Scheduler Module

roadmap/implementors-guide/guide.md

@@ -459,6 +459,8 @@ Storage layout:
 ```rust
 /// All parachains. Ordered ascending by ParaId. Parathreads are not included.
 Parachains: Vec<ParaId>,
+/// All parathreads.
+Parathreads: map ParaId => Option<()>,
 /// The head-data of every registered para.
 Heads: map ParaId => Option<HeadData>;
 /// The validation code of every live para.
@@ -496,6 +498,7 @@ OutgoingParas: Vec<ParaId>;
 1. Clean up outgoing paras. This means removing the entries under `Heads`, `ValidationCode`, `FutureCodeUpgrades`, and `FutureCode`. An according entry should be added to `PastCode`, `PastCodeMeta`, and `PastCodePruning` using the outgoing `ParaId` and removed `ValidationCode` value. This is because any outdated validation code must remain available on-chain for a determined amount of blocks, and validation code outdated by de-registering the para is still subject to that invariant.
 1. Apply all incoming paras by initializing the `Heads` and `ValidationCode` using the genesis parameters.
 1. Amend the `Parachains` list to reflect changes in registered parachains.
+1. Amend the `Parathreads` set to reflect changes in registered parathreads.
 
 #### Initialization
 
@@ -508,6 +511,7 @@ OutgoingParas: Vec<ParaId>;
 * `schedule_code_upgrade(ParaId, ValidationCode, expected_at: BlockNumber)`: Schedule a future code upgrade of the given parachain, to be applied after inclusion of a block of the same parachain executed in the context of a relay-chain block with number >= `expected_at`.
 * `note_new_head(ParaId, HeadData, BlockNumber)`: note that a para has progressed to a new head, where the new head was executed in the context of a relay-chain block with given number. This will apply pending code upgrades based on the block number provided.
 * `validation_code_at(ParaId, at: BlockNumber, assume_intermediate: Option<BlockNumber>)`: Fetches the validation code to be used when validating a block in the context of the given relay-chain height. A second block number parameter may be used to tell the lookup to proceed as if an intermediate parablock has been included at the given relay-chain height. This may return past, current, or (with certain choices of `assume_intermediate`) future code. `assume_intermediate`, if provided, must be before `at`. If the validation code has been pruned, this will return `None`.
+* `is_parathread(ParaId) -> bool`: Returns true if the para ID references any live parathread.
 
 #### Finalization
 
@@ -605,25 +609,37 @@ struct ParathreadEntry {
 // A queued parathread entry, pre-assigned to a core.
 struct QueuedParathread {
 	claim: ParathreadEntry,
-	core: CoreIndex,
+	/// offset within the set of para-threads ranged `0..config.parathread_cores`.
+	core_offset: u32,
 }
 
 struct ParathreadQueue {
 	queue: Vec<QueuedParathread>,
-	// this value is between 0 and config.parathread_cores
-	next_core: CoreIndex,
+	/// offset within the set of para-threads ranged `0..config.parathread_cores`.
+	next_core_offset: u32,
 }
 
 enum CoreOccupied {
   Parathread(ParathreadEntry), // claim & retries
   Parachain,
 }
 
+enum AssignmentKind {
+	Parachain,
+	Parathread(CollatorId, u32),
+}
+
 struct CoreAssignment {
-  core: CoreIndex,
-  para_id: ParaId,
-  collator: Option<CollatorId>,
-  group_idx: GroupIndex,
+	core: CoreIndex,
+	para_id: ParaId,
+	kind: AssignmentKind,
+	group_idx: GroupIndex,
+}
+
+// reasons a core might be freed.
+enum FreedReason {
+	Concluded,
+	TimedOut,
 }
 ```
 
@@ -662,6 +678,7 @@ Actions:
 	- First, we obtain "shuffled validators" `SV` by shuffling the validators using the `SessionChangeNotification`'s random seed.
 	- The groups are selected by partitioning `SV`. The first V % N groups will have (V / N) + 1 members, while the remaining groups will have (V / N) members each.
 1. Prune the parathread queue to remove all retries beyond `configuration.parathread_retries`.
+    - Also prune all parathread claims corresponding to de-registered parathreads.
     - all pruned claims should have their entry removed from the parathread index.
     - assign all non-pruned claims to new cores if the number of parathread cores has changed between the `new_config` and `old_config` of the `SessionChangeNotification`.
     - Assign claims in equal balance across all cores if rebalancing, and set the `next_core` of the `ParathreadQueue` by incrementing the relative index of the last assigned core and taking it modulo the number of parathread cores.
@@ -684,15 +701,16 @@ Actions:
   - `next_core` is then updated by adding 1 and taking it modulo `config.parathread_cores`.
   - The claim is then added to the claim index.
 
