CODEWITHSUNDEEP
javaconcurrencykotlin
user6513042
user6513042

Reputation:

Kotlin Synchronized

I've been studying java multi-thread on the last weeks. I learned about synchronized, and understood that synchronized avoid various threads access the same propertie at same time. I wrote this code to run two threads at the same thread.

val gate = CyclicBarrier(3)
val obj = SynchronizedCounter()

var nah = object : Thread() {
    override fun run() {
        gate.await()
        obj.increment()
    }
}

var blah = object : Thread() {
    override fun run() {
        gate.await()
        println(obj.value())
    }
}

nah.start()
blah.start()

gate.await()

class SynchronizedCounter {
    private var c = 0

    @Synchronized
    fun increment() {
        c++
    }

    @Synchronized
    fun decrement() {
        c--
    }

    @Synchronized
    fun value(): Int {
        return c
    }
}

Output: 0 Wouldn't return 1? Because the second thread is run after the one

Upvotes: 1

Views: 7815

Answers (1)

Les
Les

Reputation: 10605

Both nah and blah set up jobs to be run on a different thread than their own. So when they each call start, they are just flagging the thread scheduler to start them. start returns immediately and the current thread continues running the main line of code until something happens to make it defer. At that point, the scheduler does it's thing, running anything that is ready and waiting to run. You should not expect a particular order, nor should you try to predict an order. That is why you have synchronization constructs to use in your code.

You could run your tasks on a single threaded Executor like in this SO answer (for java though, you would have to adapt).

Upvotes: 2

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