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new e731674f61a [improve][ml] RangeCache refactoring: test race conditions
and prevent endless loops (#22814)
e731674f61a is described below
commit e731674f61a973e9b12eab9394f82731c8fc2384
Author: Lari Hotari <[email protected]>
AuthorDate: Fri May 31 23:14:50 2024 +0300
[improve][ml] RangeCache refactoring: test race conditions and prevent
endless loops (#22814)
---
.../apache/bookkeeper/mledger/util/RangeCache.java | 172 +++++++++++++--------
.../mledger/impl/EntryCacheManagerTest.java | 2 +-
.../bookkeeper/mledger/util/RangeCacheTest.java | 35 ++++-
3 files changed, 143 insertions(+), 66 deletions(-)
diff --git
a/managed-ledger/src/main/java/org/apache/bookkeeper/mledger/util/RangeCache.java
b/managed-ledger/src/main/java/org/apache/bookkeeper/mledger/util/RangeCache.java
index 46d03bea1b5..45295d71906 100644
---
a/managed-ledger/src/main/java/org/apache/bookkeeper/mledger/util/RangeCache.java
+++
b/managed-ledger/src/main/java/org/apache/bookkeeper/mledger/util/RangeCache.java
@@ -28,32 +28,36 @@ import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.Map;
-import java.util.Objects;
import java.util.concurrent.ConcurrentNavigableMap;
import java.util.concurrent.ConcurrentSkipListMap;
import java.util.concurrent.atomic.AtomicLong;
+import lombok.extern.slf4j.Slf4j;
import org.apache.bookkeeper.mledger.util.RangeCache.ValueWithKeyValidation;
import org.apache.commons.lang3.tuple.Pair;
/**
* Special type of cache where get() and delete() operations can be done over
a range of keys.
- * The implementation avoids locks and synchronization and relies on
ConcurrentSkipListMap for storing the entries.
- * Since there is no locks, there is a need to have a way to ensure that a
single entry in the cache is removed
- * exactly once. Removing an entry multiple times would result in the entries
of the cache getting released too
- * while they could still be in use.
+ * The implementation avoids locks and synchronization by relying on
ConcurrentSkipListMap for storing the entries.
+ * Since there are no locks, it's necessary to ensure that a single entry in
the cache is removed exactly once.
+ * Removing an entry multiple times could result in the entries of the cache
being released multiple times,
+ * even while they are still in use. This is prevented by using a custom
wrapper around the value to store in the map
+ * that ensures that the value is removed from the map only if the exact same
instance is present in the map.
+ * There's also a check that ensures that the value matches the key. This is
used to detect races without impacting
+ * consistency.
*
* @param <Key>
* Cache key. Needs to be Comparable
* @param <Value>
* Cache value
*/
+@Slf4j
public class RangeCache<Key extends Comparable<Key>, Value extends
ValueWithKeyValidation<Key>> {
public interface ValueWithKeyValidation<T> extends ReferenceCounted {
boolean matchesKey(T key);
}
// Map from key to nodes inside the linked list
- private final ConcurrentNavigableMap<Key, IdentityWrapper<Key, Value>>
entries;
+ private final ConcurrentNavigableMap<Key, EntryWrapper<Key, Value>>
entries;
private AtomicLong size; // Total size of values stored in cache
private final Weighter<Value> weighter; // Weighter object used to extract
the size from values
private final TimestampExtractor<Value> timestampExtractor; // Extract the
timestamp associated with a value
@@ -63,51 +67,53 @@ public class RangeCache<Key extends Comparable<Key>, Value
extends ValueWithKeyV
* the map by calling the {@link Map#remove(Object, Object)} method.
Certain race conditions could result in the
* wrong value being removed from the map. The instances of this class are
recycled to avoid creating new objects.
