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Calculation of pi with Intel® Threading Building Blocks

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7 Apr 2015CPOL4 min read 9.4K  
Intel has developed a valuable tool for developing parallel applications called Intel® Threading Building Blocks (Intel® TBB).

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Many Android* devices have processors with more than one core and knowing how to develop multithreaded applications has become important in the mobile industry. Intel has developed a valuable tool for developing parallel applications called Intel® Threading Building Blocks (Intel® TBB). The Intel® TBB is a cross-platform library of templates for creating parallel programs. It creates and synchronizes streams of data, hiding the details of the architecture and allowing you to work at a higher level of abstraction. Intel® TBB works on all architectures. For Android, use version 4.3 and above.

Build Intel® TBB

  1. Download TBB. You can download Intel® TBB here: https://www.threadingbuildingblocks.org/. I downloaded the sources of the last stable release (4.3 Update 1).
  2. Add NDK to PATH:

    For Windows*:
    • $ SET PATH=%PATH%;
    For Linux*:
    • $ export PATH=$PATH:

  3. Unzip TBB and go to the directory with source code and in src folder. $ cd /src/
  4. Run TBB for Android: $ /ndk-build –C /src/ arch=intel64 compiler=gcc target=android clean tbb tbbmalloc –j This command builds TBB for Android 64 bit. For building TBB for Android 32 bit, change arch=intel64 on arch=ia32. It will build the application for Android 64 bit architecture.
  5. The library is built. In build directory (/build/) you can find directories with libs: libgnustl_shared.so, libtbbmalloc_proxy.so, libtbbmalloc.so and libtbb.so. libtbb.so and libgnustl_shared. so we will use in our application.

Calculate π

To calculate π you can choose any formula with a definite integral from Wikipedia: https://en.wikipedia.org/wiki/List_of_formulae_involving_%CF%80#Integrals. I chose this formula:

Image 1

For this program I modified the formula:For this program I modified the formula: For this program I modified the formula:

Image 2

For integral calculating I used the rectangle method. The integrated function is divided into N = 107 equal subintervals of length h = 2·10-7. The approximation to the integral is then calculated by adding up the areas (base multiplied by height) of the N rectangles, giving the formula:

Image 3

Create Application

To create a new Android application:

Image 4

Create Main Activity

In the res/layout/activity_main.xml paste the following code:

xm
<RelativeLayout 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"
    tools:context="intel.example.pitbbcalc.MainActivity" >

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:orientation="vertical" >

        <TextView
            android:id="@+id/title"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/title"
            android:textAppearance="?android:attr/textAppearanceLarge" />

        <Button
            android:id="@+id/startButton"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/start" />

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content" >

            <TextView
                android:id="@+id/pi_equally"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@string/pi_equally"
                android:textAppearance="?android:attr/textAppearanceLarge" />

            <TextView
                android:id="@+id/pi_val"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:textAppearance="?android:attr/textAppearanceLarge" />
        </LinearLayout>

    </LinearLayout>

</RelativeLayout>

In the res/values/strings.xml add this code:

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

    <string name="app_name">PiTBBCalc</string>
    <string name="action_settings">Settings</string>
    <string name="start">Start</string>
    <string name="title">Calculation of π</string>
    <string name="pi_equally">π = </string>

</resources>

Now the main activity looks like this:

Image 5

Next we need to implement the Java* interface for our activity. In the src/intel.example.pitbbcalc/MainActivity.java file, add the following code:

Java
package intel.example.pitbbcalc;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends Activity {

	private native double onClickCalc();
	private TextView piEqually;
	private TextView piVal;
	
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		
		Button startButton = (Button) findViewById(R.id.startButton);
		piEqually = (TextView) findViewById(R.id.pi_equally);
		piVal = (TextView) findViewById(R.id.pi_val);
		piEqually.setVisibility(View.INVISIBLE);
		piVal.setVisibility(View.INVISIBLE);
		
		startButton.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				double val = onClickCalc();
				piVal.setText(String.valueOf(val));
				piEqually.setVisibility(View.VISIBLE);
				piVal.setVisibility(View.VISIBLE);
			}
		});
		
		System.loadLibrary("PiTBBCalc");
		System.loadLibrary("tbb");
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

	@Override
	public boolean onOptionsItemSelected(MenuItem item) {
		// Handle action bar item clicks here. The action bar will
		// automatically handle clicks on the Home/Up button, so long
		// as you specify a parent activity in AndroidManifest.xml.
		int id = item.getItemId();
		if (id == R.id.action_settings) {
			return true;
		}
		return super.onOptionsItemSelected(item);
	}
}

We can add native support by right-clicking on our project in Project Explorer -> Android Tools -> Add Native Support.

