Volatile properties in Kotlin?

Question

How does one mark a var in Kotlin volatile?

volatile public var tmpEndedAt: Long? = null

gives me the error:

"unresolved reference: volatile"

Can you show us more code? The web IDE let's me compile your code just fine: http://try.kotlinlang.org/#/UserProjects/117433846956340982849-2093063043/117433846956340982849-1340790681 — Kirill Rakhman, Jun 08 '15 at 15:12
Possible issues with your project: 1) it may be a JS-taregeted project 2) kotlin standard library may not be attached — Andrey Breslav, Jun 08 '15 at 16:06
Your line of code seems to be correct. In Kotlin `volatile` is not a keyword but an annotation declared in `kotlin-stdlib`. So just make sure to have it in classpath. — hotkey, Jun 08 '15 at 17:09

score 84 · Accepted Answer · edited Nov 25 '15 at 05:50

84

I decided to give Kotlin a shot by just using the "convert java to kotlin" function in IntelliJ. Apparently that set things up wrong.

I tried doing the same thing, but after applying the Kotlin Gradle plugin and placing the file in src/kotlin and it all worked. Thanks for the help anyway guys.

The code would be:

@Volatile var tmpEndedAt: Long? = null

edited Nov 25 '15 at 05:50

akhy

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answered Jun 08 '15 at 20:24

Andrew Cholakian

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I have encountered this problem before. Here's an issue, I just created: https://youtrack.jetbrains.com/issue/KT-7986 – Kirill Rakhman Jun 09 '15 at 08:56
Will it be compiled even without `kapt`? I'm asking because I have a lot of old Java classes with many lombok annotations so I can't use `kapt` with that or it breaks everything. – Vrakfall Jun 22 '19 at 10:08

score 17 · Answer 2 · edited Sep 24 '22 at 08:33

In Kotlin in order to force changes in a variable to be immediately visible to other threads, we can use the annotation @Volatile. If a variable is not shared between multiple threads, you don't need to use volatile keyword with that variable.

I.e. when you apply volatile to a field of a class, it instructs the CPU to always read it from the RAM and not from the CPU cache. It also prevents instructions reordering; it acts as a memory barrier.

Check Volatile in O’Reilly's Kotlin Quick Start Guide for more information.

score 15 · Answer 3 · edited Jun 20 '20 at 09:12

15

According to the Kotlin documentation Kotlin-@Volatile

Marks the JVM backing field of the annotated property as volatile, meaning that writes to this field are immediately made visible to other threads.

So, in Kotlin you can mark the property as volatile with @Volatile annotation.

e.g.

@Volatile var tmpEndedAt: Long? = null

edited Jun 20 '20 at 09:12

Community

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answered Aug 29 '19 at 13:35

Waqar UlHaq

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Volatile properties in Kotlin?

3 Answers3