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//=============================================================================
// Copyright 2006-2010 Daniel W. Dyer
//
// Licensed 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 org.uncommons.util.id;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* Thread-safe source for unique IDs. This particular implementation restricts
* values to those positive integer values that can be represented by the int data type.
* Provides sequenced 32-bit IDs.
* @author Daniel Dyer
*/
public final class IntSequenceIDSource implements IDSource
{
private static final long SECONDS_IN_HOUR = 3600L;
private final Lock lock = new ReentrantLock();
private final long startTime;
private int lastID = -1;
/**
* @param firstValue The value at which to start the sequence (must
* be non-negative).
*/
public IntSequenceIDSource(int firstValue)
{
if (firstValue < 0)
{
throw new IllegalArgumentException("Initial value must be non-negative.");
}
lastID = firstValue - 1;
startTime = System.currentTimeMillis();
}
/**
* Creates a sequence that starts at zero.
*/
public IntSequenceIDSource()
{
this(0);
}
/**
* {@inheritDoc}
*/
public Integer nextID()
{
lock.lock();
try
{
if (lastID == Integer.MAX_VALUE)
{
long hours = (System.currentTimeMillis() - startTime) / SECONDS_IN_HOUR;
throw new IDSourceExhaustedException("32-bit ID source exhausted after " + hours + " hours.");
}
++lastID;
return lastID;
}
finally
{
lock.unlock();
}
}
}