table of contents
CLENQUEUEMAPBUFFER(3clc) | OpenCL Manual | CLENQUEUEMAPBUFFER(3clc) |
NAME¶
clEnqueueMapBuffer - 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 size,
cl_uint num_events_in_wait_list,
const cl_event *event_wait_list,
cl_event *event,
cl_int *errcode_ret);
PARAMETERS¶
command_queueMust be a valid command-queue.
blocking_map
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 is mapped into the host
address space and the application can access the contents of the mapped region
using the pointer returned by clEnqueueMapBuffer.
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.
map_flags
A bit-bield with the following supported values.
buffer
cl_map_flags | Description |
CL_MAP_READ | This flag specifies that the region being mapped in the memory object is being mapped for reading. The pointer returned by clEnqueueMapBuffer or clEnqueueMapImage(3clc) is guaranteed to contain the latest bits in the region being mapped when the clEnqueueMapBuffer or clEnqueueMapImage(3clc) command has completed. |
CL_MAP_WRITE | This flag specifies that the region being mapped in the memory object is being mapped for writing. The pointer returned by clEnqueueMapBuffer or clEnqueueMapImage(3clc) is guaranteed to contain the latest bits in the region being mapped when the clEnqueueMapBuffer or clEnqueueMapImage(3clc) command has completed. |
CL_MAP_WRITE_INVALIDATE_REGION | This flag specifies that the region being mapped in the memory object is being mapped for writing. The contents of the region being mapped are to be discarded. This is typically the case when the region being mapped is overwritten by the host. This flag allows the implementation to no longer guarantee that the pointer returned by clEnqueueMapBuffer or clEnqueueMapImage(3clc) contains the latest bits in the region being mapped which can be a significant performance enhancement. CL_MAP_READ or CL_MAP_WRITE and CL_MAP_WRITE_INVALIDATE_REGION are mutually exclusive. |
A valid buffer object. The OpenCL context associated with
command_queue and buffer must be the same.
offset, size
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. 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
copy 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. 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.
errcode_ret
Returns an appropriate error code. If errcode_ret
is NULL, no error code is returned.
NOTES¶
The returned pointer maps a region starting at offset and is at least size bytes in size. The result of a memory access outside this region is undefined. If the buffer object is created with CL_MEM_USE_HOST_PTR set in mem_flags, the following will be true:• The host_ptr specified in
clCreateBuffer(3clc) is guaranteed to contain the latest bits in the
region being mapped when the clEnqueueMapBuffer command has
completed.
• The pointer value returned by
clEnqueueMapBuffer will be derived from the host_ptr specified
when the buffer object is created.
Mapped buffer objects are unmapped using clEnqueueUnmapMemObject(3clc).
clEnqueueMapBuffer and clEnqueueMapImage(3clc) increment the
mapped count of the memory object. The initial mapped count value of a memory
object is zero. Multiple calls to clEnqueueMapBuffer or
clEnqueueMapImage(3clc) on the same memory object will increment this
mapped count by appropriate number of calls.
clEnqueueUnmapMemObject(3clc) decrements the mapped count of the memory
object.
clEnqueueMapBuffer and clEnqueueMapImage(3clc) act as
synchronization points for a region of the buffer object being mapped.
ERRORS¶
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 and image 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 image is not a
valid image object.
•CL_INVALID_VALUE if region being mapped given by
( offset, size) is out of bounds or if size is 0 or
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 > 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_MISALIGNED_SUB_BUFFER_OFFSET if buffer
is a sub-buffer object and offset specified when the sub-buffer object
is created is not aligned to CL_DEVICE_MEM_BASE_ADDR_ALIGN value for
device associated with queue.
•CL_MAP_FAILURE if there is a failure to map the
requested region into the host address space. This error cannot occur for
image objects created with CL_MEM_USE_HOST_PTR or
CL_MEM_ALLOC_HOST_PTR.
•CL_EXEC_STATUS_ERROR_FOR_EVENTS_IN_WAIT_LIST if
the map operation is blocking and the execution status of any of the events in
event_wait_list is a negative integer value.
•CL_MEM_OBJECT_ALLOCATION_FAILURE if there is a
failure to allocate memory for data store associated with buffer.
•CL_INVALID_OPERATION if buffer has been
created with CL_MEM_HOST_WRITE_ONLY or CL_MEM_HOST_NO_ACCESS and
CL_MAP_READ is set in map_flags or if buffer has been
created with CL_MEM_HOST_READ_ONL or CL_MEM_HOST_NO_ACCESS and
CL_MAP_WRITE or CL_MAP_WRITE_INVALIDATE_REGION is set in
map_flags.
•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[1]SEE ALSO¶
clEnqueueMapImage(3clc), clEnqueueUnmapMemObject(3clc)AUTHORS¶
The Khronos GroupCOPYRIGHT¶
Copyright © 2007-2011 The Khronos Group Inc.NOTES¶
- 1.
- OpenCL Specification
page 86, section 5.2.3 - Mapping Buffer Objects
06/18/2014 | The Khronos Group |