reftest.kt

import java.lang.ref.ReferenceQueue
import java.lang.ref.WeakReference
import kotlin.concurrent.thread

class MyWeakReference<T>(val id: Int, p0: T, p1: ReferenceQueue<in T>?) : WeakReference<T>(p0, p1)

fun main() {
    val queue = ReferenceQueue<Object>()
    val upper = 10000000
    val set = (1..upper).toMutableSet()

    val t1 = thread {
        val a = ArrayList<MyWeakReference<Object>>()
        for (i in 1..upper) {
            a.add(MyWeakReference(i, Object(), queue))
        }
        println("gc 1")
        System.gc()
        println("clear")
        a.clear()
        println("gc 2")
        System.gc()
    }

    val t2 = thread {
        while (true) {
            val ref = queue.remove()
            val id = (ref as MyWeakReference).id
            synchronized(set) {
                set.remove(id)
            }
        }
    }

    val t3 = thread {
        while (true) {
            println(set.size)
            Thread.sleep(500)
        }
    }

    t1.join()
    t2.join()
    t3.join()
}