Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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diff --git a/services/sync/docs/rust-engines.rst b/services/sync/docs/rust-engines.rst
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+================================
+How Rust Engines are implemented
+================================
+
+There are 2 main components to engines implemented in Rust
+
+The bridged-engine
+==================
+
+Because Rust engines still need to work with the existing Sync infrastructure,
+there's the concept of a `bridged-engine <https://searchfox.org/mozilla-central/source/services/sync/modules/bridged_engine.js>`_.
+In short, this is just a shim between the existing
+`Sync Service <https://searchfox.org/mozilla-central/source/services/sync/modules/service.js>`_
+and the Rust code.
+
+The bridge
+==========
+
+`"Golden Gate" <https://searchfox.org/mozilla-central/source/services/sync/golden_gate>`_
+is a utility to help bridge any Rust implemented Sync engines with desktop. In
+other words, it's a "rusty bridge" - get it? Get it? Yet another of Lina's puns
+that live on!
+
+One of the key challenges with integrating a Rust Sync component with desktop
+is the different threading models. The Rust code tends to be synchronous -
+most functions block the calling thread to do the disk or network IO necessary
+to work - it assumes that the consumer will delegate this to some other thread.
+
+So golden_gate is this background thread delegation for a Rust Sync engine -
+gecko calls golden-gate on the main thread, it marshalls the call to a worker
+thread, and the result is marshalled back to the main thread.
+
+It's worth noting that golden_gate is just for the Sync engine part - other
+parts of the component (ie, the part that provides the functionality that's not
+sync related) will have its own mechanism for this. For example, the
+`webext-storage bridge <https://searchfox.org/mozilla-central/source/toolkit/components/extensions/storage/webext_storage_bridge/src>`_
+uses a similar technique `which has some in-depth documentation <../../toolkit/components/extensions/webextensions/webext-storage.html>`_.