Race condition when saving Matrix fields

[aghull]

Description

When saving matrix fieldsets under heavy load, the compiled classes fail to accurately compile the full field set, causing missing property errors.

In Craft\services\Fields#saveField the updateFieldVersion method is called. This method is run for each field in the matrix. The fieldversion is bumped on the first field saved and prevented from being bumped again in the same request:

cms/src/services/Fields.php

Line 1361 in d03dc3b

return;

If a request arrives in craft after the first field is saved but before a brand new field is saved, it caches the compiled ContentBehaviour class with the new fieldversion, but without the new field, preventing the new field from ever appearing in the compiled class.

Removing the line above that prevents multiple fieldversion changes resolves this bug.

Steps to reproduce

1. Place the site under heavy load
2. Save a large matrix field with a new field added
3. Load any front-end Craft page

Additional info

• Craft version: 3.0.22
• PHP version: 7.1.17
• Database driver & version: mysql 5.7.22

[aghull]

^^ @brandonkelly

[brandonkelly]

@aghull Thanks for looking into that and providing the fix. Your PR is merged in for the next release!