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new 81c2f0f07a Add a new keyed reentrant read/write lock
81c2f0f07a is described below
commit 81c2f0f07a517ebb2f6b791552639eb958e16524
Author: Mark Thomas <[email protected]>
AuthorDate: Wed Aug 27 10:33:04 2025 +0100
Add a new keyed reentrant read/write lock
This class will be used when Tomcat needs to manage concurrent access to
components identified by a key (e..g sessions).
---
build.xml | 3 +
.../concurrent/KeyedReentrantReadWriteLock.java | 179 +++++++++++++++++++++
.../tomcat/util/concurrent/LocalStrings.properties | 16 ++
.../TestKeyedReentrantReadWriteLock.java | 31 ++++
4 files changed, 229 insertions(+)
diff --git a/build.xml b/build.xml
index f2cf7f9519..b605ce54f5 100644
--- a/build.xml
+++ b/build.xml
@@ -448,6 +448,7 @@
<include name="org/apache/tomcat/util/buf/**" />
<include name="org/apache/tomcat/util/collections/**" />
<include name="org/apache/tomcat/util/compat/**" />
+ <include name="org/apache/tomcat/util/concurrent/**" />
<include name="org/apache/tomcat/util/file/**" />
<include name="org/apache/tomcat/util/json/**" />
<include name="org/apache/tomcat/util/res/**" />
@@ -543,6 +544,7 @@
<include name="org/apache/tomcat/util/buf/**" />
<include name="org/apache/tomcat/util/collections/**" />
<include name="org/apache/tomcat/util/compat/**" />
+ <include name="org/apache/tomcat/util/concurrent/**" />
<include name="org/apache/tomcat/util/descriptor/**" />
<include name="org/apache/tomcat/util/file/**" />
<include name="org/apache/tomcat/util/http/**" />
@@ -2461,6 +2463,7 @@
<exclude name="org/apache/tomcat/util/buf" />
<exclude name="org/apache/tomcat/util/collections" />
<exclude name="org/apache/tomcat/util/compat" />
+ <exclude name="org/apache/tomcat/util/concurrent" />
<exclude name="org/apache/tomcat/util/descriptor" />
<exclude name="org/apache/tomcat/util/file" />
<exclude name="org/apache/tomcat/util/http" />
diff --git
a/java/org/apache/tomcat/util/concurrent/KeyedReentrantReadWriteLock.java
b/java/org/apache/tomcat/util/concurrent/KeyedReentrantReadWriteLock.java
new file mode 100644
index 0000000000..d1c0541d62
--- /dev/null
+++ b/java/org/apache/tomcat/util/concurrent/KeyedReentrantReadWriteLock.java
@@ -0,0 +1,179 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.tomcat.util.concurrent;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.locks.Condition;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+import java.util.function.Function;
+
+import org.apache.tomcat.util.res.StringManager;
+
+/**
+ * Provides a reentrant read/write lock for a given key. Any locks obtained
from an instance of this class using the
+ * same key will use the same underlying reentrant read/write lock as long as
at least one lock for that key remains in
+ * use. Once no locks are in use for the given key, the lock is eligible for
GC and the next lock obtained using that key
+ * will use a new underlying reentrant read/write lock.
+ * <p>
+ * The class is used when Tomcat needs to manage concurrent access to
components identified by a key (e.g. sessions).
+ * <p>
+ * The map of keys to locks is maintained so that locks are created as
required and removed when no longer used.
+ * <p>
+ * The locks provided by this class only implement {@code Lock#lock()} and
{@code Lock#unlock()}. All other methods will
+ * throw {@code UnsupportedOperationException}.
+ */
+public class KeyedReentrantReadWriteLock {
+
+ private final Map<String,CountedLock> locksMap = new HashMap<>();
+
+
+ /**
+ * Obtain the reentrant read/write lock for the given key.
+ *
+ * @param key The key for which the lock should be obtained
+ *
+ * @return A reentrant read/write lock for the given key
+ */
+ public ReadWriteLock getLock(String key) {
+ return new ReadWriteLockImpl(locksMap, key);
+ }
+
+
+ /*
+ * Reentrant read/write lock implementation that is passed back to the
caller. It provides the lock wrappers that
+ * track usage.
