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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.concurrent;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantLock;
/**
* Holds a map of locks indexed on keys of a given type.
* This is suitable in cases where exclusive access should be granted to any one of a set of keyed objects and
* there is a finite collection of keyed objects.
*
* The returned locks are reentrant (i.e the owning thread may call lock multiple times) and auto-closable.
*
* Typical use is
* <code>
* try (Lock lock = locks.lock(id)) {
* exclusive use of the object with key id
* }
* </code>
*
* @author bratseth
*/
public class Locks<TYPE> {
private final Map<TYPE, ReentrantLock> locks = new ConcurrentHashMap<>();
private final long timeoutMs;
/** Create locks with a default timeout */
public Locks(long timeout, TimeUnit timeoutUnit) {
timeoutMs = timeoutUnit.toMillis(timeout);
}
/** Locks key. This will block until the key is acquired or the default timeout is reached. */
public Lock lock(TYPE key) {
return lock(key, timeoutMs, TimeUnit.MILLISECONDS);
}
/**
* Locks key. This will block until the key is acquired or the timeout is reached.
* Users of this <b>must</b> close any lock acquired.
*
* @param key the key to lock
* @return the acquired lock
* @throws UncheckedTimeoutException if the lock could not be acquired within the timeout
*/
public Lock lock(TYPE key, long timeout, TimeUnit timeoutUnit) {
try {
ReentrantLock lock = locks.computeIfAbsent(key, k -> new ReentrantLock(true));
boolean acquired = lock.tryLock(timeout, timeoutUnit);
if ( ! acquired)
throw new UncheckedTimeoutException("Timed out waiting for the lock to " + key);
return new Lock(lock);
} catch (InterruptedException e) {
throw new RuntimeException("Interrupted while waiting for lock of " + key);
}
}
}
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