DRAFT RFC: limited no-std I/O support using portable-io

tokio/Cargo.toml

@@ -22,8 +22,7 @@ categories = ["asynchronous", "network-programming"]
 keywords = ["io", "async", "non-blocking", "futures"]
 
 [features]
-# Include nothing by default
-default = []
+default = ["std"]
 
 # enable everything
 full = [
@@ -37,16 +36,18 @@ full = [
   "rt",
   "rt-multi-thread",
   "signal",
+  "std",
   "sync",
   "time",
 ]
 
-fs = []
+fs = ["std"]
 io-util = ["bytes"]
 # stdin, stdout, stderr
-io-std = []
-macros = ["tokio-macros"]
+io-std = ["std"]
+macros = ["std", "tokio-macros"]
 net = [
+  "std",
   "libc",
   "mio/os-poll",
   "mio/os-ext",
@@ -58,7 +59,9 @@ net = [
   "windows-sys/Win32_System_Pipes",
   "windows-sys/Win32_System_SystemServices",
 ]
+portable-io = ["parking_lot", "dep:portable-io"]
 process = [
+  "std",
   "bytes",
   "libc",
   "mio/os-poll",
@@ -70,9 +73,10 @@ process = [
   "windows-sys/Win32_System_WindowsProgramming",
 ]
 # Includes basic task execution capabilities
-rt = []
+rt = ["std"]
 rt-multi-thread = ["rt"]
 signal = [
+  "std",
   "libc",
   "mio/os-poll",
   "mio/net",
@@ -81,9 +85,10 @@ signal = [
   "windows-sys/Win32_Foundation",
   "windows-sys/Win32_System_Console",
 ]
-sync = []
+std = []
+sync = ["std"]
 test-util = ["rt", "sync", "time"]
-time = []
+time = ["std"]
 
 [dependencies]
 tokio-macros = { version = "~2.5.0", path = "../tokio-macros", optional = true }
@@ -94,6 +99,7 @@ pin-project-lite = "0.2.11"
 bytes = { version = "1.1.0", optional = true }
 mio = { version = "1.0.1", optional = true, default-features = false }
 parking_lot = { version = "0.12.0", optional = true }
+portable-io = { version = "0.0.4", optional = true }
 
 [target.'cfg(not(target_family = "wasm"))'.dependencies]
 socket2 = { version = "0.5.5", optional = true, features = ["all"] }

tokio/src/blocking.rs

@@ -10,6 +10,8 @@ cfg_rt! {
 }
 
 cfg_not_rt! {
+    use crate::alias::std;
+
     use std::fmt;
     use std::future::Future;
     use std::pin::Pin;

tokio/src/fs/canonicalize.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::asyncify;
 
 use std::io;

tokio/src/fs/copy.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::asyncify;
 use std::path::Path;
 

tokio/src/fs/create_dir.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::asyncify;
 
 use std::io;

tokio/src/fs/create_dir_all.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::asyncify;
 
 use std::io;

tokio/src/fs/dir_builder.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::asyncify;
 
 use std::io;

tokio/src/fs/file.rs

@@ -2,6 +2,7 @@
 //!
 //! [`File`]: File
 
+use crate::alias::std::{self, prelude::*};
 use crate::fs::{asyncify, OpenOptions};
 use crate::io::blocking::{Buf, DEFAULT_MAX_BUF_SIZE};
 use crate::io::{AsyncRead, AsyncSeek, AsyncWrite, ReadBuf};

tokio/src/fs/hard_link.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::asyncify;
 
 use std::io;

tokio/src/fs/metadata.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::asyncify;
 
 use std::fs::Metadata;

tokio/src/fs/mod.rs

@@ -295,7 +295,7 @@ cfg_windows! {
     pub use self::symlink_file::symlink_file;
 }
 
-use std::io;
+use crate::alias::std::io;
 
