1 #![cfg_attr(test, allow(unused))]
3 use crate::io::prelude::*;
5 use crate::cell::RefCell;
7 use crate::io::lazy::Lazy;
8 use crate::io::{self, BufReader, Initializer, IoSlice, IoSliceMut, LineWriter};
9 use crate::sync::{Arc, Mutex, MutexGuard, Once};
10 use crate::sys::stdio;
11 use crate::sys_common::remutex::{ReentrantMutex, ReentrantMutexGuard};
12 use crate::thread::LocalKey;
15 /// Stdout used by print! and println! macros
16 static LOCAL_STDOUT: RefCell<Option<Box<dyn Write + Send>>> = {
22 /// Stderr used by eprint! and eprintln! macros, and panics
23 static LOCAL_STDERR: RefCell<Option<Box<dyn Write + Send>>> = {
28 /// A handle to a raw instance of the standard input stream of this process.
30 /// This handle is not synchronized or buffered in any fashion. Constructed via
31 /// the `std::io::stdio::stdin_raw` function.
32 struct StdinRaw(stdio::Stdin);
34 /// A handle to a raw instance of the standard output stream of this process.
36 /// This handle is not synchronized or buffered in any fashion. Constructed via
37 /// the `std::io::stdio::stdout_raw` function.
38 struct StdoutRaw(stdio::Stdout);
40 /// A handle to a raw instance of the standard output stream of this process.
42 /// This handle is not synchronized or buffered in any fashion. Constructed via
43 /// the `std::io::stdio::stderr_raw` function.
44 struct StderrRaw(stdio::Stderr);
46 /// Constructs a new raw handle to the standard input of this process.
48 /// The returned handle does not interact with any other handles created nor
49 /// handles returned by `std::io::stdin`. Data buffered by the `std::io::stdin`
50 /// handles is **not** available to raw handles returned from this function.
52 /// The returned handle has no external synchronization or buffering.
53 fn stdin_raw() -> io::Result<StdinRaw> {
54 stdio::Stdin::new().map(StdinRaw)
57 /// Constructs a new raw handle to the standard output stream of this process.
59 /// The returned handle does not interact with any other handles created nor
60 /// handles returned by `std::io::stdout`. Note that data is buffered by the
61 /// `std::io::stdout` handles so writes which happen via this raw handle may
62 /// appear before previous writes.
64 /// The returned handle has no external synchronization or buffering layered on
66 fn stdout_raw() -> io::Result<StdoutRaw> {
67 stdio::Stdout::new().map(StdoutRaw)
70 /// Constructs a new raw handle to the standard error stream of this process.
72 /// The returned handle does not interact with any other handles created nor
73 /// handles returned by `std::io::stderr`.
75 /// The returned handle has no external synchronization or buffering layered on
77 fn stderr_raw() -> io::Result<StderrRaw> {
78 stdio::Stderr::new().map(StderrRaw)
81 impl Read for StdinRaw {
82 fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
86 fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
87 self.0.read_vectored(bufs)
91 fn is_read_vectored(&self) -> bool {
92 self.0.is_read_vectored()
96 unsafe fn initializer(&self) -> Initializer {
100 impl Write for StdoutRaw {
101 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
105 fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
106 self.0.write_vectored(bufs)
110 fn is_write_vectored(&self) -> bool {
111 self.0.is_write_vectored()
114 fn flush(&mut self) -> io::Result<()> {
118 impl Write for StderrRaw {
119 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
123 fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
124 self.0.write_vectored(bufs)
128 fn is_write_vectored(&self) -> bool {
129 self.0.is_write_vectored()
132 fn flush(&mut self) -> io::Result<()> {
142 impl<W: io::Write> io::Write for Maybe<W> {
143 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
145 Maybe::Real(ref mut w) => handle_ebadf(w.write(buf), buf.len()),
146 Maybe::Fake => Ok(buf.len()),
150 fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
151 let total = bufs.iter().map(|b| b.len()).sum();
153 Maybe::Real(w) => handle_ebadf(w.write_vectored(bufs), total),
154 Maybe::Fake => Ok(total),
159 fn is_write_vectored(&self) -> bool {
161 Maybe::Real(w) => w.is_write_vectored(),
166 fn flush(&mut self) -> io::Result<()> {
168 Maybe::Real(ref mut w) => handle_ebadf(w.flush(), ()),
169 Maybe::Fake => Ok(()),
174 impl<R: io::Read> io::Read for Maybe<R> {
175 fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
177 Maybe::Real(ref mut r) => handle_ebadf(r.read(buf), 0),
178 Maybe::Fake => Ok(0),
182 fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
184 Maybe::Real(r) => handle_ebadf(r.read_vectored(bufs), 0),
185 Maybe::Fake => Ok(0),
190 fn is_read_vectored(&self) -> bool {
192 Maybe::Real(w) => w.is_read_vectored(),
198 fn handle_ebadf<T>(r: io::Result<T>, default: T) -> io::Result<T> {
200 Err(ref e) if stdio::is_ebadf(e) => Ok(default),
205 /// A handle to the standard input stream of a process.
