Enqueues a command to map a region of the buffer object given by buffer into the host address space and returns a pointer to this mapped region.

void * clEnqueueMapBuffer ( cl_command_queue command_queue,
  cl_mem buffer,
  cl_bool blocking_map,
  cl_map_flags map_flags,
  size_t offset,
  size_t cb,
  cl_uint num_events_in_wait_list,
  const cl_event *event_wait_list,
  cl_event *event,
  cl_int *errcode_ret)



Must be a valid command-queue.


Indicates if the map operation is blocking or non-blocking.

If blocking_map is CL_TRUE, clEnqueueMapBuffer does not return until the specified region in buffer can be mapped.

If blocking_map is CL_FALSE i.e. map operation is non-blocking, the pointer to the mapped region returned by clEnqueueMapBuffer cannot be used until the map command has completed. The event argument returns an event object which can be used to query the execution status of the map command. When the map command is completed, the application can access the contents of the mapped region using the pointer returned by clEnqueueMapBuffer.


Is a bit-field and can be set to CL_MAP_READ to indicate that the region specified by (offset, cb) in the buffer object is being mapped for reading, and/or CL_MAP_WRITE to indicate that the region specified by (offset, cb) in the buffer object is being mapped for writing.


A valid buffer object. The OpenCL context associated with command_queue and buffer must be the same.

offset, cb

The offset in bytes and the size of the region in the buffer object that is being mapped.

event_wait_list, num_events_in_wait_list

Specify events that need to complete before this particular 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. The context associated with events in event_wait_list and command_queue must be the same.


Returns an event object that identifies this particular copy command and can be used toquery 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.


Returns an appropriate error code. If errcode_ret is NULL, no error code is returned.


The contents of the regions of a memory object mapped for writing (i.e. CL_MAP_WRITE is set in map_flags argument to clEnqueueMapBuffer or clEnqueueMapImage) are considered to be undefined until this region is unmapped. Reads and writes by a kernel executing on a device to a memory region(s) mapped for writing are undefined.

Multiple command-queues can map a region or overlapping regions of a memory object for reading (i.e. map_flags = CL_MAP_READ). The contents of the regions of a memory object mapped for reading can also be read by kernels executing on a device(s). The behavior of writes by a kernel executing on a device to a mapped region of a memory object is undefined. Mapping (and unmapping) overlapped regions of a buffer or image memory object for writing is undefined.

The behavior of OpenCL function calls that enqueue commands that write or copy to regions of a memory object that are mapped is undefined.


clEnqueueMapBuffer will return a pointer to the mapped region if the function is executed successfully. The errcode_ret is set to CL_SUCCESS.

A NULL pointer is returned otherwise with one of the following error values returned in errcode_ret:

  • CL_INVALID_COMMAND_QUEUE if command_queue is not a valid command-queue.
  • CL_INVALID_CONTEXT if the context associated with command_queue, src_image and dst_buffer are not the same or if the context associated with command_queue and events in event_wait_list are not the same.
  • CL_INVALID_MEM_OBJECT if buffer is not a valid buffer object.
  • CL_INVALID_VALUE if region being mapped given by (offset, cb) is out of bounds or if values specified in map_flags are not valid
  • CL_INVALID_EVENT_WAIT_LIST if event_wait_list is NULL and num_events_in_wait_list greater than 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_MAP_FAILURE if there is a failure to map the requested region into the host address space. This error cannot occur for buffer objects created with CL_MEM_USE_HOST_PTR or CL_MEM_ALLOC_HOST_PTR.
  • CL_MEM_OBJECT_ALLOCATION_FAILURE if there is a failure to allocate memory for data store associated with buffer.
  • CL_OUT_OF_HOST_MEMORY if there is a failure to allocate resources required by the OpenCL implementation on the host.

The pointer returned maps a region starting at offset and is atleast cb bytes in size. The result of a memory access outside this region is undefined.


OpenCL Specification

Also see

clEnqueueMapImage, clEnqueueUnmapMemObject

Copyright © 2007-2009 The Khronos Group Inc. Permission is hereby granted, free of charge, to any person obtaining a copy of this software and/or associated documentation files (the "Materials"), to deal in the Materials without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Materials, and to permit persons to whom the Materials are furnished to do so, subject to the condition that this copyright notice and permission notice shall be included in all copies or substantial portions of the Materials.