CODEWITHSUNDEEP
rubyruby-on-rails-4
Sean
Sean

Reputation: 2577

Ruby Threads within Threads

I have a file that is threading like so:

Thread.new do
   # Do something
end.join

My question is about sub threads. I know the above Thread will join with the main thread and the main thread will "wait" for this Thread to complete before it terminates the main thread.

However, how does this life cycle work in something like this example:

Thread.new do
    # Do Something

    Thread.new do
        # Do something else
    end.join
end.join

Does the inner thread join to the parent thread or does it join to the main thread? Does the outer thread "wait" on the inner thread and the main thread "wait" on the main thread?

Thanks again!

Upvotes: 1

Views: 681

Answers (1)

Amadan
Amadan

Reputation: 198466

I know the above Thread will join with the main thread and the main thread will "wait" for this Thread to complete before it terminates the main thread.

It only does it because you said .join. Ruby doesn't wait for threads; any threads unjoined by the time the program terminates are killed.

Does the inner thread join to the parent thread or does it join to the main thread?

It does exactly what it is told to do: the outer thread says "launch a thread, then join it, then end". The main thread will wait for all that to complete because it, too, was told to .join the outer thread.

main  -launch-----------------------join
outer        \---launch-----join---/
inner                  \---/

Here's an example where the opposite happens - again, only because I explicitly told it to do so:

inner = nil
outer = Thread.new do
    inner = Thread.new do
        sleep(3)
        p "Inner done"
    end

    sleep(2)
    p "Outer done"
end

sleep(1)
inner.join
p "Inner joined"
outer.join
p "Outer joined"

main  -launch----------------join---join
outer        \---launch-----/------/
inner                  \---/

Upvotes: 1

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