The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (C) 2006 The Android Open Source Project |
| 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 android.os; |
| 18 | |
| 19 | /** |
| 20 | * Class that implements the condition variable locking paradigm. |
| 21 | * |
| 22 | * <p> |
| 23 | * This differs from the built-in java.lang.Object wait() and notify() |
| 24 | * in that this class contains the condition to wait on itself. That means |
| 25 | * open(), close() and block() are sticky. If open() is called before block(), |
| 26 | * block() will not block, and instead return immediately. |
| 27 | * |
| 28 | * <p> |
Pin Ting | 14a9310 | 2012-04-25 11:27:03 +0800 | [diff] [blame] | 29 | * This class uses itself as the object to wait on, so if you wait() |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 30 | * or notify() on a ConditionVariable, the results are undefined. |
| 31 | */ |
| 32 | public class ConditionVariable |
| 33 | { |
| 34 | private volatile boolean mCondition; |
| 35 | |
| 36 | /** |
| 37 | * Create the ConditionVariable in the default closed state. |
| 38 | */ |
| 39 | public ConditionVariable() |
| 40 | { |
| 41 | mCondition = false; |
| 42 | } |
| 43 | |
| 44 | /** |
| 45 | * Create the ConditionVariable with the given state. |
| 46 | * |
| 47 | * <p> |
| 48 | * Pass true for opened and false for closed. |
| 49 | */ |
| 50 | public ConditionVariable(boolean state) |
| 51 | { |
| 52 | mCondition = state; |
| 53 | } |
| 54 | |
| 55 | /** |
| 56 | * Open the condition, and release all threads that are blocked. |
| 57 | * |
| 58 | * <p> |
| 59 | * Any threads that later approach block() will not block unless close() |
| 60 | * is called. |
| 61 | */ |
| 62 | public void open() |
| 63 | { |
| 64 | synchronized (this) { |
| 65 | boolean old = mCondition; |
| 66 | mCondition = true; |
| 67 | if (!old) { |
| 68 | this.notifyAll(); |
| 69 | } |
| 70 | } |
| 71 | } |
| 72 | |
| 73 | /** |
| 74 | * Reset the condition to the closed state. |
| 75 | * |
| 76 | * <p> |
| 77 | * Any threads that call block() will block until someone calls open. |
| 78 | */ |
| 79 | public void close() |
| 80 | { |
| 81 | synchronized (this) { |
| 82 | mCondition = false; |
| 83 | } |
| 84 | } |
| 85 | |
| 86 | /** |
| 87 | * Block the current thread until the condition is opened. |
| 88 | * |
| 89 | * <p> |
| 90 | * If the condition is already opened, return immediately. |
| 91 | */ |
| 92 | public void block() |
| 93 | { |
| 94 | synchronized (this) { |
| 95 | while (!mCondition) { |
| 96 | try { |
| 97 | this.wait(); |
| 98 | } |
| 99 | catch (InterruptedException e) { |
| 100 | } |
| 101 | } |
| 102 | } |
| 103 | } |
| 104 | |
| 105 | /** |
| 106 | * Block the current thread until the condition is opened or until |
| 107 | * timeout milliseconds have passed. |
| 108 | * |
| 109 | * <p> |
| 110 | * If the condition is already opened, return immediately. |
| 111 | * |
| 112 | * @param timeout the minimum time to wait in milliseconds. |
| 113 | * |
| 114 | * @return true if the condition was opened, false if the call returns |
| 115 | * because of the timeout. |
| 116 | */ |
| 117 | public boolean block(long timeout) |
| 118 | { |
| 119 | // Object.wait(0) means wait forever, to mimic this, we just |
| 120 | // call the other block() method in that case. It simplifies |
| 121 | // this code for the common case. |
| 122 | if (timeout != 0) { |
| 123 | synchronized (this) { |
| 124 | long now = System.currentTimeMillis(); |
| 125 | long end = now + timeout; |
| 126 | while (!mCondition && now < end) { |
| 127 | try { |
| 128 | this.wait(end-now); |
| 129 | } |
| 130 | catch (InterruptedException e) { |
| 131 | } |
| 132 | now = System.currentTimeMillis(); |
| 133 | } |
| 134 | return mCondition; |
| 135 | } |
| 136 | } else { |
| 137 | this.block(); |
| 138 | return true; |
| 139 | } |
| 140 | } |
| 141 | } |