207 /// Each handle is a shared reference to a global buffer of input data to this
208 /// process. A handle can be `lock`'d to gain full access to [`BufRead`] methods
209 /// (e.g., `.lines()`). Reads to this handle are otherwise locked with respect
212 /// This handle implements the `Read` trait, but beware that concurrent reads
213 /// of `Stdin` must be executed with care.
215 /// Created by the [`io::stdin`] method.
217 /// [`io::stdin`]: fn.stdin.html
218 /// [`BufRead`]: trait.BufRead.html
220 /// ### Note: Windows Portability Consideration
221 /// When operating in a console, the Windows implementation of this stream does not support
222 /// non-UTF-8 byte sequences. Attempting to read bytes that are not valid UTF-8 will return
224 #[stable(feature = "rust1", since = "1.0.0")]
226 inner: Arc<Mutex<BufReader<Maybe<StdinRaw>>>>,
229 /// A locked reference to the `Stdin` handle.
231 /// This handle implements both the [`Read`] and [`BufRead`] traits, and
232 /// is constructed via the [`Stdin::lock`] method.
234 /// [`Read`]: trait.Read.html
235 /// [`BufRead`]: trait.BufRead.html
236 /// [`Stdin::lock`]: struct.Stdin.html#method.lock
238 /// ### Note: Windows Portability Consideration
239 /// When operating in a console, the Windows implementation of this stream does not support
240 /// non-UTF-8 byte sequences. Attempting to read bytes that are not valid UTF-8 will return
242 #[stable(feature = "rust1", since = "1.0.0")]
243 pub struct StdinLock<'a> {
244 inner: MutexGuard<'a, BufReader<Maybe<StdinRaw>>>,
247 /// Constructs a new handle to the standard input of the current process.
249 /// Each handle returned is a reference to a shared global buffer whose access
250 /// is synchronized via a mutex. If you need more explicit control over
251 /// locking, see the [`Stdin::lock`] method.
253 /// [`Stdin::lock`]: struct.Stdin.html#method.lock
255 /// ### Note: Windows Portability Consideration
256 /// When operating in a console, the Windows implementation of this stream does not support
257 /// non-UTF-8 byte sequences. Attempting to read bytes that are not valid UTF-8 will return
262 /// Using implicit synchronization:
265 /// use std::io::{self, Read};
267 /// fn main() -> io::Result<()> {
268 /// let mut buffer = String::new();
269 /// io::stdin().read_to_string(&mut buffer)?;
274 /// Using explicit synchronization:
277 /// use std::io::{self, Read};
279 /// fn main() -> io::Result<()> {
280 /// let mut buffer = String::new();
281 /// let stdin = io::stdin();
282 /// let mut handle = stdin.lock();
284 /// handle.read_to_string(&mut buffer)?;
288 #[stable(feature = "rust1", since = "1.0.0")]
289 pub fn stdin() -> Stdin {
290 static INSTANCE: Lazy<Mutex<BufReader<Maybe<StdinRaw>>>> = Lazy::new();
292 inner: unsafe { INSTANCE.get(stdin_init).expect("cannot access stdin during shutdown") },
295 fn stdin_init() -> Arc<Mutex<BufReader<Maybe<StdinRaw>>>> {
296 // This must not reentrantly access `INSTANCE`
297 let stdin = match stdin_raw() {
298 Ok(stdin) => Maybe::Real(stdin),
302 Arc::new(Mutex::new(BufReader::with_capacity(stdio::STDIN_BUF_SIZE, stdin)))
307 /// Locks this handle to the standard input stream, returning a readable
310 /// The lock is released when the returned lock goes out of scope. The
311 /// returned guard also implements the [`Read`] and [`BufRead`] traits for
312 /// accessing the underlying data.
