Android8.0系统对异常的处理流程

最新推荐文章于 2024-04-07 08:56:28 发布

转载最新推荐文章于 2024-04-07 08:56:28 发布 · 865 阅读

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原文链接：https://blog.youkuaiyun.com/w1070216393/article/details/84781702

文章标签：

#android8.0 #crash

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本文详细解析了Android8.0系统中的异常处理流程，包括未捕获异常的处理机制、crash对话框的显示逻辑及用户交互过程，以及进程crash后的清理工作。

文章目录

Android8.0 系统异常处理流程

Android8.0 系统异常处理流程

异常处理流程

Java处理未捕获异常有个Thread.UncaughtExceptionHandler，在Android系统中当然也是通过实现其来进行未捕获异常处理。

Android 默认系统异常处理是在启动SystemServer进程时设置的。

Zygote进程启动SystemServer时会调用ZygoteInit的forkSystemServer()方法,该方法中又通过handleSystemServerProcess()方法来对SystemServer进程做一些处理,最后会调用到RuntimeInit.commonInit()方法

frameworks/base/core/java/com/android/internal/os/RuntimeInit.java

protected static final void commonInit() {
    Thread.setUncaughtExceptionPreHandler(new LoggingHandler());
    // 该出就设置了默认未捕获异常的处理Handler-KillApplicationHandler
    Thread.setDefaultUncaughtExceptionHandler(new KillApplicationHandler());
   ...
}

  
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KillApplicationHandler代码如下

frameworks/base/core/java/com/android/internal/os/RuntimeInit.java

private static class KillApplicationHandler implements Thread.UncaughtExceptionHandler {
    public void uncaughtException(Thread t, Throwable e) {
        try {
            ...
            // 1. mApplicationObject标识当前应用
            ActivityManager.getService().handleApplicationCrash(
                    mApplicationObject, new ApplicationErrorReport.ParcelableCrashInfo(e));
        } ...
        finally {
            // 无论如何都要保证出现crash的进程不存活
            Process.killProcess(Process.myPid());
            System.exit(10);
        }
    }
}

  
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注释1处的ActivityManager.getService()得到的就是ActivityManagerService的服务端代理对象，实现是通过Binder机制。看看AMS在handleApplicationCrash方法中是如何处理的

frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

public void handleApplicationCrash(IBinder app,
        ApplicationErrorReport.ParcelableCrashInfo crashInfo) {
    ProcessRecord r = findAppProcess(app, "Crash");
    final String processName = app == null ? "system_server"
            : (r == null ? "unknown" : r.processName);
<span class="token function">handleApplicationCrashInner</span><span class="token punctuation">(</span><span class="token string">"crash"</span><span class="token punctuation">,</span> r<span class="token punctuation">,</span> processName<span class="token punctuation">,</span> crashInfo<span class="token punctuation">)</span><span class="token punctuation">;</span>

}

void handleApplicationCrashInner(String eventType, ProcessRecord r, String processName,
ApplicationErrorReport.CrashInfo crashInfo) {
// 1. 将crash信息写入event log中
EventLog.writeEvent(EventLogTags.AM_CRASH, Binder.getCallingPid(),
UserHandle.getUserId(Binder.getCallingUid()), processName,
r == null ? -1 : r.info.flags,
crashInfo.exceptionClassName,
crashInfo.exceptionMessage,
crashInfo.throwFileName,
crashInfo.throwLineNumber);

<span class="token function">addErrorToDropBox</span><span class="token punctuation">(</span>eventType<span class="token punctuation">,</span> r<span class="token punctuation">,</span> processName<span class="token punctuation">,</span> null<span class="token punctuation">,</span> null<span class="token punctuation">,</span> null<span class="token punctuation">,</span> null<span class="token punctuation">,</span> null<span class="token punctuation">,</span> crashInfo<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 2. </span>
mAppErrors<span class="token punctuation">.</span><span class="token function">crashApplication</span><span class="token punctuation">(</span>r<span class="token punctuation">,</span> crashInfo<span class="token punctuation">)</span><span class="token punctuation">;</span>

