Android系统之闹钟模块浅析

关键词: JNI , HAL,Sqlite 

在手机中，闹钟功能是一个最基本的功能，也是我们一个很常用的功能，现在来分析下android是怎么实现的，下面将采用自上而下的方式讲解。

1、APP层

进入桌面闹钟应用程序，选择设置新闹钟，会调到 Alarms.java 里面的
public static long setAlarm(Context context, Alarm alarm) {
….
setNextAlert(context);
….
}
接着也会调用到
public static void setNextAlert(final Context context) {
if (!enableSnoozeAlert(context)) {

//通过查询数据库获取到一个离当前时间最近的alarm
Alarm alarm = calculateNextAlert(context); 
if (alarm != null) {
enableAlert(context, alarm, alarm.time);
} else {
disableAlert(context);
}
}
}
然后继续调用到
private static void enableAlert(Context context, final Alarm alarm, final longatTimeInMillis) {
…….

//下面参数RTC_WAKEUP, 就是保证即使系统睡眠了，都能唤醒，闹钟工作
am.set(AlarmManager.RTC_WAKEUP, atTimeInMillis, sender);…..
}

/packages/apps/DeskClock/src/com/android/deskclock/Alarms.java

2、Framework层
然后就调用到了AlarmManager.java里面方法
public void set(int type, long triggerAtTime, PendingIntent operation) {
try {
mService.set(type, triggerAtTime, operation);
} catch (RemoteException ex) {
}
}
然后就调用到了AlarmManagerService.java里面方法
public void set(int type, long triggerAtTime, PendingIntent operation) {
setRepeating(type, triggerAtTime, 0, operation);
}
然后继续调用
public void setRepeating(int type, long triggerAtTime, long interval,
PendingIntent operation) {
…..
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);

int index = addAlarmLocked(alarm);
if (index == 0) {
setLocked(alarm);
}
}
}
然后就调用到
private void setLocked(Alarm alarm)
{
……

//mDescriptor 这里的文件是 /dev/alarm
set(mDescriptor, alarm.type, alarmSeconds, alarmNanoseconds); 
…..
}

AlarmManagerService程序在系统启动时被系统服务程序SystemServer启动并初始化闹铃设备(/dev/alarm)。

./frameworks/base/core/java/android/app/AlarmManager.java
./frameworks/base/services/java/com/android/server/AlarmManagerService.java

3、JNI的层

JNI : (Java Natative Interface ) 它允许JAVA代码和其他语言的代码进行交互,比如C/C++代码.

private nativevoid set(int fd, int type, long seconds, long nanoseconds);
这就调用到了com_android_server_AlarmManagerService.cpp里面
static JNINativeMethod sMethods[] = {
/* name, signature, funcPtr */
{“init”, “()I”,(void*)android_server_AlarmManagerService_init},
{“close”, “(I)V”,(void*)android_server_AlarmManagerService_close},
{“set”, “(IIJJ)V”,(void*)android_server_AlarmManagerService_set},
{“waitForAlarm”, “(I)I”,(void*)android_server_AlarmManagerService_waitForAlarm},
{“setKernelTimezone”, “(II)I”,(void*)android_server_AlarmManagerService_setKernelTimezone},
};

set 对应的是android_server_AlarmManagerService_set，具体是
static void android_server_AlarmManagerService_set(JNIEnv* env, jobject obj,jint fd, jint type, jlong seconds, jlong nanoseconds)
{
#if HAVE_ANDROID_OS
struct timespec ts;
ts.tv_sec = seconds;
ts.tv_nsec = nanoseconds;

int result = ioctl(fd, ANDROID_ALARM_SET(type), &ts);
if (result < 0)
{
LOGE(“Unable to set alarm to %lld.%09lld: %s\n”, seconds,nanoseconds, strerror(errno));
}
#endif
}

/frameworks/base/services/jni/com_android_server_AlarmManagerService.cpp

4.HAL层

   AndroidHAL层，即硬件抽象层(Hardware abstract layer)，是Google响应厂家“希望不公开源码”的要求推出的新概念。

上面的ioctl 就调用到了alarm-dev.c
static long alarm_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
….
case ANDROID_ALARM_SET(0):
if (copy_from_user(&new_alarm_time, (void __user *)arg,
sizeof(new_alarm_time))) {
rv = -EFAULT;
goto err1;
}
from_old_alarm_set:
spin_lock_irqsave(&alarm_slock, flags);
pr_alarm(IO, “alarm %d set %ld.%09ld\n”, alarm_type,
new_alarm_time.tv_sec, new_alarm_time.tv_nsec);
alarm_enabled |= alarm_type_mask;
alarm_start_range(&alarms[alarm_type],
timespec_to_ktime(new_alarm_time),
timespec_to_ktime(new_alarm_time));
spin_unlock_irqrestore(&alarm_slock, flags);
if (ANDROID_ALARM_BASE_CMD(cmd) != ANDROID_ALARM_SET_AND_WAIT(0)
&& cmd != ANDROID_ALARM_SET_AND_WAIT_OLD)
break;
/* fall though */
….

