How to use multiple isolates to serve requests

Issue

How can a Dart server be set up to use all available cores for in coming requests (e.g. by using multiple isolates to serve requests)?

Solution

Use the shared: true argument of HttpServer.bind. Example:

import 'dart:io';
import 'dart:isolate';

import 'package:shelf/shelf.dart' as shelf;
import 'package:shelf/shelf_io.dart' as shelf_io;
import 'package:args/args.dart' show ArgParser;

main(List<String> args) {
   var parser = new ArgParser()
   ..addOption('address', abbr: 'a', defaultsTo: '0.0.0.0')
   ..addOption('port', abbr: 'p', defaultsTo: '9393')
   ..addOption('isolates', abbr: 'i', defaultsTo: '3');
   var arguments = parser.parse(args);

   var nbOfIsolates = int.parse(arguments['isolates']);
   for (int i = 1; i < nbOfIsolates; i++) {
      Isolate.spawn(_startShelfServer, [arguments['address'], int.parse(arguments['port'])]);
   }
   _startShelfServer([arguments['address'], int.parse(arguments['port'])]);
}

_startShelfServer(List args) async {
   String address = args[0];
   int port = args[1];

   var helloWorldHandler = (shelf.Request request) => new shelf.Response.ok("Hello World - from isolate ${Isolate.current.hashCode}");  
   var handler = const shelf.Pipeline()
   .addHandler(helloWorldHandler);
   var server = await HttpServer.bind(address, port, shared: true);
   await shelf_io.serveRequests(server, handler);
   print('Serving at http://${server.address.host}:${server.port} - isolate: ${Isolate.current.hashCode}');    
}

Answered By – Benjamin

Answer Checked By – Timothy Miller (FlutterFixes Admin)

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