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List:       linux-java
Subject:    Graphics.drawString)() bug ?
From:       Rob Nugent <r.nugent () unikix ! com>
Date:       1998-05-27 14:36:07
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Hi,

I am finding that I am getting exceptions when I have multiple threads
using the drawString() method
in the Graphics class. This is using RedHat Linux 5.0 and JDK 1.1.5v7
(libc5).

Take the following short testcase which creates 5 threads each of which
creates an off-screen image
and does drawString() calls.
--------------snip---------------------
import java.awt.*;

public class Draw implements Runnable
{
    private static Frame f;

    public static void main(String[] argv)
    {
 f = new Frame("Test Frame");

 f.setSize(300,30);
 f.setVisible(true);

 for (int i = 0; i < 4; i++)
 {
     Draw d = new Draw();
     Thread t = new Thread(d);
     t.setDaemon(true);
     t.start();
 }

    }

    public void run()
    {
 System.out.println("Starting");

 Image i = f.createImage(200,20);
 Graphics g = i.getGraphics();

 while (true)
 {
     g.drawString("0123456789",10,10);
 }

    }
}
--------------snip---------------------
After a little while of running, I get exceptions as follows:

java.lang.ArrayIndexOutOfBoundsException: 10
 at
 at sun.awt.motif.X11Graphics.drawMFChars(X11Graphics.java:249)
 at sun.awt.motif.X11Graphics.drawChars(X11Graphics.java:217)
 at sun.awt.motif.X11Graphics.drawString(X11Graphics.java:210)
 at Draw.run(Draw.java:33)
 at java.lang.Thread.run(Thread.java)

Note that it has walked off the end of the 10 char String.
It looks to me like something in sun.awt.motif isn't thread safe.

Does anyone have any comments ?
Might this be because libc5 isn't thread safe ? (I can't get the glibc
version to run properly, but the
errors do not occur on JDK1.1.6 on NT.
Can anyone confirm if this occurs or not on Solaris ?

Thanks !
Rob




--


Rob Nugent
Development Manager
UniKix Technologies Europe
r.nugent@unikix.com
Tel: +44 (0) 1489 585503
Fax: +44 (0) 1489 881363

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