-* `schedule(Vec<CoreIndex>)`: schedule new core assignments, with a parameter indicating previously-occupied cores which are to be considered returned.
+* `schedule(Vec<(CoreIndex, FreedReason)>)`: schedule new core assignments, with a parameter indicating previously-occupied cores which are to be considered returned and why they are being returned.
   - All freed parachain cores should be assigned to their respective parachain
-  - All freed parathread cores should have the claim removed from the claim index.
+  - All freed parathread cores whose reason for freeing was `FreedReason::Concluded` should have the claim removed from the claim index.
+  - All freed parathread cores whose reason for freeing was `FreedReason::TimedOut` should have the claim added to the parathread queue again without retries incremented.
   - All freed parathread cores should take the next parathread entry from the queue.
   - The i'th validator group will be assigned to the `(i+k)%n`'th core at any point in time, where `k` is the number of rotations that have occurred in the session, and `n` is the total number of cores. This makes upcoming rotations within the same session predictable.
 * `scheduled() -> Vec<CoreAssignment>`: Get currently scheduled core assignments.
 * `occupied(Vec<CoreIndex>). Note that the given cores have become occupied.
-  - Fails if any given cores were not scheduled.
-  - Fails if the given cores are not sorted ascending by core index
+  - Behavior undefined if any given cores were not scheduled.
+  - Behavior undefined if the given cores are not sorted ascending by core index
   - This clears them from `Scheduled` and marks each corresponding `core` in the `AvailabilityCores` as occupied.
   - Since both the availability cores and the newly-occupied cores lists are sorted ascending, this method can be implemented efficiently.
 * `core_para(CoreIndex) -> ParaId`: return the currently-scheduled or occupied ParaId for the given core.
@@ -792,8 +810,8 @@ Included: Option<()>,
 #### Entry Points
 
   * `inclusion`: This entry-point accepts two parameters: [`Bitfields`](#Signed-Availability-Bitfield) and [`BackedCandidates`](#Backed-Candidate).
-    1. The `Bitfields` are first forwarded to the `process_bitfields` routine, returning a set of freed cores. Provide a `Scheduler::core_para` as a core-lookup to the `process_bitfields` routine.
-    1. If `Scheduler::availability_timeout_predicate` is `Some`, invoke `Inclusion::collect_pending` using it, and add timed-out cores to the free cores.
+    1. The `Bitfields` are first forwarded to the `process_bitfields` routine, returning a set of freed cores. Provide a `Scheduler::core_para` as a core-lookup to the `process_bitfields` routine. Annotate each of these freed cores with `FreedReason::Concluded`.
+    1. If `Scheduler::availability_timeout_predicate` is `Some`, invoke `Inclusion::collect_pending` using it, and add timed-out cores to the free cores, annotated with `FreedReason::TimedOut`.
     1. Invoke `Scheduler::schedule(freed)`
     1. Pass the `BackedCandidates` along with the output of `Scheduler::scheduled` to the `Inclusion::process_candidates` routine, getting a list of all newly-occupied cores.
     1. Call `Scheduler::occupied` for all scheduled cores where a backed candidate was submitted.

runtime/parachains/Cargo.toml

@@ -35,6 +35,9 @@ frame-benchmarking = { git = "https://github.com/paritytech/substrate", branch =
 primitives = { package = "polkadot-primitives", path = "../../primitives", default-features = false }
 libsecp256k1 = { version = "0.3.2", default-features = false, optional = true }
 
