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javamultithreadingconcurrency
Eric Wilson
Eric Wilson

Reputation: 59405

How can you test if a thread is the only remaining thread in Java?

I want a thread in a Java program to loop until all other threads die, and then end the loop. How can I know when my loop thread is the only thread remaining?

In my situation, the loop thread will have no reference to any other threads, so I don't think isAlive() helps me.

Upvotes: 4

Views: 385

Answers (5)

Victor Grazi
Victor Grazi

Reputation: 16520

You can hack something together by using a ThreadFactory and just be sure to register all threads in a WeakHashMap.

Iterate through the map to see which threads are alive.

Another possible approach - use a ThreadJMXBean?

Upvotes: 0

Thorbjørn Ravn Andersen
Thorbjørn Ravn Andersen

Reputation: 75426

Is using Executors and invokeAll an option? I.e. can you implement your functionality as Callables?

Then it is trivially simple to do.

Upvotes: 0

John Meagher
John Meagher

Reputation: 24778

ThreadGroup has the methods you need. It will be easiest if you can create all the threads in the same ThreadGroup, but that's not really necessary. Thread.currentThread().getThreadGroup() will get you started. The enumerate methods on ThreadGroup are how you can get the list of all the threads.

Upvotes: 1

Zed
Zed

Reputation: 57678

This might or might not help, depending on your use-case.

Set your loop thread to daemon mode

setDaemon(true);

and Java will kill it for you if all the non-daemon threads are gone.

Upvotes: 11

James
James

Reputation: 82136

Would this not be a situation where you would consider the Thread Pool Pattern?

If not, would it not be better to maintain a list of active threads, removing each as they are destroyed?

Upvotes: 3

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