CODEWITHSUNDEEP
multithreadingscalaqueueblockingqueue
Théo Winterhalter
Théo Winterhalter

Reputation: 5108

Scala blocking queue, making proper wait

I have to implement a blocking and synchronized queue in scala.

If I don't miss something, synchronizing is pretty simple, but for my queue to be blocking I could only think of that (which works) :

def pop() : T = {
    this.synchronized
    {
        _read()
        if(_out.isEmpty) throw new Empty()
        val ret = _out.head
        _out = _out.tail
        _length -= 1
        return ret
    }
}

def waitPop() : T =
{

    var ret : Option[T] = None

    // Possibly wait forever
    while(ret.isEmpty)
    {
        try { ret = Some(pop) }
        catch { case e : Empty => Thread.sleep(1000) }
    }

    ret.get
}

The problem here is Thread.sleep, it could compromise performance, couldn't it ? Of course, putting a lower value would mean consuming more of the CPU. Is there a way to wait properly ?

Thanks.

Upvotes: 2

Views: 1843

Answers (1)

Théo Winterhalter
Théo Winterhalter

Reputation: 5108

Thanks to Voo, I got what I needed :

def waitPop() : T =
{
    this.synchronized
    {
        while(isEmpty) wait

        pop
    }
}

While in push, I added notifyAll (still in a synchronized block). notify was also working, but with notifyAll the result appears less deterministic.

Thanks a lot !

Upvotes: 1

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