Implement Error for a few error types (#511)

tokio-executor/src/enter.rs

@@ -1,5 +1,6 @@
 use std::prelude::v1::*;
 use std::cell::Cell;
+use std::error::Error;
 use std::fmt;
 
 #[cfg(feature = "unstable-futures")]
@@ -27,11 +28,23 @@ pub struct EnterError {
 impl fmt::Debug for EnterError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_struct("EnterError")
-            .field("reason", &"attempted to run an executor while another executor is already running")
+            .field("reason", &self.description())
             .finish()
     }
 }
 
+impl fmt::Display for EnterError {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        write!(fmt, "{}", self.description())
+    }
+}
+
+impl Error for EnterError {
+    fn description(&self) -> &str {
+        "attempted to run an executor while another executor is already running"
+    }
+}
+
 /// Marks the current thread as being within the dynamic extent of an
 /// executor.
 ///

tokio-executor/src/lib.rs

@@ -52,6 +52,9 @@ pub use global::spawn2;
 
 use futures::Future;
 
+use std::error::Error;
+use std::fmt;
+
 /// A value that executes futures.
 ///
 /// The [`spawn`] function is used to submit a future to an executor. Once
@@ -238,3 +241,15 @@ impl SpawnError {
         !self.is_shutdown
     }
 }
+
+impl fmt::Display for SpawnError {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        write!(fmt, "{}", self.description())
+    }
+}
+
+impl Error for SpawnError {
+    fn description(&self) -> &str {
+        "attempted to spawn task while the executor is at capacity or shut down"
+    }
+}

tokio-reactor/src/lib.rs

@@ -61,6 +61,7 @@ use tokio_executor::Enter;
 use tokio_executor::park::{Park, Unpark};
 
 use std::{fmt, usize};
+use std::error::Error;
 use std::io;
 use std::mem;
 use std::cell::RefCell;
@@ -771,3 +772,17 @@ fn lower_async<T>(new: futures2::Async<T>) -> futures::Async<T> {
         futures2::Async::Pending => futures::Async::NotReady,
     }
 }
+
+// ===== impl SetFallbackError =====
+
+impl fmt::Display for SetFallbackError {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        write!(fmt, "{}", self.description())
+    }
+}
+
+impl Error for SetFallbackError {
+    fn description(&self) -> &str {
+        "attempted to set fallback reactor while already configured"
+    }
+}

tokio-threadpool/src/blocking.rs

@@ -29,8 +29,8 @@ pub struct BlockingError {
 ///
 /// # Return
 ///
-/// When the blocking closure is executed, `Ok(T)` is returned, where `T` is the
-/// closure's return value.
+/// When the blocking closure is executed, `Ok(Ready(T))` is returned, where
+/// `T` is the closure's return value.
 ///
 /// If the thread pool has shutdown, `Err` is returned.
 ///