android multithreading: thread.join() does not work as expected

Question

I have trouble using thread.join in my code below. It should wait for the thread to finish before executing the codes after it, right? It was behaving differently on different occasions.

I have three cases to check if my code goes well

• App is used for the first time - works as expected but the loading page don't appear while downloading
• App is used the second time (db is up to date) - works okay
• App is used the third time (db is outdated, must update) - won't update, screen blacks out, then crashes

I think I have problems with this code on onCreate method:

dropOldSchedule();
dropThread.join();
triggerDownload();

Based on the logs, the code works until before this part... What can be the problem?

---

MainActivity.java

public class MainActivity extends Activity {

final static int INDEX_ACCTTYPE = 0; 
final static int INDEX_ECN = 1; 
final static int INDEX_TLN = 2; 
final static int INDEX_SIN = 3; 
final static int INDEX_MOBILE = 4; 
final static int INDEX_CITY = 5;
final static int INDEX_START_DATE = 6;
final static int INDEX_START_TIME = 7;
final static int INDEX_END_DATE = 8; 
final static int INDEX_END_TIME = 9; 
final static int INDEX_REASON = 10;
final static int INDEX_DETAILS = 11;

DatabaseHandler db;
String str;
ProgressDialog pd;

TextView homeText1, homeText2, homeText3, homeText4;

final private String csvFile = "http://www.meralco.com.ph/pdf/pms/pms_test.csv";
final private String uploadDateFile = "http://www.meralco.com.ph/pdf/pms/UploadDate_test.txt";

Thread dropThread = new Thread(new Runnable() {

    public void run() {
        db = new DatabaseHandler(MainActivity.this);
        db.dropOldSchedule(); 

        runOnUiThread(new Runnable() {
            public void run() {
                while (!pd.isShowing());
                db.close();
                pd.dismiss();
            }
        });
    }

});
Thread getUploadDateThread = new Thread(new Runnable() {

    public void run() {

        try {
            URL myURL = new URL(uploadDateFile);

            BufferedReader so = new BufferedReader(new InputStreamReader(myURL.openStream()));
            while (true) {
                String output = so.readLine();
                if (output != null) {
                    str = output;
                }
                else {
                    break;
                }
            }
        so.close();
        }
        catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } 

        runOnUiThread(new Runnable() {
            public void run() {
                while (!pd.isShowing());
                pd.dismiss();
            }
        });
    }

    });
Thread downloadThread = new Thread(new Runnable() {

    public void run() {

        db = new DatabaseHandler(MainActivity.this);
        db.beginTransaction();

        try {
            URL url = new URL(csvFile);

            Log.i("dl", "start");

            InputStream input = url.openStream();
            CSVReader reader = new CSVReader(new InputStreamReader(input));
            Log.i("dl", "after reading");

            String [] sched;
            while ((sched = reader.readNext()) != null) {
                if(sched[INDEX_CITY].equals("")) sched[INDEX_CITY]="OTHERS";
                try {

                    db.addRow(sched[INDEX_SIN], sched[INDEX_CITY], 
                            sched[INDEX_START_DATE], sched[INDEX_START_TIME], 
                            sched[INDEX_END_DATE], sched[INDEX_END_TIME], 
                            sched[INDEX_DETAILS], sched[INDEX_REASON]);
                } catch (IndexOutOfBoundsException e) {
                    db.addRow(sched[INDEX_SIN], sched[INDEX_CITY], 
                            sched[INDEX_START_DATE], sched[INDEX_START_TIME], 
                            sched[INDEX_END_DATE], sched[INDEX_END_TIME], 
                            "", sched[INDEX_REASON]);
                    //e.printStackTrace();
                }
            }
            input.close();
            Log.i("dl", "finished");

        } catch (MalformedURLException e) {
            e.printStackTrace();
            db.endTransaction();
        } catch (IOException e) {
            e.printStackTrace();
            db.endTransaction();
        } 
        Log.d("Count", ""+db.count());
        db.setTransactionSuccessful();
        db.endTransaction();

        writeUploadDateInTextFile();

    }

});

@SuppressWarnings("unqualified-field-access")
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.pms_main);

    Button home = (Button) findViewById(R.id.home);
    home.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            Intent intent = new Intent(MainActivity.this, MeralcoSuite_TabletActivity.class);
            intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
            startActivity(intent);

            finish();
        }
    });

    homeText1 = (TextView) findViewById(R.id.home_text1);
    homeText2 = (TextView) findViewById(R.id.home_text2);
    homeText3 = (TextView) findViewById(R.id.home_text3);
    homeText4 = (TextView) findViewById(R.id.home_text4);

    homeText1.setVisibility(View.INVISIBLE);
    homeText2.setVisibility(View.INVISIBLE);
    homeText3.setVisibility(View.INVISIBLE);
    homeText4.setVisibility(View.INVISIBLE);

    getUploadDate();
    try {
        getUploadDateThread.join();     //wait for upload date

        Log.d("getUploadDate","thread died, upload date=" + str);

        if(dbExists()){
            db = new DatabaseHandler(MainActivity.this);
            Log.d("Count", "" + db.count());
            db.close();

            if(!uploadDateEqualsDateInFile()){
                dropOldSchedule();
                    dropThread.join();
                triggerDownload();
            }
            showDisclaimer();
            Log.i("oncreate", "finished!");
            return;
        }

        triggerDownload();
        showDisclaimer();
        Log.i("oncreate", "finished!");

