Anr questions often asked in Android interviews

1.ANR Definition

Android The main thread of the application has been blocked for too long , Trigger "Application not Responding"(Anr) Error of . If the application is in the foreground , There will be pop ups .

2.ANR What happened

1. Time consuming operation of main line
2. The main thread is synchronously locked by the sub thread lock
3. The main thread is binder End to end blocking
4.binder Threads are stained
5. No system resources available

3.ANR Several types of

1.Service TimeOut Overtime
Reason for timeout :
In the implementation of the service life cycle approach :oncreate ,onstart onbind It's time-out
Timeout time : Front desk service 20s, Background services 200s
2.BroadCast TimeOut Broadcast timeout
Reason for timeout :
At the appointed time ,onReceive Method execution timed out
Timeout time : The front desk 10s, backstage 60s
3.InputDispatching Timeout
Input event timeout , If you click , No response to touch event
Timeout time :5s

ServiceTimeout Trigger mechanism

bumpServiceExecutingLocked(); Bury a bomb , The corresponding life cycle is not completed within the corresponding time , will anr, If it is finished, it will removemsg
send out

 void scheduleServiceTimeoutLocked(ProcessRecord proc) {
        if (proc.executingServices.size() == 0 || proc.thread == null) {
            return;
        }
        Message msg = mAm.mHandler.obtainMessage(
                ActivityManagerService.SERVICE_TIMEOUT_MSG);
        msg.obj = proc;
        mAm.mHandler.sendMessageDelayed(msg,
                proc.execServicesFg ? SERVICE_TIMEOUT : SERVICE_BACKGROUND_TIMEOUT);
    }

Handle SERVICE_TIMEOUT_MSG news

com.android.server.am.ActivityManagerService#SERVICE_TIMEOUT_MSG
  case SERVICE_TIMEOUT_MSG: {
                mServices.serviceTimeout((ProcessRecord)msg.obj);
            } break;

// The first scene in the log :Timeout executing service
Slog.w(TAG, "Timeout executing service: " + timeout);
StringWriter sw = new StringWriter();
PrintWriter pw = new FastPrintWriter(sw, false, 1024);
pw.println(timeout);
timeout.dump(pw, "    ");
pw.close();
mLastAnrDump = sw.toString();
mAm.mHandler.removeCallbacks(mLastAnrDumpClearer);
mAm.mHandler.postDelayed(mLastAnrDumpClearer, LAST_ANR_LIFETIME_DURATION_MSECS);
 anrMessage = "executing service " + timeout.shortInstanceName;

BroadCast Timeout Trigger mechanism :

The broadcast is divided into : Serial , parallel
The broadcast that caused the timeout is Serial radio broadcast :
Orderly broadcasting of dynamic registration
Static registration broadcast

2.ANR Positioning process

1. adopt logcat see ANR in see cpu Information and system load
apk Package name , Process number , Trigger ANR Why , The system is happening ANR For each application of the time period cpu usage
Such as input Overtime ,ANR According to the timeout , Push forward 5s, Use application is not responding Filter , Filter monkey journal

2. find anr Of log journal , Check the main thread main Of trace Log information
/data/anr
3. Location occurrence ANR Specific time period
4. Check ANR The state of the system during the occurrence period

3. avoid ANR Methods : Reduce the time-consuming operation of the main thread

1.ServiceTimeout
avoid application oncreate Time consuming
avoid service The life cycle takes time
have access to IntentService
2.BroadCastTimeout
have access to IntentService
3.InputDispatching Timeout
Avoid time-consuming main threads

4. Reasonable performance optimization can also avoid

1. avoid while or ondraw in new object
2. Use object pool Android.util.Pools
3. Check for extra background pictures , Especially the background picture of the parent layout
4. Reduce layout levels :constrainlayout,merge
5. Delay loading layout viewstub

4.ANR Detection tools

blockcanary
strictmode
leakcanary