C Specification

The following functions enqueue commands to read a 2D or 3D rectangular region from a buffer object to host memory or write a 2D or 3D rectangular region to a buffer object from host memory.

// Provided by CL_VERSION_1_1
cl_int clEnqueueReadBufferRect(
    cl_command_queue command_queue,
    cl_mem buffer,
    cl_bool blocking_read,
    const size_t* buffer_origin,
    const size_t* host_origin,
    const size_t* region,
    size_t buffer_row_pitch,
    size_t buffer_slice_pitch,
    size_t host_row_pitch,
    size_t host_slice_pitch,
    void* ptr,
    cl_uint num_events_in_wait_list,
    const cl_event* event_wait_list,
    cl_event* event);
clEnqueueReadBufferRect is missing before version 1.1. 
// Provided by CL_VERSION_1_1
cl_int clEnqueueWriteBufferRect(
    cl_command_queue command_queue,
    cl_mem buffer,
    cl_bool blocking_write,
    const size_t* buffer_origin,
    const size_t* host_origin,
    const size_t* region,
    size_t buffer_row_pitch,
    size_t buffer_slice_pitch,
    size_t host_row_pitch,
    size_t host_slice_pitch,
    const void* ptr,
    cl_uint num_events_in_wait_list,
    const cl_event* event_wait_list,
    cl_event* event);
clEnqueueWriteBufferRect is missing before version 1.1.

Parameters

  • command_queue refers is a valid host command-queue in which the read / write 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 and blocking_write indicate if the read and write operations are blocking or non-blocking (see below).

  • buffer_origin defines the (x, y, z) offset in the memory region associated with buffer. For a 2D rectangle region, the z value given by buffer_origin[2] should be 0. The offset in bytes is computed as buffer_origin[2] × buffer_slice_pitch + buffer_origin[1] × buffer_row_pitch + buffer_origin[0].

  • host_origin defines the (x, y, z) offset in the memory region pointed to by ptr. For a 2D rectangle region, the z value given by host_origin[2] should be 0. The offset in bytes is computed as host_origin[2] × host_slice_pitch + host_origin[1] × host_row_pitch + host_origin[0].

  • region defines the (width in bytes, height in rows, depth in slices) of the 2D or 3D rectangle being read or written. For a 2D rectangle copy, the depth value given by region[2] should be 1. The values in region cannot be 0.

  • buffer_row_pitch is the length of each row in bytes to be used for the memory region associated with buffer. If buffer_row_pitch is 0, buffer_row_pitch is computed as region[0].

  • buffer_slice_pitch is the length of each 2D slice in bytes to be used for the memory region associated with buffer. If buffer_slice_pitch is 0, buffer_slice_pitch is computed as region[1] × buffer_row_pitch.

  • host_row_pitch is the length of each row in bytes to be used for the memory region pointed to by ptr. If host_row_pitch is 0, host_row_pitch is computed as region[0].

  • host_slice_pitch is the length of each 2D slice in bytes to be used for the memory region pointed to by ptr. If host_slice_pitch is 0, host_slice_pitch is computed as region[1] × host_row_pitch.

  • ptr is the pointer to buffer in host memory where data is to be read into or to be written from.

  • 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 read / write command and can be used to query or queue a wait for this command to complete. If event is NULL or the enqueue is unsuccessful, no event will be created and therefore it will not be possible to query the status of this command or to wait for this command to complete. If event_wait_list and event are not NULL, event must not refer to an element of the event_wait_list array.

Description

If blocking_read is CL_TRUE i.e. the read command is blocking, clEnqueueReadBufferRect 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, clEnqueueReadBufferRect 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.

If blocking_write is CL_TRUE, the write command is blocking and does not return until the command is complete, including transfer of the data. The memory pointed to by ptr can be reused by the application after the clEnqueueWriteBufferRect call returns.

If blocking_write is CL_FALSE, the OpenCL implementation will use ptr to perform a non-blocking write. As the write is non-blocking the implementation can return immediately. The memory pointed to by ptr cannot be reused by the application after the call returns. The event argument returns an event object which can be used to query the execution status of the write command. When the write command has completed, the memory pointed to by ptr can then be reused by the application.

clEnqueueReadBufferRect and clEnqueueWriteBufferRect return CL_SUCCESS if the function is executed successfully. Otherwise, they return one of the following errors:

  • CL_INVALID_COMMAND_QUEUE if command_queue is not a valid host 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 buffer_origin, host_origin, or region is NULL.

  • CL_INVALID_VALUE if the region being read or written specified by (buffer_origin, region, buffer_row_pitch, buffer_slice_pitch) is out of bounds.

  • CL_INVALID_VALUE if any region array element is 0.

  • CL_INVALID_VALUE if buffer_row_pitch is not 0 and is less than region[0].

  • CL_INVALID_VALUE if host_row_pitch is not 0 and is less than region[0].

  • CL_INVALID_VALUE if buffer_slice_pitch is not 0 and is less than region[1] × buffer_row_pitch and not a multiple of buffer_row_pitch.

  • CL_INVALID_VALUE if host_slice_pitch is not 0 and is less than region[1] × host_row_pitch and not a multiple of host_row_pitch.

  • CL_INVALID_VALUE if ptr is NULL.

  • 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. This error code is missing before version 1.1.

  • 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. This error code is missing before version 1.1.

  • CL_MEM_OBJECT_ALLOCATION_FAILURE if there is a failure to allocate memory for data store associated with buffer.

  • CL_INVALID_OPERATION if clEnqueueReadBufferRect is called on buffer which has been created with CL_MEM_HOST_WRITE_ONLY or CL_MEM_HOST_NO_ACCESS.

  • CL_INVALID_OPERATION if clEnqueueWriteBufferRect is called on buffer which has been created with CL_MEM_HOST_READ_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.

  • CL_INVALID_OPERATION if clEnqueueWriteBufferRect is called on buffer which has been created with CL_MEM_IMMUTABLE_EXT.

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.

Calling clEnqueueReadBufferRect to read a region of the buffer object with the ptr argument value set to host_ptr and host_origin, buffer_origin values are the same, 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 same requirements given above for clEnqueueReadBuffer.

Calling clEnqueueWriteBuffer to update the latest bits in 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 written is created with CL_MEM_USE_HOST_PTR, must meet the following requirements in order to avoid undefined behavior:

  • The host memory region given by (host_ptr + offset, cb) contains the latest bits when the enqueued write 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 write command has finished execution.

Calling clEnqueueWriteBufferRect to update the latest bits in a region of the buffer object with the ptr argument value set to host_ptr and host_origin, buffer_origin values are the same, where host_ptr is a pointer to the memory region specified when the buffer object being written is created with CL_MEM_USE_HOST_PTR, must meet the following requirements in order to avoid undefined behavior:

  • The host memory region given by (buffer_origin region) contains the latest bits when the enqueued write 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 write command has finished execution.

See Also

CL_VERSION_1_1, cl_bool, cl_command_queue, cl_event, cl_mem, cl_uint

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

Copyright 2014-2025 The Khronos Group Inc.

SPDX-License-Identifier: CC-BY-4.0