Tagged transaction queue integration (#893)

* Make the graph generic.

* Adapting pool API for the graph.

* Merge pool & graph.

* Restructure.

* Fix test of transaction pool.

* Get rid of node/transaction-pool.

* Compilation fixes.

* Test7

* Fix compilation of tests.

* Revert runtime changes.

* Add validate_transaction to test-runtime.

* Fix RPC tests.

* Add clearing of the old transactions.

* Trigger pool events.

* Use new queue API.

* Fix wasm build, re-export Hasher.

* No warning if validate transaction fails.

* Get rid of Into<u64> and use As

substrate/core/transaction-pool/graph/src/base_pool.rs

@@ -0,0 +1,709 @@
+// Copyright 2018 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! A basic version of the dependency graph.
+//!
+//! For a more full-featured pool, have a look at the `pool` module.
+
+use std::{
+	hash,
+	sync::Arc,
+};
+
+use sr_primitives::traits::Member;
+use sr_primitives::transaction_validity::{
+	TransactionTag as Tag,
+	TransactionLongevity as Longevity,
+	TransactionPriority as Priority,
+};
+
+use error;
+use future::{FutureTransactions, WaitingTransaction};
+use ready::ReadyTransactions;
+
+/// Block number type.
+pub type BlockNumber = u64;
+
+/// Successful import result.
+#[derive(Debug, PartialEq, Eq)]
+pub enum Imported<Hash, Ex> {
+	/// Transaction was successfuly imported to Ready queue.
+	Ready {
+		/// Hash of transaction that was successfuly imported.
+		hash: Hash,
+		/// Transactions that got promoted from the Future queue.
+		promoted: Vec<Hash>,
+		/// Transactions that failed to be promoted from the Future queue and are now discarded.
+		failed: Vec<Hash>,
+		/// Transactions removed from the Ready pool (replaced).
+		removed: Vec<Arc<Transaction<Hash, Ex>>>,
+	},
+	/// Transaction was successfuly imported to Future queue.
+	Future {
+		/// Hash of transaction that was successfuly imported.
+		hash: Hash,
+	}
+}
+
+impl<Hash, Ex> Imported<Hash, Ex> {
+	/// Returns the hash of imported transaction.
+	pub fn hash(&self) -> &Hash {
+		use self::Imported::*;
+		match *self {
+			Ready { ref hash, .. } => hash,
+			Future { ref hash, .. } => hash,
+		}
+	}
+}
+
+/// Status of pruning the queue.
+#[derive(Debug)]
+pub struct PruneStatus<Hash, Ex> {
+	/// A list of imports that satisfying the tag triggered.
+	pub promoted: Vec<Imported<Hash, Ex>>,
+	/// A list of transactions that failed to be promoted and now are discarded.
+	pub failed: Vec<Hash>,
+	/// A list of transactions that got pruned from the ready queue.
+	pub pruned: Vec<Arc<Transaction<Hash, Ex>>>,
+}
+
+/// Immutable transaction
+#[cfg_attr(test, derive(Clone))]
+#[derive(Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub struct Transaction<Hash, Extrinsic> {
+	/// Raw extrinsic representing that transaction.
+	pub data: Extrinsic,
+	/// Transaction hash (unique)
+	pub hash: Hash,
+	/// Transaction priority (higher = better)
+	pub priority: Priority,
+	/// How many blocks the transaction is valid for.
+	pub longevity: Longevity,
+	/// Tags required by the transaction.
+	pub requires: Vec<Tag>,
+	/// Tags that this transaction provides.
+	pub provides: Vec<Tag>,
+}
+
+/// Transaction pool.
+///
+/// Builds a dependency graph for all transactions in the pool and returns
+/// the ones that are currently ready to be executed.
+///
+/// General note:
+/// If function returns some transactions it usually means that importing them
+/// as-is for the second time will fail or produce unwanted results.
+/// Most likely it is required to revalidate them and recompute set of
+/// required tags.
+#[derive(Debug)]
+pub struct BasePool<Hash: hash::Hash + Eq, Ex> {
+	future: FutureTransactions<Hash, Ex>,
+	ready: ReadyTransactions<Hash, Ex>,
+}
+
+impl<Hash: hash::Hash + Eq, Ex> Default for BasePool<Hash, Ex> {
+	fn default() -> Self {
+		BasePool {
+			future: Default::default(),
+			ready: Default::default(),
+		}
+	}
+}
+
+impl<Hash: hash::Hash + Member, Ex: ::std::fmt::Debug> BasePool<Hash, Ex> {
+	/// Imports transaction to the pool.
+	///
+	/// The pool consists of two parts: Future and Ready.
+	/// The former contains transactions that require some tags that are not yet provided by
+	/// other transactions in the pool.
+	/// The latter contains transactions that have all the requirements satisfied and are
+	/// ready to be included in the block.
+	pub fn import(
+		&mut self,
+		block_number: BlockNumber,
+		tx: Transaction<Hash, Ex>,
+	) -> error::Result<Imported<Hash, Ex>> {
+		if self.future.contains(&tx.hash) || self.ready.contains(&tx.hash) {
+			bail!(error::ErrorKind::AlreadyImported)
+		}
+
+		let tx = WaitingTransaction::new(tx, self.ready.provided_tags());
+		trace!(target: "txpool", "[{:?}] {:?}", tx.transaction.hash, tx);
+		debug!(target: "txpool", "[{:?}] Importing to {}", tx.transaction.hash, if tx.is_ready() { "ready" } else { "future" });
+
+		// If all tags are not satisfied import to future.
+		if !tx.is_ready() {
+			let hash = tx.transaction.hash.clone();
+			self.future.import(tx);
+			return Ok(Imported::Future { hash });
+		}
+
+		self.import_to_ready(block_number, tx)
+	}
+
+	/// Imports transaction to ready queue.
+	///
+	/// NOTE the transaction has to have all requirements satisfied.
+	fn import_to_ready(&mut self, block_number: BlockNumber, tx: WaitingTransaction<Hash, Ex>) -> error::Result<Imported<Hash, Ex>> {
+		let hash = tx.transaction.hash.clone();
+		let mut promoted = vec![];
+		let mut failed = vec![];
+		let mut removed = vec![];
+
+		let mut first = true;
+		let mut to_import = vec![tx];
+
+		loop {
+			// take first transaction from the list
+			let tx = match to_import.pop() {
+				Some(tx) => tx,
+				None => break,
+			};
+
+			// find transactions in Future that it unlocks
+			to_import.append(&mut self.future.satisfy_tags(&tx.transaction.provides));
+
+			// import this transaction
+			let current_hash = tx.transaction.hash.clone();
+			match self.ready.import(block_number, tx) {
+				Ok(mut replaced) => {
+					if !first {
+						promoted.push(current_hash);
+					}
+					// The transactions were removed from the ready pool. We might attempt to re-import them.
+					removed.append(&mut replaced);
+				},
+				// transaction failed to be imported.
+				Err(e) => if first {
+					debug!(target: "txpool", "[{:?}] Error importing: {:?}", current_hash, e);
+					return Err(e)
+				} else {
+					failed.push(current_hash);
+				},
+			}
+			first = false;
+		}
+
+		// An edge case when importing transaction caused
+		// some future transactions to be imported and that
+		// future transactions pushed out current transaction.
+		// This means that there is a cycle and the transactions should
+		// be moved back to future, since we can't resolve it.
+		if removed.iter().any(|tx| tx.hash == hash) {
+			// We still need to remove all transactions that we promoted
+			// since they depend on each other and will never get to the best iterator.
+			self.ready.remove_invalid(&promoted);
+
+			debug!(target: "txpool", "[{:?}] Cycle detected, bailing.", hash);
+			bail!(error::ErrorKind::CycleDetected)
+		}
+
+		Ok(Imported::Ready {
+			hash,
+			promoted,
+			failed,
+			removed,
+		})
+	}
+
+	/// Returns an iterator over ready transactions in the pool.
+	pub fn ready<'a, 'b: 'a>(&'b self) -> impl Iterator<Item=Arc<Transaction<Hash, Ex>>> + 'a {
+		self.ready.get()
+	}
+
+	/// Removes all transactions represented by the hashes and all other transactions
+	/// that depend on them.
+	///
+	/// Returns a list of actually removed transactions.
+	/// NOTE some transactions might still be valid, but were just removed because
+	/// they were part of a chain, you may attempt to re-import them later.
+	/// NOTE If you want to remove ready transactions that were already used
+	/// and you don't want them to be stored in the pool use `prune_tags` method.
+	pub fn remove_invalid(&mut self, hashes: &[Hash]) -> Vec<Arc<Transaction<Hash, Ex>>> {
+		let mut removed = self.ready.remove_invalid(hashes);
+		removed.extend(self.future.remove(hashes).into_iter().map(Arc::new));
+		removed
+	}
+
+	/// Prunes transactions that provide given list of tags.
+	///
+	/// This will cause all transactions that provide these tags to be removed from the pool,
+	/// but unlike `remove_invalid`, dependent transactions are not touched.
+	/// Additional transactions from future queue might be promoted to ready if you satisfy tags
+	/// that the pool didn't previously know about.
+	pub fn prune_tags(&mut self, block_number: BlockNumber, tags: impl IntoIterator<Item=Tag>) -> PruneStatus<Hash, Ex> {
+		let mut to_import = vec![];
+		let mut pruned = vec![];
+
+		for tag in tags {
+			// make sure to promote any future transactions that could be unlocked
+			to_import.append(&mut self.future.satisfy_tags(::std::iter::once(&tag)));
+			// and actually prune transactions in ready queue
+			pruned.append(&mut self.ready.prune_tags(tag));
+		}
+
+		let mut promoted = vec![];
+		let mut failed = vec![];
+		for tx in to_import {
+			let hash = tx.transaction.hash.clone();
+			match self.import_to_ready(block_number, tx) {
+				Ok(res) => promoted.push(res),
+				Err(e) => {
+					warn!(target: "txpool", "[{:?}] Failed to promote during pruning: {:?}", hash, e);
+					failed.push(hash)
+				},
+			}
+		}
+
+		PruneStatus {
+			pruned,
+			failed,
+			promoted,
+		}
+	}
+
+	/// Get pool status.
+	pub fn status(&self) -> Status {
+		Status {
+			ready: self.ready.len(),
