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clEnqueueWriteBuffer.adoc

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clEnqueueWriteBuffer

Enqueue commands to write to a buffer object from host memory.

cl_int clEnqueueWriteBuffer(cl_command_queue command_queue,
                            cl_mem buffer,
                            cl_bool blocking_write,
                            size_t offset,
                            size_t size,
                            const void *ptr,
                            cl_uint num_events_in_wait_list,
                            const cl_event *event_wait_list,
                            cl_event *event)

Parameters

command_queue

Is a valid host command-queue in which the 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_write

Indicates if the write operations are blocking or nonblocking.

If blocking_write is CL_TRUE, the OpenCL implementation copies the data referred to by ptr and enqueues the write operation in the command-queue. The memory pointed to by ptr can be reused by the application after the clEnqueueWriteBuffer call returns.

If blocking_write is CL_FALSE, the OpenCL implementation will use ptr to perform a nonblocking 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.

offset

The offset in bytes in the buffer object to write to.

size

The size in bytes of data being written.

ptr

The pointer to buffer in host memory where data is to be written from.

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 write 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 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 read command has finished execution.

Errors

clEnqueueWriteBuffer 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 written specified by (offset, size) is out of bounds or if ptr is a NULL value.

  • 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_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 clEnqueueWriteBuffer 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.