Flutter Can Support Multithreading

Multithreading In Flutter

  • Two or more run runs in parallel and sharingglobalvariable.While processes in multiprocessing run in separate memory spaces.Flutter has support isolates where each isolate has its own private space.
  • FlutterBy default, single-threaded tasks are processed. If a new thread is not opened, tasks are processed in the main thread by default.
  • Dart allows us to create multiple Isolates what is similar to multithreading, but it’s not.Isolates are used to do the heavy computation to avoid the slowdown of the main program.
  1. Isolates have one limitation: sharing memory between two isolates is not possible.
  • Dart/Flutter is single threaded and not possible to share global variable. As each isolate has its own memory, space and everything. To make it work like multi-threaded you have to use isolates and the communication will be used through ports by sending message to one another. If you not want to use Future you can use isolates.
  • This reminds me of the notion of processes in Unix that use pipes as parameter/data passing mechanisms. Also, Isolates do not share memory as threads do. I guess this is why they are also called Isolates? They are isolated pieces of execution that rely on input and deliver output.
  • Why should I use isolates in Flutter?
  • Anywhere we need to compute an expensive operation and do not want to block the UI, an isolate should be used.

Isolates:

  • Dart’s version of Threads.
  • Do not share memory between each other.
  • Uses Ports and Messages to communicate between them.
  • May use another processor core if available.
  • Runs code in parallel.

There are 2 ways to deal with isolates:

1) Compute

The compute function hides the message passing mechanisms from the developers.

The Compute function requires 2 parameters, the function to execute, and the parameter to pass into that function. The function must be static or a global function.

staticString getHello(String name) {
  return "Hello ${name}";
}

void_getHello(String name) async{
  String result = await compute(getHello, name);
setState((){
    welcome=result;
  });
}

2) Port

This is the low level way to write isolates, using the SendPort and ReceivePort.

  • Event queue
  • Dart are also concepts of event loops and message queues in threads, but Dart the middle thread is called isolate. After the application starts, execution begins. main() Function and run main isolate.

Eachisolate including an event loop and two event queues,event loopEvent cycles, andevent queueandmicrotaskqueueEvent queue,eventandmicrotaskQueues are somewhat iOS-likesource0andsource1

Eachisolateincluding an event loop and two event queues,event loopEvent cycles, andevent queueandmicro taskqueueEvent queue,eventandmicrotaskQueues are somewhat iOS-likesource0andsource1。

Event queue: Responsible for handling I/O events, drawing events, gesture events, receiving other eventsisolateExternal events such as messages.

Microtask queue: You can go to isolateInternal Addition of Events, Priority Ratio of EventseventqueueHigh. For example: If you use Future.delayed or Future.value it actually puts it in the Microtask queue.

  • Future with Async& Await
  • Future
  • A Future represents a task that will complete or fail sometime in the future, and you will be notified when. In this simple example, we have a Future that returns a value. It does so instantly (this is just an example). When you call myFunction(), it adds it to the Event queue, to be completed. It will continue with all the synchronous code in main() function first someOtherFunction(), then start to process each asynchronous call from the Event queue.
  • Exception: If you use Future.delayed or Future.value it actually puts it in the Microtask queue.
  • Async& Await&Streams (Asynchronous)
  • Stop the synchronous execution, while it waits for a result from an asynchronous task.
  • Async indicates that an asynchronous operation is opened, or that an asynchronous operation can be returnedfutureResult. If there is no return value, a return value is returned by default. nullOf Future.
voidmainTest() async {
debugPrint(await myFunction()); // Waits for completion
debugPrint(await myFunction()); // Waits for completion
someOtherFunction(); // Runs this code
}
  • How do you move work to a background thread?
  • Flutter is single threaded and runs an event loop (like Node.js), you don’t have to worry about thread management or spawning background threads. If you’re doing I/O-bound work, such as disk access or a network call, then you can safely use async/await and you’re done. If, on the other hand, you need to do computationally intensive work that keeps the CPU busy, you want to move it to an Isolate to avoid blocking the event loop.
  • For I/O-bound work, declare the function as an async function, and await on long-running tasks inside the function:
  • Isolates are separate execution threads that do not share any memory with the main execution memory heap. This means you can’t access variables from the main thread, or update your UI by calling setState(). Isolates are true to their name, and cannot share memory (in the form of static fields, for example).

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