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)

Parameters

command_queue

A valid command-queue.

num_objects

The number of memory objects to be released in mem_objects.

mem_objects

A pointer to a list of CL memory objects that correspond to GL objects.

event_wait_list , num_events_in_wait_list

These parameters specify events that need to complete before this command can be executed. If event_wait_list is NULL, then this particular command does not wait on any event to complete. If event_wait_list is NULL, num_events_in_wait_list must be 0. If event_wait_list is not NULL, the list of events pointed to by event_wait_list must be valid and num_events_in_wait_list must be greater than 0. The events specified in event_wait_list act as synchronization points.

event

Returns an event object that identifies this particular read/write command and can be used to query or queue a wait for the command to complete. event can be NULL in which case it will not be possible for the application to query the status of this command or queue a wait for this command to complete.

When the cl_khr_gl_event extension is enabled, If an OpenGL context is bound to the current thread, then any OpenGL commands which:

  • affect or access the contents of the memory objects listed in the mem_objects list, and
  • are issued on that context prior to the call to clEnqueueReleaseGLObjects

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.

Description

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.

Notes

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 with the event object returned by clEnqueueReleaseGLObjects, or by calling glFinish. 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 G ("Shared Objects and Multiple Contexts") of the OpenGL 3.1 Specification. For prior versions of OpenGL, the requirements are implementationdependent.

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.

Errors

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_INVALID_VALUE if num_objects is zero and mem_objects is not a NULL value or if num_objects > 0 and mem_objects is NULL.
  • CL_INVALID_MEM_OBJECT if memory objects in mem_objects are not valid OpenCL memory objects.
  • CL_INVALID_COMMAND_QUEUE if command_queue is not a valid command-queue.
  • CL_INVALID_CONTEXT if context associated with command_queue was not created from an OpenGL context.
  • CL_INVALID_GL_OBJECT if memory objects in mem_objects have not been created from a GL object(s).
  • CL_INVALID_EVENT_WAIT_LIST if event_wait_list is NULL and num_events_in_wait_list > 0, or event_wait_list is not NULL and num_events_in_wait_list is 0, or if event objects in event_wait_list are not valid events.
  • CL_OUT_OF_RESOURCES if there is a failure to allocate resources required by the OpenCL implementation on the device.
  • CL_OUT_OF_HOST_MEMORY if there is a failure to allocate resources required by the OpenCL implementation on the host.

Specification

OpenCL Specification

Also see

cl_khr_gl_sharing, clEnqueueAcquireGLObjects, cl_khr_gl_event

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