为什么只读一次循环读取logcat

Question

I run my service (write logcat to file) on any emulators and real devices from 2.3.3 to 4.1. All OK. On this devices generated right log:

--------- beginning of /dev/log/main
--------- beginning of /dev/log/system
I/ActivityManager( 3386): START {act=android.intent.action.MAIN cat=[android.intent.category.HOME] flg=0x10000000 cmp=com.android.launcher/com.androWAcivtMaae( 36:IvldakgNme W/ActivityManager( 3386): Duplcaefns eus orcitRod45c6 o.vnotsolet.tiiyilg
I/ActivityManager( 3386): Displayed com.android.calculator2/.Calculator: +9s374ms<br>
.....
.....

But when I run service on 4.1.2 (samsung (google) Nexus S (soju, crespo), SDK 16, flash 485486, build JZO54K) or 2.3.6, my service stoped after in logs.

On this devices generated wrong log:

--------- beginning of /dev/log/main

Only print one line and nothing.... Service stay in memory, but not work right...

This is my code

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
          package="com.my.logcatt"
          android:versionCode="1"
          android:versionName="0.5">
    <uses-sdk android:minSdkVersion="10" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
    <uses-permission android:name="android.permission.READ_LOGS" />
    <application android:theme="@android:style/Theme.NoTitleBar">
     <activity android:name=".ActivityMain" android:label="logcatt">
      <intent-filter>
       <action   android:name="android.intent.action.MAIN" />
       <category android:name="android.intent.category.LAUNCHER" />
       </intent-filter>
     </activity>
     <receiver android:name=".BroadcastBoot" android:enabled="true" android:exported="false">
      <intent-filter>
       <action android:name="android.intent.action.BOOT_COMPLETED" />
      </intent-filter>
     </receiver>
     <service android:name=".ServiceMain" android:enabled="true" />
    </application>
</manifest>

package com.my.logcatt;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;

public class ActivityMain extends Activity
 {
   @Override
   public void onCreate( Bundle savedInstanceState) 
    {
      super.onCreate( savedInstanceState);
      setContentView( R.layout.main);
      try { startService( new Intent( getApplicationContext(), ServiceMain.class)); }  catch( Exception e) {}
    } 
 }

package com.my.logcatt;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.InputStreamReader;

import android.app.Service;
import android.content.Intent;
import android.os.Environment;
import android.os.IBinder;


public class ServiceMain extends Service
 {
   public  static Process             procLogcatClean = null;
   public  static Process             procLogcatAM    = null;
   public  static BufferedReader      readerLogcat    = null;

   public static void fLog( String sLogMessage)
    {
      FileWriter     fileLog   = null;
      BufferedWriter bufferLog = null;
      try
        {
          fileLog = new FileWriter( Environment.getExternalStorageDirectory().getAbsolutePath() + "/123.log", true);
          if( fileLog != null)
            {
              bufferLog = new BufferedWriter( fileLog);
              bufferLog.write( sLogMessage + "\r\n");
              bufferLog.flush();
            }
        }
       catch( Exception e) {}
       finally 
        {
          if( bufferLog != null) { try { bufferLog.close(); } catch( Exception e) {} }
          if( fileLog   != null) { try { fileLog.close();   } catch( Exception e)   {} }
        }
    }

   @Override
   public void onCreate()
    {
      super.onCreate();
      startService();
    }

   @Override
   public IBinder onBind(Intent intent) 
    {
      return null;
    }

   @Override
   public void onDestroy()
    {
      super.onDestroy();
    }

   public void startService()
    {
      final Thread thread = new Thread()
       {
         public void run()
          {
            try
              {
                Runtime localRuntimeClear = Runtime.getRuntime();
                String[] sLogcatClear = new String[ 2];
                sLogcatClear[ 0] = "logcat";
                sLogcatClear[ 1] = "-c";
                procLogcatClean = localRuntimeClear.exec( sLogcatClear);
                procLogcatClean.waitFor();

                Runtime localRuntimeAM = Runtime.getRuntime();
                String[] sLogcatAM = new String[ 2];
                sLogcatAM[ 0] = "logcat";
                sLogcatAM[ 1] = "ActivityManager:I *:S";
                procLogcatAM = localRuntimeAM.exec( sLogcatAM);

                readerLogcat = new BufferedReader( new InputStreamReader( procLogcatAM.getInputStream()), 1024);

                String str = "";
                while( true)
                 {
                   str = "";
                   try
                     {
                       if( readerLogcat != null)
                         {
                           str = readerLogcat.readLine();
                           fLog( str);
                         }
                     }
                    catch( Exception e) {}

                   if( str.compareTo( "") == 0)  continue;
                 }
              }
             catch( Exception e) {}
             finally {}
           }
       };
      thread.setPriority( Thread.MAX_PRIORITY);
      thread.start();
   }
 }

What is wrong?

Answer 1

On 4.1.2., Only rooted and system applications can access logcat. If rooted, you could use "su logcat".

https://groups.google.com/forum/?fromgroups=#!topic/android-developers/6U4A5irWang

I suspect that you will find that this line throws an exception which you do not handle (bad practice btw - if you had a proper catch, you would have found this I think).

procLogcatAM = localRuntimeAM.exec( sLogcatAM);

Otherwise, check for the Android version and do something different or check for the permission refusal. Or, restrict your app to < 4.1.