zeroshade commented on code in PR #43632:
URL: https://github.com/apache/arrow/pull/43632#discussion_r1718727206
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cpp/src/arrow/c/abi.h:
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@@ -228,6 +228,65 @@ struct ArrowDeviceArrayStream {
#endif // ARROW_C_DEVICE_STREAM_INTERFACE
+#ifndef ARROW_C_ASYNC_STREAM_INTERFACE
+#define ARROW_C_ASYNC_STREAM_INTERFACE
+
+// Similar to ArrowDeviceArrayStream, except designed for an asynchronous
+// style of interaction. While ArrowDeviceArrayStream provides producer
+// defined callbacks, this is intended to be created by the consumer instead.
+// The consumer passes this handler to the producer, which in turn uses the
+// callbacks to inform the consumer of events in the stream.
+struct ArrowAsyncDeviceStreamHandler {
+ // Handler for receiving a schema. The passed in stream_schema should be
+ // released or moved by the handler (producer is giving ownership of it to
+ // the handler).
+ //
+ // The `extension_param` argument can be null or can be used by a producer
+ // to pass arbitrary extra information to the consumer (such as total number
+ // of rows, context info, or otherwise).
+ //
+ // Return value: 0 if successful, `errno`-compatible error otherwise
+ int (*on_schema)(struct ArrowAsyncDeviceStreamHandler* self,
+ struct ArrowSchema* stream_schema, void* extension_param);
+
+ // Handler for receiving an array/record batch. Always called at least once
+ // unless an error is encountered (which would result in calling on_error).
+ // An empty/released array is passed to indicate the end of the stream if no
+ // errors have been encountered.
+ //
+ // The `extension_param` argument can be null or can be used by a producer
+ // to pass arbitrary extra information to the consumer.
+ //
+ // Return value: 0 if successful, `errno`-compatible error otherwise.
+ int (*on_next)(struct ArrowAsyncDeviceStreamHandler* self,
+ struct ArrowDeviceArray* next, void* extension_param);
+
+ // Handler for encountering an error. The producer should call release after
+ // this returns to clean up any resources.
+ //
+ // If the message or metadata are non-null, they will only last as long as
this
+ // function call. The consumer would need to perform a copy of the data if
it is
+ // it is necessary for them live past the lifetime of this call.
+ //
+ // Error metadata should be encoded as with metadata in ArrowSchema, defined
in
+ // the spec at
+ //
https://arrow.apache.org/docs/format/CDataInterface.html#c.ArrowSchema.metadata
+ //
+ // After this call, producers should follow-up by calling the release
callback.
+ void (*on_error)(struct ArrowAsyncDeviceStreamHandler* self, int code,
+ const char* message, const char* metadata);
Review Comment:
This came out of the way that ADBC handles error context information. Rather
than the case like `on_schema` / `on_next` where the `extension_param` can be
anything depending on context and producer / consumer contracts. Error metadata
is almost universally key-value pairs to provide contextual information either
as strings or as interpretable bytes (i.e. grpc error codes/objects etc.)
Rather than requiring everyone figure out how to handle this key-value
management of error information themselves, it was suggested that we simply
re-utilize the existing metadata encoding.
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