Add support for graceful shutdown of the server

The server process now intercepts SIGINT and SIGTERM to initiate a
graceful shutdown of the server.

This is useful when tracking memory leaks locally, as both `hyper` and
`civet` are given a chance to return memory and shutdown cleanly.
However, this will not improve things in production as we also run an
instance of `nginx`, which will close all connections after receiving a
SIGTERM from Heroku.  From my preliminary investigation, it appears we
may need to customize the buildpack to change this behavior.

Additionally, the server will now briefly sleep before notifying Heroku
that it is ready to receive connections.  Also, when using `hyper` the
`Runtime` is configured to use 4 background threads.  This overrides
the default, which is one thread per CPU and provides consistency
between differently sized dynos.  The number of `conduit` background
threads are still configured via `SERVER_THREADS` and defaults to 50
in production.

Author: jtgeibel

Cargo.lock

@@ -78,11 +78,14 @@ conduit-git-http-backend = "0.8"
 civet = "0.9"
 conduit-hyper = "0.1.3"
 
+futures = "0.1"
+tokio = "0.1"
+hyper = "0.12"
+ctrlc = { version = "3.0", features = ["termination"] }
+
 [dev-dependencies]
 conduit-test = "0.8"
-hyper = "0.12"
 hyper-tls = "0.3"
-futures = "0.1"
 lazy_static = "1.0"
 tokio-core = "0.1"
 

Cargo.toml

@@ -1,18 +1,21 @@
 #![deny(warnings)]
 
 use cargo_registry::{boot, App, Env};
-use jemalloc_ctl;
 use std::{
     fs::File,
-    sync::{mpsc::channel, Arc},
+    sync::{mpsc::channel, Arc, Mutex},
+    thread,
+    time::Duration,
 };
 
 use civet::Server as CivetServer;
 use conduit_hyper::Service as HyperService;
+use futures::Future;
+use jemalloc_ctl;
 
 enum Server {
     Civet(CivetServer),
-    Hyper(HyperService<conduit_middleware::MiddlewareBuilder>),
+    Hyper(tokio::runtime::Runtime),
 }
 
 use Server::*;
@@ -53,7 +56,32 @@ fn main() {
 
     let server = if dotenv::var("USE_HYPER").is_ok() {
         println!("Booting with a hyper based server");
-        Hyper(HyperService::new(app, threads as usize))
+        let addr = ([127, 0, 0, 1], port).into();
+        let service = HyperService::new(app, threads as usize);
+        let server = hyper::Server::bind(&addr).serve(service);
+
+        let (tx, rx) = futures::sync::oneshot::channel::<()>();
+        let server = server
+            .with_graceful_shutdown(rx)
+            .map_err(|e| log::error!("Server error: {}", e));
+
+        ctrlc_handler(move || tx.send(()).unwrap_or(()));
+
+        let mut rt = tokio::runtime::Builder::new()
+            .core_threads(4)
+            .name_prefix("hyper-server-worker-")
+            .after_start(|| println!("Stared thread {}", thread::current().name().unwrap_or("?")))
+            .before_stop(|| {
+                println!(
+                    "Stopping thread {}",
+                    thread::current().name().unwrap_or("?")
+                )
+            })
+            .build()
+            .unwrap();
+        rt.spawn(server);
+
+        Hyper(rt)
     } else {
         println!("Booting with a civet based server");
         let mut cfg = civet::Config::new();
@@ -63,19 +91,43 @@ fn main() {
 
     println!("listening on port {}", port);
 
+    // Give tokio a chance to spawn the first worker thread
+    thread::sleep(Duration::from_millis(10));
+
     // Creating this file tells heroku to tell nginx that the application is ready
     // to receive traffic.
     if heroku {
+        println!("Writing to /tmp/app-initialized");
         File::create("/tmp/app-initialized").unwrap();
     }
 
-    if let Hyper(server) = server {
-        let addr = ([127, 0, 0, 1], port).into();
-        server.run(addr);
-    } else {
-        // Civet server is already running, but we need to block the main thread forever
-        // TODO: handle a graceful shutdown by just waiting for a SIG{INT,TERM}
-        let (_tx, rx) = channel::<()>();
-        rx.recv().unwrap();
+    // Block the main thread until the server has shutdown
+    match server {
+        Hyper(rt) => rt.shutdown_on_idle().wait().unwrap(),
+        Civet(server) => {
+            let (tx, rx) = channel::<()>();
+            ctrlc_handler(move || tx.send(()).unwrap_or(()));
+            rx.recv().unwrap();
+            drop(server);
+        }
     }
+
+    println!("Server has gracefully shutdown!");
+}
+
+fn ctrlc_handler<F>(f: F)
+where
+    F: FnOnce() + Send + 'static,
+{
+    let call_once = Mutex::new(Some(f));
+
+    ctrlc::set_handler(move || {
+        if let Some(f) = call_once.lock().unwrap().take() {
+            println!("Starting graceful shutdown");
+            f();
+        } else {
+            println!("Already sent signal to start graceful shutdown");
+        }
+    })
+    .unwrap();
 }