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Android* Tutorial: Writing a Multithreaded Application using Intel® Threading Building Blocks

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18 Sep 2014CPOL3 min read 9.9K   7  
In a recently posted stable release of Intel Threading Building Blocks (Intel® TBB), we have added experimental support for Android applications; i.e., building Intel TBB libraries for use in Android applications via the JNI interface.

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Introduction

Recently we posted the "Windows* 8 Tutorial: Writing a Multithreaded Application for the Windows Store* using Intel® Threading Building Blocks". There we stated that the parallel calculation engine can be ported easily to other mobile or desktop platforms. Android is a good example of such a mobile platform.

In a recently posted stable release of Intel Threading Building Blocks (Intel® TBB), we have added experimental support for Android applications; i.e., building Intel TBB libraries for use in Android applications via the JNI interface. You can download this release from threadingbuildingblocks.org.

To start the process on a Linux* host, unpack the Intel TBB source distribution, source the <unpacked_dir>/build/android_setup.csh script, and build the libraries. Building the libraries is necessary because development releases are distributed in source form only. The <unpacked_dir>/build/index.android.html file contains instructions to configure the environment and build the library on Linux.

Assuming that gnu make 3.81 is available in the %PATH% (on a Microsoft Windows* host platform) and $PATH (on a Linux host) we need to issue the following command in the NDK environment to build the Intel TBB libraries for Android:

gmake tbb tbbmalloc target=android

That’s all that is needed for the library build; we can now move to build the example using Eclipse*. For the example below, I’ll use Android SDK Tools Rev.21 and Android NDK Rev 8C on Windows* to illustrate the process of cross-platform development.

Create a new project using a default template «New Android Application». For simplicity, we name it "app1", the same as in the previous post:

Image 1

Select FullscreenActivity as the Activity. That’s it for the template. Please note that com.example* is not an acceptable package naming for Google Play* but it is good enough for our example.

Then add a couple of buttons to the main frame. After adding these, the XML file of the main frame (app1/res/layout/activity_fullscreen.xml) will look like this:

XML
<FrameLayout 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:background="#0099cc"

    tools:context=".FullscreenActivity" >

    <TextView

        android:id="@+id/fullscreen_content"

        android:layout_width="match_parent"

        android:layout_height="match_parent"

        android:gravity="center"

        android:keepScreenOn="true"

        android:text="@string/dummy_content"

        android:textColor="#33b5e5"

        android:textSize="50sp"

        android:textStyle="bold" />

    <FrameLayout

        android:layout_width="match_parent"

        android:layout_height="match_parent"

        android:fitsSystemWindows="true" >

        <LinearLayout

            android:id="@+id/fullscreen_content_controls"

            style="?buttonBarStyle"

            android:layout_width="match_parent"

            android:layout_height="74dp"

            android:layout_gravity="bottom|center_horizontal"

            android:background="@color/black_overlay"

            android:orientation="horizontal"

            tools:ignore="UselessParent" >

            <Button

                android:id="@+id/dummy_button1"

                style="?buttonBarButtonStyle"

                android:layout_width="0dp"

                android:layout_height="wrap_content"

                android:layout_weight="1"

                android:text="@string/dummy_button1"

                android:onClick="onClickSR" />

            <Button

                android:id="@+id/dummy_button2"

                style="?buttonBarButtonStyle"

                android:layout_width="0dp"

                android:layout_height="wrap_content"

                android:layout_weight="1"

                android:text="@string/dummy_button2"

                android:onClick="onClickDR" />

        </LinearLayout>

    </FrameLayout>

</FrameLayout>

And the string file (app1/res/values/strings.xml) will look like

XML
<?xml version="1.0" encoding="utf-8"?>

<resources>

    <string name="app_name">Sample</string>

    <string name="dummy_content">Reduce sample</string>

    <string name="dummy_button1">Simple Reduce</string>

    <string name="dummy_button2">Deterministic Reduce</string>

</resources>

Then add buttons handlers:

// JNI functions

private native float onClickDRCall();

private native float onClickSRCall();

 

      public void onClickDR(View myView) {

            TextView tv=(TextView)(this.findViewById(R.id.fullscreen_content));

            float res=onClickDRCall();

            tv.setText("Result DR is n" + res);

