| /******************************************************************************* |
| * Copyright (c) 2012, 2016 IBM Corporation and others. |
| * |
| * This program and the accompanying materials |
| * are made available under the terms of the Eclipse Public License 2.0 |
| * which accompanies this distribution, and is available at |
| * https://www.eclipse.org/legal/epl-2.0/ |
| * |
| * SPDX-License-Identifier: EPL-2.0 |
| * |
| * Contributors: |
| * IBM Corporation - initial API and implementation |
| *******************************************************************************/ |
| package org.eclipse.osgi.internal.container; |
| |
| import java.util.HashMap; |
| import java.util.Map; |
| import java.util.concurrent.TimeUnit; |
| import java.util.concurrent.atomic.AtomicInteger; |
| import java.util.concurrent.locks.ReentrantLock; |
| |
| /* |
| * Implementation note: This class does not pool ReentrantLocks for the objects |
| * that are being locked. This means that if the same object is locked and unlocked |
| * over and over then new ReentrantLocks are created each time. This set should be |
| * used with care. If the same object is going to be locked/unlocked over and over then |
| * consider using a different locking strategy. |
| * |
| * Previous implementations of this class attempted to use a WeakHashMap to cache |
| * the locks, but this proved to be a flawed approach because of the unpredictable |
| * timing of garbage collection, particularly with autoboxed types (e.g. bundle |
| * long ids). |
| */ |
| public class LockSet<T> { |
| static final class LockHolder { |
| private final AtomicInteger useCount = new AtomicInteger(0); |
| private final ReentrantLock lock = new ReentrantLock(); |
| |
| int incrementUseCount() { |
| return useCount.incrementAndGet(); |
| } |
| |
| int decremementUseCount() { |
| return useCount.decrementAndGet(); |
| } |
| |
| boolean tryLock(long time, TimeUnit unit) throws InterruptedException { |
| return !lock.isHeldByCurrentThread() && lock.tryLock(time, unit); |
| } |
| |
| void unlock() { |
| lock.unlock(); |
| } |
| } |
| |
| private final Map<T, LockHolder> locks = new HashMap<>(); |
| |
| public boolean tryLock(T t, long time, TimeUnit unit) throws InterruptedException { |
| final boolean previousInterruption = Thread.interrupted(); |
| try { |
| LockHolder lock; |
| synchronized (locks) { |
| lock = locks.get(t); |
| if (lock == null) { |
| lock = new LockHolder(); |
| locks.put(t, lock); |
| } |
| lock.incrementUseCount(); |
| } |
| // all interested threads have the lock object and the use count is the number of such threads |
| boolean acquired = false; |
| try { |
| acquired = lock.tryLock(time, unit); |
| return acquired; |
| } finally { |
| if (!acquired) { |
| synchronized (locks) { |
| // If, after failing to acquire the lock, no other thread is using the lock, discard it. |
| if (lock.decremementUseCount() == 0) { |
| locks.remove(t); |
| } |
| } |
| } |
| } |
| } finally { |
| if (previousInterruption) { |
| Thread.currentThread().interrupt(); |
| } |
| } |
| } |
| |
| public void unlock(T t) { |
| synchronized (locks) { |
| LockHolder lock = locks.get(t); |
| if (lock == null) |
| throw new IllegalStateException("No lock found."); //$NON-NLS-1$ |
| lock.unlock(); |
| // If, after unlocking, no other thread is using the lock, discard it. |
| if (lock.decremementUseCount() == 0) { |
| locks.remove(t); |
| } |
| } |
| } |
| } |