Version OpenCL 1.1 Mesa 20.3.5
Platform Profile FULL_PROFILE
Platform Extensions cl_khr_icd
Platform Extensions function suffix MESA
Platform Name Clover
Number of devices 1
Device Name AMD Radeon(TM) Vega 11 Graphics (RAVEN, DRM 3.40.0, 4.19.0-12-amd64, LLVM 11.0.1)
Device Vendor AMD
Device Vendor ID 0x1002
Device Version OpenCL 1.1 Mesa 20.3.5
Driver Version 20.3.5
Device OpenCL C Version OpenCL C 1.1
Device Type GPU
Device Profile FULL_PROFILE
Device Available Yes
Compiler Available Yes
Max compute units 11
Max clock frequency 1400MHz
Max work item dimensions 3
Max work item sizes 256x256x256
Max work group size 256
Preferred work group size multiple (kernel) 64
Preferred / native vector sizes
char 16 / 16
short 8 / 8
int 4 / 4
long 2 / 2
half 0 / 0 (n/a)
float 4 / 4
double 2 / 2 (cl_khr_fp64)
Half-precision Floating-point support (n/a)
Single-precision Floating-point support (core)
Denormals No
Infinity and NANs Yes
Round to nearest Yes
Round to zero No
Round to infinity No
IEEE754-2008 fused multiply-add No
Support is emulated in software No
Correctly-rounded divide and sqrt operations No
Double-precision Floating-point support (cl_khr_fp64)
Denormals Yes
Infinity and NANs Yes
Round to nearest Yes
Round to zero Yes
Round to infinity Yes
IEEE754-2008 fused multiply-add Yes
Support is emulated in software No
Address bits 64, Little-Endian
Global memory size 31611129856 (29.44GiB)
Error Correction support No
Max memory allocation 22127790899 (20.61GiB)
Unified memory for Host and Device No
Minimum alignment for any data type 128 bytes
Alignment of base address 32768 bits (4096 bytes)
Global Memory cache type None
Image support No
Local memory type Local
Local memory size 32768 (32KiB)
Max number of constant args 16
Max constant buffer size 67108864 (64MiB)
Max size of kernel argument 1024
Queue properties
Out-of-order execution No
Profiling Yes
Profiling timer resolution 0ns
Execution capabilities
Run OpenCL kernels Yes
Run native kernels No
Device Extensions cl_khr_byte_addressable_store cl_khr_global_int32_base_atomics cl_khr_global_int32_extended_atomics cl_khr_local_int32_base_atomics cl_khr_local_int32_extended_atomics cl_khr_int64_base_atomics cl_khr_int64_extended_atomics cl_khr_fp64
NULL platform behavior
clGetPlatformInfo(NULL, CL_PLATFORM_NAME, ...) No platform
clGetDeviceIDs(NULL, CL_DEVICE_TYPE_ALL, ...) No platform
clCreateContext(NULL, ...) [default] No platform
clCreateContext(NULL, ...) [other] Success [MESA]
clCreateContextFromType(NULL, CL_DEVICE_TYPE_DEFAULT) Success (1)
Platform Name Clover
Device Name AMD Radeon(TM) Vega 11 Graphics (RAVEN, DRM 3.40.0, 4.19.0-12-amd64, LLVM 11.0.1)
clCreateContextFromType(NULL, CL_DEVICE_TYPE_CPU) No devices found in platform
clCreateContextFromType(NULL, CL_DEVICE_TYPE_GPU) Success (1)
Platform Name Clover
Device Name AMD Radeon(TM) Vega 11 Graphics (RAVEN, DRM 3.40.0, 4.19.0-12-amd64, LLVM 11.0.1)
clCreateContextFromType(NULL, CL_DEVICE_TYPE_ACCELERATOR) No devices found in platform
clCreateContextFromType(NULL, CL_DEVICE_TYPE_CUSTOM) No devices found in platform
clCreateContextFromType(NULL, CL_DEVICE_TYPE_ALL) Success (1)
Platform Name Clover
Device Name AMD Radeon(TM) Vega 11 Graphics (RAVEN, DRM 3.40.0, 4.19.0-12-amd64, LLVM 11.0.1)

Answer 1

I checked the sample code, it executes properly. So there must be an issue with your OpenCL Runtime installation. Did a reboot fix it already? Are you on Windows or Linux?