Improve API for storing data in read streams.

Read stream callbacks receive a void pointer into the per-buffer data queue so that can store data there for later retrieval by the buffer consumer. We can improve readability and safety a bit by changing cast-and-assign or raw memcpy() to: read_stream_put_value(stream, per_buffer_data, my_int); This form infers the size and asserts that the storage space matches, generally mirroring the read_stream_get_buffer_and_value() call used for retrieving the streamed data later.

Author: macdice

src/backend/access/heap/vacuumlazy.c

@@ -1630,7 +1630,7 @@ heap_vac_scan_next_block(ReadStream *stream,
 */
 vacrel->current_block = next_block;
 blk_info |= VAC_BLK_ALL_VISIBLE_ACCORDING_TO_VM;
-*((uint8 *) per_buffer_data) = blk_info;
+read_stream_put_value(stream, per_buffer_data, blk_info);
 return vacrel->current_block;
 }
 else
@@ -1646,7 +1646,7 @@ heap_vac_scan_next_block(ReadStream *stream,
 blk_info |= VAC_BLK_ALL_VISIBLE_ACCORDING_TO_VM;
 if (vacrel->next_unskippable_eager_scanned)
 blk_info |= VAC_BLK_WAS_EAGER_SCANNED;
-*((uint8 *) per_buffer_data) = blk_info;
+read_stream_put_value(stream, per_buffer_data, blk_info);
 return vacrel->current_block;
 }
 }
@@ -2691,7 +2691,7 @@ vacuum_reap_lp_read_stream_next(ReadStream *stream,
 * Save the TidStoreIterResult for later, so we can extract the offsets.
 * It is safe to copy the result, according to TidStoreIterateNext().
 */
-memcpy(per_buffer_data, iter_result, sizeof(*iter_result));
+read_stream_put_value(stream, per_buffer_data, *iter_result);
 
 return iter_result->blkno;
 }

src/include/storage/read_stream.h

@@ -157,4 +157,13 @@ read_stream_get_buffer_and_value_with_size(ReadStream *stream,
 (AssertMacro(sizeof(**(pointer)) <= read_stream_per_buffer_data_size(stream)), \
 read_stream_next_buffer((stream), ((void **) (pointer))))
 
+/*
+* Set the per-buffer data by value. This can be called from inside a
+* callback that is returning block numbers. It asserts that the value's size
+* matches the available space.
+*/
+#define read_stream_put_value(stream, per_buffer_data, value) \
+(AssertMacro(sizeof(value) == read_stream_per_buffer_data_size(stream)), \
+memcpy((per_buffer_data), &(value), sizeof(value)))
+
 #endif /* READ_STREAM_H */