Implement graceful shutdown
Sayan Nandan
4 years ago
parent
755e8d80f4
commit
35a86c96ac
@ -0,0 +1,174 @@
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/*
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* Created on Tue Jul 21 2020
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*
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* This file is a part of the source code for the Terrabase database
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* Copyright (c) 2020, Sayan Nandan <ohsayan at outlook dot com>
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Affero General Public License for more details.
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*
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* You should have received a copy of the GNU Affero General Public License
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* along with this program. If not, see <https://www.gnu.org/licenses/>.
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*
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*/
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use crate::{Connection, CoreDB};
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use corelib::TResult;
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use std::future::Future;
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use std::sync::Arc;
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use tokio::net::TcpListener;
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use tokio::net::TcpStream;
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use tokio::sync::Semaphore;
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use tokio::sync::{broadcast, mpsc};
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use tokio::time::{self, Duration};
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/// Responsible for gracefully shutting down the server instead of dying randomly
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// Sounds very sci-fi ;)
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pub struct Terminator {
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terminate: bool,
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signal: broadcast::Receiver<()>,
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}
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impl Terminator {
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pub fn new(signal: broadcast::Receiver<()>) -> Self {
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Terminator {
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// Don't terminate on creation!
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terminate: false,
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signal,
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}
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}
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pub fn is_termination_signal(&self) -> bool {
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self.terminate
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}
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pub async fn receive_signal(&mut self) {
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// The server may have already been terminated
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// In that event, just return
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if self.terminate {
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return;
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}
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let _ = self.signal.recv().await;
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self.terminate = true;
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}
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}
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pub struct Listener {
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/// An atomic reference to the coretable
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db: CoreDB,
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/// The incoming connection listener (binding)
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listener: TcpListener,
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/// The maximum number of connections
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climit: Arc<Semaphore>,
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/// The shutdown broadcaster
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signal: broadcast::Sender<()>,
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// When all `Sender`s are dropped - the `Receiver` gets a `None` value
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// We send a clone of `terminate_tx` to each `CHandler`
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terminate_tx: mpsc::Sender<()>,
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terminate_rx: mpsc::Receiver<()>,
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}
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struct CHandler {
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db: CoreDB,
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con: Connection,
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climit: Arc<Semaphore>,
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terminator: Terminator,
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_term_sig_tx: mpsc::Sender<()>,
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}
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impl Listener {
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async fn accept(&mut self) -> TResult<TcpStream> {
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// We will steal the idea of Ethernet's backoff for connection errors
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let mut backoff = 1;
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loop {
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match self.listener.accept().await {
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// We don't need the bindaddr
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Ok((stream, _)) => return Ok(stream),
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Err(e) => {
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if backoff > 64 {
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// Too many retries, goodbye user
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return Err(e.into());
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}
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}
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}
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// Wait for the `backoff` duration
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time::delay_for(Duration::from_secs(backoff)).await;
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// We're using exponential backoff
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backoff *= 2;
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}
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}
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pub async fn run(&mut self) -> TResult<()> {
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loop {
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// Take the permit first, but we won't use it right now
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// that's why we will forget it
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self.climit.acquire().await.forget();
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let stream = self.accept().await?;
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let mut chandle = CHandler {
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db: self.db.clone(),
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con: Connection::new(stream),
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climit: self.climit.clone(),
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terminator: Terminator::new(self.signal.subscribe()),
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_term_sig_tx: self.terminate_tx.clone(),
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};
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tokio::spawn(async move {
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chandle.run().await;
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});
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}
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}
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}
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impl CHandler {
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async fn run(&mut self) {
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while !self.terminator.is_termination_signal() {
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let try_df = tokio::select! {
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tdf = self.con.read_query() => tdf,
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_ = self.terminator.receive_signal() => {
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return;
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}
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};
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match try_df {
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Ok(df) => return self.con.write_response(self.db.execute_query(df)).await,
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Err(e) => return self.con.close_conn_with_error(e).await,
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}
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}
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}
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}
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impl Drop for CHandler {
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fn drop(&mut self) {
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self.climit.add_permits(1);
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}
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}
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pub async fn run(listener: TcpListener, sig: impl Future) {
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let (signal, _) = broadcast::channel(1);
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let (terminate_tx, terminate_rx) = mpsc::channel(1);
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let mut server = Listener {
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listener,
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db: CoreDB::new(),
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climit: Arc::new(Semaphore::new(10000)),
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signal,
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terminate_tx,
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terminate_rx,
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};
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tokio::select! {
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_ = server.run() => {}
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_ = sig => {
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println!("Shuttting down...")
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}
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}
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let Listener {
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mut terminate_rx,
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terminate_tx,
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signal,
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..
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} = server;
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drop(signal);
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drop(terminate_tx);
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let _ = terminate_rx.recv().await;
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}
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