std/pipe.rs
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//! A cross-platform anonymous pipe.
//!
//! This module provides support for anonymous OS pipes, like [pipe] on Linux or [CreatePipe] on
//! Windows.
//!
//! # Behavior
//!
//! A pipe is a synchronous, unidirectional data channel between two or more processes, like an
//! interprocess [`mpsc`](crate::sync::mpsc) provided by the OS. In particular:
//!
//! * A read on a [`PipeReader`] blocks until the pipe is non-empty.
//! * A write on a [`PipeWriter`] blocks when the pipe is full.
//! * When all copies of a [`PipeWriter`] are closed, a read on the corresponding [`PipeReader`]
//! returns EOF.
//! * [`PipeReader`] can be shared, but only one process will consume the data in the pipe.
//!
//! # Capacity
//!
//! Pipe capacity is platform dependent. To quote the Linux [man page]:
//!
//! > Different implementations have different limits for the pipe capacity. Applications should
//! > not rely on a particular capacity: an application should be designed so that a reading process
//! > consumes data as soon as it is available, so that a writing process does not remain blocked.
//!
//! # Examples
//!
//! ```no_run
//! #![feature(anonymous_pipe)]
//! # #[cfg(miri)] fn main() {}
//! # #[cfg(not(miri))]
//! # fn main() -> std::io::Result<()> {
//! # use std::process::Command;
//! # use std::io::{Read, Write};
//! let (ping_rx, mut ping_tx) = std::pipe::pipe()?;
//! let (mut pong_rx, pong_tx) = std::pipe::pipe()?;
//!
//! // Spawn a process that echoes its input.
//! let mut echo_server = Command::new("cat").stdin(ping_rx).stdout(pong_tx).spawn()?;
//!
//! ping_tx.write_all(b"hello")?;
//! // Close to unblock echo_server's reader.
//! drop(ping_tx);
//!
//! let mut buf = String::new();
//! // Block until echo_server's writer is closed.
//! pong_rx.read_to_string(&mut buf)?;
//! assert_eq!(&buf, "hello");
//!
//! echo_server.wait()?;
//! # Ok(())
//! # }
//! ```
//! [pipe]: https://man7.org/linux/man-pages/man2/pipe.2.html
//! [CreatePipe]: https://learn.microsoft.com/en-us/windows/win32/api/namedpipeapi/nf-namedpipeapi-createpipe
//! [man page]: https://man7.org/linux/man-pages/man7/pipe.7.html
use crate::io;
use crate::sys::anonymous_pipe::{AnonPipe, pipe as pipe_inner};
/// Create anonymous pipe that is close-on-exec and blocking.
///
/// # Examples
///
/// See the [module-level](crate::pipe) documentation for examples.
#[unstable(feature = "anonymous_pipe", issue = "127154")]
#[inline]
pub fn pipe() -> io::Result<(PipeReader, PipeWriter)> {
pipe_inner().map(|(reader, writer)| (PipeReader(reader), PipeWriter(writer)))
}
/// Read end of the anonymous pipe.
#[unstable(feature = "anonymous_pipe", issue = "127154")]
#[derive(Debug)]
pub struct PipeReader(pub(crate) AnonPipe);
/// Write end of the anonymous pipe.
#[unstable(feature = "anonymous_pipe", issue = "127154")]
#[derive(Debug)]
pub struct PipeWriter(pub(crate) AnonPipe);
impl PipeReader {
/// Create a new [`PipeReader`] instance that shares the same underlying file description.
///
/// # Examples
///
/// ```no_run
/// #![feature(anonymous_pipe)]
/// # #[cfg(miri)] fn main() {}
/// # #[cfg(not(miri))]
/// # fn main() -> std::io::Result<()> {
/// # use std::fs;
/// # use std::io::Write;
/// # use std::process::Command;
/// const NUM_SLOT: u8 = 2;
/// const NUM_PROC: u8 = 5;
/// const OUTPUT: &str = "work.txt";
///
/// let mut jobs = vec![];
/// let (reader, mut writer) = std::pipe::pipe()?;
///
/// // Write NUM_SLOT characters the the pipe.
/// writer.write_all(&[b'|'; NUM_SLOT as usize])?;
///
/// // Spawn several processes that read a character from the pipe, do some work, then
/// // write back to the pipe. When the pipe is empty, the processes block, so only
/// // NUM_SLOT processes can be working at any given time.
