isolate_handler 0.2.0

Effortless isolates abstraction layer.

Isolate Handler

Effortless isolates abstraction layer.

Getting Started

What's an isolate?

In the words of the Dart documentation itself, isolates are:

Independent workers that are similar to threads but don't share memory, communicating only via messages.

In short, Dart is a single-threaded language, but it has support for concurrent execution of code through isolates.

This means that you can use isolates to execute code you want to run alongside your main thread, which is particularly useful for keeping your Flutter application running smoothly.

For more detailed information, please read this excellent article by Didier Boelens.

Why should I use Isolate Handler?

Short answer: Isolate Handler allows easy spawning of—as well as communication between—isolates.

Dart already has a very clean interface for spawning and interacting with isolates, using Isolate Handler instead of the regular interface only provides a slightly simpler way of keeping track of and communicating with them.

Using Isolate Handler

Spawning an isolate

Spawning an isolate with Isolate Handler is really simple:

IsolateHandler().spawn(entryPoint);

This is similar to how isolates are spawned normally, with the exception that Isolate Handler does not expect a message parameter, only an entry point. Messaging has been abstracted away and a communications channel is instead opened automatically.

Communicating with an isolate

Just spawning an isolate provides no benefit over simply using Isolate.spawn, so let's move on to a slightly more useful example; sending data to an isolate and receiving some back.

Let's do a complete project where we start an isolate and send it an integer, have it add one to our count and return the value. We will also give our isolate a name to make it easy to access from anywhere.

final isolates = IsolateHandler();
int counter = 0;

void main() {
  // Start the isolate at the `entryPoint` function.
  isolates.spawn<int>(entryPoint,
    name: "counter",
    // Executed every time data is received from the spawned isolate.
    onReceive: setCounter,
    // Executed once when spawned isolate is ready for communication.
    onInitialized: () => isolates.send(counter, to: "counter")
  );
}

// Set new count and display current count.
void setCounter(int count) {
  counter = count;
  print("Counter is now $counter");
  
  // We will no longer be needing the isolate, let's dispose of it.
  isolates.kill("counter");
}

// This function happens in the isolate.
void entryPoint(HandledIsolateContext context) {
  // Calling initialize from the entry point with the context is
  // required if communication is desired. It returns a messenger which
  // allows listening and sending information to the main isolate.
  final messenger = HandledIsolate.initialize(context);

  // Triggered every time data is received from the main isolate.
  messenger.listen((count) {
    // Add one to the count and send the new value back to the main
    // isolate.
    messenger.send(++count);
  });
}

Calls to invokeMethod from isolates

This was previously supported, but support has been removed due to changes in Flutter making it infeasible.

It is worth noting that running native plugins from a Dart isolate does not offer any performance advantage as all native code is run on the main (UI) thread by default.

In order to improve performance of a native plugin, the plugin must create its own thread on the native platform.