easy_isolate 0.0.2+2

An abstraction of the isolate providing an easy way to work with different threads

Easy Isolate

An abstraction of the isolate providing an easy way to work with different threads

How it works

A worker is responsible for 1 new thread (isolate). Everything you need to do to start a new thread is instantiate a new worker and call the init function providing 2 parameters, a MainMessageHandler and an IsolateMessageHandler.

void main() async {
  final worker = Worker();
  await worker.init(mainHandler, isolateHandler);  
}

void mainHandler(dynamic data, SendPort isolateSendPort) {
  
}

void isolateHandler(dynamic data, SendPort mainSendPort, SendErrorFunction onSendError) {
  
}

The mainHandler will receive messages coming from the isolate, and the isolateHandler the messages coming from the main thread.

Important note: Since you are working with different threads remember that they don't share the same space of memory, which means that all instances and states presents on the main thread are not available on the new threads.

Because of these particularities, the isolateHandler should be a top-level function or a static method.

Now that you have the worker ready, and with that a new thread running, the next step is understanding how to communicate between them.

Sending messages to the isolate/thread

There are two ways to communicate with the isolate, the first one is using the method available in the worker worker.sendMessage(null), and the other one is using the SendPort inside the mainHandler. Let's suppose that you are running more than one worker in your application and wants to handle all the incoming messages from the isolates to the main using only one handler. For this case, the SendPort inside the mainHandler is always related to the isolate that are sending the message.

Example using the sendMessage:

void main() async {
  final worker = Worker();
  await worker.init(mainHandler, isolateHandler);
  
  worker.sendMessage(null);
}

...

Example using the mainHandler SendPort:

...

void mainHandler(dynamic data, SendPort isolateSendPort) {
  isolateSendPort.send(null);
}

...

Sending messages to the main thread

There is only one way to communicate with the main thread through the isolate, using the main SendPort available in the isolateHandler.

...

void isolateHandler(dynamic data, SendPort mainSendPort, SendErrorFunction onSendError) {
  mainSendPort.send(null);
}

Good to know: Only primitive types can be sent on the messages, but you can send class objects between them containing the primitive values. Example: You can instantiate a Car class inside the isolate and send to the main thread, the object will be copied to another instance with all the primitive values intact.

Now that you know how to start a worker and send messages, this plugin provides more two handlers on the init function, the errorHandler and exitHandler.

The errorHandler will be called in two occasions, the first one is when any unhandled exception be thrown on the isolate sending the exception stacktrace. The other one is using the SendErrorFunction inside the isolateHandler, it can be used to send the errors manually without necessarily having an exception.

Example using the errorHandler:

void main() async {
  final worker = Worker();
  await worker.init(mainHandler, isolateHandler, errorHandler);

  worker.sendMessage(null);
}

void errorHandler(dynamic data) {
  // Handle the error here
}

...

Example sending messages manually:

...

void isolateHandler(dynamic data, SendPort mainSendPort, SendErrorFunction onSendError) {
  onSendError('Error');
}

The exitHandler is called when the worker is disposed or the isolate is closing.

Example:

void main() async {
  final worker = Worker();
  await worker.init(mainHandler, isolateHandler, errorHandler, exitHandler);

  worker.sendMessage(null);
}

void exitHandler(dynamic data) {
  // Handle the exit here
}

...

Important note: The isolate automatically closes when unhandled exceptions happens inside the isolate. One way to prevent this is using the runGuardedZone or wrapping the operations with try catchs.

Congratulation, now you are ready to use the worker in your project.

Example

The example project is a simulation of a file downloader using a separated thread for each download. It will help you to understand how it works in practice. See the code here.

Feels free to open issues or add suggestions and, if you are happy using the plugin and would like to have more plugins like this, help me with the sponsor button.