When first introduced, AsyncTasks were executed serially on a single background thread. Starting with DONUT, this was changed to a pool of threads allowing multiple tasks to operate in parallel. Starting with HONEYCOMB, tasks are executed on a single thread to avoid common application errors caused by parallel execution.
If you truly want parallel execution, you can invoke executeOnExecutor(java.util.concurrent.Executor, Object[]) with THREAD_POOL_EXECUTOR.
~ reference: AsyncTask | Android Developers
This example show how to execute multi AsyncTask at the same in parallel, by calling executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR) for (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB), in our StartAsyncTaskInParallel() method. The first three ProgressBars updated by AsyncTask execute in normal approach by calling execute(), the last two ProgressBar updated by AsyncTask execute in parallel.
MainActivity.java
package com.example.androidparallelasynctask;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ProgressBar;
import android.annotation.TargetApi;
import android.app.Activity;
import android.os.AsyncTask;
import android.os.Build;
import android.os.Bundle;
import android.os.SystemClock;
public class MainActivity extends Activity {
public class MyAsyncTask extends AsyncTask<Void, Integer, Void> {
ProgressBar myProgressBar;
public MyAsyncTask(ProgressBar target) {
myProgressBar = target;
}
@Override
protected Void doInBackground(Void... params) {
for(int i=0; i<100; i++){
publishProgress(i);
SystemClock.sleep(100);
}
return null;
}
@Override
protected void onProgressUpdate(Integer... values) {
myProgressBar.setProgress(values[0]);
}
}
Button buttonStart;
ProgressBar progressBar1, progressBar2, progressBar3, progressBar4, progressBar5;
MyAsyncTask asyncTask1, asyncTask2, asyncTask3, asyncTask4, asyncTask5;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
progressBar1 = (ProgressBar)findViewById(R.id.progressbar1);
progressBar2 = (ProgressBar)findViewById(R.id.progressbar2);
progressBar3 = (ProgressBar)findViewById(R.id.progressbar3);
progressBar4 = (ProgressBar)findViewById(R.id.progressbar4);
progressBar5 = (ProgressBar)findViewById(R.id.progressbar5);
buttonStart = (Button)findViewById(R.id.start);
buttonStart.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View v) {
asyncTask1 = new MyAsyncTask(progressBar1);
asyncTask1.execute();
asyncTask2 = new MyAsyncTask(progressBar2);
asyncTask2.execute();
asyncTask3 = new MyAsyncTask(progressBar3);
asyncTask3.execute();
asyncTask4 = new MyAsyncTask(progressBar4);
StartAsyncTaskInParallel(asyncTask4);
asyncTask5 = new MyAsyncTask(progressBar5);
StartAsyncTaskInParallel(asyncTask5);
}});
}
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
private void StartAsyncTaskInParallel(MyAsyncTask task) {
if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB)
task.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
else
task.execute();
}
}
activity_main.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:orientation="vertical"
tools:context="com.example.androidparallelasynctask.MainActivity" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:autoLink="web"
android:text="http://arteluzevida.blogspot.com/"
android:textStyle="bold" />
<Button
android:id="@+id/start"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Start"/>
<ProgressBar
android:id="@+id/progressbar1"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:max="100"
android:progress="0" />
<ProgressBar
android:id="@+id/progressbar2"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:max="100"
android:progress="0" />
<ProgressBar
android:id="@+id/progressbar3"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:max="100"
android:progress="0" />
<ProgressBar
android:id="@+id/progressbar4"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:max="100"
android:progress="0" />
<ProgressBar
android:id="@+id/progressbar5"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:max="100"
android:progress="0" />
</LinearLayout>
This video show how it run on devices running various Android version, include:
- Nexus 7 (1st generation), Android 4.4.2
- HTC One X, Android 4.2.2
- HTC Flyer, Android 3.2.1
- Nexus One, Android 2.3.6
Download the files.