}

注释1处将log记录在event log中。注释2处调用AppError的crashApplication方法

frameworks/base/services/core/java/com/android/server/am/AppErrors.java

void crashApplication(ProcessRecord r, ApplicationErrorReport.CrashInfo crashInfo) {
    final int callingPid = Binder.getCallingPid();
    final int callingUid = Binder.getCallingUid();
<span class="token keyword">final</span> <span class="token keyword">long</span> origId <span class="token operator">=</span> Binder<span class="token punctuation">.</span><span class="token function">clearCallingIdentity</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">try</span> <span class="token punctuation">{</span>
    <span class="token comment">// 调用内部的crashApplicationInner</span>
    <span class="token function">crashApplicationInner</span><span class="token punctuation">(</span>r<span class="token punctuation">,</span> crashInfo<span class="token punctuation">,</span> callingPid<span class="token punctuation">,</span> callingUid<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword">finally</span> <span class="token punctuation">{</span>
    Binder<span class="token punctuation">.</span><span class="token function">restoreCallingIdentity</span><span class="token punctuation">(</span>origId<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

}

继续看crashApplicationInner方法

frameworks/base/services/core/java/com/android/server/am/AppErrors.java

void crashApplicationInner(ProcessRecord r, ApplicationErrorReport.CrashInfo crashInfo,
        int callingPid, int callingUid) {
    ...
    synchronized (mService) {
        // 1. 处理有IActivityController的情况，如果Controller已经处理错误，则不会显示错误框
        if (handleAppCrashInActivityController(r, crashInfo, shortMsg, longMsg, stackTrace,
                timeMillis, callingPid, callingUid)) {
            return;
        }
        ...
        AppErrorDialog.Data data = new AppErrorDialog.Data();
        data.result = result;
        data.proc = r;
        ...
        // 2. 发送SHOW_ERROR_UI_MSG给AMS的mUiHandler，将弹出一个错误对话框，提示用户某进程crash
        final Message msg = Message.obtain();
        msg.what = ActivityManagerService.SHOW_ERROR_UI_MSG;
    task = data.task;
    msg.obj = data;
    mService.mUiHandler.sendMessage(msg);
}
// 3. 调用AppErrorResult的get方法，该方法内部调用了wait方法，故为阻塞状态，当用户处理了对话框后会调用AppErrorResult的set方法，该方法内部调用了notifyAll()方法来唤醒线程。
// 注意此处涉及了两个线程的工作，crashApplicationInner函数工作在Binder调用所在的线程；对话框工作于AMS的Ui线程

int res = result.get();

Intent appErrorIntent = null;
MetricsLogger.action(mContext, MetricsProto.MetricsEvent.ACTION_APP_CRASH, res);
// 4. 判断用户操作结果，然后根据结果做不同处理
if (res == AppErrorDialog.TIMEOUT || res == AppErrorDialog.CANCEL) {
    res = AppErrorDialog.FORCE_QUIT;
}
synchronized (mService) {
    // 不在提示错误
    if (res == AppErrorDialog.MUTE) {
        stopReportingCrashesLocked(r);
    }
    // 尝试重启进程
    if (res == AppErrorDialog.RESTART) {
        mService.removeProcessLocked(r, false, true, "crash");
        if (task != null) {
            try {
                mService.startActivityFromRecents(task.taskId,
                        ActivityOptions.makeBasic().toBundle());
            } ...
        }
    }
    // 强行结束进程
    if (res == AppErrorDialog.FORCE_QUIT) {
        long orig = Binder.clearCallingIdentity();
        try {
            // Kill it with fire!
            mService.mStackSupervisor.handleAppCrashLocked(r);
            if (!r.persistent) {
                mService.removeProcessLocked(r, false, false, "crash");
                mService.mStackSupervisor.resumeFocusedStackTopActivityLocked();
            }
        } finally {
            Binder.restoreCallingIdentity(orig);
        }
    }
    // 停止进程并报告错误
    if (res == AppErrorDialog.FORCE_QUIT_AND_REPORT) {
        appErrorIntent = createAppErrorIntentLocked(r, timeMillis, crashInfo);
    }
    ...
}

if (appErrorIntent != null) {
    try {
        // 启动报告错误界面
        mContext.startActivityAsUser(appErrorIntent, new UserHandle(r.userId));
    } catch (ActivityNotFoundException e) {
        Slog.w(TAG, "bug report receiver dissappeared", e);
    }
}

