      1
      2
      3
      4
      5
      6
      7
      8
      9
     10
     11
     12
     13
     14
     15
     16
     17
     18
     19
     20
     21
     22
     23
     24
     25
     26
     27
     28
     29
     30
     31
     32
     33
     34
     35
     36
     37
     38
     39
     40
     41
     42
     43
     44
     45
     46
     47
     48
     49
     50
     51
     52
     53
     54
     55
     56
     57
     58
     59
     60
     61
     62
     63
     64
     65
     66
     67
     68
     69
     70
     71
     72
     73
     74
     75
     76
     77
     78
     79
     80
     81
     82
     83
     84
     85
     86
     87
     88
     89
     90
     91
     92
     93
     94
     95
     96
     97
     98
     99
    100
    101
    102
    103
    104
    105
    106
    107
    108
    109
    110
    111
    112
    113
    114
    115
    116
    117
    118
    119
    120
    121
    122
    123
    124
    125
    126
    127
    128
    129
    130
    131
    132
    133
    134
    135
    136
    137
    138
    139
    140
    141
    142
    143
    144
    145
    146
    147
    148
    149
    150
    151
    152
    153
    154
    155
    156
    157
    158
    159
    160
    161
    162
    163
    164
    165
    166
    167
    168
    169
    170
    171
    172
    173
    174
    175
    176
    177
    178
    179
    180
    181
    182
    183
    184
    185
    186
    187
    188
    189
    190
    191
    192
    193
    194
    195
    196
    197
    198
    199
    200
    201
    202
    203
    204
    205
    206
    207
    208
    209
    210
    211
    212
    213
    214
    215
    216
    217
    218
    219
    220
    221
    222
    223
    224
    225
    226
    227
    228
    229
    230
    231
    232
    233
    234
    235
    236
    237
    238
    239
    240
    241
    242
    243
    244
    245
    246
    247
    248
    249
    250
    251
    252
    253
    254
    255
    256
    257
    258
    259
    260
    261
    262
    263
    264
    265
    266
    267
    268
    269
    270
    271
    272
    273
    274
    275
    276
    277
    278
    279
    280
    281
    282
    283
    284
    285
    286
    287
    288
    289
    290
    291
    292
    293
    294
    295
    296
    297
    298
    299
    300
    301
    302
    303
    304
    305
    306
    307
    308
    309
    310
    311
    312
    313
    314
    315
    316
    317
    318
    319
    320
    321
    322
    323
    324
    325
    326
    327
    328
    329
    330
    331
    332
    333
    334
    335
    336
    337
    338
    339
    340
    341
    342
    343
    344
    345
    346
    347
    348
    349
    350
    351
    352
    353
    354
    355
    356
    357
    358
    359
    360
    361
    362
    363
    364
    365
    366
    367
    368
    369
    370
    371
    372
    373
    374
    375
    376
    377
    378
    379
    380
    381
    382
    383
    384
    385
    386
    387
    388
    389
    390
    391
    392
    393
    394
    395
    396
    397
    398
    399
    400
    401
    402
    403
    404
    405
    406
    407
    408
    409
    410
    411
    412
    413
    414
    415
    416
    417
    418
    419
    420
    421
    422
    423
    424
    425
    426
    427
    428
    429
    430
    431
    432
    433
    434
    435
    436
    437
    438
    439
    440
    441
    442
    443
    444
    445
    446
    447
    448
    449
    450
    451
    452
    453
    454
    455
    456
    457
    458
    459
    460
    461
    462
    463
    464
    465
    466
    467
    468
    469
    470
    471
    472
    473
    474
    475
    476
    477
    478
    479
    480
    481
    482
    483
    484
    485
    486
    487
    488
    489
    490
    491
    492
    493
    494
    495
    496
    497
    498
    499
    500
    501
    502
    503
    504
    505
    506
    507
    508
    509
    510
    511
    512
    513
    514
    515
    516
    517
    518
    519
    520
    521
    522
    523
    524
    525
    526
    527
    528
    529
    530
    531
    532
    533
    534
    535
    536
    537
    538
    539
    540
    541
    542
    543
    544
    545
    546
    547
    548
    549
    550
    551
    552
    553
    554
    555
    556
    557
    558
    559
    560
    561
    562
    563
    564
    565
    566
    567
    568
    569
    570
    571
    572
    573
    574
    575
    576
    577
    578
    579
    580
    581
    582
    583
    584
    585
    586
    587
    588
    589
    590
    591
    592
    593
    594
    595
    596
    597
    598
    599
    600
    601
    602
    603
    604
    605
    606
    607
    608
    609
    610
    611
    612
    613
    614
    615
    616
    617
    618
    619
    620
    621
    622
    623
    624
    625
    626
    627
    628
    629
    630
    631
    632
    633
    634
    635
    636
    637
    638
    639
    640
    641
    642
    643
    644
    645

    // 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 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    use prelude::v1::*;
    use io::prelude::*;

    use cell::{RefCell, BorrowState};
    use fmt;
    use io::lazy::Lazy;
    use io::{self, BufReader, LineWriter};
    use sync::{Arc, Mutex, MutexGuard};
    use sys::stdio;
    use sys_common::remutex::{ReentrantMutex, ReentrantMutexGuard};
    use thread::LocalKeyState;

    /// Stdout used by print! and println! macros
    thread_local! {
        static LOCAL_STDOUT: RefCell<Option<Box<Write + Send>>> = {
            RefCell::new(None)
        }
    }

    /// A handle to a raw instance of the standard input stream of this process.
    ///
    /// This handle is not synchronized or buffered in any fashion. Constructed via
    /// the `std::io::stdio::stdin_raw` function.
    struct StdinRaw(stdio::Stdin);