314 /// [`Read`]: trait.Read.html
315 /// [`BufRead`]: trait.BufRead.html
320 /// use std::io::{self, Read};
322 /// fn main() -> io::Result<()> {
323 /// let mut buffer = String::new();
324 /// let stdin = io::stdin();
325 /// let mut handle = stdin.lock();
327 /// handle.read_to_string(&mut buffer)?;
331 #[stable(feature = "rust1", since = "1.0.0")]
332 pub fn lock(&self) -> StdinLock<'_> {
333 StdinLock { inner: self.inner.lock().unwrap_or_else(|e| e.into_inner()) }
336 /// Locks this handle and reads a line of input, appending it to the specified buffer.
338 /// For detailed semantics of this method, see the documentation on
339 /// [`BufRead::read_line`].
341 /// [`BufRead::read_line`]: trait.BufRead.html#method.read_line
348 /// let mut input = String::new();
349 /// match io::stdin().read_line(&mut input) {
351 /// println!("{} bytes read", n);
352 /// println!("{}", input);
354 /// Err(error) => println!("error: {}", error),
358 /// You can run the example one of two ways:
360 /// - Pipe some text to it, e.g., `printf foo | path/to/executable`
361 /// - Give it text interactively by running the executable directly,
362 /// in which case it will wait for the Enter key to be pressed before
364 #[stable(feature = "rust1", since = "1.0.0")]
365 pub fn read_line(&self, buf: &mut String) -> io::Result<usize> {
366 self.lock().read_line(buf)
370 #[stable(feature = "std_debug", since = "1.16.0")]
371 impl fmt::Debug for Stdin {
372 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
373 f.pad("Stdin { .. }")
377 #[stable(feature = "rust1", since = "1.0.0")]
378 impl Read for Stdin {
379 fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
380 self.lock().read(buf)
382 fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
383 self.lock().read_vectored(bufs)
386 fn is_read_vectored(&self) -> bool {
387 self.lock().is_read_vectored()
390 unsafe fn initializer(&self) -> Initializer {
393 fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
394 self.lock().read_to_end(buf)
396 fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
397 self.lock().read_to_string(buf)
399 fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
400 self.lock().read_exact(buf)
404 #[stable(feature = "rust1", since = "1.0.0")]
405 impl Read for StdinLock<'_> {
406 fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
410 fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
411 self.inner.read_vectored(bufs)
415 fn is_read_vectored(&self) -> bool {
416 self.inner.is_read_vectored()
420 unsafe fn initializer(&self) -> Initializer {
425 #[stable(feature = "rust1", since = "1.0.0")]
426 impl BufRead for StdinLock<'_> {
427 fn fill_buf(&mut self) -> io::Result<&[u8]> {
428 self.inner.fill_buf()
430 fn consume(&mut self, n: usize) {
431 self.inner.consume(n)
435 #[stable(feature = "std_debug", since = "1.16.0")]
436 impl fmt::Debug for StdinLock<'_> {
437 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
438 f.pad("StdinLock { .. }")
442 /// A handle to the global standard output stream of the current process.
444 /// Each handle shares a global buffer of data to be written to the standard
445 /// output stream. Access is also synchronized via a lock and explicit control
446 /// over locking is available via the [`lock`] method.
448 /// Created by the [`io::stdout`] method.
450 /// ### Note: Windows Portability Consideration
451 /// When operating in a console, the Windows implementation of this stream does not support
452 /// non-UTF-8 byte sequences. Attempting to write bytes that are not valid UTF-8 will return
455 /// [`lock`]: #method.lock
456 /// [`io::stdout`]: fn.stdout.html
457 #[stable(feature = "rust1", since = "1.0.0")]
459 // FIXME: this should be LineWriter or BufWriter depending on the state of
460 // stdout (tty or not). Note that if this is not line buffered it
461 // should also flush-on-panic or some form of flush-on-abort.
462 inner: Arc<ReentrantMutex<RefCell<LineWriter<Maybe<StdoutRaw>>>>>,
465 /// A locked reference to the `Stdout` handle.
467 /// This handle implements the [`Write`] trait, and is constructed via
468 /// the [`Stdout::lock`] method.
