Re: Efficient CPU usage with recursively parallelizable problem

markspace <>
Sat, 17 Oct 2009 11:09:34 -0700
chucky wrote:

This isn't directly related to my original post, but I was wondering
if the implementation of thread pool needs some special compiler
support. I can't see in the java.lang.Thread API how to use the same
thread for execution of different tasks.

No, I don't think it does. Imagine a sub-class of of Thread that does
something like this:

class PoolThread extends Thread {

   volatile Runnable task;
   volatile boolean done = true;

   synchronized public void start() {
     for( ;; ) {
       while( task == null ) {
       done = false;
       try {;
       finally {
         done = true;

Now you have a Thread class that can be re-used. If "done" is true, you
can see if the thread is still running (if it is, no errors were
thrown). If the thread is running and the done flag is set, then we can
reuse the task, set it to a different task, and notifyAll() on the
thread to wake it up and cause it to execute the next task.

If the task throws an exception, then the thread will stop, but I think
that's required. Normally after your thread does throw an exception,
it's replaced, not reused.

There's probably a better way to indicate that a task is done other than
to require polling. I just made this example quickly to illustrate the

Oh, and I'm not sure at all that this is how the Executors are
implemented, I'm just saying no special compiler support is needed.

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