+rand = { version = "0.7", default-features = false }
+rand_chacha = { version = "0.2.2", default-features = false }
+
 [dev-dependencies]
 hex-literal = "0.2.1"
 keyring = { package = "sp-keyring", git = "https://github.com/paritytech/substrate", branch = "master" }

runtime/parachains/src/configuration.rs

@@ -33,7 +33,7 @@ use system::ensure_root;
 /// All configuration of the runtime with respect to parachains and parathreads.
 #[derive(Clone, Encode, Decode, PartialEq, Default)]
 #[cfg_attr(test, derive(Debug))]
-pub struct HostConfiguration<BlockNumber: Default> {
+pub struct HostConfiguration<BlockNumber> {
 	/// The minimum frequency at which parachains can update their validation code.
 	pub validation_upgrade_frequency: BlockNumber,
 	/// The delay, in blocks, before a validation upgrade is applied.
@@ -49,7 +49,7 @@ pub struct HostConfiguration<BlockNumber: Default> {
 	pub parathread_cores: u32,
 	/// The number of retries that a parathread author has to submit their block.
 	pub parathread_retries: u32,
-	/// How often parachain groups should be rotated across parachains.
+	/// How often parachain groups should be rotated across parachains. Must be non-zero.
 	pub parachain_rotation_frequency: BlockNumber,
 	/// The availability period, in blocks, for parachains. This is the amount of blocks
 	/// after inclusion that validators have to make the block available and signal its availability to

runtime/parachains/src/initializer.rs

@@ -25,11 +25,29 @@ use primitives::{
 	parachain::{ValidatorId},
 };
 use frame_support::{
-	decl_storage, decl_module, decl_error,
+	decl_storage, decl_module, decl_error, traits::Randomness,
 };
-use crate::{configuration, paras};
+use crate::{configuration::{self, HostConfiguration}, paras, scheduler};
+
+/// Information about a session change that has just occurred.
+#[derive(Default, Clone)]
+pub struct SessionChangeNotification<BlockNumber> {
+	/// The new validators in the session.
+	pub validators: Vec<ValidatorId>,
+	/// The qeueud validators for the following session.
+	pub queued: Vec<ValidatorId>,
+	/// The configuration before handling the session change
+	pub prev_config: HostConfiguration<BlockNumber>,
+	/// The configuration after handling the session change.
+	pub new_config: HostConfiguration<BlockNumber>,
+	/// A secure random seed for the session, gathered from BABE.
+	pub random_seed: [u8; 32],
+}
 
-pub trait Trait: system::Trait + configuration::Trait + paras::Trait { }
+pub trait Trait: system::Trait + configuration::Trait + paras::Trait + scheduler::Trait {
+	/// A randomness beacon.
+	type Randomness: Randomness<Self::Hash>;
+}
 
 decl_storage! {
 	trait Store for Module<T: Trait> as Initializer {
@@ -62,14 +80,18 @@ decl_module! {
 			// - Inclusion
 			// - Validity
 			let total_weight = configuration::Module::<T>::initializer_initialize(now) +
-				paras::Module::<T>::initializer_initialize(now);
+				paras::Module::<T>::initializer_initialize(now) +
+				scheduler::Module::<T>::initializer_initialize(now);
 
 			HasInitialized::set(Some(()));
 
 			total_weight
 		}
 
 		fn on_finalize() {
+			// reverse initialization order.
+
+			scheduler::Module::<T>::initializer_finalize();
 			paras::Module::<T>::initializer_finalize();
 			configuration::Module::<T>::initializer_finalize();
 			HasInitialized::take();
@@ -90,8 +112,32 @@ impl<T: Trait> Module<T> {
 		let validators: Vec<_> = validators.map(|(_, v)| v).collect();
 		let queued: Vec<_> = queued.map(|(_, v)| v).collect();
 
+		let prev_config = <configuration::Module<T>>::config();
+
+		let random_seed = {
+			let mut buf = [0u8; 32];
+			let random_hash = T::Randomness::random(&b"paras"[..]);
+			let len = sp_std::cmp::min(32, random_hash.as_ref().len());
+			buf[..len].copy_from_slice(&random_hash.as_ref()[..len]);
+			buf
+		};
+
+		// We can't pass the new config into the thing that determines the new config,
+		// so we don't pass the `SessionChangeNotification` into this module.
 		configuration::Module::<T>::initializer_on_new_session(&validators, &queued);
-		paras::Module::<T>::initializer_on_new_session(&validators, &queued);
+
+		let new_config = <configuration::Module<T>>::config();
+
+		let notification = SessionChangeNotification {
+			validators,
+			queued,
+			prev_config,
+			new_config,
+			random_seed,
+		};
+
+		paras::Module::<T>::initializer_on_new_session(&notification);
+		scheduler::Module::<T>::initializer_on_new_session(&notification);
 	}
 }
 

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();