470 /// ### Note: Windows Portability Consideration
471 /// When operating in a console, the Windows implementation of this stream does not support
472 /// non-UTF-8 byte sequences. Attempting to write bytes that are not valid UTF-8 will return
475 /// [`Write`]: trait.Write.html
476 /// [`Stdout::lock`]: struct.Stdout.html#method.lock
477 #[stable(feature = "rust1", since = "1.0.0")]
478 pub struct StdoutLock<'a> {
479 inner: ReentrantMutexGuard<'a, RefCell<LineWriter<Maybe<StdoutRaw>>>>,
482 /// Constructs a new handle to the standard output of the current process.
484 /// Each handle returned is a reference to a shared global buffer whose access
485 /// is synchronized via a mutex. If you need more explicit control over
486 /// locking, see the [`Stdout::lock`] method.
488 /// [`Stdout::lock`]: struct.Stdout.html#method.lock
490 /// ### Note: Windows Portability Consideration
491 /// When operating in a console, the Windows implementation of this stream does not support
492 /// non-UTF-8 byte sequences. Attempting to write bytes that are not valid UTF-8 will return
497 /// Using implicit synchronization:
500 /// use std::io::{self, Write};
502 /// fn main() -> io::Result<()> {
503 /// io::stdout().write_all(b"hello world")?;
509 /// Using explicit synchronization:
512 /// use std::io::{self, Write};
514 /// fn main() -> io::Result<()> {
515 /// let stdout = io::stdout();
516 /// let mut handle = stdout.lock();
518 /// handle.write_all(b"hello world")?;
523 #[stable(feature = "rust1", since = "1.0.0")]
524 pub fn stdout() -> Stdout {
525 static INSTANCE: Lazy<ReentrantMutex<RefCell<LineWriter<Maybe<StdoutRaw>>>>> = Lazy::new();
527 inner: unsafe { INSTANCE.get(stdout_init).expect("cannot access stdout during shutdown") },
530 fn stdout_init() -> Arc<ReentrantMutex<RefCell<LineWriter<Maybe<StdoutRaw>>>>> {
531 // This must not reentrantly access `INSTANCE`
532 let stdout = match stdout_raw() {
533 Ok(stdout) => Maybe::Real(stdout),
537 let ret = Arc::new(ReentrantMutex::new(RefCell::new(LineWriter::new(stdout))));
545 /// Locks this handle to the standard output stream, returning a writable
548 /// The lock is released when the returned lock goes out of scope. The
549 /// returned guard also implements the `Write` trait for writing data.
554 /// use std::io::{self, Write};
556 /// fn main() -> io::Result<()> {
557 /// let stdout = io::stdout();
558 /// let mut handle = stdout.lock();
560 /// handle.write_all(b"hello world")?;
565 #[stable(feature = "rust1", since = "1.0.0")]
566 pub fn lock(&self) -> StdoutLock<'_> {
567 StdoutLock { inner: self.inner.lock() }
571 #[stable(feature = "std_debug", since = "1.16.0")]
572 impl fmt::Debug for Stdout {
573 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
574 f.pad("Stdout { .. }")
578 #[stable(feature = "rust1", since = "1.0.0")]
579 impl Write for Stdout {
580 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
581 self.lock().write(buf)
583 fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
584 self.lock().write_vectored(bufs)
587 fn is_write_vectored(&self) -> bool {
588 self.lock().is_write_vectored()
590 fn flush(&mut self) -> io::Result<()> {
593 fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
594 self.lock().write_all(buf)
596 fn write_fmt(&mut self, args: fmt::Arguments<'_>) -> io::Result<()> {
597 self.lock().write_fmt(args)
600 #[stable(feature = "rust1", since = "1.0.0")]
601 impl Write for StdoutLock<'_> {
602 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
603 self.inner.borrow_mut().write(buf)
605 fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
606 self.inner.borrow_mut().write_vectored(bufs)
609 fn is_write_vectored(&self) -> bool {
610 self.inner.borrow_mut().is_write_vectored()
612 fn flush(&mut self) -> io::Result<()> {
613 self.inner.borrow_mut().flush()
617 #[stable(feature = "std_debug", since = "1.16.0")]
618 impl fmt::Debug for StdoutLock<'_> {
619 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
620 f.pad("StdoutLock { .. }")
624 /// A handle to the standard error stream of a process.
626 /// For more information, see the [`io::stderr`] method.