*/
- private static class IdentityWrapper<K, V> {
- private final Handle<IdentityWrapper> recyclerHandle;
- private static final Recycler<IdentityWrapper> RECYCLER = new
Recycler<IdentityWrapper>() {
+ private static class EntryWrapper<K, V> {
+ private final Handle<EntryWrapper> recyclerHandle;
+ private static final Recycler<EntryWrapper> RECYCLER = new
Recycler<EntryWrapper>() {
@Override
- protected IdentityWrapper newObject(Handle<IdentityWrapper>
recyclerHandle) {
- return new IdentityWrapper(recyclerHandle);
+ protected EntryWrapper newObject(Handle<EntryWrapper>
recyclerHandle) {
+ return new EntryWrapper(recyclerHandle);
}
};
private K key;
private V value;
+ long size;
- private IdentityWrapper(Handle<IdentityWrapper> recyclerHandle) {
+ private EntryWrapper(Handle<EntryWrapper> recyclerHandle) {
this.recyclerHandle = recyclerHandle;
}
- static <K, V> IdentityWrapper<K, V> create(K key, V value) {
- IdentityWrapper<K, V> identityWrapper = RECYCLER.get();
- identityWrapper.key = key;
- identityWrapper.value = value;
- return identityWrapper;
+ static <K, V> EntryWrapper<K, V> create(K key, V value, long size) {
+ EntryWrapper<K, V> entryWrapper = RECYCLER.get();
+ synchronized (entryWrapper) {
+ entryWrapper.key = key;
+ entryWrapper.value = value;
+ entryWrapper.size = size;
+ }
+ return entryWrapper;
}
- K getKey() {
+ synchronized K getKey() {
return key;
}
- V getValue() {
+ synchronized V getValue(K key) {
+ if (this.key != key) {
+ return null;
+ }
return value;
}
+ synchronized long getSize() {
+ return size;
+ }
+
void recycle() {
+ key = null;
value = null;
+ size = 0;
recyclerHandle.recycle(this);
}
-
- @Override
- public boolean equals(Object o) {
- // only match exact identity of the value
- return this == o;
- }
-
- @Override
- public int hashCode() {
- return Objects.hashCode(key);
- }
}
/**
@@ -181,9 +187,10 @@ public class RangeCache<Key extends Comparable<Key>, Value
extends ValueWithKeyV
if (!value.matchesKey(key)) {
throw new IllegalArgumentException("Value '" + value + "' does
not match key '" + key + "'");
}
- IdentityWrapper<Key, Value> newWrapper =
IdentityWrapper.create(key, value);
+ long entrySize = weighter.getSize(value);
+ EntryWrapper<Key, Value> newWrapper = EntryWrapper.create(key,
value, entrySize);
if (entries.putIfAbsent(key, newWrapper) == null) {
- size.addAndGet(weighter.getSize(value));
+ this.size.addAndGet(entrySize);
return true;
} else {
// recycle the new wrapper as it was not used
@@ -207,15 +214,15 @@ public class RangeCache<Key extends Comparable<Key>,
Value extends ValueWithKeyV
return getValue(key, entries.get(key));
}
- private Value getValue(Key key, IdentityWrapper<Key, Value> valueWrapper)
{
+ private Value getValue(Key key, EntryWrapper<Key, Value> valueWrapper) {
if (valueWrapper == null) {
return null;
} else {
- if (valueWrapper.getKey() != key) {
+ Value value = valueWrapper.getValue(key);
+ if (value == null) {
// the wrapper has been recycled and contains another key
return null;
}
- Value value = valueWrapper.getValue();
try {
value.retain();
} catch (IllegalReferenceCountException e) {
@@ -247,7 +254,7 @@ public class RangeCache<Key extends Comparable<Key>, Value
extends ValueWithKeyV
List<Value> values = new ArrayList();
// Return the values of the entries found in cache
- for (Map.Entry<Key, IdentityWrapper<Key, Value>> entry :
entries.subMap(first, true, last, true).entrySet()) {
+ for (Map.Entry<Key, EntryWrapper<Key, Value>> entry :
