fastbus

fastbus is a blazing fast java event bus for projects that need simple typed events without a framework. it targets java 1.8 for compatibility.

install

<repositories>
  <repository>
    <id>tsukure-releases</id>
    <url>https://maven.tsuku.re/releases</url>
  </repository>
</repositories>

<dependencies>
  <dependency>
    <groupId>re.tsuku</groupId>
    <artifactId>fastbus</artifactId>
    <version>1.0.0</version>
  </dependency>
</dependencies>

for snapshots, use:

<repository>
  <id>tsukure-snapshots</id>
  <url>https://maven.tsuku.re/snapshots</url>
</repository>

basic usage

create an event:

import re.tsuku.fastbus.Event;

public final class LoginEvent implements Event {
    private final String username;

    public LoginEvent(String username) {
        this.username = username;
    }

    public String username() {
        return username;
    }
}

subscribe with annotated methods:

import re.tsuku.fastbus.FastBus;
import re.tsuku.fastbus.Subscribe;

public final class LoginLogger {
    @Subscribe
    public void onLogin(LoginEvent event) {
        System.out.println(event.username() + " logged in");
    }
}

FastBus bus = new FastBus();
LoginLogger logger = new LoginLogger();

bus.subscribe(logger);
bus.post(new LoginEvent("rin"));
bus.unsubscribe(logger);

subscribe with listener functions:

import re.tsuku.fastbus.EventPriority;
import re.tsuku.fastbus.FastBus;
import re.tsuku.fastbus.Subscription;

FastBus bus = new FastBus();

Subscription subscription = bus.subscribe(
    LoginEvent.class,
    event -> System.out.println(event.username()),
    EventPriority.HIGH
);

bus.post(new LoginEvent("rin"));
subscription.unsubscribe();

cancelable events can extend CancellableEvent:

import re.tsuku.fastbus.CancellableEvent;

public final class MessageEvent extends CancellableEvent {
    private final String message;

    public MessageEvent(String message) {
        this.message = message;
    }

    public String message() {
        return message;
    }
}

build

./mvnw clean test

format sources:

./mvnw formatter:format

check formatting:

./mvnw formatter:validate

benchmarks

build the jmh benchmark jar:

./mvnw -Pbenchmarks clean package -DskipTests

run the benchmark suite:

java -jar target/benchmarks.jar

for a shorter local run:

java -jar target/benchmarks.jar 'post_.*|subscribe_.*' -wi 2 -i 3 -f 1

rough local jmh numbers, averaged from short runs on jdk 21:

benchmark	throughput
fastbus direct post	~270m ops/s
fastbus annotated post	~208m ops/s
greenrobot eventbus post	~16m ops/s
guava eventbus post	~10m ops/s
fastbus direct subscribe/unsubscribe	~8.7m ops/s
guava eventbus subscribe/unsubscribe	~5.5m ops/s
fastbus annotated subscribe/unsubscribe	~5.3m ops/s
greenrobot eventbus subscribe/unsubscribe	~200k ops/s

your mileage may vary a bit depending on jvm, hardware, and listener shape.

license

mit