Github user nongli commented on a diff in the pull request:
https://github.com/apache/spark/pull/10068#discussion_r46320411
--- Diff: unsafe/src/main/java/org/apache/spark/unsafe/Platform.java ---
@@ -107,12 +107,27 @@ public static void freeMemory(long address) {
public static void copyMemory(
Object src, long srcOffset, Object dst, long dstOffset, long length) {
- while (length > 0) {
- long size = Math.min(length, UNSAFE_COPY_THRESHOLD);
- _UNSAFE.copyMemory(src, srcOffset, dst, dstOffset, size);
- length -= size;
- srcOffset += size;
- dstOffset += size;
+ // Check if dstOffset is before or after srcOffset to determine if we
should copy
+ // forward or backwards. This is necessary in case src and dst overlap.
+ if (dstOffset < srcOffset) {
--- End diff --
@davies I don't think it was chunked this way for perf. Looking at the
comment for UNSAFE_COPY_THRESHOLD, it seems to be for some other purpose. I'm
not familiar with this enough to judge if we need that.
@srowen I'm looking to see if I can find docs on what unsafe does but
haven't found anything definitive yet. The test case you originally suggested
is very similar to what I have no?
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