clEnqueueReleaseGLObjects - Release OpenCL memory objects that have been created from OpenGL objects.
cl_int clEnqueueReleaseGLObjects(cl_command_queue command_queue, cl_uint num_objects, const cl_mem *mem_objects, cl_uint num_events_in_wait_list, const cl_event *event_wait_list, cl_event *event);
event_wait_list , num_events_in_wait_list
If the cl_khr_gl_sharing(3clc) extension is supported and if an OpenGL context is bound to the current thread, then any OpenGL commands which does:
will not execute until after execution of any OpenCL commands preceding the clEnqueueReleaseGLObjects which affect or access any of those memory objects. If a non-NULL event object is returned, it will report completion before execution of such OpenGL commands.
Release OpenCL memory objects that have been created from OpenGL objects. These objects need to be released before they can be used by OpenGL. The OpenGL objects are released by the OpenCL context associated with command_queue.
In order to ensure data integrity, the application is responsible for synchronizing access to shared CL/GL objects by their respective APIs. Failure to provide such synchronization may result in race conditions and other undefined behavior including non-portability between implementations.
Prior to calling clEnqueueAcquireGLObjects, the application must ensure that any pending GL operations which access the objects specified in mem_objects have completed. This may be accomplished portably by issuing and waiting for completion of a glFinish command on all GL contexts with pending references to these objects. Implementations may offer more efficient synchronization methods; for example on some platforms calling glFlush may be sufficient, or synchronization may be implicit within a thread, or there may be vendor-specific extensions that enable placing a fence in the GL command stream and waiting for completion of that fence in the CL command queue. Note that no synchronization methods other than glFinish are portable between OpenGL implementations at this time.
Similarly, after calling clEnqueueReleaseGLObjects, the application is responsible for ensuring that any pending OpenCL operations which access the objects specified in mem_objects have completed prior to executing subsequent GL commands which reference these objects. This may be accomplished portably by calling clWaitForEvents(3clc) with the event object returned by clEnqueueReleaseGLObjects, or by calling clFinish(3clc). As above, some implementations may offer more efficient methods.
The application is responsible for maintaining the proper order of operations if the CL and GL contexts are in separate threads.
If a GL context is bound to a thread other than the one in which clEnqueueReleaseGLObjects is called, changes to any of the objects in mem_objects may not be visible to that context without additional steps being taken by the application. For an OpenGL 3.1 (or later) context, the requirements are described in Appendix D ("Shared Objects and Multiple Contexts") of the OpenGL 3.1 Specification. For prior versions of OpenGL, the requirements are implementation-dependent.
Attempting to access the data store of an OpenGL object after it has been acquired by OpenCL and before it has been released will result in undefined behavior. Similarly, attempting to access a shared CL/GL object from OpenCL before it has been acquired by the OpenCL command queue, or after it has been released, will result in undefined behavior.
If the cl_khr_gl_event(3clc) extension is supported, then the OpenCL implementation will ensure that any such pending OpenGL operations are complete for an OpenGL context bound to the same thread as the OpenCL context. This is referred to as implicit synchronization.
clEnqueueReleaseGLObjects returns CL_SUCCESS if the function is executed successfully. If num_objects is 0 and mem_objects is NULL the function does nothing and returns CL_SUCCESS. Otherwise, it returns one of the following errors:
cl_khr_gl_sharing(3clc), clEnqueueAcquireGLObjects(3clc), cl_khr_gl_event(3clc)
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- OpenCL Specification
|01/14/2021||The Khronos Group|