Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/10068#discussion_r46318319
--- 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 --
I was getting at something different -- does `_UNSAFE.copyMemory` work
reliably with overlapping memory regions? I hope so, I imagine so. But this
method's correctness still depends on it, so it's probably worth unit-testing.
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