Efficiently manages atomic operations by transforming code for various platforms. Supports atomic values, arrays, user-defined extensions, locks, and tracing operations for debugging, ensuring high performance and idiomatic usage.
Note on Beta status: the plugin is in its active development phase and changes from release to release. We do provide a compatibility of atomicfu-transformed artifacts between releases, but we do not provide strict compatibility guarantees on plugin API and its general stability between Kotlin versions.
Atomicfu is a multiplatform library that provides the idiomatic and efficient way of using atomic operations in Kotlin.
To apply the current version of the atomicfu Gradle plugin, your project has to use:
Gradle 8.2 or newer
Kotlin 2.2.0 or newer
Consider using previous versions of the plugin if your project could not meet these requirements.
Note on Kotlin version: Currently, the
kotlinx-atomicfuGradle plugin only relies on the version of Kotlin Gradle Plugin (KGP) present in the user's project. It's important to note this constraint if your project configures the custom Kotlin compiler version or modifies the Kotlin Native compiler version usingkotlin.native.versionproperty.
Let us declare a top variable for a lock-free stack implementation:
import kotlinx.atomicfu.* // import top-level functions from kotlinx.atomicfu
private val top = atomic<Node?>(null)
Use top.value to perform volatile reads and writes:
fun isEmpty() = top.value == null // volatile read
fun clear() { top.value = null } // volatile write
Use compareAndSet function directly:
if (top.compareAndSet(expect, update)) ...
Use higher-level looping primitives (inline extensions), for example:
top.loop { cur -> // while(true) loop that volatile-reads current value
...
}
Use high-level update, updateAndGet, and getAndUpdate,
when possible, for idiomatic lock-free code, for example:
fun push(v: Value) = top.update { cur -> Node(v, cur) }
fun pop(): Value? = top.getAndUpdate { cur -> cur?.next } ?.value
Declare atomic integers and longs using type inference:
val myInt = atomic(0) // note: integer initial value
val myLong = atomic(0L) // note: long initial value
Integer and long atomics provide all the usual getAndIncrement, incrementAndGet, getAndAdd, addAndGet, and etc
operations. They can be also atomically modified via += and -= operators.
New plugin id: Please pay attention, that starting from version
0.25.0the plugin id isorg.jetbrains.kotlinx.atomicfu
Add the following to your top-level build file:
plugins {
id("org.jetbrains.kotlinx.atomicfu") version "0.33.0"
}
plugins {
id 'org.jetbrains.kotlinx.atomicfu' version '0.33.0'
}
buildscript {
repositories {
mavenCentral()
}
dependencies {
classpath("org.jetbrains.kotlinx:atomicfu-gradle-plugin:0.33.0")
}
}
apply(plugin = "org.jetbrains.kotlinx.atomicfu")
buildscript {
repositories {
mavenCentral()
}
dependencies {
classpath 'org.jetbrains.kotlinx:atomicfu-gradle-plugin:0.33.0'
}
}
apply plugin: 'org.jetbrains.kotlinx.atomicfu'
Maven configuration is supported for JVM projects.
<properties>
<atomicfu.version>0.33.0</atomicfu.version>
</properties>
Configure build steps so that Kotlin compiler puts classes into a different classes-pre-atomicfu directory,
which is then transformed to a regular classes directory to be used later by tests and delivery.
private val or internal val. You can use just (public) val,
but make sure they are not directly accessed outside of your Kotlin module (outside of the source set).
Access to the atomic variable itself shall be encapsulated.private val _foo = atomic<T>(initial) // private atomic, convention is to name it with leading underscore
public var foo: T by _foo // public delegated property (val/var)
To provide a user-friendly atomic API on the frontend and efficient usage of atomic values on the backend kotlinx-atomicfu library uses the compiler plugin to transform IR for all the target backends:
java.util.concurrent.atomic.AtomicXxxFieldUpdater.To turn on IR transformations set the following properties in your gradle.properties file:
Please note, that starting from version
0.24.0of the library your project is required to useKotlin version >= 1.9.0. See the requirements section.
kotlinx.atomicfu.enableJvmIrTransformation=true // for JVM IR transformation
kotlinx.atomicfu.enableNativeIrTransformation=true // for Native IR transformation
kotlinx.atomicfu.enableJsIrTransformation=true // for JS IR transformation
Some configuration options are available for post-compilation transform tasks on JVM and JS.
To set configuration options you should create atomicfu section in a build.gradle file,
like this:
atomicfu {
dependenciesVersion = '0.33.0'
}
To turn off transformation for Kotlin/JVM set option transformJvm to false.
Configuration option jvmVariant defines the Java class that replaces atomics during bytecode transformation.
Here are the valid options:
FU – atomics are replaced with AtomicXxxFieldUpdater.VH – atomics are replaced with ,
this option is supported for JDK 9+.Starting from version
0.26.0transformJsflag does not take any effect and is disabled by default. Please ensure that this flag is not used in the atomicfu configuration of your project, you can safely remove it.
Here are all available configuration options (with their defaults):
atomicfu {
dependenciesVersion = '0.33.0' // set to null to turn-off auto dependencies
transformJvm = true // set to false to turn off JVM transformation
jvmVariant = "FU" // JVM transformation variant: FU,VH, or BOTH
}
AtomicFU provides some additional features that you can use.
You can declare arrays of all supported atomic value types.
By default arrays are transformed into the corresponding java.util.concurrent.atomic.Atomic*Array instances.
