What's the difference in semantics between `Corout...

# coroutines

[Laxystem]

What's the difference in semantics between CoroutineScope.launch { }.join() and withContext(CoroutineScope.context) { } ?

[Joffrey]

launch starts a concurrent operation, while withContext just switches the context but runs the piece of code in-place.

[Laxystem]

@Joffrey yup I forgor adding .join()

[streetsofboston]

The call to launch returns immediately, launching the coroutine and continues with what follows
The withContext waits (suspends) until the code inside of it has finished

[Joffrey]

Ah, with the edit, then the launch+join is just an overly complicated way to represent it

[Joffrey]

You should never use launch+join without code in between

[Laxystem]

as for the second comment ofc it's just for example purposes

[streetsofboston]

The join() call is a suspending call. It will be called in the CoroutineScope of whatever calls this join(), but the coroutine is launched in a separate/different CoroutineScope (the receiver part of the call to launch()). Cancellation here will be more complicated

[Joffrey]

> as for the second comment ofc it's just for example purposes
🤔 then what's your question?

[Laxystem]

@Joffrey if there's a difference in behaviour between the two

[Laxystem]

the codeblock being empty is just in this example

[Joffrey]

Ah, sorry I wasn't talking about the code block being empty. I was talking about the absence of code between launch { ...} and join(). If you chain launch { ... }.join(), then there is no point in starting a concurrent operation, because no code will effectively run concurrently with it

[Laxystem]

ahhh I get you

[Laxystem]

I do have a point tho, GLFW (esp. MacOS) threading shenanigans

[Joffrey]

But yeah it should behave pretty similarly to withContext in that case

[Joffrey]

I do have a point tho, GLFW (esp. MacOS) threading shenanigans

What is your point then? Because IMO you can always replace launch { ... }.join() with withContext(...) { ... }

[Laxystem]

@Joffrey cancelling all coroutines after glfwTerminate via a SupervisorJob

[streetsofboston]

You can call launch {}.join() only with providing a separate CoroutineScope to the launch call....

[streetsofboston]

otherScope.launch().join() and you'd call this in yet another CoroutineScope context.

[streetsofboston]

And if you use the coroutineScope { launch { ... } } instead, then a join() is not needed (since coroutineScope only resumes after all its child-coroutines have finished)