GlFinish hangs forever after clEnqueueReleaseGLObjects

Question

The following code works fine (Windows 7, Nvidia GTX 750 Ti) with Nvidia 361.91 drivers (and earlier), but freezes with newer versions such as 364.72 and 368.69. GlFinish now blocks program execution only after calling clEnqueueReleaseGLObjects. Before blaming the drivers, I suspect that something is wrong with my OpenCL / OpenGL interaction, so here is the code for a small, solid program that reproduces the problem, with the problem at the very end:

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

#include <SDL.h>
#include <gl/glew.h>
#include <SDL_opengl.h>
#include <gl/glut.h>

#pragma comment (lib, "C:\\Program Files\\NVIDIA GPU Computing Toolkit\\CUDA\\v7.5\\lib\\x64\\OpenCL.lib")
#include <CL/cl.h>
#include <CL/cl_gl.h>

cl_int init_cl_context(cl_context *context, cl_command_queue *command_queue)
{
    cl_int i, ret, pf_index=-1;
    cl_platform_id  platform_id[16];
    cl_device_id    device_id[16];
    cl_uint     ret_num_platforms;
    cl_uint     ret_num_devices;

    ret = clGetPlatformIDs(sizeof(platform_id)/sizeof(*platform_id), platform_id, &ret_num_platforms);  // get all the platforms

    for (i=0; i<ret_num_platforms; i++)     // go through all the platforms
    {
        ret = clGetDeviceIDs(platform_id[i], CL_DEVICE_TYPE_GPU, sizeof(device_id)/sizeof(*device_id), device_id, &ret_num_devices);    // get all the suitable GPU devices

        if (ret_num_devices > 0)        // stop trying platforms when a suitable device is found
        {
            pf_index = i;
            break;
        }
    }

    cl_context_properties properties[] = { CL_GL_CONTEXT_KHR, (cl_context_properties)wglGetCurrentContext(), CL_WGL_HDC_KHR, (cl_context_properties)wglGetCurrentDC(), CL_CONTEXT_PLATFORM, (cl_context_properties)platform_id[pf_index], 0 };
    *context = clCreateContextFromType(properties, CL_DEVICE_TYPE_GPU, NULL, NULL, &ret);
    *command_queue = clCreateCommandQueue(*context, device_id[0], 0*CL_QUEUE_OUT_OF_ORDER_EXEC_MODE_ENABLE | 0*CL_QUEUE_PROFILING_ENABLE, &ret);

    return ret;
}

int main(int argc, char *argv[])
{
    cl_int ret=0;
    int w = 800, h = 600;
    SDL_Window *window;
    SDL_Renderer *renderer;
    cl_context context;
    cl_command_queue command_queue;
    cl_mem cltex;           // CL buffer of type image_2d_t pointing to the GL texture
    uint32_t gltex;         // ID of the GL texture for cltex

    //**** Init SDL, OpenGL/glew ****
    SDL_Init(SDL_INIT_TIMER | SDL_INIT_VIDEO | SDL_INIT_AUDIO);

    window = SDL_CreateWindow ("Title", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, w, h, SDL_WINDOW_OPENGL);
    SDL_GetWindowSize(window, &w, &h);

    SDL_GL_CreateContext(window);
    glewExperimental = 1; 
    glewInit();

    renderer = SDL_CreateRenderer(window, -1, 0*SDL_RENDERER_PRESENTVSYNC);
    //-------------------------------

    ret = init_cl_context(&context, &command_queue);    // initialise the CL context to match GL as to make the interop possible

    // create an OpenGL 2D texture normally
    glEnable(GL_TEXTURE_2D);
    glGenTextures(1, &gltex);                                   // generate the texture ID
    glBindTexture(GL_TEXTURE_2D, gltex);                                // binding the texture
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, w, h, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);        // specify texture dimensions, format etc

    cltex = clCreateFromGLTexture(context, CL_MEM_WRITE_ONLY, GL_TEXTURE_2D, 0, gltex, &ret);   // Creating the OpenCL image corresponding to the texture (once)

    ret = clFinish(command_queue);
    //glFinish();                  // this works fine
    ret = clEnqueueReleaseGLObjects(command_queue, 1, &cltex, 0, 0, NULL);          // release the ownership from CL back to GL
    clFinish(command_queue);
    glFlush();

    printf("This blocks the execution forever:\n");
    glFinish();                   // this blocks everything
    printf("This never gets printed\n");

    return 0;
}

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Answer 1

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