+			future: self.future.len(),
+		}
+	}
+}
+
+/// Pool status
+pub struct Status {
+	/// Number of transactions in the ready queue.
+	pub ready: usize,
+	/// Number of transactions in the future queue.
+	pub future: usize,
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	type Hash = u64;
+
+	fn pool() -> BasePool<Hash, Vec<u8>> {
+		BasePool::default()
+	}
+
+	#[test]
+	fn should_import_transaction_to_ready() {
+		// given
+		let mut pool = pool();
+
+		// when
+		pool.import(1, Transaction {
+			data: vec![1u8],
+			hash: 1u64,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![],
+			provides: vec![vec![1]],
+		}).unwrap();
+
+		// then
+		assert_eq!(pool.ready().count(), 1);
+		assert_eq!(pool.ready.len(), 1);
+	}
+
+	#[test]
+	fn should_not_import_same_transaction_twice() {
+		// given
+		let mut pool = pool();
+
+		// when
+		pool.import(1, Transaction {
+			data: vec![1u8],
+			hash: 1,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![],
+			provides: vec![vec![1]],
+		}).unwrap();
+		pool.import(1, Transaction {
+			data: vec![1u8],
+			hash: 1,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![],
+			provides: vec![vec![1]],
+		}).unwrap_err();
+
+		// then
+		assert_eq!(pool.ready().count(), 1);
+		assert_eq!(pool.ready.len(), 1);
+	}
+
+
+	#[test]
+	fn should_import_transaction_to_future_and_promote_it_later() {
+		// given
+		let mut pool = pool();
+
+		// when
+		pool.import(1, Transaction {
+			data: vec![1u8],
+			hash: 1,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![vec![0]],
+			provides: vec![vec![1]],
+		}).unwrap();
+		assert_eq!(pool.ready().count(), 0);
+		assert_eq!(pool.ready.len(), 0);
+		pool.import(1, Transaction {
+			data: vec![2u8],
+			hash: 2,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![],
+			provides: vec![vec![0]],
+		}).unwrap();
+
+		// then
+		assert_eq!(pool.ready().count(), 2);
+		assert_eq!(pool.ready.len(), 2);
+	}
+
+	#[test]
+	fn should_promote_a_subgraph() {
+		// given
+		let mut pool = pool();
+
+		// when
+		pool.import(1, Transaction {
+			data: vec![1u8],
+			hash: 1,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![vec![0]],
+			provides: vec![vec![1]],
+		}).unwrap();
+		pool.import(1, Transaction {
+			data: vec![3u8],
+			hash: 3,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![vec![2]],
+			provides: vec![],
+		}).unwrap();
+		pool.import(1, Transaction {
+			data: vec![2u8],
+			hash: 2,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![vec![1]],
+			provides: vec![vec![3], vec![2]],
+		}).unwrap();
+		pool.import(1, Transaction {
+			data: vec![4u8],
+			hash: 4,
+			priority: 1_000u64,
+			longevity: 64u64,
+			requires: vec![vec![3], vec![4]],
+			provides: vec![],
+		}).unwrap();
+		assert_eq!(pool.ready().count(), 0);
+		assert_eq!(pool.ready.len(), 0);
+
+		let res = pool.import(1, Transaction {
+			data: vec![5u8],
+			hash: 5,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![],
+			provides: vec![vec![0], vec![4]],
+		}).unwrap();
+
+		// then
+		let mut it = pool.ready().into_iter().map(|tx| tx.data[0]);
+
+		assert_eq!(it.next(), Some(5));
+		assert_eq!(it.next(), Some(1));
+		assert_eq!(it.next(), Some(2));
+		assert_eq!(it.next(), Some(4));
+		assert_eq!(it.next(), Some(3));
+		assert_eq!(it.next(), None);
+		assert_eq!(res, Imported::Ready {
+			hash: 5,
+			promoted: vec![1, 2, 3, 4],
+			failed: vec![],
+			removed: vec![],
+		});
+	}
+
+	#[test]
+	fn should_handle_a_cycle() {
+		// given
+		let mut pool = pool();
+		pool.import(1, Transaction {
+			data: vec![1u8],
+			hash: 1,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![vec![0]],
+			provides: vec![vec![1]],
+		}).unwrap();
+		pool.import(1, Transaction {
+			data: vec![3u8],
+			hash: 3,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![vec![1]],
+			provides: vec![vec![2]],
+		}).unwrap();
+		assert_eq!(pool.ready().count(), 0);
+		assert_eq!(pool.ready.len(), 0);
+
+		// when
+		pool.import(1, Transaction {
+			data: vec![2u8],
+			hash: 2,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![vec![2]],
+			provides: vec![vec![0]],
+		}).unwrap();
+
+		// then
+		{
+			let mut it = pool.ready().into_iter().map(|tx| tx.data[0]);
+			assert_eq!(it.next(), None);
+		}
+		// all transactions occupy the Future queue - it's fine
+		assert_eq!(pool.future.len(), 3);
+
+		// let's close the cycle with one additional transaction
+		let res = pool.import(1, Transaction {
+			data: vec![4u8],
+			hash: 4,
+			priority: 50u64,
+			longevity: 64u64,
+			requires: vec![],
+			provides: vec![vec![0]],
+		}).unwrap();
+		let mut it = pool.ready().into_iter().map(|tx| tx.data[0]);
+		assert_eq!(it.next(), Some(4));
+		assert_eq!(it.next(), Some(1));
+		assert_eq!(it.next(), Some(3));
+		assert_eq!(it.next(), None);
+		assert_eq!(res, Imported::Ready {
+			hash: 4,
+			promoted: vec![1, 3],
+			failed: vec![2],
+			removed: vec![],
+		});
+		assert_eq!(pool.future.len(), 0);
+	}
+
+
+	#[test]
+	fn should_handle_a_cycle_with_low_priority() {
+		// given
+		let mut pool = pool();
+		pool.import(1, Transaction {
+			data: vec![1u8],
+			hash: 1,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![vec![0]],
+			provides: vec![vec![1]],
+		}).unwrap();
+		pool.import(1, Transaction {
+			data: vec![3u8],
+			hash: 3,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![vec![1]],
+			provides: vec![vec![2]],
+		}).unwrap();
+		assert_eq!(pool.ready().count(), 0);
+		assert_eq!(pool.ready.len(), 0);
+
+		// when
+		pool.import(1, Transaction {
+			data: vec![2u8],
+			hash: 2,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![vec![2]],
+			provides: vec![vec![0]],
+		}).unwrap();
+
+		// then
+		{
+			let mut it = pool.ready().into_iter().map(|tx| tx.data[0]);
+			assert_eq!(it.next(), None);
+		}
+		// all transactions occupy the Future queue - it's fine
+		assert_eq!(pool.future.len(), 3);
+
+		// let's close the cycle with one additional transaction
+		let err = pool.import(1, Transaction {
+			data: vec![4u8],
+			hash: 4,
+			priority: 1u64, // lower priority than Tx(2)
+			longevity: 64u64,
+			requires: vec![],
+			provides: vec![vec![0]],
+		}).unwrap_err();
+		let mut it = pool.ready().into_iter().map(|tx| tx.data[0]);
+		assert_eq!(it.next(), None);
+		assert_eq!(pool.ready.len(), 0);
+		assert_eq!(pool.future.len(), 0);
+		if let error::ErrorKind::CycleDetected = *err.kind() {
+		} else {
+			assert!(false, "Invalid error kind: {:?}", err.kind());
+		}
+	}
+
+	#[test]
+	fn should_remove_invalid_transactions() {
+		// given
+		let mut pool = pool();
+		pool.import(1, Transaction {
+			data: vec![5u8],
+			hash: 5,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![],
+			provides: vec![vec![0], vec![4]],
+		}).unwrap();
+		pool.import(1, Transaction {
+			data: vec![1u8],
+			hash: 1,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![vec![0]],
+			provides: vec![vec![1]],
+		}).unwrap();
+		pool.import(1, Transaction {
+			data: vec![3u8],
+			hash: 3,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![vec![2]],
+			provides: vec![],
+		}).unwrap();
+		pool.import(1, Transaction {
+			data: vec![2u8],
+			hash: 2,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![vec![1]],
+			provides: vec![vec![3], vec![2]],
+		}).unwrap();
+		pool.import(1, Transaction {
+			data: vec![4u8],
+			hash: 4,
+			priority: 1_000u64,
+			longevity: 64u64,
+			requires: vec![vec![3], vec![4]],
+			provides: vec![],
+		}).unwrap();
+		// future
+		pool.import(1, Transaction {
+			data: vec![6u8],
+			hash: 6,
+			priority: 1_000u64,
+			longevity: 64u64,
+			requires: vec![vec![11]],
+			provides: vec![],
+		}).unwrap();
+		assert_eq!(pool.ready().count(), 5);
+		assert_eq!(pool.future.len(), 1);
+
+		// when
+		pool.remove_invalid(&[6, 1]);
+
+		// then
+		assert_eq!(pool.ready().count(), 1);
+		assert_eq!(pool.future.len(), 0);
+	}
+
+
+	#[test]
+	fn should_prune_ready_transactions() {
+		// given
+		let mut pool = pool();
+		// future (waiting for 0)
+		pool.import(1, Transaction {
+			data: vec![5u8],
+			hash: 5,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![vec![0]],
+			provides: vec![vec![100]],
+		}).unwrap();
+		// ready
+		pool.import(1, Transaction {
+			data: vec![1u8],
+			hash: 1,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![],
+			provides: vec![vec![1]],
+		}).unwrap();
+		pool.import(1, Transaction {
+			data: vec![2u8],
+			hash: 2,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![vec![2]],
+			provides: vec![vec![3]],
+		}).unwrap();
+		pool.import(1, Transaction {
+			data: vec![3u8],
+			hash: 3,
+			priority: 5u64,
+			longevity: 64u64,
+			requires: vec![vec![1]],
+			provides: vec![vec![2]],
+		}).unwrap();
+		pool.import(1, Transaction {
+			data: vec![4u8],
+			hash: 4,
+			priority: 1_000u64,
+			longevity: 64u64,
+			requires: vec![vec![3], vec![2]],
+			provides: vec![vec![4]],
+		}).unwrap();
+
+		assert_eq!(pool.ready().count(), 4);
+		assert_eq!(pool.future.len(), 1);
+
+		// when
+		let result = pool.prune_tags(1, vec![vec![0], vec![2]]);
+
+		// then
+		assert_eq!(result.pruned.len(), 2);
+		assert_eq!(result.failed.len(), 0);
+		assert_eq!(result.promoted[0], Imported::Ready {
+			hash: 5,
+			promoted: vec![],
+			failed: vec![],
+			removed: vec![],
+		});
+		assert_eq!(result.promoted.len(), 1);
+		assert_eq!(pool.future.len(), 0);
+		assert_eq!(pool.ready.len(), 3);
+		assert_eq!(pool.ready().count(), 3);
+	}
+
+}