/// for _ in 0..NUM_PROC {
/// jobs.push(
/// Command::new("bash")
/// .args(["-c",
/// &format!(
/// "read -n 1\n\
/// echo -n 'x' >> '{OUTPUT}'\n\
/// echo -n '|'",
/// ),
/// ])
/// .stdin(reader.try_clone()?)
/// .stdout(writer.try_clone()?)
/// .spawn()?,
/// );
/// }
///
/// // Wait for all jobs to finish.
/// for mut job in jobs {
/// job.wait()?;
/// }
///
/// // Check our work and clean up.
/// let xs = fs::read_to_string(OUTPUT)?;
/// fs::remove_file(OUTPUT)?;
/// assert_eq!(xs, "x".repeat(NUM_PROC.into()));
/// # Ok(())
/// # }
/// ```
#[unstable(feature = "anonymous_pipe", issue = "127154")]
pub fn try_clone(&self) -> io::Result<Self> {
self.0.try_clone().map(Self)
}
}
impl PipeWriter {
/// Create a new [`PipeWriter`] instance that shares the same underlying file description.
///
/// # Examples
///
/// ```no_run
/// #![feature(anonymous_pipe)]
/// # #[cfg(miri)] fn main() {}
/// # #[cfg(not(miri))]
/// # fn main() -> std::io::Result<()> {
/// # use std::process::Command;
/// # use std::io::Read;
/// let (mut reader, writer) = std::pipe::pipe()?;
///
/// // Spawn a process that writes to stdout and stderr.
/// let mut peer = Command::new("bash")
/// .args([
/// "-c",
/// "echo -n foo\n\
/// echo -n bar >&2"
/// ])
/// .stdout(writer.try_clone()?)
/// .stderr(writer)
/// .spawn()?;
///
/// // Read and check the result.
/// let mut msg = String::new();
/// reader.read_to_string(&mut msg)?;
/// assert_eq!(&msg, "foobar");
///
/// peer.wait()?;
/// # Ok(())
/// # }
/// ```
#[unstable(feature = "anonymous_pipe", issue = "127154")]
pub fn try_clone(&self) -> io::Result<Self> {
self.0.try_clone().map(Self)
}
}
#[unstable(feature = "anonymous_pipe", issue = "127154")]
impl io::Read for &PipeReader {
fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
self.0.read(buf)
}
fn read_vectored(&mut self, bufs: &mut [io::IoSliceMut<'_>]) -> io::Result<usize> {
self.0.read_vectored(bufs)
}
#[inline]
fn is_read_vectored(&self) -> bool {
self.0.is_read_vectored()
}
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
self.0.read_to_end(buf)
}
fn read_buf(&mut self, buf: io::BorrowedCursor<'_>) -> io::Result<()> {
self.0.read_buf(buf)
}
}
#[unstable(feature = "anonymous_pipe", issue = "127154")]
impl io::Read for PipeReader {
fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
self.0.read(buf)
}
fn read_vectored(&mut self, bufs: &mut [io::IoSliceMut<'_>]) -> io::Result<usize> {
self.0.read_vectored(bufs)
}
#[inline]
fn is_read_vectored(&self) -> bool {
self.0.is_read_vectored()
}
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
self.0.read_to_end(buf)
}
fn read_buf(&mut self, buf: io::BorrowedCursor<'_>) -> io::Result<()> {
self.0.read_buf(buf)
}
}
#[unstable(feature = "anonymous_pipe", issue = "127154")]
impl io::Write for &PipeWriter {
fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
self.0.write(buf)
}
#[inline]
fn flush(&mut self) -> io::Result<()> {
Ok(())
}
fn write_vectored(&mut self, bufs: &[io::IoSlice<'_>]) -> io::Result<usize> {
self.0.write_vectored(bufs)
}
#[inline]
fn is_write_vectored(&self) -> bool {
self.0.is_write_vectored()
}
}
#[unstable(feature = "anonymous_pipe", issue = "127154")]
impl io::Write for PipeWriter {
fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
self.0.write(buf)
}
#[inline]
fn flush(&mut self) -> io::Result<()> {
Ok(())
}
fn write_vectored(&mut self, bufs: &[io::IoSlice<'_>]) -> io::Result<usize> {
self.0.write_vectored(bufs)
}
#[inline]
fn is_write_vectored(&self) -> bool {
self.0.is_write_vectored()
}
}