entries.subMap(first, true, last, true).entrySet()) {
Value value = getValue(entry.getKey(), entry.getValue());
if (value != null) {
values.add(value);
@@ -266,9 +273,9 @@ public class RangeCache<Key extends Comparable<Key>, Value
extends ValueWithKeyV
*/
public Pair<Integer, Long> removeRange(Key first, Key last, boolean
lastInclusive) {
RemovalCounters counters = RemovalCounters.create();
- Map<Key, IdentityWrapper<Key, Value>> subMap = entries.subMap(first,
true, last, lastInclusive);
- for (Map.Entry<Key, IdentityWrapper<Key, Value>> entry :
subMap.entrySet()) {
- removeEntry(entry, counters);
+ Map<Key, EntryWrapper<Key, Value>> subMap = entries.subMap(first,
true, last, lastInclusive);
+ for (Map.Entry<Key, EntryWrapper<Key, Value>> entry :
subMap.entrySet()) {
+ removeEntry(entry, counters, true);
}
return handleRemovalResult(counters);
}
@@ -279,36 +286,76 @@ public class RangeCache<Key extends Comparable<Key>,
Value extends ValueWithKeyV
BREAK_LOOP;
}
- private RemoveEntryResult removeEntry(Map.Entry<Key, IdentityWrapper<Key,
Value>> entry, RemovalCounters counters) {
- return removeEntry(entry, counters, (x) -> true);
+ private RemoveEntryResult removeEntry(Map.Entry<Key, EntryWrapper<Key,
Value>> entry, RemovalCounters counters,
+ boolean skipInvalid) {
+ return removeEntry(entry, counters, skipInvalid, x -> true);
}
- private RemoveEntryResult removeEntry(Map.Entry<Key, IdentityWrapper<Key,
Value>> entry, RemovalCounters counters,
- Predicate<Value> removeCondition) {
+ private RemoveEntryResult removeEntry(Map.Entry<Key, EntryWrapper<Key,
Value>> entry, RemovalCounters counters,
+ boolean skipInvalid,
Predicate<Value> removeCondition) {
Key key = entry.getKey();
- IdentityWrapper<Key, Value> identityWrapper = entry.getValue();
- if (identityWrapper.getKey() != key) {
- // the wrapper has been recycled and contains another key
+ EntryWrapper<Key, Value> entryWrapper = entry.getValue();
+ Value value = entryWrapper.getValue(key);
+ if (value == null) {
+ // the wrapper has already been recycled and contains another key
+ if (!skipInvalid) {
+ EntryWrapper<Key, Value> removed = entries.remove(key);
+ if (removed != null) {
+ // log and remove the entry without releasing the value
+ log.info("Key {} does not match the entry's value
wrapper's key {}, removed entry by key without "
+ + "releasing the value", key,
entryWrapper.getKey());
+ counters.entryRemoved(removed.getSize());
+ return RemoveEntryResult.ENTRY_REMOVED;
+ }
+ }
return RemoveEntryResult.CONTINUE_LOOP;
}
- Value value = identityWrapper.getValue();
try {
// add extra retain to avoid value being released while we are
removing it
value.retain();
} catch (IllegalReferenceCountException e) {
// Value was already released
+ if (!skipInvalid) {
+ // remove the specific entry without releasing the value
+ if (entries.remove(key, entryWrapper)) {
+ log.info("Value was already released for key {}, removed
entry without releasing the value", key);
+ counters.entryRemoved(entryWrapper.getSize());
+ return RemoveEntryResult.ENTRY_REMOVED;
+ }
+ }
return RemoveEntryResult.CONTINUE_LOOP;
}
+ if (!value.matchesKey(key)) {
+ // this is unexpected since the IdentityWrapper.getValue(key)
already checked that the value matches the key
+ log.warn("Unexpected race condition. Value {} does not match the
key {}. Removing entry.", value, key);
+ }
try {
if (!removeCondition.test(value)) {
return RemoveEntryResult.BREAK_LOOP;
}
- // check that the value hasn't been recycled in between
