Reorganize code

1 files changed, 791 insertions, 0 deletions

diff --git a/src/table/table_sync.rs b/src/table/table_sync.rs
new file mode 100644
index 00000000..8f6582a7
--- /dev/null
+++ b/src/table/table_sync.rs
@@ -0,0 +1,791 @@
+use rand::Rng;
+use std::collections::{BTreeMap, VecDeque};
+use std::sync::Arc;
+use std::time::{Duration, Instant};
+
+use futures::future::BoxFuture;
+use futures::{pin_mut, select};
+use futures_util::future::*;
+use futures_util::stream::*;
+use serde::{Deserialize, Serialize};
+use serde_bytes::ByteBuf;
+use tokio::sync::Mutex;
+use tokio::sync::{mpsc, watch};
+
+use crate::data::*;
+use crate::error::Error;
+use crate::rpc::membership::Ring;
+use crate::table::*;
+
+const MAX_DEPTH: usize = 16;
+const SCAN_INTERVAL: Duration = Duration::from_secs(3600);
+const CHECKSUM_CACHE_TIMEOUT: Duration = Duration::from_secs(1800);
+const TABLE_SYNC_RPC_TIMEOUT: Duration = Duration::from_secs(30);
+
+pub struct TableSyncer<F: TableSchema, R: TableReplication> {
+	table: Arc<Table<F, R>>,
+	todo: Mutex<SyncTodo>,
+	cache: Vec<Mutex<BTreeMap<SyncRange, RangeChecksumCache>>>,
+}
+
+#[derive(Serialize, Deserialize)]
+pub enum SyncRPC {
+	GetRootChecksumRange(Hash, Hash),
+	RootChecksumRange(SyncRange),
+	Checksums(Vec<RangeChecksum>, bool),
+	Difference(Vec<SyncRange>, Vec<Arc<ByteBuf>>),
+}
+
+pub struct SyncTodo {
+	todo: Vec<TodoPartition>,
+}
+
+#[derive(Debug, Clone)]
+struct TodoPartition {
+	begin: Hash,
+	end: Hash,
+	retain: bool,
+}
+
+// A SyncRange defines a query on the dataset stored by a node, in the following way:
+// - all items whose key are >= `begin`
+// - stopping at the first item whose key hash has at least `level` leading zero bytes (excluded)
+// - except if the first item of the range has such many leading zero bytes
+// - and stopping at `end` (excluded) if such an item is not found
+// The checksum itself does not store all of the items in the database, only the hashes of the "sub-ranges"
+// i.e. of ranges of level `level-1` that cover the same range
+// (ranges of level 0 do not exist and their hash is simply the hash of the first item >= begin)
+// See RangeChecksum for the struct that stores this information.
+#[derive(Hash, PartialEq, Eq, Debug, Clone, Serialize, Deserialize)]
+pub struct SyncRange {
+	begin: Vec<u8>,
+	end: Vec<u8>,
+	level: usize,
+}
+
+impl std::cmp::PartialOrd for SyncRange {
+	fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+		Some(self.cmp(other))
+	}
+}
+impl std::cmp::Ord for SyncRange {
+	fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+		self.begin
+			.cmp(&other.begin)
+			.then(self.level.cmp(&other.level))
+			.then(self.end.cmp(&other.end))
+	}
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct RangeChecksum {
+	bounds: SyncRange,
+	children: Vec<(SyncRange, Hash)>,
+	found_limit: Option<Vec<u8>>,
+
+	#[serde(skip, default = "std::time::Instant::now")]
+	time: Instant,
+}
+
+#[derive(Debug, Clone)]
+pub struct RangeChecksumCache {
+	hash: Option<Hash>, // None if no children
+	found_limit: Option<Vec<u8>>,
+	time: Instant,
+}
+
+impl<F, R> TableSyncer<F, R>
+where
+	F: TableSchema + 'static,
+	R: TableReplication + 'static,
+{
+	pub async fn launch(table: Arc<Table<F, R>>) -> Arc<Self> {
+		let todo = SyncTodo { todo: Vec::new() };
+		let syncer = Arc::new(TableSyncer {
+			table: table.clone(),
+			todo: Mutex::new(todo),
+			cache: (0..MAX_DEPTH)
+				.map(|_| Mutex::new(BTreeMap::new()))
+				.collect::<Vec<_>>(),
+		});
+
+		let (busy_tx, busy_rx) = mpsc::unbounded_channel();