On the next window enter the name of the lib of our project and click Finish.

Image 6

Now we have to implement native code for integral calculating in one thread. In the jni/PiTBBCalc.cpp file, add the following code:

C++
#include <jni.h>
#include <math.h>

double piIntFunc (const double x)
{
	return sqrt(1 - pow(x, 2.0));
}

double calcPi()
{
	const unsigned int n = pow(10.0, 7);
	double a(-1), b(1);
	double h = (b - a) / n;
	double x (a);

	for (unsigned int i (0); i < n; ++i)
	{
		sum += piIntFunc(x);
		x += h;
	}

	sum *= h;

	return 2 * sum;
}

extern "C"
JNIEXPORT jdouble JNICALL Java_intel_example_pitbbcalc_MainActivity_onClickCalc(JNIEnv *env,
		jobject obj)
{
	return calcPi();
}

Let’s try running our application and π calculation in single threaded mode.

Image 7

To add parallel implementation with Intel® TBB to our project we should edit jni/Android.mk. Android.mk is the Makefile for our project, and we need to add the Intel® TBB libs to it:

LOCAL_PATH := $(call my-dir)
TBB_PATH := <tbb_sources>
TBB_BUILD_PATH := /build/linux_intel64_gcc_android_cc4.9_NDKr10b_version_android-L_release

include $(CLEAR_VARS)

LOCAL_MODULE    := PiTBBCalc
LOCAL_SRC_FILES := PiTBBCalc.cpp
LOCAL_CFLAGS += -DTBB_USE_GCC_BUILTINS -std=c++11 -fexceptions -Wdeprecated-declarations -I$(TBB_PATH)/include -I$(TBB_PATH)$(TBB_BUILD_PATH)
LOCAL_LDLIBS := -llog -ltbb -L./ -L$(TBB_PATH)$(TBB_BUILD_PATH)
LOCAL_SHARED_LIBRARIES += libtbb

include $(BUILD_SHARED_LIBRARY)

include $(CLEAR_VARS)
LOCAL_MODULE    := libtbb
LOCAL_SRC_FILES := $(TBB_PATH)$(TBB_BUILD_PATH)/libtbb.so
include $(PREBUILT_SHARED_LIBRARY)

In the jni/ directory, create an Application.mk file and add the following lines:

APP_ABI := x86_64 APP_GNUSTL_FORCE_CPP_FEATURES := exceptions rtti APP_STL := gnustl_shared

The purpose of Application.mk is to describe which native modules (i.e., static/shared libraries) are needed by your application. In the line APP_ABI := x86_64 we specify our target architecture.

Now we can try to run our application. If you see the main screen of the application, then Intel® TBB linked successfully and we can start developing our app.

For adding parallelism to the code, we should include the Intel® TBB header: #include "tbb/tbb.h", remove the cycle and add the following code:

C++
double sum = tbb::parallel_reduce(
		tbb::blocked_range<unsigned int>(0,n),
		double(0), // identity element for summation
		[&](const tbb::blocked_range<unsigned int>& r, double sum)->double {
			for( int i=r.begin(); i!=r.end(); ++i )
			{
				sum += piIntFunc(x);
				x += h;
			}
			return sum; // body returns updated value of accumulator
		},
		[]( double x, double y )->double {
			return x+y; // joins two accumulated values
		}
	);

And now, if you run the application it will work in multithreaded mode.

Summary

As you can see, developing parallel applications is very easy. By using the calculation of π as an example we were able to successfully demonstrate how to apply the concepts here from single-threaded code to multithreaded code.

Additional Resources

License

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