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Commit b1923442 authored by Narayan Kamath's avatar Narayan Kamath
Browse files

MathUtils: Remove static Random field. 

This is unsafe because the random will be seeded in the zygote, which
means all processes on the system generate the same sequence of random
numbers. Fortunately, this code is only used in tests, so get rid of it.

Note that the Random that backs Math.random() is reseeded after every
fork to avoid a similar issue.

Bug: 35918685
Test: HwAccelerationTest
Change-Id: Ice79aa25bb9017f7a0b91659afe04112850cb74b
parent 07be4d67

core/java/android/util/MathUtils.java

+0 −23
Original line number Diff line number Diff line
@@ -24,7 +24,6 @@ import java.util.Random; 
 * @hide Pending API council approval

 */

public final class MathUtils {

    private static final Random sRandom = new Random();

    private static final float DEG_TO_RAD = 3.1415926f / 180.0f;

    private static final float RAD_TO_DEG = 180.0f / 3.1415926f;
@@ -185,28 +184,6 @@ public final class MathUtils { 
        return maxStart + (maxStart - maxStop) * ((value - minStart) / (minStop - minStart));

    }



    public static int random(int howbig) {

        return (int) (sRandom.nextFloat() * howbig);

    }



    public static int random(int howsmall, int howbig) {

        if (howsmall >= howbig) return howsmall;

        return (int) (sRandom.nextFloat() * (howbig - howsmall) + howsmall);

    }



    public static float random(float howbig) {

        return sRandom.nextFloat() * howbig;

    }



    public static float random(float howsmall, float howbig) {

        if (howsmall >= howbig) return howsmall;

        return sRandom.nextFloat() * (howbig - howsmall) + howsmall;

    }



    public static void randomSeed(long seed) {

        sRandom.setSeed(seed);

    }



    /**

     * Returns the sum of the two parameters, or throws an exception if the resulting sum would

     * cause an overflow or underflow.

tests/HwAccelerationTest/src/com/android/test/hwui/PathDestructionActivity.java

+11 −7
Original line number Diff line number Diff line
@@ -25,6 +25,8 @@ import android.os.Bundle; 
import android.util.MathUtils;

import android.view.View;



import java.util.Random;



/**

 * The point of this test is to ensure that we can cause many paths to be created, drawn,

 * and destroyed without causing hangs or crashes. This tests the native reference counting
@@ -57,10 +59,11 @@ public class PathDestructionActivity extends Activity { 


        private Path getRandomPath() {

            float left, top, right, bottom;

            left = MathUtils.random(getWidth() - MIN_SIZE);

            top = MathUtils.random(getHeight() - MIN_SIZE);

            right = left + MathUtils.random(getWidth() - left);

            bottom = top + MathUtils.random(getHeight() - top);

            Random r = new Random();

            left = r.nextFloat() * (getWidth() - MIN_SIZE);

            top = r.nextFloat() * (getHeight() - MIN_SIZE);

            right = left + r.nextFloat() * (getWidth() - left);

            bottom = top + r.nextFloat() * (getHeight() - top);

            Path path = new Path();

            path.moveTo(left, top);

            path.lineTo(right, top);
@@ -71,9 +74,10 @@ public class PathDestructionActivity extends Activity { 
        }



        private int getRandomColor() {

            int red = MathUtils.random(255);

            int green = MathUtils.random(255);

            int blue = MathUtils.random(255);

            Random r = new Random();

            int red = r.nextInt(255);

            int green = r.nextInt(255);

            int blue = r.nextInt(255);

            return 0xff000000 | red << 16 | green << 8 | blue;

        }