+
+		let s1 = syncer.clone();
+		table
+			.system
+			.background
+			.spawn_worker(
+				format!("table sync watcher for {}", table.name),
+				move |must_exit: watch::Receiver<bool>| s1.watcher_task(must_exit, busy_rx),
+			)
+			.await;
+
+		let s2 = syncer.clone();
+		table
+			.system
+			.background
+			.spawn_worker(
+				format!("table syncer for {}", table.name),
+				move |must_exit: watch::Receiver<bool>| s2.syncer_task(must_exit, busy_tx),
+			)
+			.await;
+
+		let s3 = syncer.clone();
+		tokio::spawn(async move {
+			tokio::time::delay_for(Duration::from_secs(20)).await;
+			s3.add_full_scan().await;
+		});
+
+		syncer
+	}
+
+	async fn watcher_task(
+		self: Arc<Self>,
+		mut must_exit: watch::Receiver<bool>,
+		mut busy_rx: mpsc::UnboundedReceiver<bool>,
+	) -> Result<(), Error> {
+		let mut prev_ring: Arc<Ring> = self.table.system.ring.borrow().clone();
+		let mut ring_recv: watch::Receiver<Arc<Ring>> = self.table.system.ring.clone();
+		let mut nothing_to_do_since = Some(Instant::now());
+
+		while !*must_exit.borrow() {
+			let s_ring_recv = ring_recv.recv().fuse();
+			let s_busy = busy_rx.recv().fuse();
+			let s_must_exit = must_exit.recv().fuse();
+			let s_timeout = tokio::time::delay_for(Duration::from_secs(1)).fuse();
+			pin_mut!(s_ring_recv, s_busy, s_must_exit, s_timeout);
+
+			select! {
+				new_ring_r = s_ring_recv => {
+					if let Some(new_ring) = new_ring_r {
+						debug!("({}) Adding ring difference to syncer todo list", self.table.name);
+						self.todo.lock().await.add_ring_difference(&self.table, &prev_ring, &new_ring);
+						prev_ring = new_ring;
+					}
+				}
+				busy_opt = s_busy => {
+					if let Some(busy) = busy_opt {
+						if busy {
+							nothing_to_do_since = None;
+						} else {
+							if nothing_to_do_since.is_none() {
+								nothing_to_do_since = Some(Instant::now());
+							}
+						}
+					}
+				}
+				must_exit_v = s_must_exit => {
+					if must_exit_v.unwrap_or(false) {
+						break;
+					}
+				}
+				_ = s_timeout => {
+					if nothing_to_do_since.map(|t| Instant::now() - t >= SCAN_INTERVAL).unwrap_or(false) {
+						nothing_to_do_since = None;
+						debug!("({}) Adding full scan to syncer todo list", self.table.name);
+						self.add_full_scan().await;
+					}
+				}
+			}
+		}
+		Ok(())
+	}
+
+	pub async fn add_full_scan(&self) {
+		self.todo.lock().await.add_full_scan(&self.table);
+	}
+
+	async fn syncer_task(
+		self: Arc<Self>,
+		mut must_exit: watch::Receiver<bool>,
+		busy_tx: mpsc::UnboundedSender<bool>,
+	) -> Result<(), Error> {
+		while !*must_exit.borrow() {
+			if let Some(partition) = self.todo.lock().await.pop_task() {
+				busy_tx.send(true)?;
+				let res = self
+					.clone()
+					.sync_partition(&partition, &mut must_exit)
+					.await;
+				if let Err(e) = res {
+					warn!(
+						"({}) Error while syncing {:?}: {}",
+						self.table.name, partition, e
+					);
+				}
+			} else {
+				busy_tx.send(false)?;
+				tokio::time::delay_for(Duration::from_secs(1)).await;
+			}
+		}
+		Ok(())
+	}
+
+	async fn sync_partition(
+		self: Arc<Self>,
+		partition: &TodoPartition,
+		must_exit: &mut watch::Receiver<bool>,
+	) -> Result<(), Error> {
+		let my_id = self.table.system.id;
+		let nodes = self
+			.table
+			.replication
+			.write_nodes(&partition.begin, &self.table.system)
+			.into_iter()
+			.filter(|node| *node != my_id)
+			.collect::<Vec<_>>();
+
+		debug!(
+			"({}) Preparing to sync {:?} with {:?}...",
+			self.table.name, partition, nodes
+		);