+ */
+ private static class ReadWriteLockImpl implements ReadWriteLock {
+
+ private final Map<String,CountedLock> locksMap;
+ private final String key;
+ private volatile Lock readLock;
+ private volatile Lock writeLock;
+
+ ReadWriteLockImpl(Map<String,CountedLock> locksMap, String key) {
+ this.locksMap = locksMap;
+ this.key = key;
+ }
+
+ @Override
+ public Lock readLock() {
+ if (readLock == null) {
+ readLock = new LockImpl(locksMap, key,
ReentrantReadWriteLock::readLock);
+ }
+ return readLock;
+ }
+
+ @Override
+ public Lock writeLock() {
+ if (writeLock == null) {
+ writeLock = new LockImpl(locksMap, key,
ReentrantReadWriteLock::writeLock);
+ }
+ return writeLock;
+ }
+ }
+
+
+ /*
+ * Lock wrapper implementation that provides both read locks and write
locks from the underlying lock and tracks
+ * their usage. Most of the methods throw UnsupportedOperationException as
Tomcat does not (currently) require
+ * implementations of those methods.
+ */
+ private static class LockImpl implements Lock {
+
+ private static final StringManager sm =
StringManager.getManager(LockImpl.class);
+
+ private final Map<String,CountedLock> locksMap;
+ private final String key;
+ private final Function<ReentrantReadWriteLock,Lock> function;
+
+ LockImpl(Map<String,CountedLock> locksMap, String key,
Function<ReentrantReadWriteLock,Lock> function) {
+ this.locksMap = locksMap;
+ this.key = key;
+ this.function = function;
+ }
+
+ @Override
+ public void lock() {
+ CountedLock countedLock = null;
+ synchronized (locksMap) {
+ // Lookup / create the counted lock for the given key
+ countedLock = locksMap.compute(key, (k, v) -> v == null ? new
CountedLock() : v);
+ // Increment usage count inside the sync block to ensure other
threads are aware key is in use.
+ countedLock.count.incrementAndGet();
+ }
+ // Lock outside of the sync block in case the call to lock()
blocks.
+ function.apply(countedLock.reentrantLock).lock();
+ }
+
+ @Override
+ public void unlock() {
+ CountedLock countedLock = null;
+ // Unlocking so a lock should exist in the map for the given key.
+ synchronized (locksMap) {
+ countedLock = locksMap.get(key);
+ }
+ if (countedLock == null) {
+ throw new
IllegalStateException(sm.getString("lockImpl.unlockWithoutLock"));
+ }
+ // No need to unlock inside sync block, so don't.
+ function.apply(countedLock.reentrantLock).unlock();
+ synchronized (locksMap) {
+ /*
+ * Decrement usage count and check for zero inside the sync
block to ensure usage tracking is consistent
+ * across multiple threads.
+ */
+ if (countedLock.count.decrementAndGet() == 0) {
+ locksMap.remove(key);
+ }
+ }
+ }
+
+ @Override
+ public void lockInterruptibly() throws InterruptedException {
+ throw new UnsupportedOperationException();
+ }
+
+ @Override
+ public boolean tryLock() {
+ throw new UnsupportedOperationException();
+ }
+
+ @Override
+ public boolean tryLock(long time, TimeUnit unit) throws
InterruptedException {
+ throw new UnsupportedOperationException();
+ }
+
+ @Override
+ public Condition newCondition() {
+ throw new UnsupportedOperationException();
+ }
+ }
+
+
+ /*
+ * Holds the underlying reentrant read/write lock and the counter that
tracks usage.
+ */
+ private static class CountedLock {
+ AtomicInteger count = new AtomicInteger();
+ ReentrantReadWriteLock reentrantLock = new ReentrantReadWriteLock();
+ }
+}
diff --git a/java/org/apache/tomcat/util/concurrent/LocalStrings.properties
b/java/org/apache/tomcat/util/concurrent/LocalStrings.properties
new file mode 100644
index 0000000000..c938a3b529
--- /dev/null
+++ b/java/org/apache/tomcat/util/concurrent/LocalStrings.properties
@@ -0,0 +1,16 @@
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements. See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License. You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+lockImpl.unlockWithoutLock=An attempt was made to release a lock without first
obtaining the lock
\ No newline at end of file
diff --git
a/test/org/apache/tomcat/util/concurrent/TestKeyedReentrantReadWriteLock.java
b/test/org/apache/tomcat/util/concurrent/TestKeyedReentrantReadWriteLock.java
new file mode 100644
index 0000000000..f2a1d5f77b
--- /dev/null
+++
b/test/org/apache/tomcat/util/concurrent/TestKeyedReentrantReadWriteLock.java
@@ -0,0 +1,31 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.tomcat.util.concurrent;
+
+import java.util.concurrent.locks.ReadWriteLock;
+
+import org.junit.Test;
+
+public class TestKeyedReentrantReadWriteLock {
+
+ @Test(expected = IllegalStateException.class)
+ public void testUnlockWithoutLock() {
+ KeyedReentrantReadWriteLock locks = new KeyedReentrantReadWriteLock();
+ ReadWriteLock lock = locks.getLock("any");
+ lock.readLock().unlock();
+ }
+}
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