cl_img_use_gralloc

Name Strings

cl_img_use_gralloc_ptr

Contact

Imagination Technologies Developer Forum:
https://forums.imgtec.com/

Jeremy Kemp, Imagination Technologies (Jeremy.Kemp 'at' imgtec.com)

Contributors

Robert Quill, Imagination Technologies.
Paul Fradgley, Imagination Technologies.
Jeremy Kemp, Imagination Technologies.

Notice

Status

Shipping

Version

Built On: 2020-11-10
Version: 1.0.0

Dependencies

Requires OpenCL version 1.2 or later. Android OS is required.

This extension is written against the wording of the OpenCL 3.0 Specification.

Overview

This extension extends the functionality provided by clCreateBuffer and clCreateImage. It allows applications to pass an Android memory allocation to these functions and thus avoid having to copy data back and forth between the host and the device.

New API Enums

New command types cl_command_type:

CL_COMMAND_ACQUIRE_GRALLOC_OBJECTS_IMG 0x40D2
CL_COMMAND_RELEASE_GRALLOC_OBJECTS_IMG 0x40D3

New error codes:

CL_GRALLOC_RESOURCE_NOT_ACQUIRED_IMG 0x40D4
CL_INVALID_GRALLOC_OBJECT_IMG        0x40D5

Accepted value for the flags parameter to clCreateBuffer and clCreateImage:

CL_MEM_USE_GRALLOC_PTR_IMG (1 << 28)

New API Functions

cl_int CL_API_CALL clEnqueueAcquireGrallocObjectsIMG(
    cl_command_queue command_queue,
    cl_uint num_objects,
    const cl_mem *mem_objects,
    cl_uint num_events_in_wait_list,
    const cl_event *event_wait_list,
    cl_event *event);

cl_int CL_API_CALL clEnqueueReleaseGrallocObjectsIMG(
    cl_command_queue command_queue,
    cl_uint num_objects,
    const cl_mem *mem_objects,
    cl_uint num_events_in_wait_list,
    const cl_event *event_wait_list,
    cl_event *event);

Modifications to the OpenCL API Specification

(Modify Section 5.2, Buffer Objects)

(Add the following to Table 5, List of supported memory flag values)

Memory Flags Description

Memory Flags	Description
`CL_MEM_USE_GRALLOC_PTR_IMG`	This flag is only valid of host_ptr is not `NULL`. The value given in host_ptr is an Android memory allocation. If this flag is specified to clCreateBuffer, then host_ptr must be an Android `buffer_handle_t`. It means that the application wants the OpenCL implementation to use memory referenced by the `buffer_handle_t` as the storage bits for the memory object. If this flag is specified to clCreateImage, then host_ptr must be an Android `ANativeWindowBuffer`. It means that the application wants the OpenCL implementation to use memory referenced by the `ANativeWindowBuffer` as the storage bits for the memory object. size must be 0 if this flag is set when given to clCreateBuffer. The size of the buffer is determined from the size of the Android allocation.

CL_MEM_USE_GRALLOC_PTR_IMG

This flag is only valid of host_ptr is not NULL. The value given in host_ptr is an Android memory allocation.

If this flag is specified to clCreateBuffer, then host_ptr must be an Android buffer_handle_t. It means that the application wants the OpenCL implementation to use memory referenced by the buffer_handle_t as the storage bits for the memory object.

If this flag is specified to clCreateImage, then host_ptr must be an Android ANativeWindowBuffer. It means that the application wants the OpenCL implementation to use memory referenced by the ANativeWindowBuffer as the storage bits for the memory object.

size must be 0 if this flag is set when given to clCreateBuffer. The size of the buffer is determined from the size of the Android allocation.

