paleolimbot commented on code in PR #44495:
URL: https://github.com/apache/arrow/pull/44495#discussion_r1813013801
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cpp/src/arrow/c/abi.h:
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@@ -228,6 +228,214 @@ struct ArrowDeviceArrayStream {
#endif // ARROW_C_DEVICE_STREAM_INTERFACE
+#ifndef ARROW_C_ASYNC_STREAM_INTERFACE
+# define ARROW_C_ASYNC_STREAM_INTERFACE
+
+// ArrowAsyncTask represents available data from a producer that was passed to
+// an invocation of `on_next_task` on the ArrowAsyncDeviceStreamHandler.
+//
+// The reason for this Task approach instead of the Async interface returning
+// the Array directly is to allow for more complex thread handling and reducing
+// context switching and data transfers between CPU cores (e.g. from one L1/L2
+// cache to another) if desired.
+//
+// For example, the `on_next_task` callback can be called when data is ready,
while
+// the producer puts potential "decoding" logic in the `ArrowAsyncTask`
object. This
+// allows for the producer to manage the I/O on one thread which calls
`on_next_task`
+// and the consumer can determine when the decoding (producer logic in the
`extract_data`
+// callback of the task) occurs and on which thread, to avoid a CPU core
transfer
+// (data staying in the L2 cache).
+struct ArrowAsyncTask {
+ // This callback should populate the ArrowDeviceArray associated with this
task.
+ // The order of ArrowAsyncTasks provided by the producer enables a consumer
to
+ // ensure the order of data to process.
+ //
+ // This function is expected to be synchronous, but should not perform any
blocking
+ // I/O. Ideally it should be as cheap as possible so as to not tie up the
consumer
+ // thread unnecessarily.
+ //
+ // Returns: 0 if successful, errno-compatible error otherwise.
+ //
+ // If a non-0 value is returned then it should be followed by a call to
`on_error`
+ // on the appropriate ArrowAsyncDeviceStreamHandler. This is because it's
highly
+ // likely that whatever is calling this function may be entirely
disconnected from
+ // the current control flow. Indicating an error here with a non-zero return
allows
+ // the current flow to be aware of the error occurring, while still allowing
any
+ // logging or error handling to still be centralized in the `on_error`
callback of
+ // the original Async handler.
+ //
+ // Rather than a release callback, any required cleanup should be performed
as part
+ // of the invocation of `extract_data`. Ownership of the Array is passed to
the consumer
+ // calling this, and so it must be released separately.
+ //
+ // It is only valid to call this method exactly once.
+ int (*extract_data)(struct ArrowAsyncTask* self, struct ArrowDeviceArray*
out);
Review Comment:
Got it! It makes sense to propagate it as early as possible like you've done
already 🙂
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