 #[cfg(not(test))]
 use crate::blocking::spawn_blocking;

tokio/src/fs/open_options.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::{asyncify, File};
 
 use std::io;

tokio/src/fs/read.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::asyncify;
 
 use std::{io, path::Path};

tokio/src/fs/read_dir.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::asyncify;
 
 use std::collections::VecDeque;

tokio/src/fs/read_link.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::asyncify;
 
 use std::io;

tokio/src/fs/read_to_string.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::asyncify;
 
 use std::{io, path::Path};

tokio/src/fs/remove_dir.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::asyncify;
 
 use std::io;

tokio/src/fs/remove_dir_all.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::asyncify;
 
 use std::io;

tokio/src/fs/remove_file.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::asyncify;
 
 use std::io;

tokio/src/fs/rename.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::asyncify;
 
 use std::io;

tokio/src/fs/set_permissions.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::asyncify;
 
 use std::fs::Permissions;

tokio/src/fs/symlink.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::asyncify;
 
 use std::io;

tokio/src/fs/symlink_metadata.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::asyncify;
 
 use std::fs::Metadata;

tokio/src/fs/try_exists.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::asyncify;
 
 use std::io;

tokio/src/fs/write.rs

@@ -1,3 +1,4 @@
+use crate::alias::std::{self, prelude::*};
 use crate::fs::asyncify;
 
 use std::{io, path::Path};

tokio/src/future/block_on.rs

@@ -1,3 +1,5 @@
+use crate::alias::std;
+
 use std::future::Future;
 
 cfg_rt! {

tokio/src/future/maybe_done.rs

@@ -1,5 +1,7 @@
 //! Definition of the [`MaybeDone`] combinator.
 
+use crate::alias::std;
+
 use pin_project_lite::pin_project;
 use std::future::{Future, IntoFuture};
 use std::pin::Pin;
@@ -74,11 +76,15 @@ impl<Fut: Future> Future for MaybeDone<Fut> {
 // Test for https://github.com/tokio-rs/tokio/issues/6729
 #[cfg(test)]
 mod miri_tests {
+    extern crate std;
+    use std::borrow::ToOwned;
+
     use super::maybe_done;
 
     use std::{
         future::Future,
         pin::Pin,
+        string::String,
         sync::Arc,
         task::{Context, Poll, Wake},
     };

tokio/src/future/mod.rs

@@ -23,6 +23,6 @@ cfg_trace! {
 
 cfg_not_trace! {
     cfg_rt! {
-        pub(crate) use std::future::Future;
+        pub(crate) use crate::alias::std::future::Future;
     }
 }

tokio/src/future/try_join.rs

@@ -1,3 +1,4 @@
+use crate::alias::std;
 use crate::future::maybe_done::{maybe_done, MaybeDone};
 
 use pin_project_lite::pin_project;

tokio/src/io/async_buf_read.rs

@@ -1,3 +1,6 @@
+use crate::alias::std;
+use crate::alias::std::prelude::*;
+
 use crate::io::AsyncRead;
 
 use std::io;

tokio/src/io/async_fd.rs

@@ -1,3 +1,4 @@
+use crate::alias::std;
 use crate::io::{Interest, Ready};
 use crate::runtime::io::{ReadyEvent, Registration};
 use crate::runtime::scheduler;

tokio/src/io/async_read.rs

@@ -1,4 +1,8 @@
 use super::ReadBuf;
+
+use crate::alias::std;
+use crate::alias::std::prelude::*;
+
 use std::io;
 use std::ops::DerefMut;
 use std::pin::Pin;

tokio/src/io/async_seek.rs

@@ -1,3 +1,6 @@
+use crate::alias::std;
+use crate::alias::std::prelude::*;
+
 use std::io::{self, SeekFrom};
 use std::ops::DerefMut;
 use std::pin::Pin;

tokio/src/io/async_write.rs

@@ -1,3 +1,6 @@
+use crate::alias::std;
+use crate::alias::std::prelude::*;
+
 use std::io::{self, IoSlice};
 use std::ops::DerefMut;
 use std::pin::Pin;

tokio/src/io/blocking.rs

@@ -1,3 +1,6 @@
+use crate::alias::std;
+use crate::alias::std::prelude::*;
+
 use crate::io::sys;
 use crate::io::{AsyncRead, AsyncWrite, ReadBuf};
 

tokio/src/io/interest.rs

@@ -1,5 +1,6 @@
 #![cfg_attr(not(feature = "net"), allow(dead_code, unreachable_pub))]
 
+use crate::alias::std;
 use crate::io::ready::Ready;
 
 use std::fmt;

tokio/src/io/join.rs

@@ -1,5 +1,6 @@
 //! Join two values implementing `AsyncRead` and `AsyncWrite` into a single one.
 
