HarryDeveloper

HarryDeveloper

Programming Kotlin: Difference between SupervisorJob() and supervisorScope (324, 325)

Hi @venkats,

It has been mentioned in the description of ‘Supervisory Job’ title that 2 things as mentioned below result in the same effect - preventing the parent from cancelling when an unhandled exception occurs in one of the children

  1. Passing a SupervisorJob instance to the coroutine
  2. Wrapping the children inside a supervisorScope,

However, the example provided in ‘async/cancellationbidirectional.kts’ does use ‘SupervisorJob()’ in the parent ‘launch’, and parent job fails as mentioned in the book. When I try it, the result is the same: parent job fails, there is no successful 200 response, CancellationException is caught.

Why is that SupervisorJob() instance passage to the coroutine does not result in the desired behaviour? Using supervisorScope() works as expected. Is there any difference in using SupervisorJob() and supervisorScope()?

Please advise.

Thanks,
Harry

First Post!

venkats

venkats

Author of Programming Kotlin, Rediscovering JavaScript (and 6 other titles)

Hi @HarryDeveloper,

Thank you for the query.

The supervisorScope is a syntax sugar or a convenience function for creating a SupervisorJob. If the child coroutines run in a different SupervisorJob than the parent, then the cancellation of a Chile does not propagate to the parent.

It is much better to use supervisorScope than to use SupervisorJob, but from the curiosity point of view, you may try to create a SupervisorJob, something like this:

val job = launch(Dispatchers.IO + SupervisorJob() + handler) {

val supervisor = SupervisorJob()

launch(coroutineContext + supervisor) { fetchResponse(200, 5000) }
launch(coroutineContext + supervisor) { fetchResponse(200, 1000) }
launch(coroutineContext + supervisor) { fetchResponse(200, 3000) }

supervisor.children.forEach { it. join() }

/*
supervisorScope {
  launch { fetchResponse(200, 5000) }
  launch { fetchResponse(200, 1000) }
  launch { fetchResponse(200, 3000) }
}
*/

}

job.join()

Hope that answers your question.

Regards,

Venkat

Where Next?

Popular Pragmatic Bookshelf topics Top

brianokken
Many tasks_proj/tests directories exist in chapters 2, 3, 5 that have tests that use the custom markers smoke and get, which are not decl...
New
jeremyhuiskamp
Title: Web Development with Clojure, Third Edition, vB17.0 (p9) The create table guestbook syntax suggested doesn’t seem to be accepted ...
New
New
patoncrispy
I’m new to Rust and am using this book to learn more as well as to feed my interest in game dev. I’ve just finished the flappy dragon exa...
New
jgchristopher
“The ProductLive.Index template calls a helper function, live_component/3, that in turn calls on the modal component. ” Excerpt From: Br...
New
jonmac
The allprojects block listed on page 245 produces the following error when syncing gradle: “org.gradle.api.GradleScriptException: A prob...
New
tkhobbes
After some hassle, I was able to finally run bin/setup, now I have started the rails server but I get this error message right when I vis...
New
ggerico
I got this error when executing the plot files on macOS Ventura 13.0.1 with Python 3.10.8 and matplotlib 3.6.1: programming_ML/code/03_...
New
dachristenson
@mfazio23 Android Studio will not accept anything I do when trying to use the Transformations class, as described on pp. 140-141. Googl...
New
roadbike
From page 13: On Python 3.7, you can install the libraries with pip by running these commands inside a Python venv using Visual Studio ...
New

Other popular topics Top

DevotionGeo
I know that these benchmarks might not be the exact picture of real-world scenario, but still I expect a Rust web framework performing a ...
New
Rainer
My first contact with Erlang was about 2 years ago when I used RabbitMQ, which is written in Erlang, for my job. This made me curious and...
New
PragmaticBookshelf
From finance to artificial intelligence, genetic algorithms are a powerful tool with a wide array of applications. But you don't need an ...
New
foxtrottwist
A few weeks ago I started using Warp a terminal written in rust. Though in it’s current state of development there are a few caveats (tab...
New
mafinar
This is going to be a long an frequently posted thread. While talking to a friend of mine who has taken data structure and algorithm cou...
New
New
sir.laksmana_wenk
I’m able to do the “artistic” part of game-development; character designing/modeling, music, environment modeling, etc. However, I don’t...
New
AnfaengerAlex
Hello, I’m a beginner in Android development and I’m facing an issue with my project setup. In my build.gradle.kts file, I have the foll...
New
PragmaticBookshelf
Explore the power of Ash Framework by modeling and building the domain for a real-world web application. Rebecca Le @sevenseacat and ...
New
RobertRichards
Hair Salon Games for Girls Fun Girls Hair Saloon game is mainly developed for kids. This game allows users to select virtual avatars to ...
New

Sub Categories: