Frame Impact of Extra Statements

JVM Tutorials - Herong's Tutorial Examples

∟Frame Impact of Extra Statements

This section provides a tutorial example on how to compare the frame size of two similar recursive call methods in two threads. Extra 16 bytes are needed in the frame for an extra statement in the method.

From the previous tutorial, we learned that the frame size for calling a pretty empty method is 32 bytes. In this tutorial, we will try to see the impact on the frame size when additional statements are added to the method.

Here is the first thread, StackThread1.java, that contains an almost empty recursive method:

/* StackThread1.java
 * Copyright (c) 2014, HerongYang.com, All Rights Reserved.
 */
import java.util.*;
class StackThread1 extends Thread {
   public long n;
   public void run() {
      try {
         sub();
      } catch (StackOverflowError e) {
         System.out.println("Maximum calls in Thread 1: "+n
            +" at "+System.currentTimeMillis());
      }
   }
   private void sub() {
      n++;
      sub();
   }
}

Here is the second thread, StackThread2.java, that contains a similar recursive method with one extra statement:

/* StackThread2.java
 * Copyright (c) 2014, HerongYang.com, All Rights Reserved.
 */
import java.util.*;
class StackThread2 extends Thread {
   public long n;
   public double x;
   public void run() {
      try {
         sub();
      } catch (StackOverflowError e) {
         System.out.println("Maximum calls in Thread 2: "+n
            +" at "+System.currentTimeMillis());      }
   }
   private void sub() {
      n++;
      x = Math.sin(System.currentTimeMillis());
      sub();
   }
}

The following program will run both threads as the same time to compare how many frame each thread can create:

/* StackFrameSizeTest.java
 * Copyright (c) 2014, HerongYang.com, All Rights Reserved.
 */
class StackFrameSizeTest {
   public static void main(String[] a) {
      StackThread1 t1 = new StackThread1();
      t1.start();
      StackThread2 t2 = new StackThread2();
      t2.start();
   }
}

The first test run shows that everything is working as expected:

C:\herong>\progra~1\Java\jdk1.8.0\bin\javac StackFrameSizeTest.java

C:\>\progra~1\Java\jdk1.8.0\bin\java -Xss128k StackFrameSizeTest
Maximum calls in Thread 1: 2558 at 1397254338535
Maximum calls in Thread 2: 2215 at 1397254338540

Comparing with the first thread, the second thread:

Fills its stack with 343 less frames. So its frames are larger.
Takes 5 milliseconds longer to complete 343 less method calls. So it took more time to execute the recursive method.

With more tests using different -Xss values, we should be able estimate the frame size of the sub() in both threads:

 -Xss  Thread 1  Thread 2  Thread 1  Thread 2
Stack    Frames    Frames     Frame     Frame
 Size                          Size      Size
 128k      2558      2215     51.24     59.17
 256k      5755      4984     45.55     52.60
 512k     14862     10408     35.28     50.37
   1m     30419     21339     34.47     49.14
  64m   2094643   1397600     32.04     48.02
 128m   4191644   2795731     32.02     48.01

Clearly, the frame size of thread 2 is 16 bytes larger than thread 1. This means that the "x = Math.sin(System.currentTimeMillis());" statement requires extra 16 bytes in the current frame.

This also tells us that frames created for different methods have different sizes.

Last update: 2014.

Table of Contents

About This Book

Downloading and Installing JDK 1.8.0 on Windows

Downloading and Installing JDK 1.7.0 on Windows

java.lang.Runtime Class - The JVM Instance

java.lang.System Class - The Operating System

ClassLoader Class - Class Loaders

Class Class - Class Reflections

Sun's JVM - Java HotSpot VM

JRockit JVM 28.2.7 by Oracle Corporation