628 /// [`io::stderr`]: fn.stderr.html
630 /// ### Note: Windows Portability Consideration
631 /// When operating in a console, the Windows implementation of this stream does not support
632 /// non-UTF-8 byte sequences. Attempting to write bytes that are not valid UTF-8 will return
634 #[stable(feature = "rust1", since = "1.0.0")]
636 inner: &'static ReentrantMutex<RefCell<Maybe<StderrRaw>>>,
639 /// A locked reference to the `Stderr` handle.
641 /// This handle implements the `Write` trait and is constructed via
642 /// the [`Stderr::lock`] method.
644 /// [`Stderr::lock`]: struct.Stderr.html#method.lock
646 /// ### Note: Windows Portability Consideration
647 /// When operating in a console, the Windows implementation of this stream does not support
648 /// non-UTF-8 byte sequences. Attempting to write bytes that are not valid UTF-8 will return
650 #[stable(feature = "rust1", since = "1.0.0")]
651 pub struct StderrLock<'a> {
652 inner: ReentrantMutexGuard<'a, RefCell<Maybe<StderrRaw>>>,
655 /// Constructs a new handle to the standard error of the current process.
657 /// This handle is not buffered.
659 /// ### Note: Windows Portability Consideration
660 /// When operating in a console, the Windows implementation of this stream does not support
661 /// non-UTF-8 byte sequences. Attempting to write bytes that are not valid UTF-8 will return
666 /// Using implicit synchronization:
669 /// use std::io::{self, Write};
671 /// fn main() -> io::Result<()> {
672 /// io::stderr().write_all(b"hello world")?;
678 /// Using explicit synchronization:
681 /// use std::io::{self, Write};
683 /// fn main() -> io::Result<()> {
684 /// let stderr = io::stderr();
685 /// let mut handle = stderr.lock();
687 /// handle.write_all(b"hello world")?;
692 #[stable(feature = "rust1", since = "1.0.0")]
693 pub fn stderr() -> Stderr {
694 // Note that unlike `stdout()` we don't use `Lazy` here which registers a
695 // destructor. Stderr is not buffered nor does the `stderr_raw` type consume
696 // any owned resources, so there's no need to run any destructors at some
697 // point in the future.
699 // This has the added benefit of allowing `stderr` to be usable during
700 // process shutdown as well!
701 static INSTANCE: ReentrantMutex<RefCell<Maybe<StderrRaw>>> =
702 unsafe { ReentrantMutex::new(RefCell::new(Maybe::Fake)) };
704 // When accessing stderr we need one-time initialization of the reentrant
705 // mutex, followed by one-time detection of whether we actually have a
706 // stderr handle or not. Afterwards we can just always use the now-filled-in
708 static INIT: Once = Once::new();
709 INIT.call_once(|| unsafe {
711 if let Ok(stderr) = stderr_raw() {
712 *INSTANCE.lock().borrow_mut() = Maybe::Real(stderr);
715 Stderr { inner: &INSTANCE }
719 /// Locks this handle to the standard error stream, returning a writable
722 /// The lock is released when the returned lock goes out of scope. The
723 /// returned guard also implements the `Write` trait for writing data.
728 /// use std::io::{self, Write};
730 /// fn foo() -> io::Result<()> {
731 /// let stderr = io::stderr();
732 /// let mut handle = stderr.lock();
734 /// handle.write_all(b"hello world")?;
739 #[stable(feature = "rust1", since = "1.0.0")]
740 pub fn lock(&self) -> StderrLock<'_> {
741 StderrLock { inner: self.inner.lock() }
745 #[stable(feature = "std_debug", since = "1.16.0")]
746 impl fmt::Debug for Stderr {
747 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
748 f.pad("Stderr { .. }")
752 #[stable(feature = "rust1", since = "1.0.0")]
753 impl Write for Stderr {
754 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
755 self.lock().write(buf)
757 fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
758 self.lock().write_vectored(bufs)
761 fn is_write_vectored(&self) -> bool {
762 self.lock().is_write_vectored()
764 fn flush(&mut self) -> io::Result<()> {
767 fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
768 self.lock().write_all(buf)
770 fn write_fmt(&mut self, args: fmt::Arguments<'_>) -> io::Result<()> {
771 self.lock().write_fmt(args)
774 #[stable(feature = "rust1", since = "1.0.0")]
775 impl Write for StderrLock<'_> {
776 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
777 self.inner.borrow_mut().write(buf)
779 fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
780 self.inner.borrow_mut().write_vectored(bufs)
783 fn is_write_vectored(&self) -> bool {
784 self.inner.borrow_mut().is_write_vectored()
786 fn flush(&mut self) -> io::Result<()> {
787 self.inner.borrow_mut().flush()
791 #[stable(feature = "std_debug", since = "1.16.0")]
792 impl fmt::Debug for StderrLock<'_> {
793 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
794 f.pad("StderrLock { .. }")
798 /// Resets the thread-local stderr handle to the specified writer
800 /// This will replace the current thread's stderr handle, returning the old
801 /// handle. All future calls to `panic!` and friends will emit their output to
802 /// this specified handle.
