r476.3 Wait for previous action to finish doesn't work with Save/Load

[JeFawk]

Problem description

Whatever is after a "Wait for previous action to finish" doesn't work with Save/Load.

Attach a .c3p

Wait for prev actin save load bug.c3p.zip

Steps to reproduce

1. open project
2. press the Press me button
3. save mid way
4. wait for the sprite to reach the right side, noticed the text gets changed to finished
5. press load button
6. wait for sprite to reach right side, notice the text doesn't get changed anymore

Observed result

Expected result

More details

Affected browsers/platforms: latest edge on mac

First affected release:

System details

View details

PASTE HERE

[JeFawk]

Works with "Wait x seconds" however.

[AshleyScirra]

Unfortunately this is a very tricky issue. The async action feature is often used with things that cannot be restored with savegames, such as AJAX requests: if you make a network request, and save state while waiting for that to complete, it's not possible to then restore a mid-flight network request when loading that. It could theoretically repeat the request when loading, but it seems probably undesirable to do so. A similar issue occurs with other cases like finding a path with the Pathfinding object: a path find operation that is still processing is not saved or restored for similar reasons. Internally the code deals with Promise objects which are basically opaque objects that just change to a completed state at a later time, and also cannot be saved or restored. So the async action feature currently makes no attempt to save or restore the state of things that are being waited on. (There are separate codepaths for different types of waits, like waiting for a time period or waiting for a signal, which means those are not affected.)

Having had a look at the kinds of async actions Construct generally uses, in almost all cases it seems inappropriate to attempt to save and restore them. So I think this problem is unique specifically to the Tween behavior - that looks like the only case you might actually want to save and restore the waiting state. Unfortunately that would require a significant amount of work to re-implement a significant portion of the async action feature solely to be able to handle these Tween behavior actions. Meanwhile you can work around it using the 'On finished' triggers rather than 'Wait for previous actions to complete'. So I'm afraid I think this is going to spend some time as a known issue before it's dealt with - it's the kind of thing that usually only gets done if there is some other big upgrade happening to the async action feature for some other reason.

[JeFawk]

@AshleyScirra ok I understand, thank you for the explanation, and indeed I just used the Tween "tween name" on finished condition.

Adding some tooltips on this action that it doesn't work with C3's Save/Load feature would be helpful for others.