(Add the following to Section 5.2.1, Creating Buffer Objects)

(Add the following error conditions to the list after this section): CL_INVALID_BUFER_SIZE if size is non-zero and flags contains CL_MEM_USE_GRALLOC_PTR_IMG.
(Replace the following paragraph): CL_INVALID_HOST_PTR if host_ptr is NULL and CL_MEM_USE_HOST_PTR or CL_MEM_COPY_HOST_PTR are set in flags or if host_ptr is not NULL but CL_MEM_COPY_HOST_PTR or CL_MEM_USE_HOST_PTR are not set in flags.

with

CL_INVALID_HOST_PTR if host_ptr is NULL and CL_MEM_USE_HOST_PTR, CL_MEM_COPY_HOST_PTR or CL_MEM_USE_GRALLOC_PTR_IMG are set in flags or if host_ptr is not NULL but CL_MEM_COPY_HOST_PTR, CL_MEM_USE_HOST_PTR or CL_MEM_USE_GRALLOC_PTR_IMG are not set in flags.

(Modify Section 5.3, Image Objects)

(Add the following to Section 5.3.1, Creating Image Objects)

(Replace the following paragraph): CL_INVALID_IMAGE_DESCRIPTOR if values specified in image_desc are not valid or if image_desc is NULL.

with

CL_INVALID_IMAGE_DESCRIPTOR if image_desc is NULL and flags does not contain CL_MEM_USE_GRALLOC_PTR_IMG, or if image_desc is not NULL and flags contains CL_MEM_USE_GRALLOC_PTR_IMG, or if values specified in image_desc are not valid.
(Replace the following paragraph): CL_INVALID_HOST_PTR if host_ptr is NULL and CL_MEM_USE_HOST_PTR or CL_MEM_COPY_HOST_PTR are set in flags or if host_ptr is not NULL but CL_MEM_COPY_HOST_PTR or CL_MEM_USE_HOST_PTR are not set in flags.

with

CL_INVALID_HOST_PTR if host_ptr is NULL and CL_MEM_USE_HOST_PTR, CL_MEM_COPY_HOST_PTR or CL_MEM_USE_GRALLOC_PTR_IMG are set in flags or if host_ptr is not NULL but CL_MEM_COPY_HOST_PTR, CL_MEM_USE_HOST_PTR or CL_MEM_USE_GRALLOC_PTR_IMG are not set in flags.

(Add a new Section 5.16, Sharing OpenCL and Gralloc Objects)

(Add a new Section 5.16.1, Synchronizing OpenCL and Android Access to Shared Gralloc Objects)

In order to ensure data integrity, the application is responsible for synchronizing access to shared CL/gralloc objects by their respective APIs. Failure to provide such synchronization may result in race conditions and other undefined behaviour including non-portability between implementations.

Prior to calling clEnqueueAcquireGrallocObjectsIMG, the application must ensure that any pending operations which access the objects specified in mem_objects have completed. This may be accomplished in a portable way by ceasing all client operations on the resource. Implementations may offer more efficient synchronization methods, such as synchronisation primitives or fence operations.

Similarly, after calling clEnqueueReleaseGrallocObjectsIMG, the application is responsible for ensuring that any pending OpenCL operations which access the objects specified in mem_objects have completed prior to executing subsequent commands in other APIs which reference these objects. This may be accomplished in a portable way by calling clWaitForEvents with the event object returned by clEnqueueReleaseGrallocObjects, or by calling clFinish. As above, some implementations may offer more efficient methods.

Attempting to access the data store of a gralloc allocation after it has been acquired by OpenCL and before it has been released will result in undefined behaviour. Similarly, attempting to access a shared gralloc object from OpenCL before it has been acquired by the OpenCL command queue or after it has been released, will result in undefined behaviour.

(Add a new Section 5.16.2, Sharing Memory Objects Created From Gralloc Resources With OpenCL Contexts)

The function

cl_int CL_API_CALL clEnqueueAcquireGrallocObjectsIMG(
    cl_command_queue command_queue,
    cl_uint num_objects,
    const cl_mem *mem_objects,
    cl_uint num_events_in_wait_list,
    const cl_event *event_wait_list,
    cl_event *event);

is used to acquire OpenCL memory objects that have been created from gralloc resources. The gralloc objects are acquired by the OpenCL context associated with command_queue and can therefore be used by all command-queues associated with the OpenCL context.

OpenCL memory objects created from gralloc resources must be acquired before they can be used by any OpenCL commands queued to a command-queue. If an OpenCL memory object created from a gralloc resource is used while it is not currently acquired by OpenCL, the call attempting to use that OpenCL memory object will return CL_GRALLOC_RESOURCE_NOT_ACQUIRED_IMG.

