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[fix][ML]Fix NPE when put value to RangeCache. #15707

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May 24, 2022
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[fix][ML]Fix NPE when put value to RangeCache. #15707

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3340501
Fix NPE when put value to RangeCache.
mattisonchao May 22, 2022
017f852
Fix license header
mattisonchao May 22, 2022
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mattisonchao May 23, 2022
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mattisonchao May 23, 2022
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mattisonchao May 23, 2022
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mattisonchao May 23, 2022
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12 changes: 7 additions & 5 deletions managed-ledger/src/main/java/org/apache/bookkeeper/mledger/util/RangeCache.java
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,7 @@
import java.util.concurrent.ConcurrentNavigableMap;
import java.util.concurrent.ConcurrentSkipListMap;
import java.util.concurrent.atomic.AtomicLong;
import org.apache.commons.lang3.mutable.MutableBoolean;
import org.apache.commons.lang3.tuple.Pair;

/**
Expand Down Expand Up @@ -73,12 +74,13 @@ public RangeCache(Weighter<Value> weighter, TimestampExtractor<Value> timestampE
* @return whether the entry was inserted in the cache
*/
public boolean put(Key key, Value value) {
if (entries.putIfAbsent(key, value) == null) {
MutableBoolean flag = new MutableBoolean();
entries.computeIfAbsent(key, (k) -> {
size.addAndGet(weighter.getSize(value));
return true;
} else {
return false;
}
flag.setValue(true);
return value;
});
return flag.booleanValue();
Comment on lines +77 to +83
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@mattisonchao This doesn't seem to be a thread safe change here. computeIfAbsent doesn't lock the key when ConcurrentSkipListMap is used.
You can see this in the source code of ConcurrentMap:

    default V computeIfAbsent(K key,
            Function<? super K, ? extends V> mappingFunction) {
        Objects.requireNonNull(mappingFunction);
        V oldValue, newValue;
        return ((oldValue = get(key)) == null
                && (newValue = mappingFunction.apply(key)) != null
                && (oldValue = putIfAbsent(key, newValue)) == null)
            ? newValue
            : oldValue;
    }

On the other hand, ConcurrentHashMap.computeIfAbsent does lock the key and atomically call the mappingFunction. More details in a tweet where some observations by @michaeljmarshall were shared: https://twitter.com/spyced/status/1709677859764154819 .

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@mattisonchao issue is #21301

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Yes, you are right.

}

public Value get(Key key) {
Expand Down
29 changes: 27 additions & 2 deletions managed-ledger/src/test/java/org/apache/bookkeeper/mledger/util/RangeCacheTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -29,11 +29,15 @@
import io.netty.util.ReferenceCounted;
import org.apache.commons.lang3.tuple.Pair;
import org.testng.annotations.Test;
import java.util.UUID;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

public class RangeCacheTest {

class RefString extends AbstractReferenceCounted implements ReferenceCounted {
final String s;
String s;

RefString(String s) {
super();
Expand All @@ -43,7 +47,7 @@ class RefString extends AbstractReferenceCounted implements ReferenceCounted {

@Override
protected void deallocate() {
// no-op
s = null;
}

@Override
Expand Down Expand Up @@ -122,6 +126,7 @@ public void customWeighter() {
assertEquals(cache.getNumberOfEntries(), 2);
}


@Test
public void customTimeExtraction() {
RangeCache<Integer, RefString> cache = new RangeCache<>(value -> value.s.length(), x -> x.s.length());
Expand Down Expand Up @@ -268,4 +273,24 @@ public void evictions() {
assertEquals((long) res.getRight(), 10);
assertEquals(cache.getSize(), 90);
}

@Test
public void testInParallel() {
RangeCache<String, RefString> cache = new RangeCache<>(value -> value.s.length(), x -> 0);
ScheduledExecutorService executor = Executors.newSingleThreadScheduledExecutor();
executor.scheduleWithFixedDelay(cache::clear, 10, 10, TimeUnit.MILLISECONDS);
for (int i = 0; i < 1000; i++) {
cache.put(UUID.randomUUID().toString(), new RefString("zero"));
}
executor.shutdown();
}

@Test
public void testPutSameObj() {
RangeCache<Integer, RefString> cache = new RangeCache<>(value -> value.s.length(), x -> 0);
RefString s0 = new RefString("zero");
assertEquals(s0.refCnt(), 1);
assertTrue(cache.put(0, s0));
assertFalse(cache.put(0, s0));
}
}