+		let root_cks = self
+			.root_checksum(&partition.begin, &partition.end, must_exit)
+			.await?;
+
+		let mut sync_futures = nodes
+			.iter()
+			.map(|node| {
+				self.clone().do_sync_with(
+					partition.clone(),
+					root_cks.clone(),
+					*node,
+					partition.retain,
+					must_exit.clone(),
+				)
+			})
+			.collect::<FuturesUnordered<_>>();
+
+		let mut n_errors = 0;
+		while let Some(r) = sync_futures.next().await {
+			if let Err(e) = r {
+				n_errors += 1;
+				warn!("({}) Sync error: {}", self.table.name, e);
+			}
+		}
+		if n_errors > self.table.replication.max_write_errors() {
+			return Err(Error::Message(format!(
+				"Sync failed with too many nodes (should have been: {:?}).",
+				nodes
+			)));
+		}
+
+		if !partition.retain {
+			self.table
+				.delete_range(&partition.begin, &partition.end)
+				.await?;
+		}
+
+		Ok(())
+	}
+
+	async fn root_checksum(
+		self: &Arc<Self>,
+		begin: &Hash,
+		end: &Hash,
+		must_exit: &mut watch::Receiver<bool>,
+	) -> Result<RangeChecksum, Error> {
+		for i in 1..MAX_DEPTH {
+			let rc = self
+				.range_checksum(
+					&SyncRange {
+						begin: begin.to_vec(),
+						end: end.to_vec(),
+						level: i,
+					},
+					must_exit,
+				)
+				.await?;
+			if rc.found_limit.is_none() {
+				return Ok(rc);
+			}
+		}
+		Err(Error::Message(format!(
+			"Unable to compute root checksum (this should never happen)"
+		)))
+	}
+
+	async fn range_checksum(
+		self: &Arc<Self>,
+		range: &SyncRange,
+		must_exit: &mut watch::Receiver<bool>,
+	) -> Result<RangeChecksum, Error> {
+		assert!(range.level != 0);
+
+		if range.level == 1 {
+			let mut children = vec![];
+			for item in self
+				.table
+				.store
+				.range(range.begin.clone()..range.end.clone())
+			{
+				let (key, value) = item?;
+				let key_hash = hash(&key[..]);
+				if children.len() > 0
+					&& key_hash.as_slice()[0..range.level]
+						.iter()
+						.all(|x| *x == 0u8)
+				{
+					return Ok(RangeChecksum {
+						bounds: range.clone(),
+						children,
+						found_limit: Some(key.to_vec()),
+						time: Instant::now(),
+					});
+				}
+				let item_range = SyncRange {
+					begin: key.to_vec(),
+					end: vec![],
+					level: 0,
+				};
+				children.push((item_range, hash(&value[..])));
+			}
+			Ok(RangeChecksum {
+				bounds: range.clone(),
+				children,
+				found_limit: None,
+				time: Instant::now(),
+			})
+		} else {
+			let mut children = vec![];
+			let mut sub_range = SyncRange {
+				begin: range.begin.clone(),
+				end: range.end.clone(),
+				level: range.level - 1,
+			};
+			let mut time = Instant::now();
+			while !*must_exit.borrow() {
+				let sub_ck = self
+					.range_checksum_cached_hash(&sub_range, must_exit)
+					.await?;
+
+				if let Some(hash) = sub_ck.hash {
+					children.push((sub_range.clone(), hash));
+					if sub_ck.time < time {
+						time = sub_ck.time;
+					}
+				}
+
+				if sub_ck.found_limit.is_none() || sub_ck.hash.is_none() {
+					return Ok(RangeChecksum {
+						bounds: range.clone(),
+						children,
+						found_limit: None,
+						time,
+					});
+				}
+				let found_limit = sub_ck.found_limit.unwrap();
+
+				let actual_limit_hash = hash(&found_limit[..]);
+				if actual_limit_hash.as_slice()[0..range.level]
+					.iter()
+					.all(|x| *x == 0u8)
+				{
+					return Ok(RangeChecksum {
+						bounds: range.clone(),
+						children,
+						found_limit: Some(found_limit.clone()),
+						time,
+					});
+				}
+
+				sub_range.begin = found_limit;
+			}
+			Err(Error::Message(format!("Exiting.")))
