Add racing version of each Lazy test

Run several concurrent accesses to a lazy value
many times and validate invariants.

libraries/stdlib/test/utils/LazyJVMTest.kt

@@ -4,13 +4,14 @@ package test.utils
 
 import kotlin.*
 import kotlin.test.*
-import java.util.concurrent.ConcurrentHashMap
-import java.util.concurrent.atomic.AtomicInteger
 import kotlin.concurrent.thread
 import test.io.serializeAndDeserialize
 import java.util.*
 import java.util.concurrent.ConcurrentLinkedQueue
+import java.util.concurrent.ConcurrentHashMap
+import java.util.concurrent.CyclicBarrier
 import java.util.concurrent.atomic.AtomicBoolean
+import java.util.concurrent.atomic.AtomicInteger
 
 class LazyJVMTest {
 
@@ -18,17 +19,28 @@ class LazyJVMTest {
         val counter = AtomicInteger(0)
         val lazy = lazy {
             val value = counter.incrementAndGet()
-            Thread.sleep(80)
+            Thread.sleep(16)
             value
         }
 
-        val accessThreads = List(3) { thread(start = false) { lazy.value } }
-        accessThreads.forEach { it.start() }
+        val threads = 3
+        val barrier = CyclicBarrier(threads)
+        val accessThreads = List(threads) { thread { barrier.await(); lazy.value } }
         accessThreads.forEach { it.join() }
 
         assertEquals(1, counter.get())
     }
 
+    @Test fun synchronizedLazyRace() {
+        racyTest(initialize = {
+                    val counter = AtomicInteger(0)
+                    lazy { counter.incrementAndGet() }
+                 },
+                 access = { lazy, _ -> lazy.value },
+                 validate = { result -> result.all { it == 1 } }
+        )
+    }
+
     @Test fun externallySynchronizedLazy() {
         val counter = AtomicInteger(0)
         var initialized: Boolean = false
@@ -38,7 +50,7 @@ class LazyJVMTest {
         val initializer = {
             val value = counter.incrementAndGet()
             runs += (value to initialized)
-            Thread.sleep(50)
+            Thread.sleep(16)
             initialized = true
             value
         }
@@ -55,26 +67,45 @@ class LazyJVMTest {
         }
     }
 
+    @Test fun externallySynchronizedLazyRace() {
+        val threads = 3
+        racyTest(threads,
+                 initialize = {
+                     val counter = AtomicInteger(0)
+                     var initialized = false
+                     val initializer = {
+                         (counter.incrementAndGet() to initialized).also {
+                             initialized = true
+                         }
+                     }
+                     val lock = Any()
+
+                     List(threads) { lazy(lock, initializer) }
+                 },
+                 access = { lazies, runnerIndex -> lazies[runnerIndex].value },
+                 validate = { result -> result.all { (id, initialized) -> initialized == (id != 1)} })
+    }
+
     @Test fun publishOnceLazy() {
         val counter = AtomicInteger(0)
         val initialized = AtomicBoolean(false)
         val threads = 3
         val values = Random().let { r -> List(threads) { 50 + r.nextInt(50) } }
-        data class Run(val id: Int, val value: Int, val initialized: Boolean)
+        data class Run(val value: Int, val initialized: Boolean)
         val runs = ConcurrentLinkedQueue<Run>()
 
         val initializer = {
             val id = counter.getAndIncrement()
             val value = values[id]
-            runs += Run(id, value, initialized.get())
+            runs += Run(value, initialized.get())
             Thread.sleep(value.toLong())
             initialized.set(true)
             value
         }
         val lazy = lazy(LazyThreadSafetyMode.PUBLICATION, initializer)
 
-        val accessThreads = List(threads) { thread(start = false) { lazy.value } }
-        accessThreads.forEach { it.start() }
+        val barrier = CyclicBarrier(threads)
+        val accessThreads = List(threads) { thread { barrier.await(); lazy.value } }
         val result = run { while (!lazy.isInitialized()) /* wait */; lazy.value }
         accessThreads.forEach { it.join() }
 
@@ -86,6 +117,12 @@ class LazyJVMTest {
         }
     }
 
+    @Test fun publishOnceLazyRace() {
+        racyTest(initialize = { lazy(LazyThreadSafetyMode.PUBLICATION) { Thread.currentThread().id } },
+                 access = { lazy, _ -> lazy.value },
+                 validate = { result -> result.all { v -> v == result[0] } } )
+    }
+
     @Test fun lazyInitializationForcedOnSerialization() {
         for(mode in listOf(LazyThreadSafetyMode.SYNCHRONIZED, LazyThreadSafetyMode.PUBLICATION, LazyThreadSafetyMode.NONE)) {
             val lazy = lazy(mode) { "initialized" }
@@ -96,4 +133,38 @@ class LazyJVMTest {
             assertEquals(lazy.value, lazy2.value)
         }
     }
+
+    private fun <TState : Any, TResult> racyTest(
+            threads: Int = 3, runs: Int = 5000,
+            initialize: () -> TState,
+            access: (TState, runnerIndex: Int) -> TResult,
+            validate: (List<TResult>) -> Boolean) {
+
+        val runResult = java.util.Collections.synchronizedList(mutableListOf<TResult>())
+        val invalidResults = mutableListOf<Pair<Int, List<TResult>>>()
+        lateinit var state: TState
+
+        var runId = -1
+        val barrier = CyclicBarrier(threads) {
+            if (runId >= 0) {
+                if (!validate(runResult))
+                    invalidResults.add(runId to runResult.toList())
+                runResult.clear()
+            }
+            state = initialize()
+            runId += 1
+        }
+
+        val runners = List(threads) { index -> thread {
+            barrier.await()
+            repeat(runs) {
+                runResult += access(state, index)
+                barrier.await()
+            }
+        }}
+
+        runners.forEach { it.join() }
+
+        assertTrue(invalidResults.isEmpty(), invalidResults.joinToString("\n") { (index, result) -> "At run #$index: $result" })
+    }
 }