}

注释1会优先让crash观察者进行crash处理，crash观察者通过AMS的setActivityController()方法进行设置，如果已经处理则不会再弹出错误对话框。注释2会发送SHOW_ERROR_UI_MSG消息给AMS的mUIHandler处理来请求弹出错误对话框。注释3通过调用AppErrorResult中的get()方法来使线程阻塞。需要注意的是此处涉及到两个线程，crashApplicationInner工作在Binder调用所在的线程，对话框显示则处于AMS的UI线程。具体AppErrorResult的工作后面会说到。待用户操作对话框后或者超时时间到时get()方法就会被唤醒，并且返回处理结果。注释4则根据用户操作结果进行不同的处理，例如强制停止进程，重启进程等。

这里看下注释2处是如何显示错误对话框的，AMS的UiHandler接收到了消息就会进行显示操作

crash对话框的显示和用户行为

frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

final class UiHandler extends Handler {
    @Override
    public void handleMessage(Message msg) {
        switch (msg.what) {
        // 显示错误对话框
        case SHOW_ERROR_UI_MSG: {
            mAppErrors.handleShowAppErrorUi(msg);
            ensureBootCompleted();
        } break;
        // 显示ANR对话框
        case SHOW_NOT_RESPONDING_UI_MSG: {
            mAppErrors.handleShowAnrUi(msg);
            ensureBootCompleted();
        } break;
        ...
}

 
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可以看到UiHandler对错误和ANR对话框显示的处理，这里看错误对话框的显示，其还是通过AppErrors类进行处理。

frameworks/base/services/core/java/com/android/server/am/AppErrors.java

void handleShowAppErrorUi(Message msg) {
    ...
    synchronized (mService) {
        ProcessRecord proc = data.proc;
        AppErrorResult res = data.result;
        // 1. crash 对话框已显示，故无需再显示
        if (proc != null && proc.crashDialog != null) {
            if (res != null) {
                res.set(AppErrorDialog.ALREADY_SHOWING);
            }
            return;
        }
   <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
    <span class="token keyword">final</span> <span class="token keyword">boolean</span> crashSilenced <span class="token operator">=</span> mAppsNotReportingCrashes <span class="token operator">!=</span> null <span class="token operator">&amp;&amp;</span>
            mAppsNotReportingCrashes<span class="token punctuation">.</span><span class="token function">contains</span><span class="token punctuation">(</span>proc<span class="token punctuation">.</span>info<span class="token punctuation">.</span>packageName<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token punctuation">(</span>mService<span class="token punctuation">.</span><span class="token function">canShowErrorDialogs</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">||</span> showBackground<span class="token punctuation">)</span> <span class="token operator">&amp;&amp;</span> <span class="token operator">!</span>crashSilenced<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token comment">// 2. 创建crash对话框</span>
        proc<span class="token punctuation">.</span>crashDialog <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">AppErrorDialog</span><span class="token punctuation">(</span>mContext<span class="token punctuation">,</span> mService<span class="token punctuation">,</span> data<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
        <span class="token comment">// 3. 如果AMS禁止显示错误对话框，或者当前设备处于睡眠模式则不会让显示对话框</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span>res <span class="token operator">!=</span> null<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            res<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span>AppErrorDialog<span class="token punctuation">.</span>CANT_SHOW<span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token comment">// 4. 调用Dialog show方法显示crash对话框</span>
<span class="token keyword">if</span><span class="token punctuation">(</span>data<span class="token punctuation">.</span>proc<span class="token punctuation">.</span>crashDialog <span class="token operator">!=</span> null<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    data<span class="token punctuation">.</span>proc<span class="token punctuation">.</span>crashDialog<span class="token punctuation">.</span><span class="token function">show</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