substrate/core/transaction-pool/graph/src/error.rs

@@ -0,0 +1,68 @@
+// Copyright 2018 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Transaction pool errors.
+
+use sr_primitives::transaction_validity::TransactionPriority as Priority;
+
+error_chain! {
+	errors {
+		/// Transaction is not verifiable yet, but might be in the future.
+		UnknownTransactionValidity {
+			description("Runtime cannot determine validity of the transaction yet."),
+			display("Unkown Transaction Validity"),
+		}
+		/// Transaction is invalid
+		InvalidTransaction {
+			description("Runtime check for the transaction failed."),
+			display("Invalid Transaction"),
+		}
+		/// The transaction is temporarily baned
+		TemporarilyBanned {
+			description("Transaction is temporarily banned from importing to the pool."),
+			display("Temporarily Banned"),
+		}
+		/// The transaction is already in the pool.
+		AlreadyImported {
+			description("Transaction is already in the pool."),
+			display("Already imported"),
+		}
+		/// The transaction cannot be imported cause it's a replacement and has too low priority.
+		TooLowPriority(old: Priority, new: Priority) {
+			description("The priority is too low to replace transactions already in the pool."),
+			display("Too low priority ({} > {})", old, new)
+		}
+		/// Deps cycle detected and we couldn't import transaction.
+		CycleDetected {
+			description("Transaction was not imported because of detected cycle."),
+			display("Cycle Detected"),
+		}
+	}
+}
+
+/// Transaction pool error conversion.
+pub trait IntoPoolError: ::std::error::Error + Send + Sized {
+	/// Try to extract original `Error`
+	///
+	/// This implementation is optional and used only to
+	/// provide more descriptive error messages for end users
+	/// of RPC API.
+	fn into_pool_error(self) -> ::std::result::Result<Error, Self> { Err(self) }
+}
+
+impl IntoPoolError for Error {
+	fn into_pool_error(self) -> ::std::result::Result<Error, Self> { Ok(self) }
+}

substrate/core/transaction-pool/graph/src/future.rs

@@ -0,0 +1,176 @@
+// Copyright 2018 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+use std::{
+	collections::{HashMap, HashSet},
+	hash,
+};
+
+use sr_primitives::transaction_validity::{
+	TransactionTag as Tag,
+};
+
+use base_pool::Transaction;
+
+/// Transaction with partially satisfied dependencies.
+#[derive(Debug)]
+pub struct WaitingTransaction<Hash, Ex> {
+	/// Transaction details.
+	pub transaction: Transaction<Hash, Ex>,
+	/// Tags that are required and have not been satisfied yet by other transactions in the pool.
+	pub missing_tags: HashSet<Tag>,
+}
+
+impl<Hash, Ex> WaitingTransaction<Hash, Ex> {
+	/// Creates a new `WaitingTransaction`.
+	///
+	/// Computes the set of missing tags based on the requirements and tags that
+	/// are provided by all transactions in the ready queue.
+	pub fn new(transaction: Transaction<Hash, Ex>, provided: &HashMap<Tag, Hash>) -> Self {
+		let missing_tags = transaction.requires
+			.iter()
+			.filter(|tag| !provided.contains_key(&**tag))
+			.cloned()
+			.collect();
+
+		WaitingTransaction {
+			transaction,
+			missing_tags,
+		}
+	}
+
+	/// Marks the tag as satisfied.
+	pub fn satisfy_tag(&mut self, tag: &Tag) {
+		self.missing_tags.remove(tag);
+	}
+
+	/// Returns true if transaction has all requirements satisfied.
+	pub fn is_ready(&self) -> bool {
+		self.missing_tags.is_empty()
+	}
+}
+
+/// A pool of transactions that are not yet ready to be included in the block.
+///
+/// Contains transactions that are still awaiting for some other transactions that
+/// could provide a tag that they require.
+#[derive(Debug)]
+pub struct FutureTransactions<Hash: hash::Hash + Eq, Ex> {
+	/// tags that are not yet provided by any transaction and we await for them
+	wanted_tags: HashMap<Tag, HashSet<Hash>>,
+	/// Transactions waiting for a particular other transaction
+	waiting: HashMap<Hash, WaitingTransaction<Hash, Ex>>,
+}
+
+impl<Hash: hash::Hash + Eq, Ex> Default for FutureTransactions<Hash, Ex> {
+	fn default() -> Self {
+		FutureTransactions {
+			wanted_tags: Default::default(),
+			waiting: Default::default(),
+		}
+	}
+}
+
+const WAITING_PROOF: &str = r"#
+In import we always insert to `waiting` if we push to `wanted_tags`;
+when removing from `waiting` we always clear `wanted_tags`;
+every hash from `wanted_tags` is always present in `waiting`;
+qed
+#";
+
+impl<Hash: hash::Hash + Eq + Clone, Ex> FutureTransactions<Hash, Ex> {
+	/// Import transaction to Future queue.
+	///
+	/// Only transactions that don't have all their tags satisfied should occupy
+	/// the Future queue.
+	/// As soon as required tags are provided by some other transactions that are ready
+	/// we should remove the transactions from here and move them to the Ready queue.
+	pub fn import(&mut self, tx: WaitingTransaction<Hash, Ex>) {
+		assert!(!tx.is_ready(), "Transaction is ready.");
+		assert!(!self.waiting.contains_key(&tx.transaction.hash), "Transaction is already imported.");
+
+		// Add all tags that are missing
+		for tag in &tx.missing_tags {
+			let mut entry = self.wanted_tags.entry(tag.clone()).or_insert_with(HashSet::new);
+			entry.insert(tx.transaction.hash.clone());
+		}
+
+		// Add the transaction to a by-hash waiting map
+		self.waiting.insert(tx.transaction.hash.clone(), tx);
+	}
+
+	/// Returns true if given hash is part of the queue.
+	pub fn contains(&self, hash: &Hash) -> bool {
+		self.waiting.contains_key(hash)
+	}
+
+	/// Satisfies provided tags in transactions that are waiting for them.
+	///
+	/// Returns (and removes) transactions that became ready after their last tag got
+	/// satisfied and now we can remove them from Future and move to Ready queue.
+	pub fn satisfy_tags<T: AsRef<Tag>>(&mut self, tags: impl IntoIterator<Item=T>) -> Vec<WaitingTransaction<Hash, Ex>> {
+		let mut became_ready = vec![];
+
+		for tag in tags {
+			if let Some(hashes) = self.wanted_tags.remove(tag.as_ref()) {
+				for hash in hashes {
+					let is_ready = {
+						let mut tx = self.waiting.get_mut(&hash)
+							.expect(WAITING_PROOF);
+						tx.satisfy_tag(tag.as_ref());
+						tx.is_ready()
+					};
+
+					if is_ready {
+						let tx = self.waiting.remove(&hash).expect(WAITING_PROOF);
+						became_ready.push(tx);
+					}
+				}
+			}
+		}
+
+		became_ready
+	}
+
+	/// Removes transactions for given list of hashes.
+	///
+	/// Returns a list of actually removed transactions.
+	pub fn remove(&mut self, hashes: &[Hash]) -> Vec<Transaction<Hash, Ex>> {
+		let mut removed = vec![];
+		for hash in hashes {
+			if let Some(waiting_tx) = self.waiting.remove(hash) {
+				// remove from wanted_tags as well
+				for tag in waiting_tx.missing_tags {
+					let remove = if let Some(mut wanted) = self.wanted_tags.get_mut(&tag) {
+						wanted.remove(hash);
+						wanted.is_empty()
+					} else { false };
+					if remove {
+						self.wanted_tags.remove(&tag);
+					}
+				}
+				// add to result
+				removed.push(waiting_tx.transaction)
+			}
+		}
+		removed
+	}
+
+	/// Returns number of transactions in the Future queue.
+	pub fn len(&self) -> usize {
+		self.waiting.len()
+	}
+}