- // there should be at least 2 references since this method adds
one and the cache should have one
- // it is valid that the value contains references even after the
key has been removed from the cache
- if (value.refCnt() > 1 && value.matchesKey(key) &&
entries.remove(key, identityWrapper)) {
- identityWrapper.recycle();
- counters.entryRemoved(weighter.getSize(value));
+ if (!skipInvalid) {
+ // remove the specific entry
+ boolean entryRemoved = entries.remove(key, entryWrapper);
+ if (entryRemoved) {
+ counters.entryRemoved(entryWrapper.getSize());
+ // check that the value hasn't been recycled in between
+ // there should be at least 2 references since this method
adds one and the cache should have
+ // one reference. it is valid that the value contains
references even after the key has been
+ // removed from the cache
+ if (value.refCnt() > 1) {
+ entryWrapper.recycle();
+ // remove the cache reference
+ value.release();
+ } else {
+ log.info("Unexpected refCnt {} for key {}, removed
entry without releasing the value",
+ value.refCnt(), key);
+ }
+ }
+ } else if (skipInvalid && value.refCnt() > 1 &&
entries.remove(key, entryWrapper)) {
+ // when skipInvalid is true, we don't remove the entry if it
doesn't match matches the key
+ // or the refCnt is invalid
+ counters.entryRemoved(entryWrapper.getSize());
+ entryWrapper.recycle();
// remove the cache reference
value.release();
}
@@ -334,12 +381,12 @@ public class RangeCache<Key extends Comparable<Key>,
Value extends ValueWithKeyV
public Pair<Integer, Long> evictLeastAccessedEntries(long minSize) {
checkArgument(minSize > 0);
RemovalCounters counters = RemovalCounters.create();
- while (counters.removedSize < minSize) {
- Map.Entry<Key, IdentityWrapper<Key, Value>> entry =
entries.firstEntry();
+ while (counters.removedSize < minSize &&
!Thread.currentThread().isInterrupted()) {
+ Map.Entry<Key, EntryWrapper<Key, Value>> entry =
entries.firstEntry();
if (entry == null) {
break;
}
- removeEntry(entry, counters);
+ removeEntry(entry, counters, false);
}
return handleRemovalResult(counters);
}
@@ -351,12 +398,12 @@ public class RangeCache<Key extends Comparable<Key>,
Value extends ValueWithKeyV
*/
public Pair<Integer, Long> evictLEntriesBeforeTimestamp(long maxTimestamp) {
RemovalCounters counters = RemovalCounters.create();
- while (true) {
- Map.Entry<Key, IdentityWrapper<Key, Value>> entry =
entries.firstEntry();
+ while (!Thread.currentThread().isInterrupted()) {
+ Map.Entry<Key, EntryWrapper<Key, Value>> entry =
entries.firstEntry();
if (entry == null) {
break;
}
- if (removeEntry(entry, counters, value ->
timestampExtractor.getTimestamp(value) <= maxTimestamp)
+ if (removeEntry(entry, counters, false, value ->
timestampExtractor.getTimestamp(value) <= maxTimestamp)
== RemoveEntryResult.BREAK_LOOP) {
break;
}
@@ -382,12 +429,12 @@ public class RangeCache<Key extends Comparable<Key>,
Value extends ValueWithKeyV
*/
public Pair<Integer, Long> clear() {
RemovalCounters counters = RemovalCounters.create();
- while (true) {
- Map.Entry<Key, IdentityWrapper<Key, Value>> entry =
entries.firstEntry();
+ while (!Thread.currentThread().isInterrupted()) {
+ Map.Entry<Key, EntryWrapper<Key, Value>> entry =
entries.firstEntry();
if (entry == null) {
break;
}
- removeEntry(entry, counters);
+ removeEntry(entry, counters, false);
}
return handleRemovalResult(counters);
}
@@ -421,5 +468,4 @@ public class RangeCache<Key extends Comparable<Key>, Value
