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       clSetMemObjectDestructorCallback - Registers a user callback function with a memory

       cl_int clSetMemObjectDestructorCallback(cl_mem memobj,
                                               void (CL_CALLBACK *pfn_notify) (cl_mem memobj,
                                               void *user_data), void *user_data);


           A valid memory object.

           The callback function that can be registered by the application. This callback
           function may be called asynchronously by the OpenCL implementation. It is the
           application's responsibility to ensure that the callback function is thread-safe. The
           parameters to this callback function are:

           ·   memobj: the memory object being deleted.  When the user callback is called by the
               implementation, this memory object is no longer valid.  memobj is only provided
               for reference purposes.

           ·   user_data: a pointer to user supplied data.

           Data which will be passed as the user_data argument when pfn_notify is called.
           user_data can be NULL.


       Each call to clSetMemObjectDestructorCallback registers the specified user callback
       function on a callback stack associated with memobj. The registered user callback
       functions are called in the reverse order in which they were registered. The user callback
       functions are called and then the memory object's resources are freed and the memory
       object is deleted. This provides a mechanism for the application (and libraries) using
       memobj to be notified when the memory referenced by host_ptr, specified when the memory
       object is created and used as the storage bits for the memory object, can be reused or

       When the user callback function is called by the implementation, the contents of the
       memory region pointed to by host_ptr (if the memory object is created with
       CL_MEM_USE_HOST_PTR) are undefined. The callback function is typically used by the
       application to either free or reuse the memory region pointed to by host_ptr.

       The behavior of calling expensive system routines, OpenCL API calls to create contexts or
       command-queues, or blocking OpenCL operations from the following list below, in a callback
       is undefined.

       ·   clFinish(3clc).RE

           ·   clWaitForEvents(3clc).RE

               ·    blocking calls to clEnqueueReadBuffer(3clc), clEnqueueReadBufferRect(3clc),
                   clEnqueueWriteBuffer(3clc), clEnqueueWriteBufferRect(3clc).RE

                   ·    blocking calls to clEnqueueReadImage(3clc) and

                       ·    blocking calls to clEnqueueMapBuffer(3clc) and

                           ·    blocking calls to clBuildProgram(3clc), clCompileProgram(3clc),
                               or clLinkProgram(3clc).RE

                               If an application needs to wait for completion of a routine from
                               the above list in a callback, please use the non-blocking form of
                               the function, and assign a completion callback to it to do the
                               remainder of your work. Note that when a callback (or other code)
                               enqueues commands to a command-queue, the commands are not
                               required to begin execution until the queue is flushed. In
                               standard usage, blocking enqueue calls serve this role by
                               implicitly flushing the queue. Since blocking calls are not
                               permitted in callbacks, those callbacks that enqueue commands on a
                               command queue should either call clFlush(3clc) on the queue before
                               returning or arrange for clFlush(3clc) to be called later on
                               another thread.

                               The user callback function may not call OpenCL APIs with the
                               memory object for which the callback function is invoked and for
                               such cases the behavior of OpenCL APIs is considered to be


       Returns CL_SUCCESS if the function is executed successfully. Otherwise, it returns one of
       the following errors:

       ·   CL_INVALID_MEM_OBJECT if memobj is not a valid memory object.

       ·   CL_INVALID_VALUE if pfn_notify is NULL.

       ·   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.


       OpenCL Specification[1]


       clCreateCommandQueue(3clc), clGetCommandQueueInfo(3clc), clReleaseCommandQueue(3clc),


       The Khronos Group


       Copyright © 2007-2011 The Khronos Group Inc.
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        1. OpenCL Specification
           page 119, section 5.4.1 - Retaining and Releasing Memory Objects