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Opened 5 years ago

Last modified 3 years ago

#31436 assigned enhancement

Handle conflicts in concurrent Customizer sessions — at Initial Version

Reported by: westonruter Owned by:
Milestone: Future Release Priority: normal
Severity: normal Version: 3.4
Component: Customize Keywords: needs-patch
Focuses: javascript Cc:


If two users open the Customizer at the same time and modify the same settings, the user who saves their changes last will win out, and the person who saves first will have their changes lost. (The frequency of the problem was reduced in #29983 since now only dirty settings now get POSTed.) The Customizer needs Heartbeat integration to add the “Post Locking” functionality. We don't need to lock the entire Customizer, however, from concurrent users: we need to add locking for individual settings in the Customizer. When a setting becomes dirty, we need to broadcast via Heartbeat to other users that the setting has been changed and thus any controls for this setting should be marked as "locked", with any changes prevented. This will become increasingly important as more and more settings are added to the Customizer and users go there more often to make changes.

The locking UI could provide a button to copy the other user's change into the other Customizer session, and this could result in the control being editable again, with subsequent changes pushed out to other users as well, who would then also get the corresponding setting automatically updated if it was dirty, but if it was not dirty then it would remain in its clean state but with a locking notification added.

This also should apply when a setting is modified by some means other than the Customizer: if someone is in the Customizer and another user changes a setting via an admin page or via XML-RPC or REST API, then this setting update should also be illustrated in the Customizer to note that the settings are stale and should be refreshed. This refresh could be done inline, without having to reload the entire page.

Another special consideration needs to be made for Widgets in the Customizer. Each WP_Widget 2.0 “multi-widget” gets an index number associated with each instance of a give type. When you add a widget, this number gets incremented (widget.set( 'multi_number', widget.get( 'multi_number' ) + 1 );). The initial multi-number is calculated from the next_widget_id_number() function which takes the max number currently used, and increments it by one. It is thus possible for multiple widgets to be deleted in one session (from the widgets admin page, since Customizer only removes widgets by moving them to the Inactive Widgets sidebar) then new ones added back in other sessions and the initial multi_number will not be consistent. In other words, the multi_number for each widget type needs to be synced across each Customizer session along with the actual setting values.

Some enhancements for a feature plugin: The Customizer UI would benefit from having a list of users currently in the Customizer appearing somewhere, with a list of the changes each user has made. If someone left their Customizer session open, this list would also allow an administrator to sign the user out, using something like the User Session Control plugin; or the Customizer UI could provide a way to boot a user from the Customizer.

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