[K/N] Catch concurrent modifications of HashMap

As a part of efforts to stabilize Native stdlib.

libraries/stdlib/jvm/src/kotlin/collections/builders/MapBuilder.kt

@@ -25,6 +25,18 @@ internal class MapBuilder<K, V> private constructor(
 ) : MutableMap<K, V>, Serializable {
     private var hashShift: Int = computeShift(hashSize)
 
+    /**
+     * The number of times this map is structurally modified.
+     *
+     * A modification is considered to be structural if it changes the map size,
+     * or otherwise changes it in a way that iterations in progress may return incorrect results.
+     *
+     * This value can be used by iterators of the [keys], [values] and [entries] views
+     * to provide fail-fast behavoir when a concurrent modification is detected during iteration.
+     * [ConcurrentModificationException] will be thrown in this case.
+     */
+    private var modCount: Int = 0
+
     override var size: Int = 0
         private set
 
@@ -112,6 +124,7 @@ internal class MapBuilder<K, V> private constructor(
         valuesArray?.resetRange(0, length)
         size = 0
         length = 0
+        registerModification()
     }
 
     override val keys: MutableSet<K> get() {
@@ -176,6 +189,10 @@ internal class MapBuilder<K, V> private constructor(
     internal val capacity: Int get() = keysArray.size
     private val hashSize: Int get() = hashArray.size
 
+    private fun registerModification() {
+        modCount += 1
+    }
+
     internal fun checkIsMutable() {
         if (isReadOnly) throw UnsupportedOperationException()
     }
@@ -237,6 +254,7 @@ internal class MapBuilder<K, V> private constructor(
     }
 
     private fun rehash(newHashSize: Int) {
+        registerModification()
         if (length > size) compact()
         if (newHashSize != hashSize) {
             hashArray = IntArray(newHashSize)
@@ -308,6 +326,7 @@ internal class MapBuilder<K, V> private constructor(
                     presenceArray[putIndex] = hash
                     hashArray[hash] = putIndex + 1
                     size++
+                    registerModification()
                     if (probeDistance > maxProbeDistance) maxProbeDistance = probeDistance
                     return putIndex
                 }
@@ -336,6 +355,7 @@ internal class MapBuilder<K, V> private constructor(
         removeHashAt(presenceArray[index])
         presenceArray[index] = TOMBSTONE
         size--
+        registerModification()
     }
 
     private fun removeHashAt(removedHash: Int) {
@@ -477,6 +497,7 @@ internal class MapBuilder<K, V> private constructor(
     ) {
         internal var index = 0
         internal var lastIndex: Int = -1
+        private var expectedModCount: Int = map.modCount
 
         init {
             initNext()
@@ -490,15 +511,23 @@ internal class MapBuilder<K, V> private constructor(
         fun hasNext(): Boolean = index < map.length
 
         fun remove() {
+            checkForComodification()
             check(lastIndex != -1) { "Call next() before removing element from the iterator." }
             map.checkIsMutable()
             map.removeKeyAt(lastIndex)
             lastIndex = -1
+            expectedModCount = map.modCount
+        }
+
+        internal fun checkForComodification() {
+            if (map.modCount != expectedModCount)
+                throw ConcurrentModificationException()
         }
     }
 
     internal class KeysItr<K, V>(map: MapBuilder<K, V>) : Itr<K, V>(map), MutableIterator<K> {
         override fun next(): K {
+            checkForComodification()
             if (index >= map.length) throw NoSuchElementException()
             lastIndex = index++
             val result = map.keysArray[lastIndex]
@@ -510,6 +539,7 @@ internal class MapBuilder<K, V> private constructor(
 
     internal class ValuesItr<K, V>(map: MapBuilder<K, V>) : Itr<K, V>(map), MutableIterator<V> {
         override fun next(): V {
+            checkForComodification()
             if (index >= map.length) throw NoSuchElementException()
             lastIndex = index++
             val result = map.valuesArray!![lastIndex]
@@ -521,6 +551,7 @@ internal class MapBuilder<K, V> private constructor(
     internal class EntriesItr<K, V>(map: MapBuilder<K, V>) : Itr<K, V>(map),
         MutableIterator<MutableMap.MutableEntry<K, V>> {
         override fun next(): EntryRef<K, V> {
+            checkForComodification()
             if (index >= map.length) throw NoSuchElementException()
             lastIndex = index++
             val result = EntryRef(map, lastIndex)

libraries/stdlib/native-wasm/src/kotlin/collections/HashMap.kt

@@ -10,15 +10,33 @@ import kotlin.native.FreezingIsDeprecated
 
 @OptIn(FreezingIsDeprecated::class)
 actual class HashMap<K, V> private constructor(
-        private var keysArray: Array<K>,
+    // keys in insert order
-        private var valuesArray: Array<V>?, // allocated only when actually used, always null in pure HashSet
+    private var keysArray: Array<K>,
-        private var presenceArray: IntArray,
+    // values in insert order, allocated only when actually used, always null in pure HashSet
-        private var hashArray: IntArray,
+    private var valuesArray: Array<V>?,
-        private var maxProbeDistance: Int,
+    // hash of a key by its index, -1 if a key at that index was removed
-        private var length: Int
+    private var presenceArray: IntArray,
+    // (index + 1) of a key by its hash, 0 if there is no key with that hash, -1 if collision chain continues to the hash-1
+    private var hashArray: IntArray,
+    // max length of a collision chain
+    private var maxProbeDistance: Int,
+    // index of the next key to be inserted
+    private var length: Int
 ) : MutableMap<K, V> {
     private var hashShift: Int = computeShift(hashSize)
 
