Re: notify() and wait()
Jack wrote:
My application is that: Thread1 wakes up every five hours to do a job;
Thread2 wakes up Thread1 if the application is to be shut down. So
Thread2 is mainly for preventing the program from hanging there.
So the code is like:
Static boolean conditionIsTrue = false;
//For Thread1:
while(conditionIsTrue)
{
doTheJob();
Synchronized(myObject)
{
myObject.wait(//for 5 hours);
}
}
//For Thread2:
shutDown()
{
conditionIsTrue = false;
Synchronized(myObject)
{
myObject.notify();
}
}
I note that you have ignored the requirement elucidated by Patricia
Shanahan, among others here:
You need to put the test for whether to wait inside the same
synchronized block as the wait, and the test for whether to notify
inside the same synchronized block as the notify. All code that can
affect those conditions needs to be synchronized on the same object.
That will cause grief.
Can java.util.concurrent solve my problem?
Yes, although there are other ways, of course. In this thread Tom
Anderson has shown at least one example of a java.util.concurrent
approach, using
<http://java.sun.com/javase/6/docs/api/java/util/concurrent/
CountDownLatch.html>
as you may have noticed.
Why don't you read through the Javadocs for the various
java.util.concurrent classes and packages and consider whether they'll
help you? It looks like there are several things there that could be
of use to you, depending on the subtleties of your requirements that
we cannot know.
Read and study /Java Concurrency in Practice/ by Brian Goetz, et al.
It explains 'wait()' and 'notify()' (including the need to test the
condition within the 'synchronized' block) and many of the concurrency
library structures, along with best practices for getting the most out
of them. Brian Goetz (one of the authors of the concurrency
libraries, btw) and others also write extensively on these matters in
IBM Developerworks and elsewhere.
--
Lew