+		}
+	}
+
+	fn range_checksum_cached_hash<'a>(
+		self: &'a Arc<Self>,
+		range: &'a SyncRange,
+		must_exit: &'a mut watch::Receiver<bool>,
+	) -> BoxFuture<'a, Result<RangeChecksumCache, Error>> {
+		async move {
+			let mut cache = self.cache[range.level].lock().await;
+			if let Some(v) = cache.get(&range) {
+				if Instant::now() - v.time < CHECKSUM_CACHE_TIMEOUT {
+					return Ok(v.clone());
+				}
+			}
+			cache.remove(&range);
+			drop(cache);
+
+			let v = self.range_checksum(&range, must_exit).await?;
+			trace!(
+				"({}) New checksum calculated for {}-{}/{}, {} children",
+				self.table.name,
+				hex::encode(&range.begin)
+					.chars()
+					.take(16)
+					.collect::<String>(),
+				hex::encode(&range.end).chars().take(16).collect::<String>(),
+				range.level,
+				v.children.len()
+			);
+
+			let hash = if v.children.len() > 0 {
+				Some(hash(&rmp_to_vec_all_named(&v)?[..]))
+			} else {
+				None
+			};
+			let cache_entry = RangeChecksumCache {
+				hash,
+				found_limit: v.found_limit,
+				time: v.time,
+			};
+
+			let mut cache = self.cache[range.level].lock().await;
+			cache.insert(range.clone(), cache_entry.clone());
+			Ok(cache_entry)
+		}
+		.boxed()
+	}
+
+	async fn do_sync_with(
+		self: Arc<Self>,
+		partition: TodoPartition,
+		root_ck: RangeChecksum,
+		who: UUID,
+		retain: bool,
+		mut must_exit: watch::Receiver<bool>,
+	) -> Result<(), Error> {
+		let mut todo = VecDeque::new();
+
+		// If their root checksum has level > than us, use that as a reference
+		let root_cks_resp = self
+			.table
+			.rpc_client
+			.call(
+				who,
+				TableRPC::<F>::SyncRPC(SyncRPC::GetRootChecksumRange(
+					partition.begin.clone(),
+					partition.end.clone(),
+				)),
+				TABLE_SYNC_RPC_TIMEOUT,
+			)
+			.await?;
+		if let TableRPC::<F>::SyncRPC(SyncRPC::RootChecksumRange(range)) = root_cks_resp {
+			if range.level > root_ck.bounds.level {
+				let their_root_range_ck = self.range_checksum(&range, &mut must_exit).await?;
+				todo.push_back(their_root_range_ck);
+			} else {
+				todo.push_back(root_ck);
+			}
+		} else {
+			return Err(Error::BadRequest(format!(
+				"Invalid respone to GetRootChecksumRange RPC: {}",
+				debug_serialize(root_cks_resp)
+			)));
+		}
+
+		while !todo.is_empty() && !*must_exit.borrow() {
+			let total_children = todo.iter().map(|x| x.children.len()).fold(0, |x, y| x + y);
+			trace!(
+				"({}) Sync with {:?}: {} ({}) remaining",
+				self.table.name,
+				who,
+				todo.len(),
+				total_children
+			);
+
+			let step_size = std::cmp::min(16, todo.len());
+			let step = todo.drain(..step_size).collect::<Vec<_>>();
+
+			let rpc_resp = self
+				.table
+				.rpc_client
+				.call(
+					who,
+					TableRPC::<F>::SyncRPC(SyncRPC::Checksums(step, retain)),
+					TABLE_SYNC_RPC_TIMEOUT,
+				)
+				.await?;
+			if let TableRPC::<F>::SyncRPC(SyncRPC::Difference(mut diff_ranges, diff_items)) =
+				rpc_resp
+			{
+				if diff_ranges.len() > 0 || diff_items.len() > 0 {
+					info!(
+						"({}) Sync with {:?}: difference {} ranges, {} items",
+						self.table.name,
+						who,
+						diff_ranges.len(),
+						diff_items.len()
+					);
+				}
+				let mut items_to_send = vec![];
+				for differing in diff_ranges.drain(..) {
+					if differing.level == 0 {
+						items_to_send.push(differing.begin);
+					} else {
+						let checksum = self.range_checksum(&differing, &mut must_exit).await?;
+						todo.push_back(checksum);