+    /**
+     * The number of times this map is structurally modified.
+     *
+     * A modification is considered to be structural if it changes the map size,
+     * or otherwise changes it in a way that iterations in progress may return incorrect results.
+     *
+     * This value can be used by iterators of the [keys], [values] and [entries] views
+     * to provide fail-fast behavoir when a concurrent modification is detected during iteration.
+     * [ConcurrentModificationException] will be thrown in this case.
+     */
+    private var modCount: Int = 0
+
     private var _size: Int = 0
     override actual val size: Int
         get() = _size
@@ -140,6 +158,7 @@ actual class HashMap<K, V> private constructor(
         valuesArray?.resetRange(0, length)
         _size = 0
         length = 0
+        registerModification()
     }
 
     override actual val keys: MutableSet<K> get() {
@@ -206,6 +225,10 @@ actual class HashMap<K, V> private constructor(
     private val capacity: Int get() = keysArray.size
     private val hashSize: Int get() = hashArray.size
 
+    private fun registerModification() {
+        modCount += 1
+    }
+
     internal fun checkIsMutable() {
         if (isReadOnly) throw UnsupportedOperationException()
     }
@@ -268,6 +291,7 @@ actual class HashMap<K, V> private constructor(
     }
 
     private fun rehash(newHashSize: Int) {
+        registerModification()
         if (length > _size) compact()
         if (newHashSize != hashSize) {
             hashArray = IntArray(newHashSize)
@@ -339,6 +363,7 @@ actual class HashMap<K, V> private constructor(
                     presenceArray[putIndex] = hash
                     hashArray[hash] = putIndex + 1
                     _size++
+                    registerModification()
                     if (probeDistance > maxProbeDistance) maxProbeDistance = probeDistance
                     return putIndex
                 }
@@ -367,6 +392,7 @@ actual class HashMap<K, V> private constructor(
         removeHashAt(presenceArray[index])
         presenceArray[index] = TOMBSTONE
         _size--
+        registerModification()
     }
 
     private fun removeHashAt(removedHash: Int) {
@@ -534,6 +560,7 @@ actual class HashMap<K, V> private constructor(
     ) {
         internal var index = 0
         internal var lastIndex: Int = -1
+        private var expectedModCount: Int = map.modCount
 
         init {
             initNext()
@@ -547,14 +574,23 @@ actual class HashMap<K, V> private constructor(
         fun hasNext(): Boolean = index < map.length
 
         fun remove() {
+            checkForComodification()
+            check(lastIndex != -1) { "Call next() before removing element from the iterator." }
             map.checkIsMutable()
             map.removeKeyAt(lastIndex)
             lastIndex = -1
+            expectedModCount = map.modCount
+        }
+
+        internal fun checkForComodification() {
+            if (map.modCount != expectedModCount)
+                throw ConcurrentModificationException()
         }
     }
 
     internal class KeysItr<K, V>(map: HashMap<K, V>) : Itr<K, V>(map), MutableIterator<K> {
         override fun next(): K {
+            checkForComodification()
             if (index >= map.length) throw NoSuchElementException()
             lastIndex = index++
             val result = map.keysArray[lastIndex]
@@ -566,6 +602,7 @@ actual class HashMap<K, V> private constructor(
 
     internal class ValuesItr<K, V>(map: HashMap<K, V>) : Itr<K, V>(map), MutableIterator<V> {
         override fun next(): V {
+            checkForComodification()
             if (index >= map.length) throw NoSuchElementException()
             lastIndex = index++
             val result = map.valuesArray!![lastIndex]
@@ -577,6 +614,7 @@ actual class HashMap<K, V> private constructor(
     internal class EntriesItr<K, V>(map: HashMap<K, V>) : Itr<K, V>(map),
             MutableIterator<MutableMap.MutableEntry<K, V>> {
         override fun next(): EntryRef<K, V> {
+            checkForComodification()
             if (index >= map.length) throw NoSuchElementException()
             lastIndex = index++
             val result = EntryRef(map, lastIndex)