extends ValueWithKeyV
return 1;
}
}
-
}
diff --git
a/managed-ledger/src/test/java/org/apache/bookkeeper/mledger/impl/EntryCacheManagerTest.java
b/managed-ledger/src/test/java/org/apache/bookkeeper/mledger/impl/EntryCacheManagerTest.java
index 1b02cd674c5..1ab3198498a 100644
---
a/managed-ledger/src/test/java/org/apache/bookkeeper/mledger/impl/EntryCacheManagerTest.java
+++
b/managed-ledger/src/test/java/org/apache/bookkeeper/mledger/impl/EntryCacheManagerTest.java
@@ -193,9 +193,9 @@ public class EntryCacheManagerTest extends
MockedBookKeeperTestCase {
}
cacheManager.removeEntryCache(ml1.getName());
- assertTrue(cacheManager.getSize() > 0);
assertEquals(factory2.getMbean().getCacheInsertedEntriesCount(), 20);
assertEquals(factory2.getMbean().getCacheEntriesCount(), 0);
+ assertEquals(0, cacheManager.getSize());
assertEquals(factory2.getMbean().getCacheEvictedEntriesCount(), 20);
}
diff --git
a/managed-ledger/src/test/java/org/apache/bookkeeper/mledger/util/RangeCacheTest.java
b/managed-ledger/src/test/java/org/apache/bookkeeper/mledger/util/RangeCacheTest.java
index 01b3c67bf11..4bcf2cc6c4e 100644
---
a/managed-ledger/src/test/java/org/apache/bookkeeper/mledger/util/RangeCacheTest.java
+++
b/managed-ledger/src/test/java/org/apache/bookkeeper/mledger/util/RangeCacheTest.java
@@ -30,11 +30,14 @@ import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import lombok.Cleanup;
+import lombok.Data;
import org.apache.commons.lang3.tuple.Pair;
+import org.awaitility.Awaitility;
import org.testng.annotations.Test;
public class RangeCacheTest {
+ @Data
class RefString extends AbstractReferenceCounted implements
RangeCache.ValueWithKeyValidation<Integer> {
String s;
Integer matchingKey;
@@ -288,15 +291,21 @@ public class RangeCacheTest {
@Test
public void testPutWhileClearIsCalledConcurrently() {
RangeCache<Integer, RefString> cache = new RangeCache<>(value ->
value.s.length(), x -> 0);
- int numberOfThreads = 4;
+ int numberOfThreads = 8;
@Cleanup("shutdownNow")
ScheduledExecutorService executor =
Executors.newScheduledThreadPool(numberOfThreads);
for (int i = 0; i < numberOfThreads; i++) {
executor.scheduleWithFixedDelay(cache::clear, 0, 1,
TimeUnit.MILLISECONDS);
}
- for (int i = 0; i < 100000; i++) {
+ for (int i = 0; i < 200000; i++) {
cache.put(i, new RefString(String.valueOf(i)));
}
+ executor.shutdown();
+ // ensure that no clear operation got into endless loop
+ Awaitility.await().untilAsserted(() ->
assertTrue(executor.isTerminated()));
+ // ensure that clear can be called and all entries are removed
+ cache.clear();
+ assertEquals(cache.getNumberOfEntries(), 0);
}
@Test
@@ -307,4 +316,26 @@ public class RangeCacheTest {
assertTrue(cache.put(0, s0));
assertFalse(cache.put(0, s0));
}
+
+ @Test
+ public void testRemoveEntryWithInvalidRefCount() {
+ RangeCache<Integer, RefString> cache = new RangeCache<>(value ->
value.s.length(), x -> 0);
+ RefString value = new RefString("1");
+ cache.put(1, value);
+ // release the value to make the reference count invalid
+ value.release();
+ cache.clear();
+ assertEquals(cache.getNumberOfEntries(), 0);
+ }
+
+ @Test
+ public void testRemoveEntryWithInvalidMatchingKey() {
+ RangeCache<Integer, RefString> cache = new RangeCache<>(value ->
value.s.length(), x -> 0);
+ RefString value = new RefString("1");
+ cache.put(1, value);
+ // change the matching key to make it invalid
+ value.setMatchingKey(123);
+ cache.clear();
+ assertEquals(cache.getNumberOfEntries(), 0);
+ }
}
