pitrou commented on code in PR #43632:
URL: https://github.com/apache/arrow/pull/43632#discussion_r1757469760
##########
docs/source/format/CDeviceDataInterface.rst:
##########
@@ -650,6 +652,331 @@ The stream source is not assumed to be thread-safe.
Consumers wanting to
call ``get_next`` from several threads should ensure those calls are
serialized.
+Async Device Stream Interface
+=============================
+
+The :ref:`C stream interface <_c-device-stream-interface>` provides a
synchronous
+API centered around the consumer calling the callback functions to retrieve
+the next record batch. For some bindings, use cases, and interoperability, a
more
+asynchronous, producer-focused interface may be required. These scenarios can
utilize
+the ``ArrowAsyncDeviceStreamHandler``.
+
+Semantics
+---------
+
+Rather than the producer providing a structure of callbacks for a consumer to
+call and retrieve records, the Async interface is a consumer allocated
structure.
+The consumer allocated struct provides handler callbacks for the producer to
call
+when the schema and chunks of data are available, rather than the consumer
using
+a blocking pull-style iteration.
+
+In addition to the ``ArrowAsyncDeviceStreamHandler``, there are also two
additional
+structs used for the full data flow: ``ArrowAsyncTask`` and
``ArrowAsyncProducer``.
+
+Structure Definition
+--------------------
+
+The C device async stream interface is defined with a single ``struct``
definition:
+
+.. code-block:: c
+
+ #ifndef ARROW_C_ASYNC_STREAM_INTERFACE
+ #define ARROW_C_ASYNC_STREAM_INTERFACE
+
+ struct ArrowAsyncTask {
+ int (*get_data)(struct ArrowArrayTask* self, struct ArrowDeviceArray*
out);
+
+ void* private_data;
+ };
+
+ struct ArrowAsyncProducer {
+ void (*request)(struct ArrowAsyncProducer* self, uint64_t n);
+ void (*cancel)(struct ArrowAsyncProducer* self);
+
+ void (*release)(struct ArrowAsyncProducer* self);
+ void* private_data;
+ };
+
+ struct ArrowAsyncDeviceStreamHandler {
+ // handlers
+ int (*on_schema)(struct ArrowAsyncDeviceStreamHandler* self,
+ struct ArrowAsyncProducer* producer,
+ struct ArrowSchema* stream_schema, const char*
addl_metadata);
+ int (*on_next_task)(struct ArrowAsyncDeviceStreamHandler* self,
+ struct ArrowAsyncTask* task, const char* metadata);
+ void (*on_error)(struct ArrowAsyncDeviceStreamHandler* self,
+ int code, const char* message, const char* metadata);
+
+ // release callback
+ void (*release)(struct ArrowAsyncDeviceStreamHandler* self);
+
+ // opaque handler-specific data
+ void* private_data;
+ };
+
+ #endif // ARROW_C_ASYNC_STREAM_INTERFACE
+
+.. note::
+ The canonical guard ``ARROW_C_ASYNC_STREAM_INTERFACE`` is meant to avoid
+ duplicate definitions if two projects copy the C async stream interface
+ definitions into their own headers, and a third-party project includes
+ from these two projects. It is therefore important that this guard is kept
+ exactly as-is when these definitions are copied.
+
+The ArrowAsyncDeviceStreamHandler structure
+'''''''''''''''''''''''''''''''''''''''''''
+
+The structure has the following fields:
+
+.. c:member:: int (*ArrowAsyncDeviceStreamHandler.on_schema)(struct
ArrowAsyncDeviceStreamHandler*, struct ArrowAsyncProducer*, struct
ArrowSchema*, const char*)
+
+ *Mandatory.* Handler for receiving the schema of the stream. All records
should
+ match the provided schema. If successful, the function should return 0,
otherwise
+ it should return an ``errno``-compatible error code.
+
+ The ``const char*`` parameter exists for producers to provide any extra
contextual information
+ they want, such as the total number of rows in the stream, statistics, or
otherwise. This is
+ encoded in the same format as :c:member:`ArrowSchema.metadata`. If not
``NULL``,
+ the lifetime is only the scope of the call to this function. A consumer
who wants to maintain
+ the additional metadata beyond the lifetime of this call *MUST* copy the
value themselves.
+
+ Unless the ``on_error`` handler is called, this will always get called
exactly once and will be
+ the first method called on this object. As such the producer *MUST*
provide an ``ArrowAsyncProducer``
+ object when calling this function to allow the consumer to manage
back-pressure and flow control.
+ The producer maintains ownership of the ``ArrowAsyncProducer`` and must
clean it up before or after
+ calling the release callback on this object.
+
+ A producer that receives a non-zero result here must not subsequently call
anything other than
+ the release callback on this object.
+
+.. c:member:: int (*ArrowAsyncDeviceStreamHandler.on_next_task)(struct
ArrowAsyncDeviceStreamHandler*, struct ArrowAsyncTask*, const char*)
Review Comment:
Why is it called a "task"? It's an array, so perhaps `on_next_array`.
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