Shuyi Chen | d7955ce | 2013-05-22 14:51:55 -0700 | [diff] [blame] | 1 | /* |
| 2 | * Copyright 2009 Mike Cumings |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | |
| 17 | package com.kenai.jbosh; |
| 18 | |
| 19 | import java.security.SecureRandom; |
| 20 | import java.util.concurrent.atomic.AtomicLong; |
| 21 | import java.util.concurrent.locks.Lock; |
| 22 | import java.util.concurrent.locks.ReentrantLock; |
| 23 | |
| 24 | /** |
| 25 | * Request ID sequence generator. This generator generates a random first |
| 26 | * RID and then manages the sequence from there on out. |
| 27 | */ |
| 28 | final class RequestIDSequence { |
| 29 | |
| 30 | /** |
| 31 | * Maximum number of bits available for representing request IDs, according |
| 32 | * to the XEP-0124 spec.s |
| 33 | */ |
| 34 | private static final int MAX_BITS = 53; |
| 35 | |
| 36 | /** |
| 37 | * Bits devoted to incremented values. |
| 38 | */ |
| 39 | private static final int INCREMENT_BITS = 32; |
| 40 | |
| 41 | /** |
| 42 | * Minimum number of times the initial RID can be incremented before |
| 43 | * exceeding the maximum. |
| 44 | */ |
| 45 | private static final long MIN_INCREMENTS = 1L << INCREMENT_BITS; |
| 46 | |
| 47 | /** |
| 48 | * Max initial value. |
| 49 | */ |
| 50 | private static final long MAX_INITIAL = (1L << MAX_BITS) - MIN_INCREMENTS; |
| 51 | |
| 52 | /** |
| 53 | * Max bits mask. |
| 54 | */ |
| 55 | private static final long MASK = ~(Long.MAX_VALUE << MAX_BITS); |
| 56 | |
| 57 | /** |
| 58 | * Random number generator. |
| 59 | */ |
| 60 | private static final SecureRandom RAND = new SecureRandom(); |
| 61 | |
| 62 | /** |
| 63 | * Internal lock. |
| 64 | */ |
| 65 | private static final Lock LOCK = new ReentrantLock(); |
| 66 | |
| 67 | /** |
| 68 | * The last reqest ID used, or <= 0 if a new request ID needs to be |
| 69 | * generated. |
| 70 | */ |
| 71 | private AtomicLong nextRequestID = new AtomicLong(); |
| 72 | |
| 73 | /////////////////////////////////////////////////////////////////////////// |
| 74 | // Constructors: |
| 75 | |
| 76 | /** |
| 77 | * Prevent direct construction. |
| 78 | */ |
| 79 | RequestIDSequence() { |
| 80 | nextRequestID = new AtomicLong(generateInitialValue()); |
| 81 | } |
| 82 | |
| 83 | /////////////////////////////////////////////////////////////////////////// |
| 84 | // Public methods: |
| 85 | |
| 86 | /** |
| 87 | * Calculates the next request ID value to use. This number must be |
| 88 | * initialized such that it is unlikely to ever exceed 2 ^ 53, according |
| 89 | * to XEP-0124. |
| 90 | * |
| 91 | * @return next request ID value |
| 92 | */ |
| 93 | public long getNextRID() { |
| 94 | return nextRequestID.getAndIncrement(); |
| 95 | } |
| 96 | |
| 97 | /////////////////////////////////////////////////////////////////////////// |
| 98 | // Private methods: |
| 99 | |
| 100 | /** |
| 101 | * Generates an initial RID value by generating numbers until a number is |
| 102 | * found which is smaller than the maximum allowed value and greater |
| 103 | * than zero. |
| 104 | * |
| 105 | * @return random initial value |
| 106 | */ |
| 107 | private long generateInitialValue() { |
| 108 | long result; |
| 109 | LOCK.lock(); |
| 110 | try { |
| 111 | do { |
| 112 | result = RAND.nextLong() & MASK; |
| 113 | } while (result > MAX_INITIAL); |
| 114 | } finally { |
| 115 | LOCK.unlock(); |
| 116 | } |
| 117 | return result; |
| 118 | } |
| 119 | |
| 120 | } |