Cosmetic refactor

- turn log::error! into log::warn! as it doesn't throw any error
- add Clone and Copy impls for Cancelled making it cheap to operate with
- apply rustfmt

actix-threadpool/src/lib.rs

@@ -1,34 +1,34 @@
 //! Thread pool for blocking operations
 
-use std::future::Future;
-use std::task::{Poll,Context};
+use std::{
+    future::Future,
+    pin::Pin,
+    task::{Context, Poll},
+};
 
 use derive_more::Display;
 use futures::channel::oneshot;
 use parking_lot::Mutex;
 use threadpool::ThreadPool;
-use std::pin::Pin;
 
-/// Env variable for default cpu pool size
+/// Env variable for default cpu pool size.
 const ENV_CPU_POOL_VAR: &str = "ACTIX_THREADPOOL";
 
 lazy_static::lazy_static! {
     pub(crate) static ref DEFAULT_POOL: Mutex<ThreadPool> = {
-        let default = match std::env::var(ENV_CPU_POOL_VAR) {
-            Ok(val) => {
-                if let Ok(val) = val.parse() {
-                    val
-                } else {
-                    log::error!("Can not parse ACTIX_THREADPOOL value");
-                    num_cpus::get() * 5
-                }
-            }
-            Err(_) => num_cpus::get() * 5,
-        };
+        let num = std::env::var(ENV_CPU_POOL_VAR)
+            .map_err(|_| ())
+            .and_then(|val| {
+                val.parse().map_err(|_| log::warn!(
+                    "Can not parse {} value, using default",
+                    ENV_CPU_POOL_VAR,
+                ))
+            })
+            .unwrap_or_else(|_| num_cpus::get() * 5);
         Mutex::new(
             threadpool::Builder::new()
                 .thread_name("actix-web".to_owned())
-                .num_threads(default)
+                .num_threads(num)
                 .build(),
         )
     };
@@ -40,8 +40,8 @@ thread_local! {
     };
 }
 
-/// Blocking operation execution error
-#[derive(Debug, Display)]
+/// Error of blocking operation execution being cancelled.
+#[derive(Clone, Copy, Debug, Display)]
 #[display(fmt = "Thread pool is gone")]
 pub struct Cancelled;
 
@@ -71,12 +71,11 @@ pub struct CpuFuture<I> {
 }
 
 impl<I> Future for CpuFuture<I> {
-    type Output = Result<I,Cancelled>;
+    type Output = Result<I, Cancelled>;
 
     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        let rx  = Pin::new(&mut Pin::get_mut(self).rx);
+        let rx = Pin::new(&mut Pin::get_mut(self).rx);
         let res = futures::ready!(rx.poll(cx));
         Poll::Ready(res.map_err(|_| Cancelled))
     }
-
 }