substrate/core/transaction-pool/graph/src/lib.rs

@@ -0,0 +1,53 @@
+// Copyright 2018 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+// tag::description[]
+//! Generic Transaction Pool
+//!
+//! The pool is based on dependency graph between transactions
+//! and their priority.
+//! The pool is able to return an iterator that traverses transaction
+//! graph in the correct order taking into account priorities and dependencies.
+//!
+//! TODO [ToDr]
+//! - [ ] Longevity handling (remove obsolete transactions periodically)
+//! - [ ] Multi-threading (getting ready transactions should not block the pool)
+// end::description[]
+
+#![warn(missing_docs)]
+#![warn(unused_extern_crates)]
+
+extern crate futures;
+extern crate parking_lot;
+extern crate sr_primitives;
+
+#[macro_use] extern crate error_chain;
+#[macro_use] extern crate log;
+#[macro_use] extern crate serde_derive;
+
+mod future;
+mod listener;
+mod pool;
+mod ready;
+mod rotator;
+
+pub mod base_pool;
+pub mod error;
+pub mod watcher;
+
+pub use self::error::IntoPoolError;
+pub use self::base_pool::{Transaction, Status};
+pub use self::pool::{Pool, Options, ChainApi, EventStream, ExtrinsicFor, BlockHash, ExHash, NumberFor, TransactionFor};

substrate/core/transaction-pool/graph/src/listener.rs

@@ -0,0 +1,98 @@
+
+// Copyright 2018 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+use std::{
+	collections::HashMap,
+	hash,
+};
+use watcher;
+use sr_primitives::traits;
+
+/// Extrinsic pool default listener.
+pub struct Listener<H: hash::Hash + Eq, H2> {
+	watchers: HashMap<H, watcher::Sender<H, H2>>
+}
+
+impl<H: hash::Hash + Eq, H2> Default for Listener<H, H2> {
+	fn default() -> Self {
+		Listener {
+			watchers: Default::default(),
+		}
+	}
+}
+
+impl<H: hash::Hash + traits::Member, H2: Clone> Listener<H, H2> {
+	fn fire<F>(&mut self, hash: &H, fun: F) where F: FnOnce(&mut watcher::Sender<H, H2>) {
+		let clean = if let Some(h) = self.watchers.get_mut(hash) {
+			fun(h);
+			h.is_done()
+		} else {
+			false
+		};
+
+		if clean {
+			self.watchers.remove(hash);
+		}
+	}
+
+	/// Creates a new watcher for given verified extrinsic.
+	///
+	/// The watcher can be used to subscribe to lifecycle events of that extrinsic.
+	pub fn create_watcher(&mut self, hash: H) -> watcher::Watcher<H, H2> {
+		let sender = self.watchers.entry(hash).or_insert_with(watcher::Sender::default);
+		sender.new_watcher()
+	}
+
+	/// Notify the listeners about extrinsic broadcast.
+	pub fn broadcasted(&mut self, hash: &H, peers: Vec<String>) {
+		self.fire(hash, |watcher| watcher.broadcast(peers));
+	}
+
+	/// New transaction was added to the ready pool or promoted from the future pool.
+	pub fn ready(&mut self, tx: &H, old: Option<&H>) {
+		if let Some(old) = old {
+			self.fire(old, |watcher| watcher.usurped(tx.clone()));
+		}
+	}
+
+	/// New transaction was added to the future pool.
+	pub fn future(&mut self, _tx: &H) {
+	}
+
+	/// Transaction was dropped from the pool because of the limit.
+	pub fn dropped(&mut self, tx: &H, by: Option<&H>) {
+		self.fire(tx, |watcher| match by {
+			Some(t) => watcher.usurped(t.clone()),
+			None => watcher.dropped(),
+		})
+	}
+
+	/// Transaction was rejected from the pool.
+	pub fn rejected(&mut self, tx: &H, is_invalid: bool) {
+		warn!(target: "transaction-pool", "Extrinsic rejected ({}): {:?}", is_invalid, tx);
+	}
+
+	/// Transaction was removed as invalid.
+	pub fn invalid(&mut self, tx: &H) {
+		warn!(target: "transaction-pool", "Extrinsic invalid: {:?}", tx);
+	}
+
+	/// Transaction was pruned from the pool.
+	pub fn pruned(&mut self, header_hash: H2, tx: &H) {
+		self.fire(tx, |watcher| watcher.finalised(header_hash))
+	}
+}

