也许一些使用alarmmanager做定时任务的同学遇到过这样的问题：设定alarm后，进入设置-->应用程序管理-->强行停止app后，定时任务就失效了。
简单的讲就是：force stop会导致alarm失效。
最典型的例子就是我碰到过的一个bug，使用android手机的时钟app设置一个闹钟，然后进入设置-->应用程序管理里面，将时钟这个app
force stop掉，结果闹钟就不响了。
其实这不是bug，这是android系统的新加入的机制。下面我来详细分析一下来龙去脉。
1. 在设置的应用程序管理里面强行停止app:
这里会最终会调用到
ActivityManagerService的forceStopPackageLocked（）
源代码如下：
<SPAN style="FONT-SIZE: 18px"> private void forceStopPackageLocked(final String packageName, int uid) {
forceStopPackageLocked(packageName, uid, false, false, true, false);
Intent intent = new Intent(Intent.ACTION_PACKAGE_RESTARTED,
Uri.fromParts("package", packageName, null));
if (!mProcessesReady) {
intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY);
}
intent.putExtra(Intent.EXTRA_UID, uid);
broadcastIntentLocked(null, null, intent,
null, null, 0, null, null, null,
false, false, MY_PID, Process.SYSTEM_UID);
}</SPAN>
private void forceStopPackageLocked(final String packageName, int uid) {
forceStopPackageLocked(packageName, uid, false, false, true, false);
Intent intent = new Intent(Intent.ACTION_PACKAGE_RESTARTED,
Uri.fromParts("package", packageName, null));
if (!mProcessesReady) {
intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY);
}
intent.putExtra(Intent.EXTRA_UID, uid);
broadcastIntentLocked(null, null, intent,
null, null, 0, null, null, null,
false, false, MY_PID, Process.SYSTEM_UID);
}
代码里面发送了一个广播：ACTION_PACKAGE_RESTARTED，这个广播大有文章。
2. 再看看AlarmManagerService.java的代码，可以看一个内部类UninstallReceiver
源代码如下：
[java]
<SPAN style="FONT-SIZE: 18px">class UninstallReceiver extends BroadcastReceiver {
public UninstallReceiver() {
IntentFilter filter = new IntentFilter();
filter.addAction(Intent.ACTION_PACKAGE_REMOVED);
filter.addAction(Intent.ACTION_PACKAGE_RESTARTED);
filter.addAction(Intent.ACTION_QUERY_PACKAGE_RESTART);
filter.addDataScheme("package");
mContext.registerReceiver(this, filter);
// Register for events related to sdcard installation.
IntentFilter sdFilter = new IntentFilter();
sdFilter.addAction(Intent.ACTION_EXTERNAL_APPLICATIONS_UNAVAILABLE);
mContext.registerReceiver(this, sdFilter);
}@Override
public void onReceive(Context context, Intent intent) {
synchronized (mLock) {
String action = intent.getAction();
String pkgList[] = null;
if (Intent.ACTION_QUERY_PACKAGE_RESTART.equals(action)) {
pkgList = intent.getStringArrayExtra(Intent.EXTRA_PACKAGES);
for (String packageName : pkgList) {
if (lookForPackageLocked(packageName)) {
setResultCode(Activity.RESULT_OK);
return;
}
}
return;
} else if (Intent.ACTION_EXTERNAL_APPLICATIONS_UNAVAILABLE.equals(action)) {
pkgList = intent.getStringArrayExtra(Intent.EXTRA_CHANGED_PACKAGE_LIST);
} else {
if (Intent.ACTION_PACKAGE_REMOVED.equals(action)
&& intent.getBooleanExtra(Intent.EXTRA_REPLACING, false)) {
// This package is being updated; don‘t kill its alarms.
return;
}
Uri data = intent.getData();
if (data != null) {
String pkg = data.getSchemeSpecificPart();
if (pkg != null) {
pkgList = new String[]{pkg};
}
}
}
if (pkgList != null && (pkgList.length > 0)) {
for (String pkg : pkgList) {
removeLocked(pkg);
mBroadcastStats.remove(pkg);
}
}
}
}
}</SPAN>
class UninstallReceiver extends BroadcastReceiver {
public UninstallReceiver() {
IntentFilter filter = new IntentFilter();
filter.addAction(Intent.ACTION_PACKAGE_REMOVED);
filter.addAction(Intent.ACTION_PACKAGE_RESTARTED);
filter.addAction(Intent.ACTION_QUERY_PACKAGE_RESTART);
filter.addDataScheme("package");
mContext.registerReceiver(this, filter);
// Register for events related to sdcard installation.
