MemoryTest.kt

package com.memorytest

import platform.Foundation.NSProcessInfo
import kotlin.native.internal.GC
import kotlin.test.Test

// Test case displaying apparent memory leak in macOS. Watch process memory usage in
// Activity Monitor (sort by PID descending to view it at the top when test is run).
// Usage should increase over 25 second period and never go down even after GC collect.
//
// NOTE: This test does not assert anything so it's not a valid test case, it is used
//       only to demonstrate that the GC does not seem to be disposing of some NSObjects
//       appropriately. I can give the timer class a single instance of NSProcessInfo
//       that it reuses for each call to elapsedRealtime, but the problem would still
//       exist that the NSObjects are not being deallocated properly whenever they are
//       used elsewhere
class MemoryTest {

    @Test
    fun `test memory leak`() {
        println("testing memory leak")
        val timer = Timer()

        val startTime = timer.elapsedRealtime()
        var currentTime = startTime
        
        // Run loop for 25 seconds to build up lots of NSProcessInfo allocations
        while (currentTime - startTime < 25_000L) {
            currentTime = timer.elapsedRealtime()
        }

        GC.start()
        GC.collect()
        println("GC collected")
    }

    @Test
    fun `endless loop`() {
        println("looping forever (check memory usage)")
        while (true) {}
    }
}

class Timer {
    fun elapsedRealtime() = (NSProcessInfo().systemUptime * MILLISECONDS_PER_SECOND).toLong()

    companion object {
        private const val MILLISECONDS_PER_SECOND = 1000
    }
}