diff --git a/src/libstd/io/stdio.rs b/src/libstd/io/stdio.rs index 53f67766ea6..d361f17cbe4 100644 --- a/src/libstd/io/stdio.rs +++ b/src/libstd/io/stdio.rs @@ -11,7 +11,7 @@ use prelude::v1::*; use io::prelude::*; -use cell::RefCell; +use cell::{RefCell, BorrowState}; use cmp; use fmt; use io::lazy::Lazy; @@ -264,9 +264,8 @@ impl Write for Stdout { fn write_all(&mut self, buf: &[u8]) -> io::Result<()> { self.lock().write_all(buf) } - fn write_fmt(&mut self, fmt: fmt::Arguments) -> io::Result<()> { - self.lock().write_fmt(fmt) - } + // Don't override write_fmt as it's possible to run arbitrary code during a + // write_fmt, allowing the possibility of a recursive lock (aka deadlock) } #[stable(feature = "rust1", since = "1.0.0")] impl<'a> Write for StdoutLock<'a> { @@ -334,9 +333,7 @@ impl Write for Stderr { fn write_all(&mut self, buf: &[u8]) -> io::Result<()> { self.lock().write_all(buf) } - fn write_fmt(&mut self, fmt: fmt::Arguments) -> io::Result<()> { - self.lock().write_fmt(fmt) - } + // Don't override write_fmt for the same reasons as Stdout } #[stable(feature = "rust1", since = "1.0.0")] impl<'a> Write for StderrLock<'a> { @@ -395,10 +392,15 @@ pub fn set_print(sink: Box) -> Option> { reason = "implementation detail which may disappear or be replaced at any time")] #[doc(hidden)] pub fn _print(args: fmt::Arguments) { - if let Err(e) = LOCAL_STDOUT.with(|s| match s.borrow_mut().as_mut() { - Some(w) => w.write_fmt(args), - None => stdout().write_fmt(args) - }) { + let result = LOCAL_STDOUT.with(|s| { + if s.borrow_state() == BorrowState::Unused { + if let Some(w) = s.borrow_mut().as_mut() { + return w.write_fmt(args); + } + } + stdout().write_fmt(args) + }); + if let Err(e) = result { panic!("failed printing to stdout: {}", e); } } diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs index 8de6e5257ec..5f5f2fed567 100644 --- a/src/libstd/lib.rs +++ b/src/libstd/lib.rs @@ -127,6 +127,7 @@ #![feature(str_char)] #![feature(into_cow)] #![feature(slice_patterns)] +#![feature(std_misc)] #![cfg_attr(test, feature(test, rustc_private, std_misc))] // Don't link to std. We are std. diff --git a/src/test/run-pass/issue-23781.rs b/src/test/run-pass/issue-23781.rs new file mode 100644 index 00000000000..23ac8d2b782 --- /dev/null +++ b/src/test/run-pass/issue-23781.rs @@ -0,0 +1,38 @@ +// Copyright 2015 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +use std::fmt; + +struct Foo; +impl fmt::Debug for Foo { + fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { + println!("::fmt()"); + + write!(fmt, "") + } +} + +fn test1() { + let foo_str = format!("{:?}", Foo); + + println!("{}", foo_str); +} + +fn test2() { + println!("{:?}", Foo); +} + +fn main() { + // This works fine + test1(); + + // This fails + test2(); +}