Selfish Threads

• Threads should occasionally sleep or yeild, to give other threads a chance to run.
• sleep(int millis) makes a thread sleep for the specified number of milliseconds.  This gives a good opportunity for lower priority threads to run, since this thread can't run for that time.
• yeild() simply allows the operating system to pick a thread to run, including the thread that is yeilding.  Thus, if the highest priority thread yeilds, there is a good chance that it will be selected to run again, and other threads still will not have a chance to run.
• If a thread does not sleep or yeild, it is considered selfish.
• Let's take the sleep() call out of our previous program and see what happens when we try to run additional threads.
• This is not 100% predictable from system to system, since we know that operating systems tend to handle threads in different ways.
• The only code change was commenting out Thread.sleep(20); and changing the call in public static void main(String args[]).  Instead of re-posting the code, I'll allow you to do that on your own.
• As we see in the screen capture below, there is much less mingling of the threads.  A block of priority #2 runs, then #4, then #6.  It continues in that manner throughout the JList, with most threads running in solid blocks.

 

Created by:  Brandan Jones December 17, 2001