+use crate::alias::std;
 use crate::io::{AsyncBufRead, AsyncRead, AsyncWrite, ReadBuf};
 
 use std::io;

tokio/src/io/mod.rs

@@ -194,6 +194,8 @@ cfg_io_blocking! {
     pub(crate) mod blocking;
 }
 
+use crate::alias::std;
+
 mod async_buf_read;
 pub use self::async_buf_read::AsyncBufRead;
 

tokio/src/io/poll_evented.rs

@@ -1,3 +1,4 @@
+use crate::alias::std;
 use crate::io::interest::Interest;
 use crate::runtime::io::Registration;
 use crate::runtime::scheduler;

tokio/src/io/read_buf.rs

@@ -1,3 +1,5 @@
+use crate::alias::std;
+
 use std::fmt;
 use std::mem::MaybeUninit;
 

tokio/src/io/ready.rs

@@ -1,5 +1,6 @@
 #![cfg_attr(not(feature = "net"), allow(unreachable_pub))]
 
+use crate::alias::std;
 use crate::io::interest::Interest;
 
 use std::fmt;

tokio/src/io/seek.rs

@@ -1,3 +1,4 @@
+use crate::alias::std;
 use crate::io::AsyncSeek;
 
 use pin_project_lite::pin_project;

tokio/src/io/split.rs

@@ -4,12 +4,19 @@
 //! To restore this read/write object from its `split::ReadHalf` and
 //! `split::WriteHalf` use `unsplit`.
 
+use crate::alias::std;
 use crate::io::{AsyncRead, AsyncWrite, ReadBuf};
 
 use std::fmt;
 use std::io;
 use std::pin::Pin;
 use std::sync::Arc;
+#[cfg(all(
+    feature = "parking_lot",
+    not(feature = "std"),
+))]
+use parking_lot::Mutex;
+#[cfg(feature = "std")]
 use std::sync::Mutex;
 use std::task::{Context, Poll};
 
@@ -57,6 +64,12 @@ struct Inner<T> {
 
 impl<T> Inner<T> {
     fn with_lock<R>(&self, f: impl FnOnce(Pin<&mut T>) -> R) -> R {
+        #[cfg(all(
+            feature = "parking_lot",
+            not(feature = "std"),
+        ))]
+        let mut guard = self.stream.lock();
+        #[cfg(feature = "std")]
         let mut guard = self.stream.lock().unwrap();
 
         // safety: we do not move the stream.
@@ -92,6 +105,12 @@ impl<T> ReadHalf<T> {
                 .ok()
                 .expect("`Arc::try_unwrap` failed");
 
+            #[cfg(all(
+                feature = "parking_lot",
+                not(feature = "std"),
+            ))]
+            return inner.stream.into_inner();
+            #[cfg(feature = "std")]
             inner.stream.into_inner().unwrap()
         } else {
             panic!("Unrelated `split::Write` passed to `split::Read::unsplit`.")

tokio/src/io/stderr.rs

@@ -1,3 +1,4 @@
+use crate::alias::std;
 use crate::io::blocking::Blocking;
 use crate::io::stdio_common::SplitByUtf8BoundaryIfWindows;
 use crate::io::AsyncWrite;
@@ -79,6 +80,8 @@ cfg_io_std! {
 
 #[cfg(unix)]
 mod sys {
+    use crate::alias::std;
+
     use std::os::unix::io::{AsFd, AsRawFd, BorrowedFd, RawFd};
 
     use super::Stderr;