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From gatorsmile <...@git.apache.org>
Subject [GitHub] spark pull request: [SPARK-12030] Fix Platform.copyMemory to handl...
Date Wed, 02 Dec 2015 02:44:09 GMT
Github user gatorsmile commented on a diff in the pull request:

    https://github.com/apache/spark/pull/10068#discussion_r46371653
  
    --- 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 still have a question. Both `dstOffset` and `srcOffset` are offsets. They are not absolute
addresses. 
    
    Based on the code changes, I do not understand how it works. Could anybody give me a hint?
Thank you! 


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