diff --git a/library/std/src/io/pipe.rs b/library/std/src/io/pipe.rs index 47243806cd2d9..16727d445416c 100644 --- a/library/std/src/io/pipe.rs +++ b/library/std/src/io/pipe.rs @@ -38,30 +38,44 @@ use crate::sys_common::{FromInner, IntoInner}; /// > 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 +/// # Example /// /// ```no_run /// # #[cfg(miri)] fn main() {} /// # #[cfg(not(miri))] /// # fn main() -> std::io::Result<()> { +/// use std::io::{Read, Write, pipe}; /// use std::process::Command; -/// use std::io::{pipe, Read, Write}; -/// let (ping_rx, mut ping_tx) = pipe()?; -/// let (mut pong_rx, pong_tx) = pipe()?; +/// let (ping_reader, mut ping_writer) = pipe()?; +/// let (mut pong_reader, pong_writer) = pipe()?; /// -/// // Spawn a process that echoes its input. -/// let mut echo_server = Command::new("cat").stdin(ping_rx).stdout(pong_tx).spawn()?; +/// // Spawn a child process that echoes its input. +/// let mut echo_command = Command::new("cat"); +/// echo_command.stdin(ping_reader); +/// echo_command.stdout(pong_writer); +/// let mut echo_child = echo_command.spawn()?; /// -/// ping_tx.write_all(b"hello")?; -/// // Close to unblock echo_server's reader. -/// drop(ping_tx); +/// // Send input to the child process. Note that because we're writing all the input before we +/// // read any output, this could deadlock if the child's input and output pipe buffers both +/// // filled up. Those buffers are usually at least a few KB, so "hello" is fine, but for longer +/// // inputs we'd need to read and write at the same time, e.g. using threads. +/// ping_writer.write_all(b"hello")?; +/// +/// // `cat` exits when it reads EOF from stdin, but that can't happen while any ping writer +/// // remains open. We need to drop our ping writer, or read_to_string will deadlock below. +/// drop(ping_writer); +/// +/// // The pong reader can't report EOF while any pong writer remains open. Our Command object is +/// // holding a pong writer, and again read_to_string will deadlock if we don't drop it. +/// drop(echo_command); /// /// let mut buf = String::new(); -/// // Block until echo_server's writer is closed. -/// pong_rx.read_to_string(&mut buf)?; +/// // Block until `cat` closes its stdout (a pong writer). +/// pong_reader.read_to_string(&mut buf)?; /// assert_eq!(&buf, "hello"); /// -/// echo_server.wait()?; +/// // At this point we know `cat` has exited, but we still need to wait to clean up the "zombie". +/// echo_child.wait()?; /// # Ok(()) /// # } /// ```