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

abtin
page 20: … protoc command… I had to additionally run the following go get commands in order to be able to compile protobuf code using go...
New
jimschubert
In Chapter 3, the source for index introduces Config on page 31, followed by more code including tests; Config isn’t introduced until pag...
New
simonpeter
When I try the command to create a pair of migration files I get an error. user=> (create-migration "guestbook") Execution error (Ill...
New
rmurray10127
Title: Intuitive Python: docker run… denied error (page 2) Attempted to run the docker command in both CLI and Powershell PS C:\Users\r...
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
jskubick
I think I might have found a problem involving SwitchCompat, thumbTint, and trackTint. As entered, the SwitchCompat changes color to hol...
New
jskubick
I found an issue in Chapter 7 regarding android:backgroundTint vs app:backgroundTint. How to replicate: load chapter-7 from zipfile i...
New
brunogirin
When I run the coverage example to report on missing lines, I get: pytest --cov=cards --report=term-missing ch7 ERROR: usage: pytest [op...
New
dsmith42
Hey there, I’m enjoying this book and have learned a few things alredayd. However, in Chapter 4 I believe we are meant to see the “>...
New
mert
AWDWR 7, page 152, page 153: Hello everyone, I’m a little bit lost on the hotwire part. I didn’t fully understand it. On page 152 @rub...
New

Other popular topics Top

PragmaticBookshelf
Brace yourself for a fun challenge: build a photorealistic 3D renderer from scratch! In just a couple of weeks, build a ray tracer that r...
New
DevotionGeo
I know that -t flag is used along with -i flag for getting an interactive shell. But I cannot digest what the man page for docker run com...
New
AstonJ
Continuing the discussion from Thinking about learning Crystal, let’s discuss - I was wondering which languages don’t GC - maybe we can c...
New
PragmaticBookshelf
Create efficient, elegant software tests in pytest, Python's most powerful testing framework. Brian Okken @brianokken Edited by Kat...
New
PragmaticBookshelf
Author Spotlight Rebecca Skinner @RebeccaSkinner Welcome to our latest author spotlight, where we sit down with Rebecca Skinner, auth...
New
PragmaticBookshelf
Programming Ruby is the most complete book on Ruby, covering both the language itself and the standard library as well as commonly used t...
New
DevotionGeo
I have always used antique keyboards like Cherry MX 1800 or Cherry MX 8100 and almost always have modified the switches in some way, like...
New
PragmaticBookshelf
Get the comprehensive, insider information you need for Rails 8 with the new edition of this award-winning classic. Sam Ruby @rubys ...
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
Fight complexity and reclaim the original spirit of agility by learning to simplify how you develop software. The result: a more humane a...
New

Sub Categories: