org.glowroot.api.FastThreadLocal Maven / Gradle / Ivy
/*
* Copyright 2015 the original author or authors.
*
* 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 org.glowroot.api;
/**
* Wrapper that implements optimized {@link ThreadLocal} access pattern ideal for heavily used
* ThreadLocals.
*
* It is faster to use a mutable holder object and always perform ThreadLocal.get() and never use
* ThreadLocal.set(), because the value is more likely to be found in the ThreadLocalMap direct hash
* slot and avoid the slow path ThreadLocalMap.getEntryAfterMiss().
*
* Important: this thread local will live in ThreadLocalMap forever, so use with care.
*/
public class FastThreadLocal {
@SuppressWarnings("nullness:type.argument.type.incompatible")
private final ThreadLocal> threadLocal = new ThreadLocal>() {
@Override
protected Holder initialValue() {
return new Holder(FastThreadLocal.this.initialValue());
}
};
public T get() {
return threadLocal.get().value;
}
public void set(T value) {
threadLocal.get().value = value;
}
protected T initialValue() {
return null;
}
}
class Holder {
T value;
Holder(T value) {
this.value = value;
}
}