`move_to_page` moves to an incorrect page

[HolgerGerhardt]

This can be tested with the following simple code:

class P1(Page):
    @classmethod
    def after_once(page, player):
        move_to_page(player, P3)

class P2(Page):
    pass

class P3(Page):
    pass

class P4(Page):
    @classmethod
    def after_once(page, player):
        move_to_page(player, P6)

class P5(Page):
    pass

class P6(Page):
    pass


page_order = [
    P1,
    P2,
    P3,
    P4,
    P5,
    P6,
]

Instead of moving to P3 from P1, one is forwarded to P4. From there, one is forwarded to End.html rather than P6.

[mrpg]

Please pull the changes and try again.

[HolgerGerhardt]

move_to_page now forwards to the correct page when used in before_once or after_once.

It still incorrectly forwards to the subsequent page of the target page when used in timeout_reached or validate.

[HolgerGerhardt]

Maybe some (page) counter has already been increased when timeout_reached or validate is executed?

Attached is an app, test_move_to_page.zip, to test the behavior of move_to_page inside the four different page functions,

• before_once,
• after_once,
• timeout_reached, and
• validate.

[HolgerGerhardt]

In this context, when using before_once or all_here to test whether a group field has a particular value—to advance all players in the group to a particular page—there seems to be a race condition: before_once and all_here retrieve a newly set value of a group field correctly for some players but retrieve the outdated value for other players.

In the following example, the top center pseudo-participant should not see the “Final page” but rather the yellow “Time limit violated by a fellow group member” page:

That is, correct would be:

[HolgerGerhardt]

Maybe some (page) counter has already been increased when timeout_reached or validate is executed?

Attached is an app, test_move_to_page.zip, to test the behavior of move_to_page inside the four different page functions,

• before_once,
• after_once,
• timeout_reached, and
• validate.

#186 (comment)

Since after_once is executed after timeout_reached and validate, constructions like the following can be used as workarounds:

    @classmethod
    def validate(page, player, data):
        player.skip = False
        if data.get("skip_to_08"):
            #move_to_page(player, P08)  # This incorrectly forwards to P09, use workaround:
            player.skip = True
    
    @classmethod
    def after_once(page, player):
        if player.skip:
            move_to_page(player, P08)

and

    @classmethod
    def timeout(page, player):
        player.timed_out = False
        return 10

    @classmethod
    def timeout_reached(page, player):
        #move_to_page(player, P11)  # This incorrectly forwards to P12, use workaround:
        player.timed_out = True
    
    @classmethod
    def after_once(page, player):
        if player.timed_out:
            move_to_page(player, P11)

Complete app is attached: test_move_to_page_workaround.zip.

[HolgerGerhardt]

In this context, when using before_once or all_here to test whether a group field has a particular value—to advance all players in the group to a particular page—there seems to be a race condition: before_once and all_here retrieve a newly set value of a group field correctly for some players but retrieve the outdated value for other players.
#186 (comment)

The described issue is, in fact, a combination of two issues:

1. One move_to_page in all_here is ineffective (while two are effective).
2. Using the “Multiview” function—or observing multiple browser windows simultaneously—causes an incorrect page to be displayed when move_to_page is executed in before_once.

To replicate this, the attached app, test_group_move_to_page.zip, can be used (it uses a group size of 3 and 3 rounds):

1. Create a session with 3 participants.
2. Open them in “Multiview” or in 3 separate browser windows that are all visible simultaneously.
3. Let one participant time out (or select “Abort after this page”).
4. Press the “Next” button in time for 2 participants.

Then, the player who advanced last (i.e., for whom the “Next” button was pressed last or who timed out) will incorrectly display the ShowGrouping page, even though they should see the DropoutInfo page. See the following screenshot:

Issue 1

As you can see in the screenshot, the page to be displayed for the lower left participant is supposed to be DropoutInfo according to the testing elements, but the contents are those of ShowGroup.

This does not seem to happen when using separate browser tabs that are not all visible at the same time.

Issue 2

Irrespective of Issue 1, if a timeout occurs in the final round, the participant to advance last progresses to AllGood instead of being forwarded to DropoutInfo.

This is despite the print statements

all_here: Moving player um9da
all_here: Moving player brdf6
all_here: Moving player ti55c

indicating that all three players should have been moved—but only two were. One move_to_page in all_here remains ineffective.

If the timeout occurs in earlier rounds, the print statements indicate the same failure: One move_to_page in all_here is ineffective, and for the affected participant the move_to_page in before_once becomes effective:

all_here: Moving player u6gwb
all_here: Moving player xwar6
all_here: Moving player lheb5
before_once: Moving player lheb5

It is this move_to_page in before_once for which “Multiview” displays the incorrect page (Issue 1).

[HolgerGerhardt]

With 6db21da, the simple, linear app https://github.com/user-attachments/files/25584567/test_move_to_page.zip works flawlessly. I will test more complicated scenarios shortly.

[HolgerGerhardt]

I just tested 6db21da in the more complex app https://github.com/user-attachments/files/25616738/test_group_move_to_page.zip:

Issue 1 described in #186 (comment) (the incorrect display of a page in “Multiview” upon move_to_page in before_once) appears to be fixed.

Issue 2, however, apparently still exists: One move_to_page is ineffective in the loop included in all_here so that before_once needs to take over:

all_here: Moving player qdyq5
all_here: Moving player fg8of
all_here: Moving player iedor
before_once: Moving player iedor

[mrpg]

Thank you. @HolgerGerhardt kindly check out (with) the latest commit.