IntentFilter sdFilter = new IntentFilter();
sdFilter.addAction(Intent.ACTION_EXTERNAL_APPLICATIONS_UNAVAILABLE);
mContext.registerReceiver(this, sdFilter);
}@Override
public void onReceive(Context context, Intent intent) {
synchronized (mLock) {
String action = intent.getAction();
String pkgList[] = null;
if (Intent.ACTION_QUERY_PACKAGE_RESTART.equals(action)) {
pkgList = intent.getStringArrayExtra(Intent.EXTRA_PACKAGES);
for (String packageName : pkgList) {
if (lookForPackageLocked(packageName)) {
setResultCode(Activity.RESULT_OK);
return;
}
}
return;
} else if (Intent.ACTION_EXTERNAL_APPLICATIONS_UNAVAILABLE.equals(action)) {
pkgList = intent.getStringArrayExtra(Intent.EXTRA_CHANGED_PACKAGE_LIST);
} else {
if (Intent.ACTION_PACKAGE_REMOVED.equals(action)
&& intent.getBooleanExtra(Intent.EXTRA_REPLACING, false)) {
// This package is being updated; don‘t kill its alarms.
return;
}
Uri data = intent.getData();
if (data != null) {
String pkg = data.getSchemeSpecificPart();
if (pkg != null) {
pkgList = new String[]{pkg};
}
}
}
if (pkgList != null && (pkgList.length > 0)) {
for (String pkg : pkgList) {
removeLocked(pkg);
mBroadcastStats.remove(pkg);
}
}
}
}
}可见AlarmManagerService接受了ACTION_PACKAGE_RESTARTED广播，而且执行了removeLocked（pkg）
removeLocked()是做什么的呢？继续看源码：[java]
<SPAN style="FONT-SIZE: 18px"> public void removeLocked(String packageName) {
removeLocked(mRtcWakeupAlarms, packageName);
removeLocked(mRtcAlarms, packageName);
removeLocked(mElapsedRealtimeWakeupAlarms, packageName);
removeLocked(mElapsedRealtimeAlarms, packageName);
}private void removeLocked(ArrayList<Alarm> alarmList,
String packageName) {
if (alarmList.size() <= 0) {
return;
}// iterator over the list removing any it where the intent match
Iterator<Alarm> it = alarmList.iterator();while (it.hasNext()) {
Alarm alarm = it.next();
if (alarm.operation.getTargetPackage().equals(packageName)) {
it.remove();
}
}
}</SPAN>
public void removeLocked(String packageName) {
removeLocked(mRtcWakeupAlarms, packageName);
removeLocked(mRtcAlarms, packageName);
removeLocked(mElapsedRealtimeWakeupAlarms, packageName);
removeLocked(mElapsedRealtimeAlarms, packageName);
}
private void removeLocked(ArrayList<Alarm> alarmList,
String packageName) {
if (alarmList.size() <= 0) {
return;
}
// iterator over the list removing any it where the intent match
Iterator<Alarm> it = alarmList.iterator();while (it.hasNext()) {
Alarm alarm = it.next();
if (alarm.operation.getTargetPackage().equals(packageName)) {
it.remove();
}
}
}
看到这里，大家应该明白了，removeLocked就是将对应package设置的所有类型的alarm都remove掉。
看到这里大家应该知道为什么自己设置的alarm会不起作用了吧？
思考：
为什么google要加入这样的机制呢？
应该是出于系统安全的考虑，google在4.0系统中在安全方面做了很多努力。
很多病毒程序都不希望自己的进程被用户强行停止，希望自己的病毒程序可以一直运行，而常见的方式就是通过设置alarm，在病毒进程被杀死后，通过定时发送广播来拉起病毒进程，来实现病毒进程的重新启动。
google也正是看到了这个一点，所以加入了forceStopPackage的这一机制，让用户能够有机会干掉病毒进程。
android安全：forceStopPackage对android的Alarm的影响,布布扣,bubuko.com