substrate/core/transaction-pool/graph/src/pool.rs

@@ -0,0 +1,333 @@
+// Copyright 2018 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+use std::{
+	collections::HashMap,
+	hash,
+	sync::Arc,
+	time,
+};
+
+use base_pool as base;
+use error;
+use listener::Listener;
+use rotator::PoolRotator;
+use watcher::Watcher;
+
+use futures::sync::mpsc;
+use parking_lot::{Mutex, RwLock};
+use sr_primitives::{
+	generic::BlockId,
+	traits::{self, As},
+	transaction_validity::{TransactionValidity, TransactionTag as Tag},
+};
+
+/// Modification notification event stream type;
+pub type EventStream = mpsc::UnboundedReceiver<()>;
+
+/// Extrinsic hash type for a pool.
+pub type ExHash<A> = <A as ChainApi>::Hash;
+/// Block hash type for a pool.
+pub type BlockHash<A> = <<A as ChainApi>::Block as traits::Block>::Hash;
+/// Extrinsic type for a pool.
+pub type ExtrinsicFor<A> = <<A as ChainApi>::Block as traits::Block>::Extrinsic;
+/// Block number type for the ChainApi
+pub type NumberFor<A> = traits::NumberFor<<A as ChainApi>::Block>;
+/// A type of transaction stored in the pool
+pub type TransactionFor<A> = Arc<base::Transaction<ExHash<A>, TxData<ExtrinsicFor<A>>>>;
+
+/// Concrete extrinsic validation and query logic.
+pub trait ChainApi: Send + Sync {
+	/// Block type.
+	type Block: traits::Block;
+	/// Hash type
+	type Hash: hash::Hash + Eq + traits::Member;
+	/// Error type.
+	type Error: From<error::Error> + error::IntoPoolError;
+
+	/// Verify extrinsic at given block.
+	fn validate_transaction(&self, at: &BlockId<Self::Block>, uxt: &ExtrinsicFor<Self>) -> Result<TransactionValidity, Self::Error>;
+
+	/// Returns a block number given the block id.
+	fn block_id_to_number(&self, at: &BlockId<Self::Block>) -> Result<Option<NumberFor<Self>>, Self::Error>;
+
+	/// Returns a block hash given the block id.
+	fn block_id_to_hash(&self, at: &BlockId<Self::Block>) -> Result<Option<BlockHash<Self>>, Self::Error>;
+
+	/// Hash the extrinsic.
+	fn hash(&self, uxt: &ExtrinsicFor<Self>) -> Self::Hash;
+}
+
+/// Maximum time the transaction will be kept in the pool.
+///
+/// Transactions that don't get included within the limit are removed from the pool.
+const POOL_TIME: time::Duration = time::Duration::from_secs(60 * 5);
+
+/// Additional transaction data
+#[derive(Debug, Serialize, Deserialize)]
+pub struct TxData<Ex> {
+	/// Raw data stored by the user.
+	pub raw: Ex,
+	/// Transaction validity deadline.
+	/// TODO [ToDr] Should we use longevity instead?
+	#[serde(skip)]
+	pub valid_till: Option<time::Instant>,
+}
+
+/// Pool configuration options.
+#[derive(Debug, Clone, Default)]
+pub struct Options;
+
+/// Extrinsics pool.
+pub struct Pool<B: ChainApi> {
+	api: B,
+	listener: RwLock<Listener<ExHash<B>, BlockHash<B>>>,
+	pool: RwLock<base::BasePool<
+		ExHash<B>,
+		TxData<ExtrinsicFor<B>>,
+	>>,
+	import_notification_sinks: Mutex<Vec<mpsc::UnboundedSender<()>>>,
+	rotator: PoolRotator<ExHash<B>>,
+}
+
+impl<B: ChainApi> Pool<B> {
+
+	/// Imports a bunch of unverified extrinsics to the pool
+	pub fn submit_at<T>(&self, at: &BlockId<B::Block>, xts: T) -> Result<Vec<Result<ExHash<B>, B::Error>>, B::Error> where
+		T: IntoIterator<Item=ExtrinsicFor<B>>
+	{
+		let block_number = self.api.block_id_to_number(at)?
+			.ok_or_else(|| error::ErrorKind::Msg(format!("Invalid block id: {:?}", at)).into())?;
+
+		Ok(xts
+			.into_iter()
+			.map(|xt| -> Result<_, B::Error> {
+				let hash = self.api.hash(&xt);
+				if self.rotator.is_banned(&hash) {
+					return Err(error::ErrorKind::TemporarilyBanned.into())?;
+				}
+
+				match self.api.validate_transaction(at, &xt)? {
+					TransactionValidity::Valid(priority, requires, provides, longevity)=> {
+						Ok(base::Transaction {
+							data: TxData {
+								raw: xt,
+								valid_till: Some(time::Instant::now() + POOL_TIME),
+							},
+							hash,
+							priority,
+							requires,
+							provides,
+							longevity,
+						})
+					},
+					TransactionValidity::Invalid => {
+						bail!(error::Error::from(error::ErrorKind::InvalidTransaction))
+					},
+					TransactionValidity::Unknown => {
+						self.listener.write().rejected(&hash, false);
+						bail!(error::Error::from(error::ErrorKind::UnknownTransactionValidity))
+					},
+				}
+			})
+			.map(|tx| {
+				let imported = self.pool.write().import(block_number.as_(), tx?)?;
+
+				self.import_notification_sinks.lock().retain(|sink| sink.unbounded_send(()).is_ok());
+
+				let mut listener = self.listener.write();
+				fire_events(&mut *listener, &imported);
+				Ok(imported.hash().clone())
+			})
+			.collect())
+	}
+
+	/// Imports one unverified extrinsic to the pool
+	pub fn submit_one(&self, at: &BlockId<B::Block>, xt: ExtrinsicFor<B>) -> Result<ExHash<B>, B::Error> {
+		Ok(self.submit_at(at, ::std::iter::once(xt))?.pop().expect("One extrinsic passed; one result returned; qed")?)
+	}
+
+	/// Import a single extrinsic and starts to watch their progress in the pool.
+	pub fn submit_and_watch(&self, at: &BlockId<B::Block>, xt: ExtrinsicFor<B>) -> Result<Watcher<ExHash<B>, BlockHash<B>>, B::Error> {
+		let xt = self.submit_one(at, xt)?;
+		Ok(self.listener.write().create_watcher(xt))
+	}
+
+	/// Prunes ready transactions that provide given list of tags.
+	pub fn prune_tags(&self, at: &BlockId<B::Block>, tags: impl IntoIterator<Item=Tag>) -> Result<(), B::Error> {
+		let block_number = self.api.block_id_to_number(at)?
+			.ok_or_else(|| error::ErrorKind::Msg(format!("Invalid block id: {:?}", at)).into())?;
+
+		let status = self.pool.write().prune_tags(block_number.as_(), tags);
+		{
+			let mut listener = self.listener.write();
+			for promoted in &status.promoted {
+				fire_events(&mut *listener, promoted);
+			}
+			for f in &status.failed {
+				listener.dropped(f, None);
+			}
+		}
+		// try to re-submit pruned transactions since some of them might be still valid.
+		let hashes = status.pruned.iter().map(|tx| tx.hash.clone()).collect::<Vec<_>>();
+		let results = self.submit_at(at, status.pruned.into_iter().map(|tx| tx.data.raw.clone()))?;
+		// Fire mined event for transactions that became invalid.
+		let hashes = results.into_iter().enumerate().filter_map(|(idx, r)| match r.map_err(error::IntoPoolError::into_pool_error) {
+			Err(Ok(err)) => match err.kind() {
+				error::ErrorKind::InvalidTransaction => Some(hashes[idx].clone()),
+				_ => None,
+			},
+			_ => None,
+		});
+		{
+			let header_hash = self.api.block_id_to_hash(at)?
+				.ok_or_else(|| error::ErrorKind::Msg(format!("Invalid block id: {:?}", at)).into())?;
+			let mut listener = self.listener.write();
+			for h in hashes {
+				listener.pruned(header_hash, &h)
+			}
+		}
+		// clear old transactions
+		self.clear_stale(at)?;
+		Ok(())
+	}
+
+	/// Removes stale transactions from the pool.
+	///
+	/// Stale transactions are transaction beyond their longevity period.
+	/// Note this function does not remove transactions that are already included in the chain.
+	/// See `prune_tags` ifyou want this.
+	pub fn clear_stale(&self, _at: &BlockId<B::Block>) -> Result<(), B::Error> {
+		let now = time::Instant::now();
+		let to_remove = self.ready(|pending| pending
+			.filter(|tx| self.rotator.ban_if_stale(&now, &tx))
+			.map(|tx| tx.hash.clone())
+			.collect::<Vec<_>>()
+		);
+		// removing old transactions
+		self.remove_invalid(&to_remove);
+		// clear banned transactions timeouts
+		self.rotator.clear_timeouts(&now);
+
+		Ok(())
+	}
+}
+
+impl<B: ChainApi> Pool<B> {
+	/// Create a new transaction pool.
+	/// TODO [ToDr] Options
+	pub fn new(_options: Options, api: B) -> Self {
+		Pool {
+			api,
+			listener: Default::default(),
+			pool: Default::default(),
+			import_notification_sinks: Default::default(),
+			rotator: Default::default(),
+		}
+	}
+
+	/// Return an event stream of transactions imported to the pool.
+	pub fn import_notification_stream(&self) -> EventStream {
+		let (sink, stream) = mpsc::unbounded();
+		self.import_notification_sinks.lock().push(sink);
+		stream
+	}
+
+	/// Invoked when extrinsics are broadcasted.
+	pub fn on_broadcasted(&self, propagated: HashMap<ExHash<B>, Vec<String>>) {
+		let mut listener = self.listener.write();
+		for (hash, peers) in propagated.into_iter() {
+			listener.broadcasted(&hash, peers);
+		}
+	}
+
+	/// Remove from the pool.
+	pub fn remove_invalid(&self, hashes: &[ExHash<B>]) -> Vec<TransactionFor<B>> {
+		// temporarily ban invalid transactions
+		debug!(target: "txpool", "Banning invalid transactions: {:?}", hashes);
+		self.rotator.ban(&time::Instant::now(), hashes);
+
+		let invalid = self.pool.write().remove_invalid(hashes);
+
+		let mut listener = self.listener.write();
+		for tx in &invalid {
+			listener.invalid(&tx.hash);
+		}
+
+		invalid
+	}
+
+	/// Get ready transactions ordered by priority
+	pub fn ready<F, X>(&self, f: F) -> X where
+		F: FnOnce(&mut Iterator<Item=TransactionFor<B>>) -> X,
+	{
+		let pool = self.pool.read();
+		let mut ready = pool.ready();
+		f(&mut ready)
+	}
+
+	/// Returns all transactions in the pool.
+	///
+	/// Be careful with large limit values, as querying the entire pool might be time consuming.
+	pub fn all(&self, limit: usize) -> Vec<ExtrinsicFor<B>> {
+		self.ready(|it| it.take(limit).map(|ex| ex.data.raw.clone()).collect())
+	}
+
+	/// Returns pool status.
+	pub fn status(&self) -> base::Status {
+		self.pool.read().status()
+	}
+
+	/// Returns transaction hash
+	pub fn hash_of(&self, xt: &ExtrinsicFor<B>) -> ExHash<B> {
+		self.api.hash(xt)
+	}
+}
+
+fn fire_events<H, H2, Ex>(
+	listener: &mut Listener<H, H2>,
+	imported: &base::Imported<H, Ex>,
+) where
+	H: hash::Hash + Eq + traits::Member,
+	H2: Clone,
+{
+	match *imported {
+		base::Imported::Ready { ref promoted, ref failed, ref removed, ref hash } => {
+			listener.ready(hash, None);
+			for f in failed {
+				listener.rejected(f, true);
+			}
+			for r in removed {
+				listener.dropped(&r.hash, Some(hash));
+			}
+			for p in promoted {
+				listener.ready(p, None);
+			}
+		},
+		base::Imported::Future { ref hash } => {
+			listener.future(hash)
+		},
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	#[test]
+	#[ignore]
+	fn should_have_some_basic_tests() {
+		assert_eq!(true, false);
+	}
+}

