io.netty.util.concurrent.FastThreadLocal Maven / Gradle / Ivy
/*
* Copyright 2014 The Netty Project
*
* The Netty Project 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 io.netty.util.concurrent;
import io.netty.util.internal.InternalThreadLocalMap;
import io.netty.util.internal.PlatformDependent;
import java.util.Collections;
import java.util.IdentityHashMap;
import java.util.Set;
/**
* A special variant of {@link ThreadLocal} that yields higher access performance when accessed from a
* {@link FastThreadLocalThread}.
*
* Internally, a {@link FastThreadLocal} uses a constant index in an array, instead of using hash code and hash table,
* to look for a variable. Although seemingly very subtle, it yields slight performance advantage over using a hash
* table, and it is useful when accessed frequently.
*
* To take advantage of this thread-local variable, your thread must be a {@link FastThreadLocalThread} or its subtype.
* By default, all threads created by {@link DefaultThreadFactory} are {@link FastThreadLocalThread} due to this reason.
*
* Note that the fast path is only possible on threads that extend {@link FastThreadLocalThread}, because it requires
* a special field to store the necessary state. An access by any other kind of thread falls back to a regular
* {@link ThreadLocal}.
*
*
* @param the type of the thread-local variable
* @see ThreadLocal
*/
public class FastThreadLocal {
private static final int variablesToRemoveIndex = InternalThreadLocalMap.nextVariableIndex();
/**
* Removes all {@link FastThreadLocal} variables bound to the current thread. This operation is useful when you
* are in a container environment, and you don't want to leave the thread local variables in the threads you do not
* manage.
*/
public static void removeAll() {
InternalThreadLocalMap threadLocalMap = InternalThreadLocalMap.getIfSet();
if (threadLocalMap == null) {
return;
}
try {
Object v = threadLocalMap.indexedVariable(variablesToRemoveIndex);
if (v != null && v != InternalThreadLocalMap.UNSET) {
@SuppressWarnings("unchecked")
Set> variablesToRemove = (Set>) v;
FastThreadLocal[] variablesToRemoveArray =
variablesToRemove.toArray(new FastThreadLocal[0]);
for (FastThreadLocal tlv: variablesToRemoveArray) {
tlv.remove(threadLocalMap);
}
}
} finally {
InternalThreadLocalMap.remove();
}
}
/**
* Returns the number of thread local variables bound to the current thread.
*/
public static int size() {
InternalThreadLocalMap threadLocalMap = InternalThreadLocalMap.getIfSet();
if (threadLocalMap == null) {
return 0;
} else {
return threadLocalMap.size();
}
}
/**
* Destroys the data structure that keeps all {@link FastThreadLocal} variables accessed from
* non-{@link FastThreadLocalThread}s. This operation is useful when you are in a container environment, and you
* do not want to leave the thread local variables in the threads you do not manage. Call this method when your
* application is being unloaded from the container.
*/
public static void destroy() {
InternalThreadLocalMap.destroy();
}
@SuppressWarnings("unchecked")
private static void addToVariablesToRemove(InternalThreadLocalMap threadLocalMap, FastThreadLocal variable) {
Object v = threadLocalMap.indexedVariable(variablesToRemoveIndex);
Set> variablesToRemove;
if (v == InternalThreadLocalMap.UNSET || v == null) {
variablesToRemove = Collections.newSetFromMap(new IdentityHashMap, Boolean>());
threadLocalMap.setIndexedVariable(variablesToRemoveIndex, variablesToRemove);
} else {
variablesToRemove = (Set>) v;
}
variablesToRemove.add(variable);
}
private static void removeFromVariablesToRemove(
InternalThreadLocalMap threadLocalMap, FastThreadLocal variable) {
Object v = threadLocalMap.indexedVariable(variablesToRemoveIndex);
if (v == InternalThreadLocalMap.UNSET || v == null) {
return;
}
@SuppressWarnings("unchecked")
Set> variablesToRemove = (Set>) v;
variablesToRemove.remove(variable);
}
private final int index;
public FastThreadLocal() {
index = InternalThreadLocalMap.nextVariableIndex();
}
/**
* Returns the current value for the current thread
*/
@SuppressWarnings("unchecked")
public final V get() {
InternalThreadLocalMap threadLocalMap = InternalThreadLocalMap.get();
Object v = threadLocalMap.indexedVariable(index);
if (v != InternalThreadLocalMap.UNSET) {
return (V) v;
}
return initialize(threadLocalMap);
}
/**
* Returns the current value for the current thread if it exists, {@code null} otherwise.
