1920245 - Add extension task queue helper

Status: RESOLVED FIXED

(WebExtensions :: General, task, P2)

Description

[Rob Wu [:robwu]]

An ordered task queue is occasionally needed in extension code. Because there was no generic utility, there are multiple implementations of queues, and even implicit ordering.

Examples:

• Queue class in ExtensionDNRStore - used for sequential initialization (internal data structures from file on disk), and data updates.
• extPermAccessQueues + _synchronizeExtPermAccess in ExtensionPermissions - ensuring that permission reads/writes are run in order, to fix data races in bug 1902011.
• scripting API implementation of register / update / unregister maintains an in-memory structure, and tries to ensure data consistency by ensuring that the implementation is fully synchronous, from the start of a method call, to reading internal data structures, validating a modification and registering the modifications. This currently works, but if future code were to add await in the method, the logic would break. This ordering requirement is not obvious and thus fragile.

There are more use cases:

• userScripts API also needs to register/update/unregister scripts. Unlike the scripting API, I don't want to force the implementation to be synchronous, because that is very restrictive and would force suboptimal implementation design choices, such as having to keep too much data in memory.

Comment 1

[Rob Wu [:robwu]]

Attachment: Bug 1920245 - Add read/write task queue helper

This patch provides a task queue helper that supports the following:

• Parallel reads + sequential writes. Running tasks as fast as possible.

• Queue lifetime tied to extension lifetime, but without requiring an
  Extension to be around, because that is not always available
  (e.g. for operations past add-on uninstall).

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/ecef33a461c9
Add read/write task queue helper r=zombie

Comment 3

[Serban Stanca [:SerbanS]]

https://hg.mozilla.org/mozilla-central/rev/ecef33a461c9