}

注释1先对crash进程是否已经显示对话框做了判断，如果已经显示则无需显示。注释2处，手机没有息屏，AMS也允许显示crash对话框，则创建对话框，否则走注释3处，直接说明不显示。如果走到注释4则需要显示crash对话框，故直接调用Dialog的show()方法。这里对注释1和注释3处的res.set()方法做以解释，这res就是AppErrorResult,也就是在crashApplicationInner方法中创建的，该方法在请求AMS显示对话框时调用了result.get()使其阻塞，调用set方法后则会唤醒Binder调用线程，接着走下面代码，进而对结果进行判断。

看下AppErrorResult get()和set()的实现

frameworks/base/services/core/java/com/android/server/am/AppErrorResult.java

final class AppErrorResult {
    public void set(int res) {
        synchronized (this) {
            mHasResult = true;
            // 1. set方法设置mResult的值
            mResult = res;
            // 2.  调用notifyAll唤醒持有当前对象锁且处于阻塞状态的所有线程
            notifyAll();
        }
    }
<span class="token keyword">public</span> <span class="token keyword">int</span> <span class="token function">get</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">synchronized</span> <span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">while</span> <span class="token punctuation">(</span><span class="token operator">!</span>mHasResult<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">try</span> <span class="token punctuation">{</span>
                <span class="token comment">//3. 实质通过wait()使当前线程阻塞</span>
                <span class="token function">wait</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
            <span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">InterruptedException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
    <span class="token comment">// 4. 返回mResult</span>
    <span class="token keyword">return</span> mResult<span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token keyword">boolean</span> mHasResult <span class="token operator">=</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
<span class="token keyword">int</span> mResult<span class="token punctuation">;</span>

}

通过get()方法线程阻塞，通过set方法更新mResult的值并唤醒处于等待队列的线程，此时接着get()方法wait后面的代码执行，将set()方法中更新的mResult值作为返回值。

当错误对话框弹出后，用户操作或者超时时间到时又是怎样的？我们一起看下AppErrorDialog

frameworks/base/services/core/java/com/android/server/am/AppErrorDialog.java

@Override
public void onClick(View v) {
    // 1. 判断点击控件，来决定操作
    switch (v.getId()) {
        // 请求重启进程
        case com.android.internal.R.id.aerr_restart:
            mHandler.obtainMessage(RESTART).sendToTarget();
            break;
        // 请求反馈报错问题
        case com.android.internal.R.id.aerr_report:
            mHandler.obtainMessage(FORCE_QUIT_AND_REPORT).sendToTarget();
            break;
        // 请求关闭crash Dialog并杀死进程
        case com.android.internal.R.id.aerr_close:
            mHandler.obtainMessage(FORCE_QUIT).sendToTarget();
            break;
        // 请求不再提示对话框
        case com.android.internal.R.id.aerr_mute:
            mHandler.obtainMessage(MUTE).sendToTarget();
            break;
        default:
            break;
    }
}

// 2. 受到请求信息后调用setResult()方法并关闭对话框
private final Handler mHandler = new Handler() {
public void handleMessage(Message msg) {
setResult(msg.what);
dismiss();
}
};
private void setResult(int result) {
synchronized (mService) {
if (mProc != null && mProc.crashDialog == AppErrorDialog.this) {
mProc.crashDialog = null;
}
}
// 3. 调用AppErrorResult的set方法使阻塞线程运行，并将用户点击结果告知
mResult.set(result);

mHandler<span class="token punctuation">.</span><span class="token function">removeMessages</span><span class="token punctuation">(</span>TIMEOUT<span class="token punctuation">)</span><span class="token punctuation">;</span>

}

注释的步骤写的已经很清楚了，最终通过mResult.set()方法唤线程，是线程代码接着执行

frameworks/base/services/core/java/com/android/server/am/AppErrors.java

void crashApplicationInner(ProcessRecord r, ApplicationErrorReport.CrashInfo crashInfo,
        int callingPid, int callingUid) {
    ...
    // 3. 阻塞线程直至超时或者用户操作对话框
    int res = result.get();
    // 4. 判断用户操作结果，然后根据结果做不同处理
    ...
}

