If I have the mouse focused on a container (in this case, a Frame) which contains
a TextField, the TextField seems to busywait for X input events, consuming 50%
of CPU time in the process.

An interesting symptom of this is that the cursor only blinks if the TextField's
container notices an input event.

A rather odd effect of this is that I can make my applications consume less CPU
time by continuously wiggling the mouse.
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I'm adding this user's description of this problem because it includes a good code example and a very accurate description.
 
Category: AWT

Priority: CRITICAL! (Low/Medium/High/Critical)

JDK version: JDK-1_0-solaris2-sparc.tar.Z

Platforms: Solaris2.4, SPARCStation20


Synopsis
--------

Motif textfield blocks repainting while it has the focus


Description
-----------

This bug occurs on Motif.

Click inside a textfield. Notice that the text cursor should be
blinking, but is not. As you move the mouse, the text cursor will
start to blink erratically.

Repaints appear to be blocked while a textfield has the focus. When
the mouse is moved, the queued up repaints will then be unblocked.
When the mouse stops moving again, repainting once again becomes
blocked.


Test Case
---------

- Compile and run textfield.java:

javac textfield.java
java textfield

- The button has the focus. Notice the label updating every second.

- Click on the textfield. Notice that the label does not update anymore,
  nor is the textfield cursor blinking.

- Move the mouse about. The label starts to update again, and the textfield
  cursor begins to blink.

- Stop moving the mouse. The label doesn't update, and the textfield cursor
  doesn't blink.

- Click on the button. The textfield no longer has focus, so the label
  continues to update.


Workaround
----------

Calling setText on a label will cause pending repaints to be
unblocked. The call to setText must contain a new value for the
label, otherwise the label won't update.
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X-Sun-Data-Name: textfield.java
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import java.awt.*;

class CanvasLabel extends Canvas {
  private String text;

  public CanvasLabel (String text) {
    this.text = text;
  }

  public void setText(String text) {
    this.text = text;
    repaint();
  }

  public Dimension minimumSize() {
    int w, h;
    FontMetrics fm = getFontMetrics(getFont());
    w = fm.stringWidth(text);
    h = fm.getHeight();
    return new Dimension(w, h);
  }

  public Dimension preferredSize() {
    return minimumSize();
  }

  public void paint(Graphics g) {
    int x, y;

    Dimension d = size();
    FontMetrics fm = getFontMetrics(getFont());

    x = (d.width - fm.stringWidth(text))/2;
    y = d.height - 3;

    g.setFont(getFont());
    g.setColor(getForeground());
    g.drawString(text, x, y);
  }
}

public class textfield extends Frame {
  public static void main(String argv[]) {
    new textfield();
  }

  public textfield() {
    Button button = new Button("Button");
    TextField textfield = new TextField("TextField");
    CanvasLabel label = new CanvasLabel("0");

    add("North", button);
    add("Center", textfield);
    add("South", label);

    show();
    resize(preferredSize());
    validate();

    for (int i=0; ; i++) {
      label.setText(Integer.toString(i));
      try { Thread.sleep(1000); } catch (Exception ex) {}
    }
  }
}