com.sun.util.reentrant.ReentrantContextProviderTL Maven / Gradle / Ivy
/*
* Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package com.sun.util.reentrant;
import java.lang.ref.Reference;
/**
* This ReentrantContextProvider implementation uses a ThreadLocal to hold
* the first ReentrantContext per thread and a ReentrantContextProviderCLQ to
* store child ReentrantContext instances needed during recursion.
*
* Note: this implementation may keep up to one context in memory per thread.
* Child contexts for recursive uses are stored in the queue using a WEAK
* reference by default unless specified in the 2 argument constructor.
*
* @param ReentrantContext subclass
*/
public abstract class ReentrantContextProviderTL
extends ReentrantContextProvider
{
// Thread-local storage:
private final ThreadLocal> ctxTL
= new ThreadLocal>();
// ReentrantContext CLQ provider for child contexts:
private final ReentrantContextProviderCLQ ctxProviderCLQ;
/**
* Create a new ReentrantContext provider using the given reference type
* among hard, soft or weak.
* It uses weak reference for the child contexts.
*
* @param refType reference type
*/
public ReentrantContextProviderTL(final int refType) {
this(refType, REF_WEAK);
}
/**
* Create a new ReentrantContext provider using the given reference types
* among hard, soft or weak
*
* @param refTypeTL reference type used by ThreadLocal
* @param refTypeCLQ reference type used by ReentrantContextProviderCLQ
*/
public ReentrantContextProviderTL(final int refTypeTL, final int refTypeCLQ)
{
super(refTypeTL);
final ReentrantContextProviderTL parent = this;
this.ctxProviderCLQ = new ReentrantContextProviderCLQ(refTypeCLQ) {
@Override
protected K newContext() {
return parent.newContext();
}
};
}
/**
* Give a ReentrantContext instance for the current thread
*
* @return ReentrantContext instance
*/
@Override
public final K acquire() {
K ctx = null;
final Reference ref = ctxTL.get();
if (ref != null) {
ctx = ref.get();
}
if (ctx == null) {
// create a new ReentrantContext if none is available
ctx = newContext();
// update thread local reference:
ctxTL.set(getOrCreateReference(ctx));
}
// Check reentrance:
if (ctx.usage == USAGE_TL_INACTIVE) {
ctx.usage = USAGE_TL_IN_USE;
} else {
// get or create another ReentrantContext from CLQ provider:
ctx = ctxProviderCLQ.acquire();
}
return ctx;
}
/**
* Restore the given ReentrantContext instance for reuse
*
* @param ctx ReentrantContext instance
*/
@Override
public final void release(final K ctx) {
if (ctx.usage == USAGE_TL_IN_USE) {
ctx.usage = USAGE_TL_INACTIVE;
} else {
ctxProviderCLQ.release(ctx);
}
}
}