ctubbsii commented on code in PR #4910:
URL: https://github.com/apache/accumulo/pull/4910#discussion_r1767660709
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server/tserver/src/main/java/org/apache/accumulo/tserver/NativeMapCleanerUtil.java:
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@@ -43,14 +44,37 @@ public static Cleanable deleteNM(Object obj, Logger log,
AtomicLong nmPtr) {
});
}
+ // Chose 7 cleaners because each cleaner creates a thread, so do not want
too many threads. This
+ // should reduce lock contention for scans by a 7th vs a single cleaner, so
that is good
+ // reduction and 7 does not seem like too many threads to add. This array is
indexed using
+ // pointers addresses from native code, so there is a good chance those are
memory aligned on
+ // a multiple of 4, 8, 16, etc. So if changing the array size avoid
multiples of 2.
+ private static final Cleaner[] NMI_CLEANERS = new Cleaner[7];
+
+ static {
+ for (int i = 0; i < NMI_CLEANERS.length; i++) {
+ NMI_CLEANERS[i] = Cleaner.create();
+ }
+ }
+
public static Cleanable deleteNMIterator(Object obj, AtomicLong nmiPtr) {
requireNonNull(nmiPtr);
- return CleanerUtil.CLEANER.register(obj, () -> {
+
+ long ptr = Math.abs(nmiPtr.get());
+ if (ptr == Long.MIN_VALUE) {
+ ptr = 0;
+ }
+ int cleanerIndex = (int) (ptr % NMI_CLEANERS.length);
Review Comment:
You can avoid the absolute value and handling of the `Long.MIN_VALUE` by
just fixing Java's negative answer for modulus:
```suggestion
int cleanerIndex = (int) (nmiPtr.get() % NMI_CLEANERS.length);
if (cleanerIndex < 0) {
cleanerIndex += NMI_CLEANERS.length;
}
```
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