case ANDROID_ALARM_SET_RTC:
if (copy_from_user(&new_rtc_time, (void __user *)arg,
sizeof(new_rtc_time))) {
rv = -EFAULT;
goto err1;
}
rv = alarm_set_rtc(new_rtc_time);
spin_lock_irqsave(&alarm_slock, flags);
alarm_pending |= ANDROID_ALARM_TIME_CHANGE_MASK;
wake_up(&alarm_wait_queue);
spin_unlock_irqrestore(&alarm_slock, flags);
if (rv < 0)
goto err1;
break;
….
}

然后这边根据用户上层传过来的CMD就调用到了alarm_start_range设置闹钟，alarm_set_rtc 设置RTC时间，这些函数的具体实现在alarm.c文件中;

/* set rtc while preserving elapsed realtime */
int alarm_set_rtc(const struct timespec ts);

下面看alarm.c里面实现：
int alarm_set_rtc(struct timespec new_time)
{
….
ret = rtc_set_time(alarm_rtc_dev, &rtc_new_rtc_time);
….
}

上面会调用到了interface.c 
intrtc_set_time(struct rtc_device *rtc, struct rtc_time *tm)
{
….
err =rtc->ops->set_time(rtc->dev.parent, tm);
….
}

文件位置

kernel/drivers/rtc/alarm-dev.c
kernel/drivers/rtc/alarm.c

4. Drive层
然后set_time 就看到具体的是那个RTC芯片，这边我们参考rtc-pcf8563.c
static conststruct rtc_class_ops  pcf8563_rtc_ops = {
.read_time =pcf8563_rtc_read_time,
.set_time =pcf8563_rtc_set_time,
.read_alarm= pcf8563_rtc_read_alarm,
.set_alarm =pcf8563_rtc_set_alarm,
};
然后就到了
static intpcf8563_rtc_set_time(struct device *dev, struct rtc_time *tm)
{
unsignedchar buf[TIME_NUM];
int ret;

ret =data_calc(buf, tm, TIME_NUM);
if (ret < 0)
goto out;
//这边就调用i2c统一接口，往pcf8563rtc芯片寄存器里面写出数据

ret= i2c_smbus_write_i2c_block_data(pcf8563_info->client,PCF8563_RTC_SEC, TIME_NUM, buf);
out:
return ret;
}
文件位置

kernel/drivers/rtc/rtc-pcf8563.c

以上就是闹钟从应用层到驱动层的整个流程。

                   问题分析

问题一：设置闹钟后，系统如何在后台轮询的

AlarmManagerService 里面有个AlarmThread 会一直轮询/dev/alarm文件，如果打开失败就直接返回，成功就会做一些动作，比如查找时间最近的
alarm，比如睡眠被闹钟唤醒的时候，这边就发一个intent出去，然后在AlarmReceiver.java里面弹出里面会收到就会调用下面的
context.startActivity(alarmAlert);

然后弹出alarm 这个界面
Class c = AlarmAlert.class;
其中publicclass AlarmAlert extends AlarmAlertFullScreen 所以系统睡眠之后被alarm唤醒弹出的alarm就是这边start的
public class AlarmReceiver extends BroadcastReceiver {

/** If the alarm is older than STALE_WINDOW, ignore. It
is probably the result of a time or timezone change */
private final static int STALE_WINDOW = 30 * 60 * 1000;

@Override
public void onReceive(Context context, Intent intent) {
………
handleIntent(Context context, Intent intent)
……..
}

问题二：数据库操作：添加和删除闹钟

当我们设置闹钟的时候,会进入到设置闹钟的窗口,当用户确认点击保存后,会来到 (SetAlarm.java)

private long saveAlarm() {

….

time = Alarms.setAlarm(this, alarm);

……

}

继续跟进会来到(Alarms)

public static long setAlarm(Context context, Alarm alarm){

…..

       ContentValues values = createContentValues(alarm);

       ContentResolver resolver = context.getContentResolver();

       resolver.update(

               ContentUris.withAppendedId(Alarm.Columns.CONTENT_URI, alarm.id),

               values, null, null);

…..

}

到此就完成了闹钟添加到数据库的功能,想了解其中怎么实现的,可以去了解下

ContentResolver ,ContentProvider,SQLiteOpenHelper .从它们那里能找到你要的答案

问题三: 定时短信

对于这个功能实现的方式很多，我讲下我个人的思路,然后做了个小demo.

思路1:使用AlarmManager的set方法来实现该功能,当时间到时发送短信。

思路2:后台开启一个Server ,采用轮询的方式来实现该功能.

数据存储可以采用sqlite 或者 SharedPerferences 方式。