+					}
+				}
+				if retain && diff_items.len() > 0 {
+					self.table.handle_update(&diff_items[..]).await?;
+				}
+				if items_to_send.len() > 0 {
+					self.send_items(who, items_to_send).await?;
+				}
+			} else {
+				return Err(Error::BadRequest(format!(
+					"Unexpected response to sync RPC checksums: {}",
+					debug_serialize(&rpc_resp)
+				)));
+			}
+		}
+		Ok(())
+	}
+
+	async fn send_items(&self, who: UUID, item_list: Vec<Vec<u8>>) -> Result<(), Error> {
+		info!(
+			"({}) Sending {} items to {:?}",
+			self.table.name,
+			item_list.len(),
+			who
+		);
+
+		let mut values = vec![];
+		for item in item_list.iter() {
+			if let Some(v) = self.table.store.get(&item[..])? {
+				values.push(Arc::new(ByteBuf::from(v.as_ref())));
+			}
+		}
+		let rpc_resp = self
+			.table
+			.rpc_client
+			.call(who, TableRPC::<F>::Update(values), TABLE_SYNC_RPC_TIMEOUT)
+			.await?;
+		if let TableRPC::<F>::Ok = rpc_resp {
+			Ok(())
+		} else {
+			Err(Error::Message(format!(
+				"Unexpected response to RPC Update: {}",
+				debug_serialize(&rpc_resp)
+			)))
+		}
+	}
+
+	pub async fn handle_rpc(
+		self: &Arc<Self>,
+		message: &SyncRPC,
+		mut must_exit: watch::Receiver<bool>,
+	) -> Result<SyncRPC, Error> {
+		match message {
+			SyncRPC::GetRootChecksumRange(begin, end) => {
+				let root_cks = self.root_checksum(&begin, &end, &mut must_exit).await?;
+				Ok(SyncRPC::RootChecksumRange(root_cks.bounds))
+			}
+			SyncRPC::Checksums(checksums, retain) => {
+				self.handle_checksums_rpc(&checksums[..], *retain, &mut must_exit)
+					.await
+			}
+			_ => Err(Error::Message(format!("Unexpected sync RPC"))),
+		}
+	}
+
+	async fn handle_checksums_rpc(
+		self: &Arc<Self>,
+		checksums: &[RangeChecksum],
+		retain: bool,
+		must_exit: &mut watch::Receiver<bool>,
+	) -> Result<SyncRPC, Error> {
+		let mut ret_ranges = vec![];
+		let mut ret_items = vec![];
+
+		for their_ckr in checksums.iter() {
+			let our_ckr = self.range_checksum(&their_ckr.bounds, must_exit).await?;
+			for (their_range, their_hash) in their_ckr.children.iter() {
+				let differs = match our_ckr
+					.children
+					.binary_search_by(|(our_range, _)| our_range.cmp(&their_range))
+				{
+					Err(_) => {
+						if their_range.level >= 1 {
+							let cached_hash = self
+								.range_checksum_cached_hash(&their_range, must_exit)
+								.await?;
+							cached_hash.hash.map(|h| h != *their_hash).unwrap_or(true)
+						} else {
+							true
+						}
+					}
+					Ok(i) => our_ckr.children[i].1 != *their_hash,
+				};
+				if differs {
+					ret_ranges.push(their_range.clone());
+					if retain && their_range.level == 0 {
+						if let Some(item_bytes) =
+							self.table.store.get(their_range.begin.as_slice())?
+						{
+							ret_items.push(Arc::new(ByteBuf::from(item_bytes.to_vec())));
+						}
+					}
+				}
+			}
+			for (our_range, _hash) in our_ckr.children.iter() {
+				if let Some(their_found_limit) = &their_ckr.found_limit {
+					if our_range.begin.as_slice() > their_found_limit.as_slice() {
+						break;
+					}
+				}
+
+				let not_present = our_ckr
+					.children
+					.binary_search_by(|(their_range, _)| their_range.cmp(&our_range))
+					.is_err();
+				if not_present {
+					if our_range.level > 0 {
+						ret_ranges.push(our_range.clone());
+					}
+					if retain && our_range.level == 0 {
+						if let Some(item_bytes) =
+							self.table.store.get(our_range.begin.as_slice())?
