线程同步 ConditionVariable

ConditionVariable类位于android.os.ConditionVariable，它可以帮助Android线程同步。在SDK上的介绍ConditionVariable不同于标准Java位于java.lang.Object wait() 和 notify() ，这个类可以等待自己，这就意味着 open(), close() 和 block() 可能会假死，如果使用ConditionVariable类的open()在调用 block() 之前， block() 将不会阻塞，相反将会返回立即。

该类一共有4个方法

boolean block(long timeout)
阻止当前线程知道条件是open，或直到超时，这里参数long timeout为超时设置，Android123提示大家如果你们从事过Win32开发，这个方法类似DWORD WaitForSingleObject(HANDLE hHandle,DWORD dwMilliseconds); 函数。

void block()
阻止当前线程知道条件 open ，是上面的无超时等待重载版本。

void close()
重置条件为 close状态。

void open()
Open条件，释放所有线程的阻塞.

ConditionVariable在创建时还有一种构造方法是 public ConditionVariable (boolean state) ，如果为true，默认时为opened，如果为false则是closed. ，默认public ConditionVariable()为close()

给出api中一个demo：

/* * Copyright (C) 2007 The Android Open Source Project * * 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.example.android.apis.app; // Need the following import to get access to the app resources, since this // class is in a sub-package. import com.example.android.apis.R; import android.app.Notification; import android.app.NotificationManager; import android.app.PendingIntent; import android.app.Service; import android.content.Intent; import android.os.Binder; import android.os.ConditionVariable; import android.os.IBinder; import android.os.Parcel; import android.os.RemoteException; import android.widget.RemoteViews; /** * This is an example of service that will update its status bar balloon * every 5 seconds for a minute. * */ public class NotifyingService extends Service { // Use a layout id for a unique identifier private static int MOOD_NOTIFICATIONS = R.layout.status_bar_notifications; // variable which controls the notification thread private ConditionVariable mCondition;//它可以帮助Android线程同步 @Override public void onCreate() { mNM = (NotificationManager) getSystemService(NOTIFICATION_SERVICE); // Start up the thread running the service. Note that we create a // separate thread because the service normally runs in the process's // main thread, which we don't want to block. Thread notifyingThread = new Thread(null, mTask, "NotifyingService"); mCondition = new ConditionVariable(false); notifyingThread.start(); } @Override public void onDestroy() { // Cancel the persistent notification. mNM.cancel(MOOD_NOTIFICATIONS); // Stop the thread from generating further notifications mCondition.open(); } private Runnable mTask = new Runnable() { public void run() { for (int i = 0; i < 4; ++i) { showNotification(R.drawable.stat_happy, R.string.status_bar_notifications_happy_message); if (mCondition.block(5 * 1000)) break; showNotification(R.drawable.stat_neutral, R.string.status_bar_notifications_ok_message); if (mCondition.block(5 * 1000)) break; showNotification(R.drawable.stat_sad, R.string.status_bar_notifications_sad_message); if (mCondition.block(5 * 1000)) break; } // Done with our work... stop the service! NotifyingService.this.stopSelf(); } }; @Override public IBinder onBind(Intent intent) { return mBinder; } private void showNotification(int moodId, int textId) { // In this sample, we'll use the same text for the ticker and the expanded notification CharSequence text = getText(textId); // Set the icon, scrolling text and timestamp. // Note that in this example, we pass null for tickerText. We update the icon enough that // it is distracting to show the ticker text every time it changes. We strongly suggest // that you do this as well. (Think of of the "New hardware found" or "Network connection // changed" messages that always pop up) Notification notification = new Notification(moodId, null, System.currentTimeMillis()); // The PendingIntent to launch our activity if the user selects this notification PendingIntent contentIntent = PendingIntent.getActivity(this, 0, new Intent(this, NotifyingController.class), 0); // Set the info for the views that show in the notification panel. notification.setLatestEventInfo(this, getText(R.string.status_bar_notifications_mood_title), text, contentIntent); // Send the notification. // We use a layout id because it is a unique number. We use it later to cancel. mNM.notify(MOOD_NOTIFICATIONS, notification); } // This is the object that receives interactions from clients. See // RemoteService for a more complete example. private final IBinder mBinder = new Binder() { @Override protected boolean onTransact(int code, Parcel data, Parcel reply, int flags) throws RemoteException { return super.onTransact(code, data, reply, flags); } }; private NotificationManager mNM; }

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