Auto merge of #29491 - alexcrichton:avoid-stdio-tls, r=brson
Currently if a print happens while a thread is being torn down it may cause a panic if the LOCAL_STDOUT TLS slot has been destroyed by that point. This adds a guard to check and prints to the process stdout if that's the case (as we do for if the slot is already borrowed). Closes #29488
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commit
7512808ac9
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@ -16,11 +16,12 @@ use cmp;
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use fmt;
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use io::lazy::Lazy;
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use io::{self, BufReader, LineWriter};
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use libc;
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use sync::{Arc, Mutex, MutexGuard};
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use sys::stdio;
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use sys_common::io::{read_to_end_uninitialized};
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use sys_common::remutex::{ReentrantMutex, ReentrantMutexGuard};
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use libc;
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use thread::LocalKeyState;
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/// Stdout used by print! and println! macros
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thread_local! {
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@ -576,14 +577,31 @@ pub fn set_print(sink: Box<Write + Send>) -> Option<Box<Write + Send>> {
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issue = "0")]
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#[doc(hidden)]
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pub fn _print(args: fmt::Arguments) {
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let result = LOCAL_STDOUT.with(|s| {
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if s.borrow_state() == BorrowState::Unused {
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if let Some(w) = s.borrow_mut().as_mut() {
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return w.write_fmt(args);
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}
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// As an implementation of the `println!` macro, we want to try our best to
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// not panic wherever possible and get the output somewhere. There are
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// currently two possible vectors for panics we take care of here:
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//
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// 1. If the TLS key for the local stdout has been destroyed, accessing it
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// would cause a panic. Note that we just lump in the uninitialized case
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// here for convenience, we're not trying to avoid a panic.
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// 2. If the local stdout is currently in use (e.g. we're in the middle of
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// already printing) then accessing again would cause a panic.
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//
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// If, however, the actual I/O causes an error, we do indeed panic.
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let result = match LOCAL_STDOUT.state() {
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LocalKeyState::Uninitialized |
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LocalKeyState::Destroyed => stdout().write_fmt(args),
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LocalKeyState::Valid => {
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LOCAL_STDOUT.with(|s| {
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if s.borrow_state() == BorrowState::Unused {
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if let Some(w) = s.borrow_mut().as_mut() {
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return w.write_fmt(args);
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}
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}
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stdout().write_fmt(args)
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})
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}
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stdout().write_fmt(args)
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});
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};
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if let Err(e) = result {
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panic!("failed printing to stdout: {}", e);
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}
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@ -0,0 +1,30 @@
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// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use std::thread;
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struct Foo;
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impl Drop for Foo {
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fn drop(&mut self) {
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println!("test2");
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}
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}
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thread_local!(static FOO: Foo = Foo);
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fn main() {
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// Off the main thread due to #28129, be sure to initialize FOO first before
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// calling `println!`
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thread::spawn(|| {
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FOO.with(|_| {});
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println!("test1");
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}).join().unwrap();
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}
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