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/*
* Copyright 2009 Mike Cumings
*
* 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 com.kenai.jbosh;
import java.security.SecureRandom;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* Request ID sequence generator. This generator generates a random first
* RID and then manages the sequence from there on out.
*/
final class RequestIDSequence {
/**
* Maximum number of bits available for representing request IDs, according
* to the XEP-0124 spec.s
*/
private static final int MAX_BITS = 53;
/**
* Bits devoted to incremented values.
*/
private static final int INCREMENT_BITS = 32;
/**
* Minimum number of times the initial RID can be incremented before
* exceeding the maximum.
*/
private static final long MIN_INCREMENTS = 1L << INCREMENT_BITS;
/**
* Max initial value.
*/
private static final long MAX_INITIAL = (1L << MAX_BITS) - MIN_INCREMENTS;
/**
* Max bits mask.
*/
private static final long MASK = ~(Long.MAX_VALUE << MAX_BITS);
/**
* Random number generator.
*/
private static final SecureRandom RAND = new SecureRandom();
/**
* Internal lock.
*/
private static final Lock LOCK = new ReentrantLock();
/**
* The last reqest ID used, or <= 0 if a new request ID needs to be
* generated.
*/
private AtomicLong nextRequestID = new AtomicLong();
///////////////////////////////////////////////////////////////////////////
// Constructors:
/**
* Prevent direct construction.
*/
RequestIDSequence() {
nextRequestID = new AtomicLong(generateInitialValue());
}
///////////////////////////////////////////////////////////////////////////
// Public methods:
/**
* Calculates the next request ID value to use. This number must be
* initialized such that it is unlikely to ever exceed 2 ^ 53, according
* to XEP-0124.
*
* @return next request ID value
*/
public long getNextRID() {
return nextRequestID.getAndIncrement();
}
///////////////////////////////////////////////////////////////////////////
// Private methods:
/**
* Generates an initial RID value by generating numbers until a number is
* found which is smaller than the maximum allowed value and greater
* than zero.
*
* @return random initial value
*/
private long generateInitialValue() {
long result;
LOCK.lock();
try {
do {
result = RAND.nextLong() & MASK;
} while (result > MAX_INITIAL);
} finally {
LOCK.unlock();
}
return result;
}
}
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