This function has no affect on memory objects in mem_objects that have already been acquired, ignoring them silently. The function returns CL_SUCCESS even if all of the memory objects are ignored in this way.

command_queue is a valid command-queue.

num_objects is the number of memory objects to be acquired in mem_objects.

mem_objects is a pointer to a list of OpenCL memory objects that were created from gralloc resources, within the context associate with command_queue.

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.

event returns an event object that identifies this particular 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.

clEnqueueAcquireGrallocObjectsIMG returns CL_SUCCESS if the function is executed successfully. If num_objects is 0 and mem_objects is NULL then the function does nothing and returns CL_SUCCESS. Otherwise it returns one of the following errors:

CL_INVALID_VALUE if num_objects is zero and mem_objects is not a NULL value or if num_objects 0 and mem_objects is NULL.
CL_INVALID_MEM_OBJECT if memory objects in mem_objects are not valid OpenCL memory objects in the context associated with command_queue.
CL_INVALID_GRALLOC_OBJECT_IMG if memory objects in mem_objects have not been created from gralloc resources.
CL_INVALID_COMMAND_QUEUE if command_queue is not a valid command-queue.
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_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 the queue on which the command is enqueued is associated with a device which does not support cl_img_use_gralloc_ptr.

The function

cl_int CL_API_CALL clEnqueueReleaseGrallocObjectsIMG(
    cl_command_queue command_queue,
    cl_uint num_objects,
    const cl_mem *mem_objects,
    cl_uint num_events_in_wait_list,
    const cl_event *event_wait_list,
    cl_event *event);

is used to release OpenCL memory objects that have been created from gralloc resources. The gralloc objects are released by the OpenCL context associated with command_queue.

OpenCL memory objects created from gralloc resources which have been acquired by OpenCL must be released by OpenCL before they may be accessed by Android client APIs. Accessing a gralloc resource while its corresponding OpenCL memory object is acquired is in error and will result in undefined behaviour, including but not limited to possible OpenCL errors, data corruption, and program termination.

command_queue is a valid command-queue.

mem_objects is a pointer to a list of OpenCL memory objects that were created from gralloc resources, within the context associated with command_queue.

clEnqueueReleaseGrallocObjectsIMG returns CL_SUCCESS if the function is executed successfully. If num_objects is 0 and mem_objects is NULL the function does nothing and returns CL_SUCCESS. Otherwise it returns one of the following errors:

CL_INVALID_VALUE if num_objects is zero and mem_objects is not a NULL value or if num_objects 0 and mem_objects is NULL.
CL_INVALID_MEM_OBJECT if memory objects in mem_objects are not valid OpenCL memory objects in the context associated with command_queue.
CL_INVALID_GRALLOC_OBJECT_IMG if memory objects in mem_objects have not been created from gralloc resources.
CL_INVALID_COMMAND_QUEUE if command_queue is not a valid command-queue.
CL_GRALLOC_RESOURCE_NOT_ACQUIRED_IMG if memory objects in mem_objects have not previously acquired with clEnqueueAcquireGrallocObjectsIMG, or have been released using clEnqueueReleaseGrallocObjectsIMG since the last time that they were acquired.
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_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.

Issues

This extension does not support reference counting of the images, so the onus is on the application to behave sensibly and not release the underlying cl_mem object while the gralloc object is still being used.

INFORMATION
In order to ensure data integrity, the application is responsible for synchronizing access to shared CL/gralloc objects by their respective APIs. Failure to provide such synchronization may result in race conditions and other undefined behaviour. This may be accomplished by calling clWaitForEvents with the event objects returned by any OpenCL commands which use the shared image object or by calling clFinish.

INFORMATION
Currently restricted to buffer objects.

RESOLVED

Revision History

Version	Date	Author	Changes
1.0.0	2020-11-10	Jeremy Kemp	Refreshed to AsciiDoc. Updated Contributors. Updated copyright notice. Updated the OpenCL spec which this extension spec is written against. Spelling fixes.
0.2.0	2017-10-17	Paul Fradgley	Added support for images.
0.1.0	2014-08-08	Robert Quill	Initial revision.