Summary

The java.awt.Robot.delay(int) method is under-specified and has surprising behavior. The method is re-specified to clearly specify how it behaves with thread interruption and the side effect of printing a stack trace is removed.

Problem

• If the delay method is invoked with the interrupt status set, or a thread blocked in delay is interrupted, then it clears the interrupt status, prints a stack trace, and completes without waiting the specified time.
• Due to the method being synchronized, if several threads invoke delay on the same Robot instance then they will queue up and delay sequentially.

Solution

• Do not print the stack trace to stderr
• Re-assert the "interrupt" flag if the thread was interrupted
• Remove the synchronization to avoid queueing
• Clarify the spec on what happens if the thread is interrupted

Specification

src/java.desktop/share/classes/java/awt/Robot.java

     /**
      * Sleeps for the specified time.
-     * To catch any {@code InterruptedException}s that occur,
-     * {@code Thread.sleep()} may be used instead.
+     * <p>
+     * If the invoking thread is interrupted while waiting, then it will
+     * return immediately with the interrupt status set. This method
+     * does nothing if invoked with the interrupt status set.
      *........
      *........
      */
-    public synchronized void delay(int ms) {
+    public void delay(int ms) {