87 lines
2.9 KiB
Java
87 lines
2.9 KiB
Java
/*
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* Copyright (c) 2007, 2018, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package nsk.share.locks;
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import nsk.share.*;
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/*
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* DeadlockLocker - class used for deadlock creation
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*
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* To create deadlock second 'inner' instance of DeadlockLocker is required.
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*
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* Deadlock creation scenario:
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* - object acquires its resource
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* - notify 'inner' through Wicket step1 that resource is locked and 'inner' can try to acquire this object's resource
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* - wait notification through Wicket step2 from 'inner' that 'inner' acquired its resource
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* - call readyWicket.unlock to notify thread waiting deadlock creation
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* - try acquire locked inner's resource, at the same time inner trying to acquire locked this object's resource - deadlock is created
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*
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* Subclasses should implement method doLock() taking in account described scenario.
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*
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* Objects of DeadlockLocker should not be created directly, to create deadlocked threads use class DeadlockMaker
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*/
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abstract public class DeadlockLocker {
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protected DeadlockLocker inner;
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protected Wicket step1;
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protected Wicket step2;
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// 'readyWicket' is used to notify DeadlockMacker that deadlock is almost created
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protected Wicket readyWicket;
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public DeadlockLocker(Wicket step1, Wicket step2, Wicket readyWicket) {
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this.step1 = step1;
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this.step2 = step2;
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this.readyWicket = readyWicket;
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}
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public void setInner(DeadlockLocker inner) {
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this.inner = inner;
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}
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protected void checkInnerLocker() {
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if (inner == null) {
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throw new IllegalStateException(getClass().getName() + " deadlockLocker's inner locker is null");
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}
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}
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protected abstract void doLock();
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abstract public Object getLock();
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private int lockCount;
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final public void lock() {
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// call this method once
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if (lockCount++ > 1)
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return;
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// check that inner locker was set
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checkInnerLocker();
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doLock();
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}
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}
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