As I study about flutter, I notices that there is a thing called isolate.
What is it for? And how do we implement that? Can you give me a simple example?
Thank you in advance.
Isolate in flutter, similar with threading.
"Flutter is single-threaded but it is capable of doing multi-threading
stuff using Isolates (many processes). When Dart starts, there will be
one main Isolate(Thread). This is the main executing thread of the
application, also referred to as the UI Thread. In simple Flutter apps
you will only ever use one Isolate, and your app will run smoothly.
Isolates are:
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."
Docs & Simple Example
"Concurrent programming using isolates: independent workers that are
similar to threads but don't share memory, communicating only via
messages."
Official Docs
Related
I'm going to use ObjectBox in my Flutter project. But I noticed that the get method is synchronous. So should I use ObjectBox in a separate isolate to avoid blocking the UI thread?
There's rarely a need to do so. ObjectBox achieves hundreds of thousands of read objects per second on mobile so you should be fine unless you're doing something very excessive.
objectbox-dart v1.4.0 adds Store.runIsolated to run database operations (asynchronous) in the background.
https://github.com/objectbox/objectbox-dart/releases/tag/v1.4.0
As we know flutter app runs in an isolates. Somewhere I read that isolates are not system processes. So what really an isolate is and how it's different from process.
Good question. But there is no definite answer, because it depends on the language implementation.
Let me just quote the docs (emphasis mine):
Within an app, all Dart code runs in an isolate. Each Dart isolate has
a single thread of execution and shares no mutable objects with other
isolates. To communicate with each other, isolates use message
passing. Although Dart’s isolate model is built with underlying
primitives such as processes and threads that the operating system
provides, the Dart VM’s use of these primitives is an implementation
detail that this page doesn’t discuss.
Many Dart apps use only one isolate (the main isolate), but you can
create additional isolates, enabling parallel code execution on
multiple processor cores.
As you might know, threads and processes are managed by OS.
Isolates are managed by Dart runtime, and they use underlying OS threads and processes.
The Dart runtime controls the main isolate (where code normally runs)
and any other isolates that the app creates.
Within our flutter app we are doing some background processing. For that, we need to create new flutter isolate in our native code so we can run code when activity is not open, based on this guide: https://medium.com/#chetan882777/initiating-calls-to-dart-from-the-native-side-in-the-background-with-flutter-plugin-7d46aed32c47
Now, to not duplicate code and to not cause any concurrency issues, we would also like to have access to that background processing isolate from main flutter UI isolate. That way we can begin processing from both native code and from flutter UI code.
However, there does not seem to be a way for native to pass this Isolate / ControlPort to the main UI side so it can communicate with it. Is there a way I can achieve this (communicate to the same Isolate from both native and UI side)?
From what I see, only way to do this would require native to be the broker between the two sides (send the task to native and then native sends it back to the other side), but it seems like a lot of hassle for one flutter talking to another flutter.
Solution to this is the IsolateNameServer.
One side can call IsolateNameServer.registerPortWithName() and other side can then send messages to that port via IsolateNameServer.lookupPortByName()
What's the difference between Thread, Isolate and a Process in Dart?
As far as I know Dart is a single-threaded language, but it can spawn many isolates which don't share memories with each other and we can do the heavy lifting work on them and return the result without blocking the UI.
But what Process is for, is that a part of an Isolate? Can anyone describe above three in more detail.
And when we do asynchronous programming using Future and let's see we are doing heavy lifting in it, will that block the UI thread in case it is awaited using the await keyword.
A Process is a native OS (Unix, Windows, MacOS) construct, which consists of one or more threads with their own address space and execution environment. In Dart, an application consists of one or more threads, one of which is the main UI thread, while the rest are typically called Isolates.
In contrast to what the previous answer said, All Dart code runs in an isolate.
Actually, your understanding is correct, based on what you said in the comments.
From the docs (emphasis mine):
Within an app, all Dart code runs in an isolate. Each Dart isolate has
a single thread of execution and shares no mutable objects with other
isolates. To communicate with each other, isolates use message
passing. Although Dart’s isolate model is built with underlying
primitives such as processes and threads that the operating system
provides, the Dart VM’s use of these primitives is an implementation
detail that this page doesn’t discuss.
Many Dart apps use only one isolate (the main isolate), but you can
create additional isolates, enabling parallel code execution on
multiple processor cores.
Your question hasn't been answered yet, and it will not be answered easily, because it depends on the language implementation.
Also, your another question: "And when we do asynchronous programming using Future and let's see we are doing heavy lifting in it, will that block the UI thread in case it is awaited using the await keyword."
-> Yes, it will block the UI, unless you use another isolate.
can you guys explain what a background and main threads are?
I'm a junior iOS Developer(swift) and I've been programming for 6 month and never heard of this before.
Thanks in advance.
Threads allow you to execute multiple code paths concurrently inside a single application.
iOS apps have a main thread which processes all the UI logic and base of your app. Sometimes you need to push your heavy code (such as a network call) to a different (background) thread so it doesn't clog up the main thread and block your UI from changing for example. It also allows you to do multiple things at one, or run multiple network calls.
This article explains in more detail:
https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/Multithreading/Introduction/Introduction.html#//apple_ref/doc/uid/10000057i-CH1-SW1