Re: wait vs. yield?

Eric Sosman <esosman@ieee-dot-org.invalid>
Sat, 29 May 2010 15:42:35 -0400
On 5/29/2010 12:45 PM, Marcin Rodzik wrote:

I've looked at this: but still have some
doubts... I'm implementing a thread pool containing multiple threads,

     In other words, as Owen Jacobson points out, you're reinventing
the wheel. Why? Are you hoping to make it squarer?

The problem is how to perform the "wait" operation. For just poor
esthetic reasons I prefer using the Thread.yield() or eg.
Thread.sleep(500) method. But examples I found in the Internet tend to
use another object (let's say lock) and its Object.wait() method. This
causes that the Object.notify() method must be invoked after ordering
the job (the assignment).

My questions:
1) Which one of these two basic methods is better and, which is more
important for my, WHY?

     Object.wait() with Object.notify() or Object.notifyAll() is better.
The waiting thread, which can't do anything useful until other threads
have made progress, allows those other threads to use "all" the CPU
cycles and doesn't slow them down. Also, the waiting thread wakes up
"immediately" when there's something for it to do; it doesn't sit idle
while a silly timeout runs its course.

2) What is better: using sleep or yield in the first method?

     Thread.sleep() is better than Thread.yield(), because it gives
other threads a chance to use CPU cycles.

     Thread.yield() is better than Thread.sleep() because it "notices"
the change of state sooner.

     But you're asking whether Holofernes is better than Haman. Both
techniques are *vastly* inferior to wait(). And (again, read Owen
Jacobson's response) all this work has already been done for you, most
likely by someone with greater expertise than you possess at the moment.

Eric Sosman

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