*/
@SuppressWarnings("unchecked")
public final V getIfExists() {
InternalThreadLocalMap threadLocalMap = InternalThreadLocalMap.getIfSet();
if (threadLocalMap != null) {
Object v = threadLocalMap.indexedVariable(index);
if (v != InternalThreadLocalMap.UNSET) {
return (V) v;
}
}
return null;
}
/**
* Returns the current value for the specified thread local map.
* The specified thread local map must be for the current thread.
*/
@SuppressWarnings("unchecked")
public final V get(InternalThreadLocalMap threadLocalMap) {
Object v = threadLocalMap.indexedVariable(index);
if (v != InternalThreadLocalMap.UNSET) {
return (V) v;
}
return initialize(threadLocalMap);
}
private V initialize(InternalThreadLocalMap threadLocalMap) {
V v = null;
try {
v = initialValue();
} catch (Exception e) {
PlatformDependent.throwException(e);
}
threadLocalMap.setIndexedVariable(index, v);
addToVariablesToRemove(threadLocalMap, this);
return v;
}
/**
* Set the value for the current thread.
*/
public final void set(V value) {
if (value != InternalThreadLocalMap.UNSET) {
InternalThreadLocalMap threadLocalMap = InternalThreadLocalMap.get();
setKnownNotUnset(threadLocalMap, value);
} else {
remove();
}
}
/**
* Set the value for the specified thread local map. The specified thread local map must be for the current thread.
*/
public final void set(InternalThreadLocalMap threadLocalMap, V value) {
if (value != InternalThreadLocalMap.UNSET) {
setKnownNotUnset(threadLocalMap, value);
} else {
remove(threadLocalMap);
}
}
/**
* @return see {@link InternalThreadLocalMap#setIndexedVariable(int, Object)}.
*/
private void setKnownNotUnset(InternalThreadLocalMap threadLocalMap, V value) {
if (threadLocalMap.setIndexedVariable(index, value)) {
addToVariablesToRemove(threadLocalMap, this);
}
}
/**
* Returns {@code true} if and only if this thread-local variable is set.
*/
public final boolean isSet() {
return isSet(InternalThreadLocalMap.getIfSet());
}
/**
* Returns {@code true} if and only if this thread-local variable is set.
* The specified thread local map must be for the current thread.
*/
public final boolean isSet(InternalThreadLocalMap threadLocalMap) {
return threadLocalMap != null && threadLocalMap.isIndexedVariableSet(index);
}
/**
* Sets the value to uninitialized; a proceeding call to get() will trigger a call to initialValue().
*/
public final void remove() {
remove(InternalThreadLocalMap.getIfSet());
}
/**
* Sets the value to uninitialized for the specified thread local map;
* a proceeding call to get() will trigger a call to initialValue().
* The specified thread local map must be for the current thread.
*/
@SuppressWarnings("unchecked")
public final void remove(InternalThreadLocalMap threadLocalMap) {
if (threadLocalMap == null) {
return;
}
Object v = threadLocalMap.removeIndexedVariable(index);
removeFromVariablesToRemove(threadLocalMap, this);
if (v != InternalThreadLocalMap.UNSET) {
try {
onRemoval((V) v);
} catch (Exception e) {
PlatformDependent.throwException(e);
}
}
}
/**
* Returns the initial value for this thread-local variable.
*/
protected V initialValue() throws Exception {
return null;
}
/**
* Invoked when this thread local variable is removed by {@link #remove()}. Be aware that {@link #remove()}
* is not guaranteed to be called when the `Thread` completes which means you can not depend on this for
* cleanup of the resources in the case of `Thread` completion.
*/
protected void onRemoval(@SuppressWarnings("UnusedParameters") V value) throws Exception { }
}