substrate/core/transaction-pool/graph/src/ready.rs

@@ -0,0 +1,579 @@
+// Copyright 2018 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+use std::{
+	collections::{HashMap, HashSet, BTreeSet},
+	cmp,
+	hash,
+	sync::Arc,
+};
+
+use sr_primitives::traits::Member;
+use sr_primitives::transaction_validity::{
+	TransactionTag as Tag,
+};
+
+use error;
+use future::WaitingTransaction;
+use base_pool::{BlockNumber, Transaction};
+
+#[derive(Debug)]
+pub struct TransactionRef<Hash, Ex> {
+	pub transaction: Arc<Transaction<Hash, Ex>>,
+	pub valid_till: BlockNumber,
+	pub insertion_id: u64,
+}
+
+impl<Hash, Ex> Clone for TransactionRef<Hash, Ex> {
+	fn clone(&self) -> Self {
+		TransactionRef {
+			transaction: self.transaction.clone(),
+			valid_till: self.valid_till,
+			insertion_id: self.insertion_id,
+		}
+	}
+}
+
+impl<Hash, Ex> Ord for TransactionRef<Hash, Ex> {
+	fn cmp(&self, other: &Self) -> cmp::Ordering {
+		self.transaction.priority.cmp(&other.transaction.priority)
+			.then(other.valid_till.cmp(&self.valid_till))
+			.then(other.insertion_id.cmp(&self.insertion_id))
+	}
+}
+
+impl<Hash, Ex> PartialOrd for TransactionRef<Hash, Ex> {
+	fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
+		Some(self.cmp(other))
+	}
+}
+
+impl<Hash, Ex> PartialEq for TransactionRef<Hash, Ex> {
+	fn eq(&self, other: &Self) -> bool {
+		self.cmp(other) == cmp::Ordering::Equal
+	}
+}
+impl<Hash, Ex> Eq for TransactionRef<Hash, Ex> {}
+
+#[derive(Debug)]
+struct ReadyTx<Hash, Ex> {
+	/// A reference to a transaction
+	pub transaction: TransactionRef<Hash, Ex>,
+	/// A list of transactions that get unlocked by this one
+	pub unlocks: Vec<Hash>,
+	/// How many required tags are provided inherently
+	///
+	/// Some transactions might be already pruned from the queue,
+	/// so when we compute ready set we may consider this transactions ready earlier.
+	pub requires_offset: usize,
+}
+
+const HASH_READY: &str = r#"
+Every time transaction is imported its hash is placed in `ready` map and tags in `provided_tags`;
+Every time transaction is removed from the queue we remove the hash from `ready` map and from `provided_tags`;
+Hence every hash retrieved from `provided_tags` is always present in `ready`;
+qed
+"#;
+
+#[derive(Debug)]
+pub struct ReadyTransactions<Hash: hash::Hash + Eq, Ex> {
+	/// Insertion id
+	insertion_id: u64,
+	/// tags that are provided by Ready transactions
+	provided_tags: HashMap<Tag, Hash>,
+	/// Transactions that are ready (i.e. don't have any requirements external to the pool)
+	ready: HashMap<Hash, ReadyTx<Hash, Ex>>,
+	// ^^ TODO [ToDr] Consider wrapping this into `Arc<RwLock<>>` and allow multiple concurrent iterators
+	/// Best transactions that are ready to be included to the block without any other previous transaction.
+	best: BTreeSet<TransactionRef<Hash, Ex>>,
+}
+
+impl<Hash: hash::Hash + Eq, Ex> Default for ReadyTransactions<Hash, Ex> {
+	fn default() -> Self {
+		ReadyTransactions {
+			insertion_id: Default::default(),
+			provided_tags: Default::default(),
+			ready: Default::default(),
+			best: Default::default(),
+		}
+	}
+}
+
+impl<Hash: hash::Hash + Member, Ex> ReadyTransactions<Hash, Ex> {
+	/// Borrows a map of tags that are provided by transactions in this queue.
+	pub fn provided_tags(&self) -> &HashMap<Tag, Hash> {
+		&self.provided_tags
+	}
+
+	/// Returns an iterator of ready transactions.
+	///
+	/// Transactions are returned in order:
+	/// 1. First by the dependencies:
+	///	- never return transaction that requires a tag, which was not provided by one of the previously returned transactions
+	/// 2. Then by priority:
+	/// - If there are two transactions with all requirements satisfied the one with higher priority goes first.
+	/// 3. Then by the ttl that's left
+	/// - transactions that are valid for a shorter time go first
+	/// 4. Lastly we sort by the time in the queue
+	/// - transactions that are longer in the queue go first
+	pub fn get<'a>(&'a self) -> impl Iterator<Item=Arc<Transaction<Hash, Ex>>> + 'a {
+		BestIterator {
+			all: &self.ready,
+			best: self.best.clone(),
+			awaiting: Default::default(),
+		}
+	}
+
+	/// Imports transactions to the pool of ready transactions.
+	///
+	/// The transaction needs to have all tags satisfied (be ready) by transactions
+	/// that are in this queue.
+	pub fn import(
+		&mut self,
+		block_number: BlockNumber,
+		tx: WaitingTransaction<Hash, Ex>,
+	) -> error::Result<Vec<Arc<Transaction<Hash, Ex>>>> {
+		assert!(tx.is_ready(), "Only ready transactions can be imported.");
+		assert!(!self.ready.contains_key(&tx.transaction.hash), "Transaction is already imported.");
+
+		self.insertion_id += 1;
+		let insertion_id = self.insertion_id;
+		let hash = tx.transaction.hash.clone();
+		let tx = tx.transaction;
+
+		let replaced = self.replace_previous(&tx)?;
+
+		let mut goes_to_best = true;
+		// Add links to transactions that unlock the current one
+		for tag in &tx.requires {
+			// Check if the transaction that satisfies the tag is still in the queue.
+			if let Some(other) = self.provided_tags.get(tag) {
+				let mut tx = self.ready.get_mut(other).expect(HASH_READY);
+				tx.unlocks.push(hash.clone());
+				// this transaction depends on some other, so it doesn't go to best directly.
+				goes_to_best = false;
+			}
+	 	}
+
+		// update provided_tags
+		for tag in tx.provides.clone() {
+			self.provided_tags.insert(tag, hash.clone());
+		}
+
+		let transaction = TransactionRef {
+			insertion_id,
+			valid_till: block_number.saturating_add(tx.longevity),
+			transaction: Arc::new(tx),
+		};
+
+		// insert to best if it doesn't require any other transaction to be included before it
+		if goes_to_best {
+			self.best.insert(transaction.clone());
+		}
+
+		// insert to Ready
+		self.ready.insert(hash, ReadyTx {
+			transaction,
+			unlocks: vec![],
+			requires_offset: 0,
+		});
+
+		Ok(replaced)
+	}
+
+	/// Returns true if given hash is part of the queue.
+	pub fn contains(&self, hash: &Hash) -> bool {
+		self.ready.contains_key(hash)
+	}
+
+	/// Removes invalid transactions from the ready pool.
+	///
+	/// NOTE removing a transaction will also cause a removal of all transactions that depend on that one
+	/// (i.e. the entire subgraph that this transaction is a start of will be removed).
+	/// All removed transactions are returned.
+	pub fn remove_invalid(&mut self, hashes: &[Hash]) -> Vec<Arc<Transaction<Hash, Ex>>> {
+		let mut removed = vec![];
+		let mut to_remove = hashes.iter().cloned().collect::<Vec<_>>();
+
+		loop {
+			let hash = match to_remove.pop() {
+				Some(hash) => hash,
+				None => return removed,
+			};
+
+			if let Some(mut tx) = self.ready.remove(&hash) {
+				// remove entries from provided_tags
+				for tag in &tx.transaction.transaction.provides {
+					self.provided_tags.remove(tag);
+				}
+				// remove from unlocks
+				for tag in &tx.transaction.transaction.requires {
+					if let Some(hash) = self.provided_tags.get(tag) {
+						if let Some(tx) = self.ready.get_mut(hash) {
+							remove_item(&mut tx.unlocks, &hash);
+						}
+					}
+				}
+
+				// remove from best
+				self.best.remove(&tx.transaction);
+
+				// remove all transactions that the current one unlocks
+				to_remove.append(&mut tx.unlocks);
+
+				// add to removed
+				debug!(target: "txpool", "[{:?}] Removed as invalid: ", hash);
+				removed.push(tx.transaction.transaction);
+			}
+		}
+	}
+
+	/// Removes transactions that provide given tag.
+	///
+	/// All transactions that lead to a transaction, which provides this tag
+	/// are going to be removed from the queue, but no other transactions are touched -
+	/// i.e. all other subgraphs starting from given tag are still considered valid & ready.
+	pub fn prune_tags(&mut self, tag: Tag) -> Vec<Arc<Transaction<Hash, Ex>>> {
+		let mut removed = vec![];
+		let mut to_remove = vec![tag];
+
+		loop {
+			let tag = match to_remove.pop() {
+				Some(tag) => tag,
+				None => return removed,
+			};
+
+			let res = self.provided_tags.remove(&tag)
+					.and_then(|hash| self.ready.remove(&hash));
+
+			if let Some(tx) = res {
+				let unlocks = tx.unlocks;
+				let tx = tx.transaction.transaction;
+
+				// prune previous transactions as well
+				{
+					let hash = &tx.hash;
+					let mut find_previous = |tag| -> Option<Vec<Tag>> {
+						let prev_hash = self.provided_tags.get(tag)?;
+						let tx2 = self.ready.get_mut(&prev_hash)?;
+						remove_item(&mut tx2.unlocks, hash);
+						// We eagerly prune previous transactions as well.
+						// But it might not always be good.
+						// Possible edge case:
+						// - tx provides two tags
+						// - the second tag enables some subgraph we don't know of yet
+						// - we will prune the transaction
+						// - when we learn about the subgraph it will go to future
+						// - we will have to wait for re-propagation of that transaction
+						// Alternatively the caller may attempt to re-import these transactions.
