[GitHub] [arrow] lidavidm commented on a diff in pull request #34972: GH-34971: [Format] Enhance C-Data API to support non-cpu cases

["lidavidm (via GitHub)" <gi...@apache.org>]

lidavidm commented on code in PR #34972:
URL: https://github.com/apache/arrow/pull/34972#discussion_r1161260923


##########
cpp/src/arrow/c/abi.h:
##########
@@ -65,6 +65,69 @@ struct ArrowArray {
 
 #endif  // ARROW_C_DATA_INTERFACE
 
+#ifndef ARROW_C_DEVICE_DATA_INTERFACE
+#define ARROW_C_DEVICE_DATA_INTERFACE
+
+// ArrowDeviceType is compatible with dlpack DLDeviceType for portability

Review Comment:
   It would be great to have docstrings for enums, new structs, etc.



##########
cpp/src/arrow/c/abi.h:
##########
@@ -65,6 +65,69 @@ struct ArrowArray {
 
 #endif  // ARROW_C_DATA_INTERFACE
 
+#ifndef ARROW_C_DEVICE_DATA_INTERFACE
+#define ARROW_C_DEVICE_DATA_INTERFACE
+
+// ArrowDeviceType is compatible with dlpack DLDeviceType for portability
+// it uses the same values for each enum as the equivalent kDL<type> from dlpack.h
+#ifdef __cplusplus
+typedef enum : int32_t {
+#else
+typedef enum {
+#endif
+  // CPU device, same as using ArrowArray directly
+  kArrowCPU = 1,

Review Comment:
   Should we explicitly have `0` as the 'unset' value then?



##########
cpp/src/arrow/c/abi.h:
##########
@@ -106,6 +169,77 @@ struct ArrowArrayStream {
 
 #endif  // ARROW_C_STREAM_INTERFACE
 
+#ifndef ARROW_C_DEVICE_STREAM_INTERFACE
+#define ARROW_C_DEVICE_STREAM_INTERFACE
+
+struct ArrowDeviceArrayStream {
+  // The device that this stream produces data on.
+  // All ArrowDeviceArrays that are produced by this
+  // stream should have the same device_type as set
+  // here. The device_type needs to be provided here
+  // so that consumers can provide the correct type
+  // of stream_ptr when calling get_next.
+  ArrowDeviceType device_type;
+
+  // Callback to get the stream schema
+  // (will be the same for all arrays in the stream).
+  //
+  // Return value: 0 if successful, an `errno`-compatible error code otherwise.
+  //
+  // If successful, the ArrowSchema must be released independently from the stream.
+  int (*get_schema)(struct ArrowDeviceArrayStream*, struct ArrowSchema* out);
+
+  // Callback to get the device id for the next array.
+  // This is necessary so that the proper/correct stream pointer can be provided
+  // to get_next. The parameter provided must not be null.
+  //
+  // Return value: 0 if successful, an `errno`-compatible error code otherwise.
+  //
+  // The next call to `get_next` should provide an ArrowDeviceArray whose
+  // device_id matches what is provided here, and whose device_type is the
+  // same as the device_type member of this stream.
+  int (*get_next_device_id)(struct ArrowDeviceArrayStream*, int* out_device_id);
+
+  // Callback to get the next array
+  // (if no error and the array is released, the stream has ended)
+  //
+  // the provided stream_ptr should be the appropriate stream, or

Review Comment:
   to be clear, this is "CUDA stream"?
   
   while this is a draft, the language here is a little imprecise/feels like it assumes too much knowledge of a particular programming model. It would be great to define any terminology needed so that things can reasonably stand alone.



##########
cpp/src/arrow/c/abi.h:
##########
@@ -65,6 +65,69 @@ struct ArrowArray {
 
 #endif  // ARROW_C_DATA_INTERFACE
 
+#ifndef ARROW_C_DEVICE_DATA_INTERFACE
+#define ARROW_C_DEVICE_DATA_INTERFACE
+
+// ArrowDeviceType is compatible with dlpack DLDeviceType for portability
+// it uses the same values for each enum as the equivalent kDL<type> from dlpack.h
+#ifdef __cplusplus
+typedef enum : int32_t {
+#else
+typedef enum {
+#endif

Review Comment:
   Explicit `int32_t` should be safe AFAIK, but I agree it's a little goofy + is inconsistent with existing use of `#define`s



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