Do not allow using getOrPut on concurrent maps.

#KT-5800 In Progress

libraries/stdlib/src/kotlin/collections/MapsJVM.kt

@@ -5,6 +5,7 @@ import java.util.LinkedHashMap
 import java.util.Properties
 import java.util.SortedMap
 import java.util.TreeMap
+import java.util.concurrent.ConcurrentMap
 
 /**
  * Allows to use the index operator for storing values in a mutable map.
@@ -12,6 +13,14 @@ import java.util.TreeMap
 // this code is JVM-specific, because JS has native set function
 public fun <K, V> MutableMap<K, V>.set(key: K, value: V): V? = put(key, value)
 
+/**
+ * getOrPut is not supported on [ConcurrentMap] since it cannot be implemented correctly in terms of concurrency.
+ * Use [ConcurrentMap.putIfAbsent] instead, or cast this to a [MutableMap] if you want to sacrifice the concurrent-safety.
+ */
+deprecated("Use putIfAbsent instead or cast this map to MutableMap.")
+public inline fun <K, V> ConcurrentMap<K, V>.getOrPut(key: K, defaultValue: () -> V): Nothing =
+    throw UnsupportedOperationException("getOrPut is not supported on ConcurrentMap.")
+
 /**
  * Converts this [Map] to a [SortedMap] so iteration order will be in key order.
  *

libraries/stdlib/test/collections/MapJVMTest.kt

@@ -1,5 +1,6 @@
 package test.collections
 
+import java.util.concurrent.ConcurrentHashMap
 import kotlin.test.*
 import org.junit.Test as test
 
@@ -37,4 +38,15 @@ class MapJVMTest {
         assertEquals("A", prop.getProperty("a", "fail"))
         assertEquals("B", prop.getProperty("b", "fail"))
     }
+
+    test fun getOrPutFailsOnConcurrentMap() {
+        val map = ConcurrentHashMap<String, Int>()
+
+        fails {
+            map.getOrPut("x") { 1 }
+        }
+        expect(1) {
+            (map as MutableMap<String, Int>).getOrPut("x") { 1 }
+        }
+    }
 }