+						if tx2.unlocks.is_empty() {
+							Some(tx2.transaction.transaction.provides.clone())
+						} else {
+							None
+						}
+					};
+
+					// find previous transactions
+					for tag in &tx.requires {
+						if let Some(mut tags_to_remove) = find_previous(tag) {
+							to_remove.append(&mut tags_to_remove);
+						}
+					}
+				}
+
+				// add the transactions that just got unlocked to `best`
+				for hash in unlocks {
+					if let Some(tx) = self.ready.get_mut(&hash) {
+						tx.requires_offset += 1;
+						// this transaction is ready
+						if tx.requires_offset == tx.transaction.transaction.requires.len() {
+							self.best.insert(tx.transaction.clone());
+						}
+					}
+				}
+
+				debug!(target: "txpool", "[{:?}] Pruned.", tx.hash);
+				removed.push(tx);
+			}
+		}
+	}
+
+	/// Checks if the transaction is providing the same tags as other transactions.
+	///
+	/// In case that's true it determines if the priority of transactions that
+	/// we are about to replace is lower than the priority of the replacement transaction.
+	/// We remove/replace old transactions in case they have lower priority.
+	///
+	/// In case replacement is succesful returns a list of removed transactions.
+	fn replace_previous(&mut self, tx: &Transaction<Hash, Ex>) -> error::Result<Vec<Arc<Transaction<Hash, Ex>>>> {
+		let mut to_remove = {
+			// check if we are replacing a transaction
+			let replace_hashes = tx.provides
+				.iter()
+				.filter_map(|tag| self.provided_tags.get(tag))
+				.collect::<HashSet<_>>();
+
+			// early exit if we are not replacing anything.
+			if replace_hashes.is_empty() {
+				return Ok(vec![]);
+			}
+
+			// now check if collective priority is lower than the replacement transaction.
+			let old_priority = replace_hashes
+				.iter()
+				.filter_map(|hash| self.ready.get(hash))
+				.fold(0u64, |total, tx| total.saturating_add(tx.transaction.transaction.priority));
+
+			// bail - the transaction has too low priority to replace the old ones
+			if old_priority >= tx.priority {
+				bail!(error::ErrorKind::TooLowPriority(old_priority, tx.priority))
+			}
+
+			replace_hashes.into_iter().cloned().collect::<Vec<_>>()
+		};
+
+		let new_provides = tx.provides.iter().cloned().collect::<HashSet<_>>();
+		let mut removed = vec![];
+		loop {
+			let hash = match to_remove.pop() {
+				Some(hash) => hash,
+				None => return Ok(removed),
+			};
+
+			let tx = self.ready.remove(&hash).expect(HASH_READY);
+			// check if this transaction provides stuff that is not provided by the new one.
+			let (mut unlocks, tx) = (tx.unlocks, tx.transaction.transaction);
+			{
+				let invalidated = tx.provides
+					.iter()
+					.filter(|tag| !new_provides.contains(&**tag));
+
+				for tag in invalidated {
+					// remove the tag since it's no longer provided by any transaction
+					self.provided_tags.remove(tag);
+					// add more transactions to remove
+					to_remove.append(&mut unlocks);
+				}
+			}
+
+			removed.push(tx);
+		}
+	}
+
+	/// Returns number of transactions in this queue.
+	pub fn len(&self) -> usize {
+		self.ready.len()
+	}
+
+}
+
+pub struct BestIterator<'a, Hash: 'a, Ex: 'a> {
+	all: &'a HashMap<Hash, ReadyTx<Hash, Ex>>,
+	awaiting: HashMap<Hash, (usize, TransactionRef<Hash, Ex>)>,
+	best: BTreeSet<TransactionRef<Hash, Ex>>,
+}
+
+impl<'a, Hash: 'a + hash::Hash + Member, Ex: 'a> BestIterator<'a, Hash, Ex> {
+	/// Depending on number of satisfied requirements insert given ref
+	/// either to awaiting set or to best set.
+	fn best_or_awaiting(&mut self, satisfied: usize, tx_ref: TransactionRef<Hash, Ex>) {
+		if satisfied == tx_ref.transaction.requires.len() {
+			// If we have satisfied all deps insert to best
+			self.best.insert(tx_ref);
+
+		} else {
+			// otherwise we're still awaiting for some deps
+			self.awaiting.insert(tx_ref.transaction.hash.clone(), (satisfied, tx_ref));
+		}
+	}
+}
+
+impl<'a, Hash: 'a + hash::Hash + Member, Ex: 'a> Iterator for BestIterator<'a, Hash, Ex> {
+	type Item = Arc<Transaction<Hash, Ex>>;
+
+	fn next(&mut self) -> Option<Self::Item> {
+		let best = self.best.iter().next_back()?.clone();
+		let best = self.best.take(&best)?;
+
+		let ready = match self.all.get(&best.transaction.hash) {
+			Some(ready) => ready,
+			// The transaction is not in all, maybe it was removed in the meantime?
+			None => return self.next(),
+		};
+
+		// Insert transactions that just got unlocked.
+		for hash in &ready.unlocks {
+			// first check local awaiting transactions
+			if let Some((mut satisfied, tx_ref)) = self.awaiting.remove(hash) {
+				satisfied += 1;
+				self.best_or_awaiting(satisfied, tx_ref);
+			// then get from the pool
+			} else if let Some(next) = self.all.get(hash) {
+				self.best_or_awaiting(next.requires_offset + 1, next.transaction.clone());
+			}
+		}
+
+		Some(best.transaction.clone())
+	}
+}
+
+// See: https://github.com/rust-lang/rust/issues/40062
+fn remove_item<T: PartialEq>(vec: &mut Vec<T>, item: &T) {
+	if let Some(idx) = vec.iter().position(|i| i == item) {
+		vec.swap_remove(idx);
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	fn tx(id: u8) -> Transaction<u64, Vec<u8>> {
+		Transaction {
+			data: vec![id],
+			hash: id as u64,
+			priority: 1,
+			longevity: 2,
+			requires: vec![vec![1], vec![2]],
+			provides: vec![vec![3], vec![4]],
+		}
+	}
+
+	#[test]
+	fn should_replace_transaction_that_provides_the_same_tag() {
+		// given
+		let mut ready = ReadyTransactions::default();
+		let block_number = 1;
+		let mut tx1 = tx(1);
+		tx1.requires.clear();
+		let mut tx2 = tx(2);
+		tx2.requires.clear();
+		tx2.provides = vec![vec![3]];
+		let mut tx3 = tx(3);
+		tx3.requires.clear();
+		tx3.provides = vec![vec![4]];
+
+		// when
+		let x = WaitingTransaction::new(tx2, &ready.provided_tags());
+		ready.import(block_number, x).unwrap();
+		let x = WaitingTransaction::new(tx3, &ready.provided_tags());
+		ready.import(block_number, x).unwrap();
+		assert_eq!(ready.get().count(), 2);
+
+		// too low priority
+		let x = WaitingTransaction::new(tx1.clone(), &ready.provided_tags());
+		ready.import(block_number, x).unwrap_err();
+
+		tx1.priority = 10;
+		let x = WaitingTransaction::new(tx1.clone(), &ready.provided_tags());
+		ready.import(block_number, x).unwrap();
+
+		// then
+		assert_eq!(ready.get().count(), 1);
+	}
+
+
+	#[test]
+	fn should_return_best_transactions_in_correct_order() {
+		// given
+		let mut ready = ReadyTransactions::default();
+		let mut tx1 = tx(1);
+		tx1.requires.clear();
+		let mut tx2 = tx(2);
+		tx2.requires = tx1.provides.clone();
+		tx2.provides = vec![vec![106]];
+		let mut tx3 = tx(3);
+		tx3.requires = vec![tx1.provides[0].clone(), vec![106]];
+		tx3.provides = vec![];
+		let mut tx4 = tx(4);
+		tx4.requires = vec![tx1.provides[0].clone()];
+		tx4.provides = vec![];
+		let block_number = 1;
+		let tx5 = Transaction {
+			data: vec![5],
+			hash: 5,
+			priority: 1,
+			longevity: u64::max_value(),	// use the max_value() here for testing.
+			requires: vec![tx1.provides[0].clone()],
+			provides: vec![],
+		};
+
+		// when
+		let x = WaitingTransaction::new(tx1, &ready.provided_tags());
+		ready.import(block_number, x).unwrap();
+		let x = WaitingTransaction::new(tx2, &ready.provided_tags());
+		ready.import(block_number, x).unwrap();
+		let x = WaitingTransaction::new(tx3, &ready.provided_tags());
+		ready.import(block_number, x).unwrap();
+		let x = WaitingTransaction::new(tx4, &ready.provided_tags());
+		ready.import(block_number, x).unwrap();
+		let x = WaitingTransaction::new(tx5, &ready.provided_tags());
+		ready.import(block_number, x).unwrap();
+
+		// then
+		assert_eq!(ready.best.len(), 1);
+
+		let mut it = ready.get().map(|tx| tx.data[0]);
+
+		assert_eq!(it.next(), Some(1));
+		assert_eq!(it.next(), Some(2));
+		assert_eq!(it.next(), Some(3));
+		assert_eq!(it.next(), Some(4));
+		assert_eq!(it.next(), Some(5));
+		assert_eq!(it.next(), None);
+	}
+
+	#[test]
+	fn should_order_refs() {
+		let mut id = 1;
+		let mut with_priority = |priority| {
+			id += 1;
+			let mut tx = tx(id);
+			tx.priority = priority;
+			tx
+		};
+		// higher priority = better
+		assert!(TransactionRef {
+			transaction: Arc::new(with_priority(3)),
+			valid_till: 3,
+			insertion_id: 1,
+		} > TransactionRef {
+			transaction: Arc::new(with_priority(2)),
+			valid_till: 3,
+			insertion_id: 2,
+		});
+		// lower validity = better
+		assert!(TransactionRef {
+			transaction: Arc::new(with_priority(3)),
+			valid_till: 2,
+			insertion_id: 1,
+		} > TransactionRef {
+			transaction: Arc::new(with_priority(3)),
+			valid_till: 3,
+			insertion_id: 2,
+		});
+		// lower insertion_id = better
+		assert!(TransactionRef {
+			transaction: Arc::new(with_priority(3)),
+			valid_till: 3,
+			insertion_id: 1,
+		} > TransactionRef {
+			transaction: Arc::new(with_priority(3)),
+			valid_till: 3,
+			insertion_id: 2,
+		});
+	}
+}

