Waking up by push notification

Question

Suppose:

There is some object (e.g., an array a) and a condition dependent on the object (e.g., such as a.empty?).
Some threads other than the current thread can manipulate the object (a), so the truthness of the evaluated value of the condition changes over the time.

How can I let the current thread sleep at some point in the code and continue (wake up) by push notification when the condition is satisfied?

I do not want to do polling like this:

...
sleep 1 until a.empty?
...

Perhaps using Fiber will be a clue.

Whatever the condition is, write a hook that is invoked any time your behavior is invoked. It can hold a collection of objects, perhaps threads or fibers, that can be processed at that time. This would be similar in fashion to perhaps [this project](https://github.com/kristinalim/ruby_hooks) — vgoff, Jul 14 '13 at 05:27

score 2 · Accepted Answer · edited Jul 14 '13 at 07:11

Maybe I do not quite understand your question, but I guess ConditionVariable is a good approach for such problem.

So, ConditionVariable can be used to signal threads when something happens. Let's see:

require 'thread'

a = [] # array a is empty now
mutex = Mutex.new
condvar = ConditionVariable.new 

Thread.new do
  mutex.synchronize do
    sleep(5)
    a << "Hey hey!"
    # Now we have value in array; it's time to signal about it
    condvar.signal
  end
end

mutex.synchronize do
  condvar.wait(mutex)
  # This happens only after 5 seconds, when condvar recieves signal
  puts "Hey. Array a is not empty now!"
end

Waking up by push notification

1 Answers1

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