table of contents
CLENQUEUEREADBUFFER(3clc) | OpenCL Manual | CLENQUEUEREADBUFFER(3clc) |
NAME¶
clEnqueueReadBuffer - Enqueue commands to read from a buffer object to host memory.¶
cl_int
clEnqueueReadBuffer(cl_command_queue command_queue,
cl_mem buffer,
cl_bool blocking_read,
size_t offset, size_t size,
void *ptr,
cl_uint num_events_in_wait_list,
const cl_event *event_wait_list,
cl_event *event);
PARAMETERS¶
command_queueRefers to the command-queue in which the read command
will be queued. command_queue and buffer must be created with
the same OpenCL context.
buffer
Refers to a valid buffer object.
blocking_read
Indicates if the read operations are blocking or
non-blocking.
If blocking_read is CL_TRUE i.e. the read command is blocking,
clEnqueueReadBuffer does not return until the buffer data has been read
and copied into memory pointed to by ptr.
If blocking_read is CL_FALSE i.e. the read command is
non-blocking, clEnqueueReadBuffer queues a non-blocking
read command and returns. The contents of the buffer that ptr points to
cannot be used until the read command has completed. The event argument
returns an event object which can be used to query the execution status of the
read command. When the read command has completed, the contents of the buffer
that ptr points to can be used by the application.
offset
The offset in bytes in the buffer object to read
from.
size
The size in bytes of data being read.
ptr
The pointer to buffer in host memory where data is to be
read into.
event_wait_list ,
num_events_in_wait_list
event_wait_list and 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
read 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.
NOTES¶
Calling clEnqueueReadBuffer to read a region of the buffer object with the ptr argument value set to host_ptr + offset, where host_ptr is a pointer to the memory region specified when the buffer object being read is created with CL_MEM_USE_HOST_PTR, must meet the following requirements in order to avoid undefined behavior:• All commands that use this buffer object or a
memory object (buffer or image) created from this buffer object have finished
execution before the read command begins execution.
• The buffer object or memory objects created from
this buffer object are not mapped.
• The buffer object or memory objects created from
this buffer object are not used by any command-queue until the read command
has finished execution.
ERRORS¶
clEnqueueReadBuffer 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 command-queue.
•CL_INVALID_CONTEXT if the context associated with
command_queue and 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 the region being read
specified by ( offset, size) is out of bounds or if ptr
is a NULL value or if size is 0.
•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_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_EXEC_STATUS_ERROR_FOR_EVENTS_IN_WAIT_LIST if
the read and write operations are 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
clEnqueueReadBuffer is called on buffer which has been created
with CL_MEM_HOST_WRITE_ONLY or CL_MEM_HOST_NO_ACCESS.
•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¶
clEnqueueCopyBuffer(3clc), clEnqueueWriteBuffer(3clc), clEnqueueWriteBufferRect(3clc), clEnqueueReadBufferRect(3clc)AUTHORS¶
The Khronos GroupCOPYRIGHT¶
Copyright © 2007-2010 The Khronos Group Inc.NOTES¶
- 1.
- OpenCL Specification
page 72, section 5.2.2 - Reading, Writing, Copying Buffer
Objects
06/18/2014 | The Khronos Group |