io.perfmark.impl.ConcurrentThreadLocal Maven / Gradle / Ivy
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/*
* Copyright 2023 Carl Mastrangelo
*
* Licensed 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 io.perfmark.impl;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
/**
* A "thread local" variable that uses weak refs to track the thread to value mapping.
* This class is useful when {@link ThreadLocal} instances are inconvenient.
*
* Like All classes in this package, this class is not API stable.
*/
public class ConcurrentThreadLocal {
private final ConcurrentMap refs = new ConcurrentHashMap();
private final ReferenceQueue queue = new ReferenceQueue();
public T get() {
T value;
if ((value = ThreadRef.get(refs)) != null) {
return value;
}
if ((value = initialValueInternal()) != null) {
refs.put(ThreadRef.newRef(queue), value);
}
return value;
}
public void remove() {
ThreadRef.removeAndClearRef(refs);
drainQueue();
}
public void set(T value) {
ThreadRef.removeAndClearRef(refs);
refs.put(ThreadRef.newRef(queue), value);
}
protected T initialValue() {
return null;
}
private T initialValueInternal() {
drainQueue();
return initialValue();
}
private void drainQueue() {
Reference ref = queue.poll();
if (ref == null) {
return;
}
drainQueue(ref);
}
private void drainQueue(Reference ref) {
do {
refs.remove((ThreadRef) ref);
} while ((ref = queue.poll()) != null);
}
}