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ADROID 2.1 架构解析——闹钟分析透彻，有点基础都能看懂！ 1 设置定时时间文件：packages/apps/alarmclock/src//android/alarmclock/Alarms.java private static void enableAlert(Context context, final Alarm alarm, final long atTimeInMillis) { AlarmManager am = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE); ... am.set(AlarmManager.RTC_WAKEUP, atTimeInMillis, sender); ... } 由闹钟管理器设置定时时间。 2 闹钟管理器 2.1 定时设置文件：frameworks/base/core/java/android/app/AlarmManager.java public static final int RTC_WAKEUP = 0; public static final int RTC = 1; public static final int ELAPSED_REALTIME_WAKEUP = 2; public static final int ELAPSED_REALTIME = 3; AlarmManager(IAlarmManager service) { mService = service; } public void set(int type, long triggerAtTime, PendingIntent operation) { try { mService.set(type, triggerAtTime, operation); } catch (RemoteException ex) { } } 将type, triggerAtTime, operation等参数转向闹钟管理器服务。 3 闹钟管理器服务文件：frameworks/base/services/java//android/server/AlarmManagerService.java 3.1 定时设置 public AlarmManagerService(Context context) { mDescriptor = init(); ... } public void set(int type, long triggerAtTime, PendingIntent operation) { setRepeating(type, triggerAtTime, 0, operation); } public void setRepeating(int type, long triggerAtTime, long interval, PendingIntent operation) { if (operation == null) { Log.w(TAG, "set/setRepeating ignored because there is no intent"); return; } synchronized (mLock) { Alarm alarm = new Alarm(); alarm.type = type; alarm.when = triggerAtTime; alarm.repeatInterval = interval; alarm.operation = operation; // Remove this alarm if already scheduled. removeLocked(operation); if (localLOGV) Log.v(TAG, "set: " + alarm); int index = addAlarmLocked(alarm); if (index == 0) { setLocked(alarm); } } } private void setLocked(Alarm alarm) { if (mDescriptor != -1) { set(mDescriptor, alarm.type, (alarm.when * 1000 * 1000)); } else { Message msg = Message.obtain(); msg.what = ALARM_EVENT; mHandler.removeMessages(ALARM_EVENT); mHandler.sendMessageAtTime(msg, alarm.when); } } Init,set 为底层操作函数，set(mDescriptor, alarm.type, (alarm.when * 1000 * 1000)); 由底层来完成定时设置。 3.2等待计时完毕 private class AlarmThread extends Thread { public void run() { ... while (true) { int result = waitForAlarm(mDescriptor); ... if ((result & RTC_WAKEUP_MASK) != 0) triggerAlarmsLocked(mRtcWakeupAlarms, triggerList, nowRTC); if ((result & RTC_MASK) != 0) triggerAlarmsLocked(mRtcAlarms, triggerList, nowRTC); if ((result & ELAPSED_REALTIME_WAKEUP_MASK) != 0) triggerAlarmsLocked(mElapsedRealtimeWakeupAlarms,triggerList, nowELAPSED); if ((result & ELAPSED_REALTIME_MASK) != 0) triggerAlarmsLocked(mElapsedRealtimeAlarms, triggerList, nowELAPSED); ... } } } 在服务里采用线程来处理计时完毕返回的信息，根据等待计时完毕返回的信息触发不同的操作。 4 硬件调用（JNI机制）文件：frameworks/base/services/jni/_android_server_AlarmManagerService.cpp 4.1 定时设置 static jint android_server_AlarmManagerService_init(JNIEnv* env, jobject obj) { #if HAVE_ANDROID_OS return open("/dev/alarm", O_RDWR); #else return -1; #endif } static void android_server_AlarmManagerService_close(JNIEnv* env, jobject obj, jint fd) { #if HAVE_ANDROID_OS close(fd); #endif } static void android_server_AlarmManagerService_set(JNIEnv* env, jobject obj, jint fd, jint type, jlong nanoseconds) { #if HAVE_ANDROID_OS struct timespec ts; ts.tv_sec = NANOSECONDS_TO_SECONDS(nanoseconds); ts.tv_nsec = nanoseconds - SECONDS_TO_NANOSECONDS(ts.tv_sec); int result = ioctl(fd, ANDROID_ALARM_SET(type), &ts); if (result < 0) { LOGE("Unable to set alarm to %lld: %s\n", nanoseconds, strerror(errno)); } #endif } 以上函数的绑定如下： {"init", "()I", (void*)android_server_AlarmManagerService_init}, {"close", "(I)V", (void*)android_server_AlarmManagerService_close}, {"set", "(IIJ)V", (void*)android_server_AlarmManagerService_set}, 由上可知，通过ioctl接口，设置定时时间。 4.2 等待计时完毕 static jint android_server_AlarmManagerService_waitForAlarm(JNIEnv* env, jobject obj, jint fd) { #if HAVE_ANDROID_OS int result = 0; do { result = ioctl(fd, ANDROID_ALARM_WAIT); } while (result < 0 && errno == EINTR); if (result < 0) { LOGE("Unable to wait on alarm: %s\n", strerror(errno)); return 0; } return result; #endif } 以上函数的绑定如下： {"waitForAlarm", "(I)I", (void*)android_server_AlarmManagerService_waitForAlarm}, 由上可知，代码阻塞方式等待计时完毕或由意外中断完毕。 4 杂项 4.1 闹钟类型 public static final int ELAPSED_REALTIME //当系统进入睡眠状态时，这种类型的闹铃不会唤醒系统。直到系统下次被唤醒才传递它，该闹铃所用的时间是相对时间，是从系统启动后开始计时的,包括睡眠时间，可以通过调用SystemClock.elapsedRealtime()获得。系统值是3 (0x00000003)。 public static final int ELAPSED_REALTIME_WAKEUP //能唤醒系统，用法同ELAPSED_REALTIME，系统值是2 (0x00000002) 。 public static final int RTC //当系统进入睡眠状态时，这种类型的闹铃不会唤醒系统。直到系统下次被唤醒才传递它，该闹铃所用的时间是绝对时间，所用时间是UTC时间，可以通过调用 System.currentTimeMillis()获得。系统值是1 (0x00000001) 。 public static final int RTC_WAKEUP //能唤醒系统，用法同RTC类型，系统值为 0 (0x00000000) 。 Public static final int POWER_OFF_WAKEUP //能唤醒系统，它是一种关机闹铃，就是说设备在关机状态下也可以唤醒系统，所以我们把它称之为关机闹铃。使用方法同RTC类型，系统值为4(0x00000004)。 4.2 底层实现在IOCTL中ANDROID_ALARM_SET(0)设置闹钟；在IOCTL中ANDROID_ALARM_WAIT: 等待闹钟时间，其中 rv = wait_event_interruptible(alarm_wait_queue, alarm_pending); 会阻塞，在## mins后alarm_timer_triggered函数中改变alarm_pending值为真，并唤醒等待队列。 wake_up(&alarm_wait_queue); 在ANDROID_ALARM_WAIT的最后释放alarm_rtc_wake_lock。 5 / 5

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