If you configure variant = "VH" an array will be transformed to plain array using
VarHandle to support atomic operations.
val a = atomicArrayOfNulls<T>(size) // similar to Array constructor
val x = a[i].value // read value
a[i].value = x // set value
a[i].compareAndSet(expect, update) // do atomic operations
You can expose the value of an atomic property to the public, using a delegated property declared in the same scope:
private val _foo = atomic<T>(initial) // private atomic, convention is to name it with leading underscore
public var foo: T by _foo // public delegated property (val/var)
You can also delegate a property to the atomic factory invocation, that is equal to declaring a volatile property:
public var foo: T by atomic(0)
This feature is only supported for the IR transformation mode, see the atomicfu compiler plugin section for details.
You can define you own extension functions on AtomicXxx types but they must be inline and they cannot
be public and be used outside of the module they are defined in. For example:
@Suppress("NOTHING_TO_INLINE")
private inline fun AtomicBoolean.tryAcquire(): Boolean = compareAndSet(false, true)
This project includes kotlinx.atomicfu.locks package providing multiplatform locking primitives that
require no additional runtime dependencies on Kotlin/JVM and Kotlin/JS with a library implementation for
Kotlin/Native.
Note that package
kotlinx.atomicfu.locksis experimental explicitly even while atomicfu is experimental itself, meaning that no ABI guarantees are provided whatsoever. API from this package is not recommended to use in libraries that other projects depend on.
You can debug your tests tracing atomic operations with a special trace object:
private val trace = Trace()
private val current = atomic(0, trace)
fun update(x: Int): Int {
// custom trace message
trace { "calling update($x)" }
// automatic tracing of modification operations
return current.getAndAdd(x)
}
All trace messages are stored in a cyclic array inside trace.
You can optionally set the size of trace's message array and format function. For example, you can add a current thread name to the traced messages:
private val trace = Trace(size = 64) {
index, // index of a trace message
text // text passed when invoking trace { text }
-> "$index: [${Thread.currentThread().name}] $text"
}
trace is only seen before transformation and completely erased after on Kotlin/JVM and Kotlin/JS.
Since Kotlin/Native does not generally provide binary compatibility between versions,
you should use the same version of Kotlin compiler as was used to build AtomicFU.
See gradle.properties in AtomicFU project for its kotlin_version.
Available Kotlin/Native targets are based on non-deprecated official targets Tier list with the corresponding compatibility guarantees.
Gradle Build Scans can provide insights into an Atomicfu Build. JetBrains runs a Gradle Develocity server. that can be used to automatically upload reports.
To automatically opt in add the following to $GRADLE_USER_HOME/gradle.properties.
org.jetbrains.atomicfu.build.scan.enabled=true
# optionally provide a username that will be attached to each report
org.jetbrains.atomicfu.build.scan.username=John Wick
A Build Scan may contain identifiable information. See the Terms of Use https://gradle.com/legal/terms-of-use/.
Surfaced from shared tags and platforms — no rankings paid for.
atomic(0), but run it in production efficiently:
java.util.concurrent.atomic.AtomicXxxFieldUpdater from the Java standard library.kotlinx-atomicfu library is used as a runtime dependency.loop, update, updateAndGet functions).<dependencies>
<dependency>
<groupId>org.jetbrains.kotlinx</groupId>
<artifactId>atomicfu</artifactId>
<version>${atomicfu.version}</version>
<scope>provided</scope>
</dependency>
</dependencies>
<build>
<plugins>
<!-- compile Kotlin files to staging directory -->
<plugin>
<groupId>org.jetbrains.kotlin</groupId>
<artifactId>kotlin-maven-plugin</artifactId>
<version>${kotlin.version}</version>
<executions>
<execution>
<id>compile</id>
<phase>compile</phase>
<goals>
<goal>compile</goal>
</goals>
<configuration>
<output>${project.build.directory}/classes-pre-atomicfu</output>
</configuration>
</execution>
</executions>
</plugin>
<!-- transform classes with AtomicFU plugin -->
<plugin>
<groupId>org.jetbrains.kotlinx</groupId>
<artifactId>atomicfu-maven-plugin</artifactId>
<version>${atomicfu.version}</version>
<executions>
<execution>
<goals>
<goal>transform</goal>
</goals>
<configuration>
<input>${project.build.directory}/classes-pre-atomicfu</input>
<!-- "VH" to use Java 9 VarHandle, "BOTH" to produce multi-version code -->
<variant>FU</variant>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
top.compareAndSet(...) is ok, while val tmp = top; tmp... is not.top.value = complex_expression and top.compareAndSet(cur, complex_expression) are not supported
(more specifically, complex_expression should not have branches in its compiled representation).
Extract complex_expression into a variable when needed.For Kotlin >= 1.7.20
kotlinx.atomicfu.enableJvmIrTransformation=true // for JVM IR transformation
kotlinx.atomicfu.enableNativeIrTransformation=true // for Native IR transformation
kotlinx.atomicfu.enableJsIrTransformation=true // for JS IR transformation
For Kotlin >= 1.6.20 and Kotlin < 1.7.20
kotlinx.atomicfu.enableIrTransformation=true // only JS IR transformation is supported
Also for JS backend make sure that ir or both compiler mode is set:
kotlin.js.compiler=ir // or both
BOTH – multi-release jar file will be created with both AtomicXxxFieldUpdater for JDK <= 8 and VarHandle for JDK 9+.SynchronizedObject is designed for inheritance. You write class MyClass : SynchronizedObject() and then
use synchronized(instance) { ... } extension function similarly to the
synchronized
function from the standard library that is available for JVM. The SynchronizedObject superclass gets erased
(transformed to Any) on JVM and JS, with synchronized leaving no trace in the code on JS and getting
replaced with built-in monitors for locking on JVM.
ReentrantLock is designed for delegation. You write val lock = reentrantLock() to construct its instance and
use lock/tryLock/unlock functions or lock.withLock { ... } extension function similarly to the way
jucl.ReentrantLock
is used on JVM. On JVM it is a typealias to the later class, erased on JS.