main: Use crossbeam channel for tokio contention check

I observed a panic due to a bug in std rust-lang/rust#39364,
switching to crossbeam fixes that and improves performance,
which reduces the effect of the channel in the timing.

Author: leoyvens

Cargo.lock

@@ -10,6 +10,7 @@ futures = "0.1.21"
 git-testament = "0.1"
 graphql-parser = "0.2.1"
 http = "0.1"
+
 # We're using the latest ipfs-api for the HTTPS support that was merged in
 # https://github.com/ferristseng/rust-ipfs-api/commit/55902e98d868dcce047863859caf596a629d10ec
 # but has not been released yet.
@@ -18,6 +19,7 @@ itertools = "0.7"
 lazy_static = "1.2.0"
 sentry = "0.15.1"
 url = "1.7.1"
+crossbeam-channel = "0.3.8"
 graph = { path = "../graph" }
 graph-core = { path = "../core" }
 graph-datasource-ethereum = { path = "../datasource/ethereum" }

node/Cargo.toml

@@ -575,15 +575,15 @@ fn async_main() -> impl Future<Item = (), Error = ()> + Send + 'static {
     // Periodically check for contention in the tokio threadpool. First spawn a
     // task that simply responds to "ping" requests. Then spawn a separate
     // thread to periodically ping it and check responsiveness.
-    let (ping_send, ping_receive) = mpsc::channel::<std::sync::mpsc::Sender<()>>(1);
+    let (ping_send, ping_receive) = mpsc::channel::<crossbeam_channel::Sender<()>>(1);
     tokio::spawn(
         ping_receive
             .for_each(move |pong_send| pong_send.clone().send(()).map(|_| ()).map_err(|_| ())),
     );
     let contention_logger = logger.clone();
     std::thread::spawn(move || loop {
         std::thread::sleep(Duration::from_millis(100));
-        let (pong_send, pong_receive) = std::sync::mpsc::channel();
+        let (pong_send, pong_receive) = crossbeam_channel::bounded(1);
         ping_send.clone().send(pong_send).wait().unwrap();
         let mut timeout = Duration::from_millis(1);
         while pong_receive.recv_timeout(timeout).is_err() {