5 files changed, 19 insertions, 0 deletions
diff --git a/futures/src/executor.rs b/futures/src/executor.rs
index b2ff043e..c2b9cc72 100644
--- a/futures/src/executor.rs
+++ b/futures/src/executor.rs
@@ -29,13 +29,26 @@ pub use wasm_bindgen::WasmBindgen;
 
 use futures::Future;
 
+/// A type that can run futures.
 pub trait Executor: Sized {
+    /// Creates a new [`Executor`].
+    ///
+    /// [`Executor`]: trait.Executor.html
     fn new() -> Result<Self, futures::io::Error>
     where
         Self: Sized;
 
+    /// Spawns a future in the [`Executor`].
+    ///
+    /// [`Executor`]: trait.Executor.html
     fn spawn(&self, future: impl Future<Output = ()> + Send + 'static);
 
+    /// Runs the given closure inside the [`Executor`].
+    ///
+    /// Some executors, like `tokio`, require some global state to be in place
+    /// before creating futures. This method can be leveraged to set up this
+    /// global state, call a function, restore the state, and obtain the result
+    /// of the call.
     fn enter<R>(&self, f: impl FnOnce() -> R) -> R {
         f()
     }
diff --git a/futures/src/executor/async_std.rs b/futures/src/executor/async_std.rs
index b056b23d..641dfbd2 100644
--- a/futures/src/executor/async_std.rs
+++ b/futures/src/executor/async_std.rs
@@ -2,6 +2,8 @@ use crate::Executor;
 
 use futures::Future;
 
+/// A type representing the `async-std` runtime.
+#[derive(Debug)]
 pub struct AsyncStd;
 
 impl Executor for AsyncStd {
diff --git a/futures/src/executor/null.rs b/futures/src/executor/null.rs
index 722073bb..6d5cf982 100644
--- a/futures/src/executor/null.rs
+++ b/futures/src/executor/null.rs
@@ -2,6 +2,8 @@ use crate::Executor;
 
 use futures::Future;
 
+/// An executor that drops all the futures, instead of spawning them.
+#[derive(Debug)]
 pub struct Null;
 
 impl Executor for Null {
diff --git a/futures/src/executor/thread_pool.rs b/futures/src/executor/thread_pool.rs
index 6393d0d5..09cb4d21 100644
--- a/futures/src/executor/thread_pool.rs
+++ b/futures/src/executor/thread_pool.rs
@@ -2,6 +2,7 @@ use crate::Executor;
 
 use futures::Future;
 
+/// A thread pool for futures.
 pub type ThreadPool = futures::executor::ThreadPool;
 
 impl Executor for futures::executor::ThreadPool {
diff --git a/futures/src/executor/tokio.rs b/futures/src/executor/tokio.rs
index aafa7e7b..4c609686 100644
--- a/futures/src/executor/tokio.rs
+++ b/futures/src/executor/tokio.rs
@@ -2,6 +2,7 @@ use crate::Executor;
 
 use futures::Future;
 
+/// The `tokio` runtime.
 pub type Tokio = tokio::runtime::Runtime;
 
 impl Executor for Tokio {