+						{
+							ret_items.push(Arc::new(ByteBuf::from(item_bytes.to_vec())));
+						}
+					}
+				}
+			}
+		}
+		let n_checksums = checksums
+			.iter()
+			.map(|x| x.children.len())
+			.fold(0, |x, y| x + y);
+		if ret_ranges.len() > 0 || ret_items.len() > 0 {
+			trace!(
+				"({}) Checksum comparison RPC: {} different + {} items for {} received",
+				self.table.name,
+				ret_ranges.len(),
+				ret_items.len(),
+				n_checksums
+			);
+		}
+		Ok(SyncRPC::Difference(ret_ranges, ret_items))
+	}
+
+	pub async fn invalidate(self: Arc<Self>, item_key: Vec<u8>) -> Result<(), Error> {
+		for i in 1..MAX_DEPTH {
+			let needle = SyncRange {
+				begin: item_key.to_vec(),
+				end: vec![],
+				level: i,
+			};
+			let mut cache = self.cache[i].lock().await;
+			if let Some(cache_entry) = cache.range(..=needle).rev().next() {
+				if cache_entry.0.begin <= item_key && cache_entry.0.end > item_key {
+					let index = cache_entry.0.clone();
+					drop(cache_entry);
+					cache.remove(&index);
+				}
+			}
+		}
+		Ok(())
+	}
+}
+
+impl SyncTodo {
+	fn add_full_scan<F: TableSchema, R: TableReplication>(&mut self, table: &Table<F, R>) {
+		let my_id = table.system.id;
+
+		self.todo.clear();
+
+		let ring = table.system.ring.borrow().clone();
+		let split_points = table.replication.split_points(&ring);
+
+		for i in 0..split_points.len() - 1 {
+			let begin = split_points[i];
+			let end = split_points[i + 1];
+			let nodes = table.replication.replication_nodes(&begin, &ring);
+
+			let retain = nodes.contains(&my_id);
+			if !retain {
+				// Check if we have some data to send, otherwise skip
+				if table.store.range(begin..end).next().is_none() {
+					continue;
+				}
+			}
+
+			self.todo.push(TodoPartition { begin, end, retain });
+		}
+	}
+
+	fn add_ring_difference<F: TableSchema, R: TableReplication>(
+		&mut self,
+		table: &Table<F, R>,
+		old_ring: &Ring,
+		new_ring: &Ring,
+	) {
+		let my_id = table.system.id;
+
+		// If it is us who are entering or leaving the system,
+		// initiate a full sync instead of incremental sync
+		if old_ring.config.members.contains_key(&my_id)
+			!= new_ring.config.members.contains_key(&my_id)
+		{
+			self.add_full_scan(table);
+			return;
+		}
+
+		let mut all_points = None
+			.into_iter()
+			.chain(table.replication.split_points(old_ring).drain(..))
+			.chain(table.replication.split_points(new_ring).drain(..))
+			.chain(self.todo.iter().map(|x| x.begin))
+			.chain(self.todo.iter().map(|x| x.end))
+			.collect::<Vec<_>>();
+		all_points.sort();
+		all_points.dedup();
+
+		let mut old_todo = std::mem::replace(&mut self.todo, vec![]);
+		old_todo.sort_by(|x, y| x.begin.cmp(&y.begin));
+		let mut new_todo = vec![];
+
+		for i in 0..all_points.len() - 1 {
+			let begin = all_points[i];
+			let end = all_points[i + 1];
+			let was_ours = table
+				.replication
+				.replication_nodes(&begin, &old_ring)
+				.contains(&my_id);
+			let is_ours = table
+				.replication
+				.replication_nodes(&begin, &new_ring)
+				.contains(&my_id);
+
+			let was_todo = match old_todo.binary_search_by(|x| x.begin.cmp(&begin)) {
+				Ok(_) => true,
+				Err(j) => {
+					(j > 0 && old_todo[j - 1].begin < end && begin < old_todo[j - 1].end)
+						|| (j < old_todo.len()
+							&& old_todo[j].begin < end && begin < old_todo[j].end)
+				}
+			};
+			if was_todo || (is_ours && !was_ours) || (was_ours && !is_ours) {
+				new_todo.push(TodoPartition {
+					begin,
+					end,
+					retain: is_ours,
+				});
+			}
+		}
+
+		self.todo = new_todo;
+	}
+
+	fn pop_task(&mut self) -> Option<TodoPartition> {
+		if self.todo.is_empty() {
+			return None;
+		}
+
+		let i = rand::thread_rng().gen_range::<usize, _, _>(0, self.todo.len());
+		if i == self.todo.len() - 1 {
+			self.todo.pop()
+		} else {
+			let replacement = self.todo.pop().unwrap();
+			let ret = std::mem::replace(&mut self.todo[i], replacement);
+			Some(ret)
+		}
+	}
+}