804 /// Note that this does not need to be called for all new threads; the default
805 /// output handle is to the process's stderr stream.
807 feature = "set_stdio",
808 reason = "this function may disappear completely or be replaced \
809 with a more general mechanism",
813 pub fn set_panic(sink: Option<Box<dyn Write + Send>>) -> Option<Box<dyn Write + Send>> {
815 LOCAL_STDERR.with(move |slot| mem::replace(&mut *slot.borrow_mut(), sink)).and_then(|mut s| {
821 /// Resets the thread-local stdout handle to the specified writer
823 /// This will replace the current thread's stdout handle, returning the old
824 /// handle. All future calls to `print!` and friends will emit their output to
825 /// this specified handle.
827 /// Note that this does not need to be called for all new threads; the default
828 /// output handle is to the process's stdout stream.
830 feature = "set_stdio",
831 reason = "this function may disappear completely or be replaced \
832 with a more general mechanism",
836 pub fn set_print(sink: Option<Box<dyn Write + Send>>) -> Option<Box<dyn Write + Send>> {
838 LOCAL_STDOUT.with(move |slot| mem::replace(&mut *slot.borrow_mut(), sink)).and_then(|mut s| {
844 /// Write `args` to output stream `local_s` if possible, `global_s`
845 /// otherwise. `label` identifies the stream in a panic message.
847 /// This function is used to print error messages, so it takes extra
848 /// care to avoid causing a panic when `local_s` is unusable.
849 /// For instance, if the TLS key for the local stream is
850 /// already destroyed, or if the local stream is locked by another
851 /// thread, it will just fall back to the global stream.
853 /// However, if the actual I/O causes an error, this function does panic.
855 args: fmt::Arguments<'_>,
856 local_s: &'static LocalKey<RefCell<Option<Box<dyn Write + Send>>>>,
864 // Note that we completely remove a local sink to write to in case
865 // our printing recursively panics/prints, so the recursive
866 // panic/print goes to the global sink instead of our local sink.
867 let prev = s.borrow_mut().take();
868 if let Some(mut w) = prev {
869 let result = w.write_fmt(args);
870 *s.borrow_mut() = Some(w);
873 global_s().write_fmt(args)
875 .unwrap_or_else(|_| global_s().write_fmt(args));
877 if let Err(e) = result {
878 panic!("failed printing to {}: {}", label, e);
883 feature = "print_internals",
884 reason = "implementation detail which may disappear or be replaced at any time",
889 pub fn _print(args: fmt::Arguments<'_>) {
890 print_to(args, &LOCAL_STDOUT, stdout, "stdout");
894 feature = "print_internals",
895 reason = "implementation detail which may disappear or be replaced at any time",
900 pub fn _eprint(args: fmt::Arguments<'_>) {
901 print_to(args, &LOCAL_STDERR, stderr, "stderr");
905 pub use realstd::io::{_eprint, _print};
910 use crate::panic::{RefUnwindSafe, UnwindSafe};
914 fn stdout_unwind_safe() {
915 assert_unwind_safe::<Stdout>();
918 fn stdoutlock_unwind_safe() {
919 assert_unwind_safe::<StdoutLock<'_>>();
920 assert_unwind_safe::<StdoutLock<'static>>();
923 fn stderr_unwind_safe() {
924 assert_unwind_safe::<Stderr>();
927 fn stderrlock_unwind_safe() {
928 assert_unwind_safe::<StderrLock<'_>>();
929 assert_unwind_safe::<StderrLock<'static>>();
932 fn assert_unwind_safe<T: UnwindSafe + RefUnwindSafe>() {}
935 #[cfg_attr(target_os = "emscripten", ignore)]
936 fn panic_doesnt_poison() {