Synchronisation: Using the class instance as monitor object

Observation

• Observe that Since we have synchronized the increment and decrement functions the result of the counter is always 0 no matter how many times we execute the program.
• This is because the increment and decrement are executed by two different threads in parallel but increment and decrement happen 3 times and the result should be 0 since we have synchronized.

Output

<---------------Start of execution--------------->

Incremented 1 by {Thread-0}
Decremented 0 by {Thread-1}
Incremented 1 by {Thread-0}
Decremented 0 by {Thread-1}
Decremented -1 by {Thread-1}
Incremented 0 by {Thread-0}

Result of the counter:-> 0

<---------------End of execution----------------->

Code

fun main(args: Array<String>) {

    println("<---------------Start of execution--------------->")
    println()

    val sharedResource = SharedResource()

    // Create a thread-1
    val runnable1 = Runnable {
        for (i in 1..3){
            sharedResource.increment()
            Thread.sleep(20)
        }
    }

    // Create a thread-2
    val runnable2 = Runnable {
        for(i in 1..3){
            sharedResource.decrement()
            Thread.sleep(20)
        }
    }

    val thread1 = Thread(runnable1)
    val thread2 = Thread(runnable2)

    thread1.start()
    thread2.start()

    thread1.join()
    thread2.join()

    println()
    println("Result of the counter:-> ${sharedResource.getResult()}")
    println()

    println("<---------------End of execution----------------->")

}



class SharedResource {

    private var counter = 0

    @Synchronized
    fun increment(){
        counter++
        println("Incremented $counter by {${Thread.currentThread().name}}")
    }

    @Synchronized
    fun decrement(){
        counter--
        println("Decremented $counter by {${Thread.currentThread().name}}")
    }

    @Synchronized
    fun getResult(): Int {
        return counter
    }

}