diff --git a/library/std/src/macros.rs b/library/std/src/macros.rs index ce2a979475c..a5003c66fca 100644 --- a/library/std/src/macros.rs +++ b/library/std/src/macros.rs @@ -27,12 +27,23 @@ macro_rules! panic { /// necessary to use [`io::stdout().flush()`][flush] to ensure the output is emitted /// immediately. /// +/// The `print!` macro will lock the standard output on each call. If you call +/// `print!` within a hot loop, this behavior may be the bottleneck of the loop. +/// To avoid this, lock stdout with [`io::stdout().lock()`][lock]: +/// ``` +/// use std::io::{stdout, Write}; +/// +/// let mut lock = stdout().lock(); +/// write!(lock, "hello world").unwrap(); +/// ``` +/// /// Use `print!` only for the primary output of your program. Use /// [`eprint!`] instead to print error and progress messages. /// /// [flush]: crate::io::Write::flush /// [`println!`]: crate::println /// [`eprint!`]: crate::eprint +/// [lock]: crate::io::Stdout /// /// # Panics /// @@ -75,11 +86,22 @@ macro_rules! print { /// This macro uses the same syntax as [`format!`], but writes to the standard output instead. /// See [`std::fmt`] for more information. /// +/// The `println!` macro will lock the standard output on each call. If you call +/// `println!` within a hot loop, this behavior may be the bottleneck of the loop. +/// To avoid this, lock stdout with [`io::stdout().lock()`][lock]: +/// ``` +/// use std::io::{stdout, Write}; +/// +/// let mut lock = stdout().lock(); +/// writeln!(lock, "hello world").unwrap(); +/// ``` +/// /// Use `println!` only for the primary output of your program. Use /// [`eprintln!`] instead to print error and progress messages. /// /// [`std::fmt`]: crate::fmt /// [`eprintln!`]: crate::eprintln +/// [lock]: crate::io::Stdout /// /// # Panics ///