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clCreateEventFromEGLSyncKHR.adoc

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clCreateEventFromEGLSyncKHR

Creates a linked event object.

cl_event clCreateEventFromEGLSyncKHR(cl_context context,
                                     CLeglSyncKHR sync,
                                     CLeglDisplayKHR display,
                                     cl_int *errcode_ret)

Parameters

context

A valid OpenCL context created from an OpenGL context or share group, using the cl_khr_gl_sharing extension.

sync

The name of a sync object of type EGL_SYNC_FENCE_KHR created with respect to EGLDisplay display.

Description

An event object may be created by linking to an EGL sync object. Completion of such an event object is equivalent to waiting for completion of the fence command associated with the linked EGL sync object.

Notes

The parameters of an event object linked to an EGL sync object will return the following values when queried with clGetEventInfo:

  • The CL_EVENT_COMMAND_QUEUE of a linked event is NULL, because the event is not associated with any OpenCL command queue.

  • The CL_EVENT_COMMAND_TYPE of a linked event is CL_COMMAND_EGL_FENCE_SYNC_OBJECT_KHR, indicating that the event is associated with a EGL sync object, rather than an OpenCL command.

  • The CL_EVENT_COMMAND_EXECUTION_STATUS of a linked event is either CL_SUBMITTED, indicating that the fence command associated with the sync object has not yet completed, or CL_COMPLETE, indicating that the fence command has completed.

clCreateEventFromEGLSyncKHR performs an implicit clRetainEvent on the returned event object. Creating a linked event object also places a reference on the linked EGL sync object. When the event object is deleted, the reference will be removed from the EGL sync object.

Events returned from clCreateEventFromEGLSyncKHR may only be consumed by clEnqueueAcquire*** commands. Passing such events to any other CL API that enqueues commands will generate a CL_INVALID_EVENT error."

Event objects can also be used to reflect the status of an EGL fence sync object. The sync object in turn refers to a fence command executing in an EGL client API command stream. This provides another method of coordinating sharing of EGL / EGL client API objects with OpenCL. Completion of EGL / EGL client API commands may be determined by placing an EGL fence command after commands using eglCreateSyncKHR, creating an event from the resulting EGL sync object using clCreateEventFromEGLSyncKHR and then specifying it in the event_wait_list of a clEnqueueAcquire*** command. This method may be considerably more efficient than calling operations like glFinish, and is referred to as explicit synchronization. The application is responsible for ensuring the command stream associated with the EGL fence is flushed to ensure the CL queue is submitted to the device. Explicit synchronization is most useful when an EGL client API context bound to another thread is accessing the memory objects.

Errors

Returns a valid OpenCL event object and errcode_ret is set to CL_SUCCESS if the event object is created successfully. Otherwise, it returns a NULL value with one of the following error values returned in errcode_ret:

  • CL_INVALID_CONTEXT if context is not a valid context or was not created from a GL context.

  • CL_INVALID_EGL_OBJECT_KHR if sync is not a valid EGLSyncKHR handle created with respect to EGLDisplay display.

  • CL_INVALID_EGL_OBJECT_KHR if sync is not a valid EGLSyncKHR object of type EGL_SYNC_FENCE_KHR created with respect to EGLDisplay display.