      }

 

      public void onClickSR(View myView) {

            TextView tv=(TextView)(this.findViewById(R.id.fullscreen_content));

            float res=onClickSRCall();

            tv.setText("Result SR is n" + res);

      }

and library loads to the FullscreenActivity.java file:

       @Override

      protected void onCreate(Bundle savedInstanceState) {

            super.onCreate(savedInstanceState);

&hellip;

            System.loadLibrary("gnustl_shared");

            System.loadLibrary("tbb");

            System.loadLibrary("jni-engine");       

      }

In the case of the "tbb" library everything should be clear, and the "gnustl_shared" library is required to support the C++ language features of TBB. However, for the "jni-engine" library we need to go into more details.

"jni-engine" is a С++ library that implements a calculation engine and exports C-interfaces for JNI calls named onClickSRCall() and onClickSRCall().

According to NDK development rules, create folder "jni" inside the workspace and create 3 files there specific for our "jni-engine" library.

These files are:

Android.mk

(text in <> brackets there is something that should be replaced with actual values)

C++
LOCAL_PATH := $(call my-dir)

TBB_PATH := <path_to_the_package>

 

include $(CLEAR_VARS)

LOCAL_MODULE    := jni-engine

LOCAL_SRC_FILES := jni-engine.cpp 

LOCAL_CFLAGS += -DTBB_USE_GCC_BUILTINS -std=c++11 -I$(TBB_PATH)/include

LOCAL_LDLIBS := -ltbb -L./ -L$(TBB_PATH)/<path_to_libtbb_so>

include $(BUILD_SHARED_LIBRARY)

 

include $(CLEAR_VARS)

LOCAL_MODULE    := libtbb

LOCAL_SRC_FILES := libtbb.so

include $(PREBUILT_SHARED_LIBRARY)

Application.mk

C++
APP_ABI := x86

APP_GNUSTL_FORCE_CPP_FEATURES := exceptions rtti

APP_STL := gnustl_shared

jni-engine.cpp

C++
 #include <jni.h>

#include "tbb/parallel_reduce.h"

#include "tbb/blocked_range.h"

float SR_Click()

{

    int N=10000000;

    float fr = 1.0f/(float)N;

    float sum = tbb::parallel_reduce(

        tbb::blocked_range<int>(0,N), 0.0f,

        [=](const tbb::blocked_range<int>& r, float sum)->float 

        {

            for( int i=r.begin(); i!=r.end(); ++i )

                sum += fr;

            return sum;

        },

        []( float x, float y )->float 

        {

            return x+y;

        }

    );

    return sum;   

}

 

float DR_Click()

{

    int N=10000000;

    float fr = 1.0f/(float)N;

    float sum = tbb::parallel_deterministic_reduce(

        tbb::blocked_range<int>(0,N), 0.0f,

        [=](const tbb::blocked_range<int>& r, float sum)->float 

        {

            for( int i=r.begin(); i!=r.end(); ++i )

                sum += fr;

            return sum;

        },

        []( float x, float y )->float 

        {

            return x+y;

        }

    );      

    return sum;   

}

 

 extern "C" JNIEXPORT jfloat JNICALL Java_com_example_app1_FullscreenActivity_onClickDRCall(JNIEnv *env, jobject obj)

{

    return DR_Click();

}

 

extern "C" JNIEXPORT jfloat JNICALL Java_com_example_app1_FullscreenActivity_onClickSRCall(JNIEnv *env, jobject obj)

{

    return SR_Click();

}

We use the same algorithms that we used in the previous blog.

When we use the NDK to build, it compiles libraries to the required folders including our libraries libjni-engine.so, libgnustl_shared.so and libtbb.so.

Next, switch back to Eclipse and build the app1.apk file. Now the application is ready to install on AVD or actual hardware. On AVD it looks like

Image 2

That’s it! This simple application is ready and should be a good start towards writing a more complex parallel application for Android. And for those who used code from the previous blog, the application was successfully ported to Android.

* Other names and brands may be claimed as the property of others.

Related Articles and Resources

To learn more about Intel tools for the Android developer, visit Intel® Developer Zone for Android.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


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