Add historian
A microservice that continuously generates hashes, only stopping to tag messages with the latest hash. Fixes #8
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@ -12,6 +12,7 @@
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/// Though processing power varies across nodes, the network gives priority to the
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/// fastest processor. Duration should therefore be estimated by assuming that the hash
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/// was generated by the fastest processor at the time the entry was logged.
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#[derive(Debug, PartialEq, Eq, Clone)]
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pub struct Event {
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pub num_hashes: u64,
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pub end_hash: u64,
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@ -23,6 +24,7 @@ pub struct Event {
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/// be generated in 'num_hashes' hashes and verified in 'num_hashes' hashes. By logging
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/// a hash alongside the tick, each tick and be verified in parallel using the 'end_hash'
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/// of the preceding tick to seed its hashing.
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#[derive(Debug, PartialEq, Eq, Clone)]
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pub enum EventData {
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Tick,
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UserDataKey(u64),
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@ -0,0 +1,125 @@
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//! The `historian` crate provides a microservice for generating a Proof-of-History.
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//! It logs EventData items on behalf of its users. It continuously generates
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//! new hashes, only stopping to check if it has been sent an EventData item. It
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//! tags each EventData with an Event and sends it back. The Event includes the
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//! EventData, the latest hash, and the number of hashes since the last event.
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//! The resulting Event stream represents ordered events in time.
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use std::thread::JoinHandle;
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use std::sync::mpsc::{Receiver, Sender};
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use event::{Event, EventData};
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pub struct Historian {
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pub sender: Sender<EventData>,
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pub receiver: Receiver<Event>,
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pub thread_hdl: JoinHandle<(Event, EventThreadExitReason)>,
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}
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pub enum EventThreadExitReason {
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RecvDisconnected,
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SendDisconnected,
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}
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fn drain_queue(
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receiver: &Receiver<EventData>,
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sender: &Sender<Event>,
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num_hashes: u64,
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end_hash: u64,
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) -> Result<u64, (Event, EventThreadExitReason)> {
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use std::sync::mpsc::TryRecvError;
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let mut num_hashes = num_hashes;
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loop {
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match receiver.try_recv() {
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Ok(data) => {
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let e = Event {
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end_hash,
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num_hashes,
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data: data.clone(),
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};
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if let Err(_) = sender.send(e) {
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let e = Event {
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end_hash,
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num_hashes,
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data,
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};
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return Err((e, EventThreadExitReason::SendDisconnected));
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}
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num_hashes = 0;
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}
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Err(TryRecvError::Empty) => {
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return Ok(num_hashes);
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}
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Err(TryRecvError::Disconnected) => {
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let e = Event {
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end_hash,
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num_hashes,
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data: EventData::Tick,
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};
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return Err((e, EventThreadExitReason::RecvDisconnected));
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}
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}
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}
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}
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/// A background thread that will continue tagging received EventData messages and
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/// sending back Event messages until either the receiver or sender channel is closed.
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pub fn event_stream(
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start_hash: u64,
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receiver: Receiver<EventData>,
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sender: Sender<Event>,
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) -> JoinHandle<(Event, EventThreadExitReason)> {
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use std::collections::hash_map::DefaultHasher;
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use std::hash::{Hash, Hasher};
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use std::thread;
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thread::spawn(move || {
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let mut end_hash = start_hash;
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let mut hasher = DefaultHasher::new();
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let mut num_hashes = 0;
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loop {
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match drain_queue(&receiver, &sender, num_hashes, end_hash) {
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Ok(n) => num_hashes = n,
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Err(e) => return e,
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}
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end_hash.hash(&mut hasher);
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end_hash = hasher.finish();
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num_hashes += 1;
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}
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})
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}
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impl Historian {
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pub fn new(start_hash: u64) -> Self {
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use std::sync::mpsc::channel;
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let (sender, event_data_receiver) = channel();
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let (event_sender, receiver) = channel();
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let thread_hdl = event_stream(start_hash, event_data_receiver, event_sender);
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Historian {
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sender,
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receiver,
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thread_hdl,
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}
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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use event::*;
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#[test]
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fn test_historian() {
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let hist = Historian::new(0);
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let data = EventData::Tick;
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hist.sender.send(data.clone()).unwrap();
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let e0 = hist.receiver.recv().unwrap();
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assert_eq!(e0.data, data);
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let data = EventData::UserDataKey(0xdeadbeef);
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hist.sender.send(data.clone()).unwrap();
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let e1 = hist.receiver.recv().unwrap();
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assert_eq!(e1.data, data);
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verify_slice(&[e0, e1], 0);
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}
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}
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@ -1,4 +1,5 @@
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#![cfg_attr(feature = "unstable", feature(test))]
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pub mod event;
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pub mod historian;
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extern crate itertools;
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extern crate rayon;
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