How to synchronize 4 threads.

[jseidelREMOVECAPS]

I need to synchronize 4 different threads. I dont think wait() and
notifyall() will work.

Could someone explain how to do this?

Jerry

 

[Matt Humphrey]

I need to synchronize 4 different threads. I dont think wait() and
notifyall() will work.

wait () and notifyall are perfectly fine. Rather, you're really going to
have to explain what you mean by "synchronize"

Could someone explain how to do this?

Only after you tell us what you want it to do.

Jerry

Cheers,
Matt Humphrey (e-mail address removed) http://www.iviz.com/

 

[Robert]

Roger that. Need more info.

 

[Eric Sosman]

I need to synchronize 4 different threads. I dont think wait() and
notifyall() will work.

Could someone explain how to do this?

If by "synchronize" you mean you want each thread to
run until it reaches a certain point in its execution and
then pause there until the other three have reached their
corresponding points, try something like this:

public class Barrier {
private int count;

public Barrier(int count) {
if (count <= 0)
throw new IllegalArgumentException();
this.count = count;
}

synchronized
public void stall() {
if (count <= 0)
throw new IllegalStateException();
--count;
while (count > 0) {
try {
wait();
}
catch (InterruptedException ex) {
// who cares?
}
}
notifyAll();
}
}

If you mean something else, you'll need to explain it.

 

[jseidelREMOVECAPS]

I am running 4 and sometimes more threads. Each thread needs to
iterate through a Hashmap. And 3 threads add and remove from the
hashmap. I want to prevent a thread from iterating during an add or
remove operation. Do I need to run them one at a time? and if so,
how. Im fairly new to threads.

Thank you

Jerry

 

[Kevin McMurtrie]

I am running 4 and sometimes more threads. Each thread needs to
iterate through a Hashmap. And 3 threads add and remove from the
hashmap. I want to prevent a thread from iterating during an add or
remove operation. Do I need to run them one at a time? and if so,
how. Im fairly new to threads.

Thank you

Jerry

They should all synchronize on a common object, like the Hashmap itself,
during their operations on it. Only one thread will be able to enter
the synchronized block at a time.

If the computations are very long, like database lookups, synchronize on
the Hashmap while transferring batches of work data to/from it. You can
then perform lengthy processing on the local batch copy without holding
a lock on the shared Hashmap. You can also swap the Hashmap references
during a synchronization lock but you'll need to use some other object
for synchronization.

Also check out wait() and notify() while you're learning about threads.