fs: use async fn instead of custom futures (#1381)

Also update all the doc examples.

tokio-fs/src/lib.rs

@@ -2,6 +2,7 @@
 #![deny(missing_docs, missing_debug_implementations, rust_2018_idioms)]
 #![cfg_attr(test, deny(warnings))]
 #![doc(test(no_crate_inject, attr(deny(rust_2018_idioms))))]
+#![feature(async_await)]
 
 //! Asynchronous file and standard stream adaptation.
 //!
@@ -32,9 +33,10 @@
 
 mod create_dir;
 mod create_dir_all;
-pub mod file;
+mod file;
 mod hard_link;
 mod metadata;
+mod open_options;
 pub mod os;
 mod read;
 mod read_dir;
@@ -50,28 +52,28 @@ mod stdout;
 mod symlink_metadata;
 mod write;
 
-pub use crate::create_dir::{create_dir, CreateDirFuture};
-pub use crate::create_dir_all::{create_dir_all, CreateDirAllFuture};
+pub use crate::create_dir::create_dir;
+pub use crate::create_dir_all::create_dir_all;
 pub use crate::file::File;
-pub use crate::file::OpenOptions;
-pub use crate::hard_link::{hard_link, HardLinkFuture};
-pub use crate::metadata::{metadata, MetadataFuture};
-pub use crate::read::{read, ReadFile};
-pub use crate::read_dir::{read_dir, DirEntry, ReadDir, ReadDirFuture};
-pub use crate::read_link::{read_link, ReadLinkFuture};
-pub use crate::remove_dir::{remove_dir, RemoveDirFuture};
-pub use crate::remove_dir_all::{remove_dir_all, RemoveDirAllFuture};
-pub use crate::remove_file::{remove_file, RemoveFileFuture};
-pub use crate::rename::{rename, RenameFuture};
-pub use crate::set_permissions::{set_permissions, SetPermissionsFuture};
+pub use crate::hard_link::hard_link;
+pub use crate::metadata::metadata;
+pub use crate::open_options::OpenOptions;
+pub use crate::read::read;
+pub use crate::read_dir::{read_dir, DirEntry, ReadDir};
+pub use crate::read_link::read_link;
+pub use crate::remove_dir::remove_dir;
+pub use crate::remove_dir_all::remove_dir_all;
+pub use crate::remove_file::remove_file;
+pub use crate::rename::rename;
+pub use crate::set_permissions::set_permissions;
 pub use crate::stderr::{stderr, Stderr};
 pub use crate::stdin::{stdin, Stdin};
 pub use crate::stdout::{stdout, Stdout};
-pub use crate::symlink_metadata::{symlink_metadata, SymlinkMetadataFuture};
-pub use crate::write::{write, WriteFile};
+pub use crate::symlink_metadata::symlink_metadata;
+pub use crate::write::write;
 
 use std::io;
-use std::io::ErrorKind::{Other, WouldBlock};
+use std::io::ErrorKind::Other;
 use std::task::Poll;
 use std::task::Poll::*;
 
@@ -86,19 +88,14 @@ where
     }
 }
 
-fn would_block<F, T>(f: F) -> io::Result<T>
+async fn asyncify<F, T>(f: F) -> io::Result<T>
 where
     F: FnOnce() -> io::Result<T>,
 {
-    match tokio_threadpool::blocking(f) {
-        Ready(Ok(Ok(v))) => Ok(v),
-        Ready(Ok(Err(err))) => {
-            debug_assert_ne!(err.kind(), WouldBlock);
-            Err(err)
-        }
-        Ready(Err(_)) => Err(blocking_err()),
-        Pending => Err(blocking_err()),
-    }
+    use futures_util::future::poll_fn;
+
+    let mut f = Some(f);
+    poll_fn(move |_| blocking_io(|| f.take().unwrap()())).await
 }
 
 fn blocking_err() -> io::Error {