goankur commented on code in PR #13572:
URL: https://github.com/apache/lucene/pull/13572#discussion_r1828364953
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lucene/core/src/java21/org/apache/lucene/internal/vectorization/PanamaVectorUtilSupport.java:
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@@ -291,25 +296,125 @@ private float squareDistanceBody(float[] a, float[] b,
int limit) {
return res1.add(res2).reduceLanes(ADD);
}
- // Binary functions, these all follow a general pattern like this:
- //
- // short intermediate = a * b;
- // int accumulator = (int)accumulator + (int)intermediate;
- //
- // 256 or 512 bit vectors can process 64 or 128 bits at a time, respectively
- // intermediate results use 128 or 256 bit vectors, respectively
- // final accumulator uses 256 or 512 bit vectors, respectively
- //
- // We also support 128 bit vectors, going 32 bits at a time.
- // This is slower but still faster than not vectorizing at all.
-
+ /**
+ * This method SHOULD NOT be used directly when the native dot-product is
enabled. This is because
+ * it allocates off-heap memory in the hot code-path and copies the input
byte-vectors onto it.
+ * This is necessary even with Panama APIs because native code is given a
pointer to a memory
+ * address and if the content at that address can be moved at anytime (by
Java GC in case of heap
+ * allocated memory) then safety of the native computation cannot be
guaranteed. If we try to pass
+ * MemorySegment backing on-heap memory to native code we get
+ * "java.lang.UnsupportedOperationException: Not a native address"
+ *
+ * <p>Stack overflow thread:
Review Comment:
ok! removed in the next revision.
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