 
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后续清理工作

根据前面的流程，我们知道当进程crash后，最终将被kill掉，此时AMS还需要完成后续的清理工作。

我们先来回忆一下进程启动后，注册到AMS的部分流程

frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

// 进程启动后，对应的ActivityThread会attach到AMS上
private final boolean attachApplicationLocked(IApplicationThread thread,
            int pid) {
    ...
    final String processName = app.processName;
    try {
        // 1.  创建“讣告”接收者
        AppDeathRecipient adr = new AppDeathRecipient(
                app, pid, thread);
        thread.asBinder().linkToDeath(adr, 0);
        app.deathRecipient = adr;
    } 
    ...
}

 
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当进程注册到AMS时，AMS注册了一个“讣告”接收者注册到进程中。
因此，当crash进程被kill后，AppDeathRecipient中的binderDied方法将被回调。看源码知道bindDied()方法中又会调用到appDiedLocked()方法

frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

final void appDiedLocked(ProcessRecord app, int pid, IApplicationThread thread,
        boolean fromBinderDied) {
    ...
    // 1. 该进程没有杀死，则杀死进程
    if (!app.killed) {
        if (!fromBinderDied) {
            killProcessQuiet(pid);
        }
        killProcessGroup(app.uid, pid);
        app.killed = true;
    }
<span class="token keyword">if</span> <span class="token punctuation">(</span>app<span class="token punctuation">.</span>pid <span class="token operator">==</span> pid <span class="token operator">&amp;&amp;</span> app<span class="token punctuation">.</span>thread <span class="token operator">!=</span> null <span class="token operator">&amp;&amp;</span>
        app<span class="token punctuation">.</span>thread<span class="token punctuation">.</span><span class="token function">asBinder</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">==</span> thread<span class="token punctuation">.</span><span class="token function">asBinder</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
    <span class="token comment">// 2. </span>
    <span class="token function">handleAppDiedLocked</span><span class="token punctuation">(</span>app<span class="token punctuation">,</span> <span class="token boolean">false</span><span class="token punctuation">,</span> <span class="token boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">}</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>

}

注释1会将进程杀死，注释2处为app死亡的关键处理

frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

private final void handleAppDiedLocked(ProcessRecord app,
        boolean restarting, boolean allowRestart) {
    int pid = app.pid;
    // 1. 进行进程中service、ContentProvider、BroadcastReceiver等的收尾工作
    boolean kept = cleanUpApplicationRecordLocked(app, restarting, allowRestart, -1,
            false /*replacingPid*/);
    if (!kept && !restarting) {
        removeLruProcessLocked(app);
        if (pid > 0) {
            ProcessList.remove(pid);
        }
    }
<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token comment">// 2. 判断是否还存在可见的Activity</span>
<span class="token keyword">boolean</span> hasVisibleActivities <span class="token operator">=</span> mStackSupervisor<span class="token punctuation">.</span><span class="token function">handleAppDiedLocked</span><span class="token punctuation">(</span>app<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 清除activity列表</span>
app<span class="token punctuation">.</span>activities<span class="token punctuation">.</span><span class="token function">clear</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token keyword">try</span> <span class="token punctuation">{</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span>restarting <span class="token operator">&amp;&amp;</span> hasVisibleActivities
            <span class="token operator">&amp;&amp;</span> <span class="token operator">!</span>mStackSupervisor<span class="token punctuation">.</span><span class="token function">resumeFocusedStackTopActivityLocked</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token comment">// 3. 若当前crash进程中存在可视Activity，那么AMS还是会确保所有可见Activity正常运行，故会重启该进程</span>
        mStackSupervisor<span class="token punctuation">.</span><span class="token function">ensureActivitiesVisibleLocked</span><span class="token punctuation">(</span>null<span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">,</span> <span class="token operator">!</span>PRESERVE_WINDOWS<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span> <span class="token keyword">finally</span> <span class="token punctuation">{</span>
    mWindowManager<span class="token punctuation">.</span><span class="token function">continueSurfaceLayout</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

}

注释1比较重要的是对于crash进程中的Bounded Service而言，会清理掉service与客户端之间的联系，此外若service的客户端重要性过低，还会被直接kill掉。注释2处判断是否应用还存在可见的Activity，注释3处对于可见的Activity系统要保证其正常运行，还会重新启动进程。