IR: make lazyVar synchronized

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/lazyUtil.kt

@@ -8,22 +8,30 @@ package org.jetbrains.kotlin.ir.declarations.lazy
 import kotlin.properties.ReadWriteProperty
 import kotlin.reflect.KProperty
 
-fun <T> lazyVar(initializer: () -> T): ReadWriteProperty<Any?, T> = UnsafeLazyVar(initializer)
+fun <T> lazyVar(initializer: () -> T): ReadWriteProperty<Any?, T> = SynchronizedLazyVar(initializer)
 
-private class UnsafeLazyVar<T>(initializer: () -> T) : ReadWriteProperty<Any?, T> {
+private class SynchronizedLazyVar<T>(initializer: () -> T) : ReadWriteProperty<Any?, T> {
+    @Volatile
     private var isInitialized = false
+
     private var initializer: (() -> T)? = initializer
+
+    @Volatile
     private var _value: Any? = null
 
     private val value: T
         get() {
-            if (!isInitialized) {
-                _value = initializer!!()
-                isInitialized = true
-                initializer = null
-            }
             @Suppress("UNCHECKED_CAST")
-            return _value as T
+            if (isInitialized) return _value as T
+            synchronized(this) {
+                if (!isInitialized) {
+                    _value = initializer!!()
+                    isInitialized = true
+                    initializer = null
+                }
+                @Suppress("UNCHECKED_CAST")
+                return _value as T
+            }
         }
 
     override fun toString(): String = if (isInitialized) value.toString() else "Lazy value not initialized yet."
@@ -31,7 +39,9 @@ private class UnsafeLazyVar<T>(initializer: () -> T) : ReadWriteProperty<Any?, T
     override fun getValue(thisRef: Any?, property: KProperty<*>): T = value
 
     override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
-        this._value = value
-        isInitialized = true
+        synchronized(this) {
+            this._value = value
+            isInitialized = true
+        }
     }
 }