Session Delayed Para Changes / Actions Queue (#2406)

* initial implementation of lifecycles and upgrades * clean up a bit * fix doc comment * more rigid lifecycle checks * include paras which are transitioning, and lifecycle query * format guide * update api * update guide * explicit outgoing state, fix genesis * handle outgoing with transitioning paras * do not include transitioning paras in identifier * Update roadmap/implementers-guide/src/runtime/paras.md * Update roadmap/implementers-guide/src/runtime/paras.md * Update roadmap/implementers-guide/src/runtime/paras.md * Apply suggestions from code review * Use matches macro * Correct terms * Apply suggestions from code review * actions queue * Revert "actions queue" This reverts commit b2e9011ec8937d6c73e99292416c9692aeb30f73. * collapse onboarding state * starting actions queue * consolidate actions queue * schedule para initialize result * more actions queue for upgrade/downgrade * clean up with fully implemented actions queue * fix tests * fix scheduler tests * fix hrmp tests * fix test * doc fixes * fix hrmp test w/ valid para * Update paras.md * fix paras registrar * Update propose_parachain.rs * fix merge * Introduce "shared" module * fix rococo build * fix up and use shared * guide updates * add shared config to common tests * add shared to test-runtime * remove println * fix note Co-authored-by: Gavin Wood <gavin@parity.io>
2026-05-30 22:11:02 +00:00 · 2021-02-18 23:20:18 -04:00
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+# Shared Module
+
+This module is responsible for managing shared storage and configuration for other modules.
+
+It is important that other pallets are able to use the Shared Module, so it should not have a
+dependency on any other modules in the Parachains Runtime.
+
+For the moment, it is used exclusively to track the current session index across the Parachains
+Runtime system, and when it should be allowed to schedule future changes to Paras or Configurations.
+
+## Constants
+
+```rust
+// `SESSION_DELAY` is used to delay any changes to Paras registration or configurations.
+// Wait until the session index is 2 larger then the current index to apply any changes,
+// which guarantees that at least one full session has passed before any changes are applied.
+pub(crate) const SESSION_DELAY: SessionIndex = 2;
+```
+
+## Storage
+
+```rust
+// The current session index within the Parachains Runtime system.
+CurrentSessionIndex: SessionIndex;
+```
+
+## Initialization
+
+The Shared Module currently has no initialization routines.
+
+The Shared Module is initialized directly after the Configuration module, but before all other
+modules. It is important to update the Shared Module before any other module since its state may be
+used within the logic of other modules, and it is important that the state is consistent across
+them.
+
+## Session Change
+
+During a session change, the Shared Module receives and stores the current Session Index for that
+block through the Session Change Notification.
+
+This information is used in the:
+
+* Configuration Module: For delaying updates to configurations until at lease one full session has
+  passed.
+* Paras Module: For delaying updates to paras until at least one full session has passed.
+
+## Finalization
+
+The Shared Module currently has no finalization routines.
+
+## Functions
+
+* `scheduled_sessions() -> SessionIndex`: Return the next session index where updates to the
+  Parachains Runtime system would be safe to apply.
+* `set_session_index(SessionIndex)`: For tests. Set the current session index in the Shared Module.