substrate/core/transaction-pool/graph/src/rotator.rs

@@ -0,0 +1,215 @@
+// Copyright 2018 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Rotate extrinsic inside the pool.
+//!
+//! Keeps only recent extrinsic and discard the ones kept for a significant amount of time.
+//! Discarded extrinsics are banned so that they don't get re-imported again.
+
+use std::{
+	collections::HashMap,
+	hash,
+	time::{Duration, Instant},
+};
+use parking_lot::RwLock;
+
+use base_pool::Transaction;
+use pool::TxData;
+
+/// Expected size of the banned extrinsics cache.
+const EXPECTED_SIZE: usize = 2048;
+
+/// Pool rotator is responsible to only keep fresh extrinsics in the pool.
+///
+/// Extrinsics that occupy the pool for too long are culled and temporarily banned from entering
+/// the pool again.
+pub struct PoolRotator<Hash> {
+	/// How long the extrinsic is banned for.
+	ban_time: Duration,
+	/// Currently banned extrinsics.
+	banned_until: RwLock<HashMap<Hash, Instant>>,
+}
+
+impl<Hash: hash::Hash + Eq> Default for PoolRotator<Hash> {
+	fn default() -> Self {
+		PoolRotator {
+			ban_time: Duration::from_secs(60 * 30),
+			banned_until: Default::default(),
+		}
+	}
+}
+
+impl<Hash: hash::Hash + Eq + Clone> PoolRotator<Hash> {
+	/// Returns `true` if extrinsic hash is currently banned.
+	pub fn is_banned(&self, hash: &Hash) -> bool {
+		self.banned_until.read().contains_key(hash)
+	}
+
+	/// Bans given set of hashes.
+	pub fn ban(&self, now: &Instant, hashes: &[Hash]) {
+		let mut banned = self.banned_until.write();
+
+		for hash in hashes {
+			banned.insert(hash.clone(), *now + self.ban_time);
+		}
+
+		if banned.len() > 2 * EXPECTED_SIZE {
+			while banned.len() > EXPECTED_SIZE {
+				if let Some(key) = banned.keys().next().cloned() {
+					banned.remove(&key);
+				}
+			}
+		}
+	}
+
+
+	/// Bans extrinsic if it's stale.
+	///
+	/// Returns `true` if extrinsic is stale and got banned.
+	pub fn ban_if_stale<Ex>(&self, now: &Instant, xt: &Transaction<Hash, TxData<Ex>>) -> bool {
+		match xt.data.valid_till {
+			Some(ref valid_till) if valid_till > now => {
+				return false;
+			}
+			_ => {},
+		}
+
+		self.ban(now, &[xt.hash.clone()]);
+		true
+	}
+
+	/// Removes timed bans.
+	pub fn clear_timeouts(&self, now: &Instant) {
+		let mut banned = self.banned_until.write();
+
+		banned.retain(|_, &mut v| v >= *now);
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	type Hash = u64;
+	type Ex = ();
+
+	fn rotator() -> PoolRotator<Hash> {
+		PoolRotator {
+			ban_time: Duration::from_millis(10),
+			..Default::default()
+		}
+	}
+
+	fn tx() -> (Hash, Transaction<Hash, TxData<Ex>>) {
+		let hash = 5u64;
+		let tx = Transaction {
+			data: TxData {
+				raw: (),
+				valid_till: Some(Instant::now()),
+			},
+			hash: hash.clone(),
+			priority: 5,
+			longevity: 3,
+			requires: vec![],
+			provides: vec![],
+		};
+
+		(hash, tx)
+	}
+
+	#[test]
+	fn should_not_ban_if_not_stale() {
+		// given
+		let (hash, tx) = tx();
+		let rotator = rotator();
+		assert!(!rotator.is_banned(&hash));
+		let past = Instant::now() - Duration::from_millis(1000);
+
+		// when
+		assert!(!rotator.ban_if_stale(&past, &tx));
+
+		// then
+		assert!(!rotator.is_banned(&hash));
+	}
+
+	#[test]
+	fn should_ban_stale_extrinsic() {
+		// given
+		let (hash, tx) = tx();
+		let rotator = rotator();
+		assert!(!rotator.is_banned(&hash));
+
+		// when
+		assert!(rotator.ban_if_stale(&Instant::now(), &tx));
+
+		// then
+		assert!(rotator.is_banned(&hash));
+	}
+
+
+	#[test]
+	fn should_clear_banned() {
+		// given
+		let (hash, tx) = tx();
+		let rotator = rotator();
+		assert!(rotator.ban_if_stale(&Instant::now(), &tx));
+		assert!(rotator.is_banned(&hash));
+
+		// when
+		let future = Instant::now() + rotator.ban_time + rotator.ban_time;
+		rotator.clear_timeouts(&future);
+
+		// then
+		assert!(!rotator.is_banned(&hash));
+	}
+
+	#[test]
+	fn should_garbage_collect() {
+		// given
+		fn tx_with(i: u64, time: Instant) -> Transaction<Hash, TxData<Ex>> {
+			let hash = i;
+			Transaction {
+				data: TxData {
+					raw: (),
+					valid_till: Some(time),
+				},
+				hash,
+				priority: 5,
+				longevity: 3,
+				requires: vec![],
+				provides: vec![],
+			}
+		}
+
+		let rotator = rotator();
+
+		let now = Instant::now();
+		let past = now - Duration::from_secs(1);
+
+		// when
+		for i in 0..2*EXPECTED_SIZE {
+			let tx = tx_with(i as u64, past);
+			assert!(rotator.ban_if_stale(&now, &tx));
+		}
+		assert_eq!(rotator.banned_until.read().len(), 2*EXPECTED_SIZE);
+
+		// then
+		let tx = tx_with(2*EXPECTED_SIZE as u64, past);
+		// trigger a garbage collection
+		assert!(rotator.ban_if_stale(&now, &tx));
+		assert_eq!(rotator.banned_until.read().len(), EXPECTED_SIZE);
+	}
+}

substrate/core/transaction-pool/graph/src/watcher.rs

@@ -0,0 +1,116 @@
+// Copyright 2018 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Extrinsics status updates.
+
+use futures::{
+	Stream,
+	sync::mpsc,
+};
+
+/// Possible extrinsic status events
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub enum Status<H, H2> {
+	/// Extrinsic is part of the future queue.
+	Future,
+	/// Extrinsic is part of the ready queue.
+	Ready,
+	/// Extrinsic has been finalised in block with given hash.
+	Finalised(H2),
+	/// Some state change (perhaps another extrinsic was included) rendered this extrinsic invalid.
+	Usurped(H),
+	/// The extrinsic has been broadcast to the given peers.
+	Broadcast(Vec<String>),
+	/// Extrinsic has been dropped from the pool because of the limit.
+	Dropped,
+}
+
+/// Extrinsic watcher.
+///
+/// Represents a stream of status updates for particular extrinsic.
+#[derive(Debug)]
+pub struct Watcher<H, H2> {
+	receiver: mpsc::UnboundedReceiver<Status<H, H2>>,
+}
+
+impl<H, H2> Watcher<H, H2> {
+	/// Pipe the notifications to given sink.
+	///
+	/// Make sure to drive the future to completion.
+	pub fn into_stream(self) -> impl Stream<Item=Status<H, H2>, Error=()> {
+		// we can safely ignore the error here, `UnboundedReceiver` never fails.
+		self.receiver.map_err(|_| ())
+	}
+}
+
+/// Sender part of the watcher. Exposed only for testing purposes.
+#[derive(Debug)]
+pub struct Sender<H, H2> {
+	receivers: Vec<mpsc::UnboundedSender<Status<H, H2>>>,
+	finalised: bool,
+}
+
+impl<H, H2> Default for Sender<H, H2> {
+	fn default() -> Self {
+		Sender {
+			receivers: Default::default(),
+			finalised: false,
+		}
+	}
+}
+
+impl<H: Clone, H2: Clone> Sender<H, H2> {
+	/// Add a new watcher to this sender object.
+	pub fn new_watcher(&mut self) -> Watcher<H, H2> {
+		let (tx, receiver) = mpsc::unbounded();
+		self.receivers.push(tx);
+		Watcher {
+			receiver,
+		}
+	}
+
+	/// Some state change (perhaps another extrinsic was included) rendered this extrinsic invalid.
+	pub fn usurped(&mut self, hash: H) {
+		self.send(Status::Usurped(hash))
+	}
+
+	/// Extrinsic has been finalised in block with given hash.
+	pub fn finalised(&mut self, hash: H2) {
+		self.send(Status::Finalised(hash));
+		self.finalised = true;
+	}
+
+	/// Transaction has been dropped from the pool because of the limit.
+	pub fn dropped(&mut self) {
+		self.send(Status::Dropped);
+	}
+
+	/// The extrinsic has been broadcast to the given peers.
+	pub fn broadcast(&mut self, peers: Vec<String>) {
+		self.send(Status::Broadcast(peers))
+	}
+
+
+	/// Returns true if the are no more listeners for this extrinsic or it was finalised.
+	pub fn is_done(&self) -> bool {
+		self.finalised || self.receivers.is_empty()
+	}
+
+	fn send(&mut self, status: Status<H, H2>) {
+		self.receivers.retain(|sender| sender.unbounded_send(status.clone()).is_ok())
+	}
+}