    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

public void dropOldSchedule(){

    if(pd!=null && pd.isShowing())
        pd.setTitle("Getting upload date...");
    else
        pd = ProgressDialog.show(this, "Getting upload date", 
            "This may take a few minutes...", true, false);


    dropThread.start();
}
public void triggerDownload() {

    if (!checkInternet()) {
        showAlert("An internet connection is required to perform an update, please check that you are connected to the internet");
        return;
    }

    if(pd!=null && pd.isShowing())
        pd.setTitle("Getting upload date...");
    else
        pd = ProgressDialog.show(this, "Getting upload date", 
            "This may take a few minutes...", true, false);

    downloadThread.start();

}

public void getUploadDate() {

    Log.d("getUploadDate", "getting upload date of schedule");

    if(pd!=null && pd.isShowing())
        pd.setTitle("Getting upload date...");
    else
        pd = ProgressDialog.show(this, "Getting upload date", 
            "This may take a few minutes...", true, false);


    getUploadDateThread.start();

}

public void writeUploadDateInTextFile() {
    Log.d("writeUploadDateTextFile", "writing:"+str);

    try {
        OutputStreamWriter out = new OutputStreamWriter(openFileOutput(
                "update.txt", 0));
        out.write(str);
        out.close();
    } catch (java.io.IOException e) {
        e.printStackTrace();
    }
}

public void showDisclaimer() {
    Log.d("ShowDisclaimer", "showing disclaimer");

    homeText3
    .setText("..." + str
            + "...");


    homeText1.setVisibility(View.VISIBLE);
    homeText2.setVisibility(View.VISIBLE);
    homeText3.setVisibility(View.VISIBLE);
    homeText4.setVisibility(View.VISIBLE);

    Log.d("showDisclaimer", "finished showing disclaimer");

}

public boolean uploadDateEqualsDateInFile() {
    Log.d("uploadDateEqualsDateInFile","comparing schedule upload dates");

    try {
            String recordedDate = "";
            InputStream instream = openFileInput("update.txt");
            if (instream != null) { // if file the available for reading
                Log.d("uploadDateEqualsDateInFile","update.txt found!");

                InputStreamReader inputreader = new InputStreamReader(instream);
                BufferedReader buffreader = new BufferedReader(inputreader);

                String line = null;
                while ((line = buffreader.readLine()) != null) {
                    recordedDate = line;
                    Log.d("uploadDateEqualsDateInFile","recorded:"+recordedDate);
                }

                Log.d("uploadDateEqualsDateInFile","last upload date: " + str + ", recorded:" +recordedDate);

                if(str.equals(recordedDate)) return true;
                return false;
            }
            Log.d("uploadDateEqualsDateInFile","update.txt is null!");
            return false;   

    } catch (FileNotFoundException e) {
        e.printStackTrace();
        return false;
    } catch (IOException e) {
        e.printStackTrace();
        return false;
    }
}

public boolean checkInternet() {
    ConnectivityManager cm = (ConnectivityManager) this
            .getSystemService(Context.CONNECTIVITY_SERVICE);

    NetworkInfo infos[] = cm.getAllNetworkInfo();

    for (NetworkInfo info : infos)
        if (info.getState() == NetworkInfo.State.CONNECTED
                || info.getState() == NetworkInfo.State.CONNECTING) {
            return true;
        }

    return false;
}

public boolean dbExists() {

    File database=getApplicationContext().getDatabasePath(DatabaseHandler.DATABASE_NAME);

    if (!database.exists()) {
        Log.i("Database", "Not Found");
        return false;
    }

    Log.i("Database", "Found");
    return true;

}

@Override
protected void onDestroy() {
    super.onDestroy();
    if (db != null) {
        db.close();
    }
}
@Override
protected void onPause() {
    super.onPause();
    if (db != null) {
        db.close();
    }
}

}

Answer 1

I think the problem that your facing is that you are blocking the UI thread when you call join in the onCreate() method. You should move this code into another thread which should execute in the background and once its done you can update the UI.

Here is a sample code:

    final Thread t1 = new Thread();
    final Thread t2 = new Thread();
    t1.start();
    t2.start();
    new Thread(new Runnable() {

        @Override
        public void run() {
            // Perform all your thread joins here.
            try {
                t1.join();
                t2.join();
            } catch (Exception e) {
                // TODO: handle exception
            }


            // This thread wont move forward unless all your threads
            // mentioned above are executed or timed out.
            // ------ Update UI using this method
            runOnUiThread(new Runnable() {

                @Override
                public void run() {
                    // Update UI code goes here

                }
            });

        }
    }).start();

Answer 2

It was already mentioned that AsyncTask is the better alternative. However, it may be the case, that your call to join will throw InterruptedException. Try to use it like this:

while(getUploadDateThread.isRunning()){
    try{
        getUploadDateThread.join();
    } catch (InterruptedException ie){}
}
// code after join

Answer 3

Sorry but I couldn't find mistakes or problems in your code. But I would strongly recommend you to use AsyncTask for doing something in different thread. AsyncTask is very easy to use and I would say that it is one of the biggest advantages of java. I really miss it in obj-c.

http://labs.makemachine.net/2010/05/android-asynctask-example/

http://marakana.com/s/video_tutorial_android_application_development_asynctask_preferences_and_options_menu,257/index.html

check those links hope that will help you.