libraries/stdlib/test/collections/ConcurrentModificationTest.kt

@@ -166,6 +166,128 @@ class ConcurrentModificationTest {
             }
         }
     }
+
+    @Test
+    fun mutableSet() {
+        if (TestPlatform.current == TestPlatform.Js) return
+
+        val operations = listOf<CollectionOperation<MutableSet<String>>>(
+            CollectionOperation("add(non-existing)") { add("e") },
+            CollectionOperation("add(existing)", throwsCME = false) { add("d") },
+
+            CollectionOperation("remove(non-existing)", throwsCME = false) { remove("e") },
+            CollectionOperation("remove(existing)") { remove("d") },
+
+            CollectionOperation("addAll(emptyList())", throwsCME = false) { addAll(emptyList()) },
+            CollectionOperation("addAll(existing)", throwsCME = false) { addAll(listOf("d", "b")) },
+            CollectionOperation("addAll(some exist)") { addAll(listOf("d", "e")) },
+            CollectionOperation("addAll(non-existing)") { addAll(listOf("e", "f")) },
+
+            CollectionOperation("removeAll(non-existing)", throwsCME = false) { removeAll(listOf("e", "f")) },
+            CollectionOperation("removeAll(some exist") { removeAll(listOf("d", "e")) },
+            CollectionOperation("removeAll(emptyList())", throwsCME = false) { removeAll(emptyList()) },
+
+            CollectionOperation("retainAll(this.toMutableSet())", throwsCME = false) { retainAll(this.toMutableSet()) },
+            CollectionOperation("retainAll(non-existing)") { retainAll(listOf("e", "f")) },
+            CollectionOperation("retainAll(some exist)") { retainAll(listOf("d", "e")) },
+            CollectionOperation("retainAll(emptyList())") { retainAll(emptyList()) },
+
+            CollectionOperation("clear()") { clear() },
+            CollectionOperation("iterator.remove()") { iterator().apply { next(); remove() } },
+        )
+
+        fun testThrowsCME(withMutableSet: WithCollection<MutableSet<String>>) {
+            for (setOp in operations) {
+                for (iteratorOp in iteratorOperations<String>()) {
+                    testThrowsCME(withMutableSet, { iterator() }, setOp, iteratorOp)
+                }
+            }
+        }
+
+        // Because platform implementations may have different load factor and rehash strategy,
+        // make sure there is enough capacity to avoid rehash.
+
+        val elements = listOf("a", "b", "c", "d")
+
+        testThrowsCME { action ->
+            LinkedHashSet<String>(10).apply {
+                addAll(elements)
+                action(this)
+            }
+        }
+        testThrowsCME { action ->
+            HashSet<String>(10).apply {
+                addAll(elements)
+                action(this)
+            }
+        }
+
+        testThrowsCME { action ->
+            buildSet(10) {
+                addAll(elements)
+                action(this)
+            }
+        }
+    }
+
+    @Test
+    fun mutableMap() {
+        if (TestPlatform.current == TestPlatform.Js) return
+
+        val operations = listOf<CollectionOperation<MutableMap<String, String>>>(
+            CollectionOperation("put(non-existing)") { put("e", "e") },
+            CollectionOperation("put(existing)", throwsCME = false) { put("d", "d") },
+            CollectionOperation("put(update value)", throwsCME = false) { put("d", "D") },
+
+            CollectionOperation("remove(non-existing)", throwsCME = false) { remove("e") },
+            CollectionOperation("remove(existing)") { remove("d") },
+
+            CollectionOperation("putAll(emptyList())", throwsCME = false) { putAll(emptyMap()) },
+            CollectionOperation("putAll(existing)", throwsCME = false) { putAll(mapOf("d" to "d", "b" to "b")) },
+            CollectionOperation("putAll(update values)", throwsCME = false) { putAll(mapOf("d" to "D", "b" to "B")) },
+            CollectionOperation("putAll(some exist)") { putAll(mapOf("d" to "d", "e" to "e")) },
+            CollectionOperation("putAll(non-existing)") { putAll(mapOf("e" to "e", "f" to "f")) },
+
+            CollectionOperation("clear()") { clear() },
+            CollectionOperation("iterator.remove()") { iterator().apply { next(); remove() } },
+        )
+
+        fun testThrowsCME(withMutableMap: WithCollection<MutableMap<String, String>>) {
+            for (mapOp in operations) {
+                for (iteratorOp in iteratorOperations<String>()) {
+                    testThrowsCME(withMutableMap, { keys.iterator() }, mapOp, iteratorOp)
+                    testThrowsCME(withMutableMap, { values.iterator() }, mapOp, iteratorOp)
+                }
+                for (iteratorOp in iteratorOperations<MutableMap.MutableEntry<String, String>>()) {
+                    testThrowsCME(withMutableMap, { entries.iterator() }, mapOp, iteratorOp)
+                }
+            }
+        }
+
+        // Because platform implementations may have different load factor and rehash strategy,
+        // make sure there is enough capacity to avoid rehash.
+
+        val entries = mapOf("a" to "a", "b" to "b", "c" to "c", "d" to "d")
+
+        testThrowsCME { action ->
+            LinkedHashMap<String, String>(10).apply {
+                putAll(entries)
+                action(this)
+            }
+        }
+        testThrowsCME { action ->
+            HashMap<String, String>(10).apply {
+                putAll(entries)
+                action(this)
+            }
+        }
+        testThrowsCME { action ->
+            buildMap(10) {
+                putAll(entries)
+                action(this)
+            }
+        }
+    }
 }
 
 private typealias WithCollection<C> = (action: (C) -> Unit) -> Unit