Scheduler Module (#1162)

* scheduler module skeleton

* update scheduler skeleton to match latest version of guide

* better session change notification

* add mock randomness and fix test compilation

* shuffle validators into groups

* finish implementing session change logic for scheduler

* tweak core assignment type to track retries of parathread

* reframe queued parathread core as offset

* implement initialzation and finalization routines

* implement parathread claim queuing

* implement core_para

* implement the group_validators routine and fix errors

* add a reason for freeing cores

* implement `schedule` function

* add some docs to the scheduled function

* implement `occupied` helper

* implement availability predicate

* fix some warnings

* integrate scheduler into initializer

* integrate scheduler into mock module

* avoid conflict with Substrate's scheduler storage

* add parathreads index to paras module

* implement parathreads map in paras module

* add is_parathread to paras

* test adding parathread claim

* test that you cannot add claims when no parathread cores exist

* check session change parathread queue pruning

* test validator shuffling

* add allow_unused to scheduler items

* add test for scheduling

* add some more tests for scheduling logic

* test core rotation

* check parathread claim pruning after retries

* add bound notes

* Apply suggestions from code review

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>
Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

* more suggestions from review

* test availability predicate, add box to please compiler

* add changes to guide

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>
Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

polkadot/runtime/parachains/src/mock.rs

@@ -30,7 +30,7 @@ use primitives::{
 };
 use frame_support::{
 	impl_outer_origin, impl_outer_dispatch, parameter_types,
-	weights::Weight,
+	weights::Weight, traits::Randomness as RandomnessT,
 };
 
 /// A test runtime struct.
@@ -47,6 +47,14 @@ impl_outer_dispatch! {
 	}
 }
 
+pub struct TestRandomness;
+
+impl RandomnessT<H256> for TestRandomness {
+	fn random(_subject: &[u8]) -> H256 {
+		Default::default()
+	}
+}
+
 parameter_types! {
 	pub const BlockHashCount: u32 = 250;
 	pub const MaximumBlockWeight: Weight = 4 * 1024 * 1024;
@@ -80,12 +88,16 @@ impl system::Trait for Test {
 	type OnKilledAccount = ();
 }
 
-impl crate::initializer::Trait for Test { }
+impl crate::initializer::Trait for Test {
+	type Randomness = TestRandomness;
+}
 
 impl crate::configuration::Trait for Test { }
 
 impl crate::paras::Trait for Test { }
 
+impl crate::scheduler::Trait for Test { }
+
 pub type System = system::Module<Test>;
 
 /// Mocked initializer.
@@ -97,6 +109,9 @@ pub type Configuration = crate::configuration::Module<Test>;
 /// Mocked paras.
 pub type Paras = crate::paras::Module<Test>;
 
+/// Mocked scheduler.
+pub type Scheduler = crate::scheduler::Module<Test>;
+
 /// Create a new set of test externalities.
 pub fn new_test_ext(state: GenesisConfig) -> TestExternalities {
 	let mut t = state.system.build_storage::<Test>().unwrap();