Computer scienceProgramming languagesKotlinConcurrency and parallelismParallelismSynchronization

Collections and thread-safety

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The code snippet below looks fine, but surprisingly, the list size is less than 200_000. Take a look at the code snippet and explain what's wrong.

import java.util.*
import kotlin.concurrent.thread

fun addNumbers(numbers: MutableList<Int>) {
    for (i in 0 until 100_000) numbers.add(i)
}

fun main() {
    val numbers: MutableList<Int> = Vector<Int>()
    val thread = thread(start = false, name = "Thread 1", block = {
        addNumbers(numbers)
    })

    thread.start()
    addNumbers(numbers)

    println(numbers.size) // 200_000
}

Select one option from the list

Vector is not thread-safe, need to use Stack instead

Vector is not thread-safe, need to use MutableList instead

thread.join() is missing, so the custom thread is not completed when the list size is printed

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