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diff --git a/services/sync/docs/rust-engines.rst b/services/sync/docs/rust-engines.rst new file mode 100644 index 0000000000..af00fd6619 --- /dev/null +++ b/services/sync/docs/rust-engines.rst @@ -0,0 +1,37 @@ +================================ +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>`_. |