C Specification

To enqueue a command to unmap a previously mapped region of a memory object, call the function

cl_int clEnqueueUnmapMemObject(
    cl_command_queue command_queue,
    cl_mem memobj,
    void* mapped_ptr,
    cl_uint num_events_in_wait_list,
    const cl_event* event_wait_list,
    cl_event* event);


  • command_queue must be a valid host command-queue.

  • memobj is a valid memory (buffer or image) object. The OpenCL context associated with command_queue and memobj must be the same.

  • mapped_ptr is the host address returned by a previous call to clEnqueueMapBuffer, or clEnqueueMapImage for memobj.

  • event_wait_list and num_events_in_wait_list specify events that need to complete before clEnqueueUnmapMemObject can be executed. If event_wait_list is NULL, then clEnqueueUnmapMemObject 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. The context associated with events in event_wait_list and command_queue must be the same. The memory associated with event_wait_list can be reused or freed after the function returns.

  • event returns an event object that identifies this particular command and can be used to query or queue a wait for this particular 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. clEnqueueBarrierWithWaitList can be used instead. If the event_wait_list and the event arguments are not NULL, the event argument should not refer to an element of the event_wait_list array.


Reads or writes from the host using the pointer returned by clEnqueueMapBuffer or clEnqueueMapImage are considered to be complete.

clEnqueueMapBuffer and clEnqueueMapImage increment the mapped count of the memory object. The initial mapped count value of the memory object is zero. Multiple calls to clEnqueueMapBuffer, or clEnqueueMapImage on the same memory object will increment this mapped count by appropriate number of calls. clEnqueueUnmapMemObject decrements the mapped count of the memory object.

clEnqueueMapBuffer, and clEnqueueMapImage act as synchronization points for a region of the buffer object being mapped.

clEnqueueUnmapMemObject returns CL_​SUCCESS if the function is executed successfully. Otherwise, it returns one of the following errors:

  • CL_​INVALID_​COMMAND_​QUEUE if command_queue is not a valid host command-queue.

  • CL_​INVALID_​MEM_​OBJECT if memobj is not a valid memory object or is a pipe object.

  • CL_​INVALID_​VALUE if mapped_ptr is not a valid pointer returned by clEnqueueMapBuffer or clEnqueueMapImage for memobj.

  • CL_​INVALID_​EVENT_​WAIT_​LIST if event_wait_list is NULL and num_events_in_wait_list > 0, or if 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.

  • CL_​INVALID_​CONTEXT if context associated with command_queue and memobj are not the same or if the context associated with command_queue and events in event_wait_list are not the same.

See Also

Document Notes

For more information, see the OpenCL Specification

This page is extracted from the OpenCL Specification. Fixes and changes should be made to the Specification, not directly.

Copyright (c) 2014-2020 Khronos Group. This work is licensed under a Creative Commons Attribution 4.0 International License.