Android database app constantly "starts / waits for gc alloc lock"

Question

I looked specifically at the addButtonClicked () method and DBHandler itself. I can’t understand why the program basically gets stuck in an infinite loop when I try to add something to the database. Every time I run it and try to add something to the database, it just freezes and sends this message again and again.

Error:

10-27 20:34:50.303 2849-2849/? I/art: Not late-enabling -Xcheck:jni (already on) 10-27 20:34:50.303 2849-2849/? I/art: Late-enabling JIT 10-27 20:34:50.312 2849-2849/? I/art: JIT created with code_cache_capacity=2MB compile_threshold=1000 10-27 20:34:50.408 2849-2849/com.example.test.assignment W/System: ClassLoader referenced unknown path: /data/app/com.example.test.assignment-2/lib/x86 10-27 20:34:50.966 2849-2860/com.example.test.assignment W/art: Suspending all threads took: 6.223ms 10-27 20:34:51.033 2849-2860/com.example.test.assignment I/art: Background partial concurrent mark sweep GC freed 423(15KB) AllocSpace objects, 418(7MB) LOS objects, 38% free, 6MB/10MB, paused 6.686ms total 54.772ms 10-27 20:34:51.577 2849-2860/com.example.test.assignment W/art: Suspending all threads took: 6.097ms 10-27 20:34:51.816 2849-2860/com.example.test.assignment I/art: WaitForGcToComplete blocked for 11.994ms for cause Background 10-27 20:34:52.017 2849-2860/com.example.test.assignment W/art: Suspending all threads took: 9.393ms 10-27 20:34:52.023 2849-2860/com.example.test.assignment I/art: Background sticky concurrent mark sweep GC freed 845(30KB) AllocSpace objects, 843(41MB) LOS objects, 76% free, 1233KB/5MB, paused 10.623ms total 31.789ms 10-27 20:34:52.132 2849-2860/com.example.test.assignment I/art: Background partial concurrent mark sweep GC freed 752(27KB) AllocSpace objects, 747(37MB) LOS objects, 15% free, 21MB/25MB, paused 20.980ms total 40.058ms 10-27 20:34:53.000 2849-2849/com.example.test.assignment I/art: Waiting for a blocking GC Alloc 10-27 20:34:53.001 2849-2849/com.example.test.assignment I/art: Starting a blocking GC Alloc 10-27 20:34:53.123 2849-2849/com.example.test.assignment I/art: Waiting for a blocking GC Alloc 10-27 20:34:53.126 2849-2849/com.example.test.assignment I/art: Starting a blocking GC Alloc 10-27 20:34:53.195 2849-2849/com.example.test.assignment I/art: Waiting for a blocking GC Alloc 10-27 20:34:53.205 2849-2849/com.example.test.assignment I/art: WaitForGcToComplete blocked for 10.178ms for cause Alloc 

It just keeps working over and over, and printSelectedDatabase () never starts because it does not appear in the text view.

Primary activity:

 import android.os.Bundle; import android.support.v7.app.AppCompatActivity; import android.view.View; import android.widget.EditText; import android.widget.TextView; public class MainActivity extends AppCompatActivity { EditText dataInput; TextView showText; DBHandler dbHandler; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); dataInput = (EditText) findViewById(R.id.dataInput); showText = (TextView) findViewById(R.id.showText); dbHandler = new DBHandler(this, null, null, 1); printSelectedDatabase(); } public void addButtonClicked(View view){ Animals animal = new Animals(dataInput.getText().toString()); dbHandler.addAnimal(animal); printSelectedDatabase(); } public void deleteButtonClicked(View view){ String string = dataInput.getText().toString(); dbHandler.deleteAnimal(string); printSelectedDatabase(); } public void printSelectedDatabase(){ String string = dbHandler.printDatabase(); showText.setText(string); dataInput.setText(""); } } 

Setter / Getters:

 public class Animals { private int _id; private String _animalName; public Animals(){ } public Animals(String animalName) { this._animalName = animalName; } public void set_id(int _id) { this._id = _id; } public void set_animalname(String _animalName) { this._animalName = _animalName; } public int get_id() { return _id; } public String get_animalName() { return _animalName; } } 

DBHandler:

 import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; import android.database.Cursor; import android.content.Context; import android.content.ContentValues; public class DBHandler extends SQLiteOpenHelper { private static final int DATABASE_VERSION = 1; private static final String DATABASE_NAME = "animals.db"; public static final String TABLE_ANIMALS = "animals"; public static final String COLUMN_ID = "_id"; public static final String COLUMN_ANIMALS = "animalName"; public DBHandler(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) { super(context, DATABASE_NAME, factory, DATABASE_VERSION); } @Override public void onCreate(SQLiteDatabase db) { String query = "CREATE TABLE " + TABLE_ANIMALS + "(" + COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + COLUMN_ANIMALS + " TEXT " + ");"; db.execSQL(query); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { db.execSQL("DROP TABLE IF EXISTS " + TABLE_ANIMALS); onCreate(db); } //Add Animal public void addAnimal(Animals animal){ ContentValues values = new ContentValues(); values.put(COLUMN_ANIMALS, animal.get_animalName()); SQLiteDatabase db = getWritableDatabase(); db.insert(TABLE_ANIMALS, null, values); db.close(); } //Delete Animal public void deleteAnimal(String animalName){ SQLiteDatabase db = getWritableDatabase(); db.execSQL("DELETE FROM " + TABLE_ANIMALS + " WHERE " + COLUMN_ANIMALS + "=\"" + animalName + "\";"); } //Print Animals public String printDatabase(){ String string = ""; SQLiteDatabase db = getWritableDatabase(); String query = "SELECT * FROM " + TABLE_ANIMALS + " WHERE 1"; Cursor cursor = db.rawQuery(query, null); cursor.moveToFirst(); while(!cursor.isAfterLast()){ if(cursor.getString(cursor.getColumnIndex("animalName"))!=null){ string += cursor.getString(cursor.getColumnIndex("animalName")); string += "\n"; } } db.close(); return string; } } 

Answer 1

I found out in case someone encounters this specific error. In my DBHandler, I was missing a jump to the next line inside the while statement.

Original:

  while(!cursor.isAfterLast()){ if(cursor.getString(cursor.getColumnIndex("animalName"))!=null){ string += cursor.getString(cursor.getColumnIndex("animalName")); string += "\n"; } } 

Must be:

 while(!cursor.isAfterLast()){ if(cursor.getString(cursor.getColumnIndex("animalName"))!=null){ string += cursor.getString(cursor.getColumnIndex("animalName")); string += "\n"; } cursor.moveToNext(); } 

Answer 2

Just add your answer. Instead:

 while(!cursor.isAfterLast()){ // do stuff with cursor cursor.moveToNext(); } 

your code will be more concise:

 while (cursor.moveToNext()) { // do stuff with cursor } 

When you execute a query, the cursor object is positioned BEFORE the first record. Calling cursor.moveToNext() moves to the next position AND returns true if there is actually an entry to go to and false otherwise.

Also, avoid calling cursor.getColumnIndex("columnName") from the loop. You better cache the column index in the int variable and reference that variable inside the loop.

 int animalNameColumn = cursor.getColumnIndex("animalName"); while (cursor.moveToNext()) { if(cursor.getString(animalNameColumn)!=null){ string += cursor.getString(animalNameColumn); string += "\n"; } }