    /// A handle to a raw instance of the standard output stream of this process.
    ///
    /// This handle is not synchronized or buffered in any fashion. Constructed via
    /// the `std::io::stdio::stdout_raw` function.
    struct StdoutRaw(stdio::Stdout);

    /// A handle to a raw instance of the standard output stream of this process.
    ///
    /// This handle is not synchronized or buffered in any fashion. Constructed via
    /// the `std::io::stdio::stderr_raw` function.
    struct StderrRaw(stdio::Stderr);

    /// Constructs a new raw handle to the standard input of this process.
    ///
    /// The returned handle does not interact with any other handles created nor
    /// handles returned by `std::io::stdin`. Data buffered by the `std::io::stdin`
    /// handles is **not** available to raw handles returned from this function.
    ///
    /// The returned handle has no external synchronization or buffering.
    fn stdin_raw() -> io::Result<StdinRaw> { stdio::Stdin::new().map(StdinRaw) }

    /// Constructs a new raw handle to the standard output stream of this process.
    ///
    /// The returned handle does not interact with any other handles created nor
    /// handles returned by `std::io::stdout`. Note that data is buffered by the
    /// `std::io::stdout` handles so writes which happen via this raw handle may
    /// appear before previous writes.
    ///
    /// The returned handle has no external synchronization or buffering layered on
    /// top.
    fn stdout_raw() -> io::Result<StdoutRaw> { stdio::Stdout::new().map(StdoutRaw) }

    /// Constructs a new raw handle to the standard error stream of this process.
    ///
    /// The returned handle does not interact with any other handles created nor
    /// handles returned by `std::io::stderr`.
    ///
    /// The returned handle has no external synchronization or buffering layered on
    /// top.
    fn stderr_raw() -> io::Result<StderrRaw> { stdio::Stderr::new().map(StderrRaw) }

    impl Read for StdinRaw {
        fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> { self.0.read(buf) }
        fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
            self.0.read_to_end(buf)
        }
    }
    impl Write for StdoutRaw {
        fn write(&mut self, buf: &[u8]) -> io::Result<usize> { self.0.write(buf) }
        fn flush(&mut self) -> io::Result<()> { Ok(()) }
    }
    impl Write for StderrRaw {
        fn write(&mut self, buf: &[u8]) -> io::Result<usize> { self.0.write(buf) }
        fn flush(&mut self) -> io::Result<()> { Ok(()) }
    }

    enum Maybe<T> {
        Real(T),
        Fake,
    }

    impl<W: io::Write> io::Write for Maybe<W> {
        fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
            match *self {
                Maybe::Real(ref mut w) => handle_ebadf(w.write(buf), buf.len()),
                Maybe::Fake => Ok(buf.len())
            }
        }

        fn flush(&mut self) -> io::Result<()> {
            match *self {
                Maybe::Real(ref mut w) => handle_ebadf(w.flush(), ()),
                Maybe::Fake => Ok(())
            }
        }
    }

    impl<R: io::Read> io::Read for Maybe<R> {
        fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
            match *self {
                Maybe::Real(ref mut r) => handle_ebadf(r.read(buf), 0),
                Maybe::Fake => Ok(0)
            }
        }
        fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
            match *self {
                Maybe::Real(ref mut r) => handle_ebadf(r.read_to_end(buf), 0),
                Maybe::Fake => Ok(0)
            }
        }
    }

    fn handle_ebadf<T>(r: io::Result<T>, default: T) -> io::Result<T> {
        #[cfg(windows)]
        const ERR: i32 = ::sys::c::ERROR_INVALID_HANDLE as i32;
        #[cfg(not(windows))]
        const ERR: i32 = ::libc::EBADF as i32;

        match r {
            Err(ref e) if e.raw_os_error() == Some(ERR) => Ok(default),
            r => r
        }
    }

    /// A handle to the standard input stream of a process.
    ///
    /// Each handle is a shared reference to a global buffer of input data to this
    /// process. A handle can be `lock`'d to gain full access to [`BufRead`] methods
    /// (e.g. `.lines()`). Reads to this handle are otherwise locked with respect
    /// to other reads.
    ///
    /// This handle implements the `Read` trait, but beware that concurrent reads
    /// of `Stdin` must be executed with care.
    ///
    /// Created by the [`io::stdin`] method.
    ///
    /// [`io::stdin`]: fn.stdin.html
    /// [`BufRead`]: trait.BufRead.html
    #[stable(feature = "rust1", since = "1.0.0")]
    pub struct Stdin {
        inner: Arc<Mutex<BufReader<Maybe<StdinRaw>>>>,
    }

    /// A locked reference to the `Stdin` handle.
    ///
    /// This handle implements both the [`Read`] and [`BufRead`] traits, and
    /// is constructed via the [`Stdin::lock`] method.
    ///
    /// [`Read`]: trait.Read.html
    /// [`BufRead`]: trait.BufRead.html
    /// [`Stdin::lock`]: struct.Stdin.html#method.lock
    #[stable(feature = "rust1", since = "1.0.0")]
    pub struct StdinLock<'a> {
        inner: MutexGuard<'a, BufReader<Maybe<StdinRaw>>>,
    }

    /// Constructs a new handle to the standard input of the current process.
    ///
    /// Each handle returned is a reference to a shared global buffer whose access
    /// is synchronized via a mutex. If you need more explicit control over
    /// locking, see the [`lock() method`][lock].
    ///
    /// [lock]: struct.Stdin.html#method.lock
    ///
    /// # Examples
    ///
    /// Using implicit synchronization:
    ///
    /// ```
    /// use std::io::{self, Read};
    ///
    /// # fn foo() -> io::Result<String> {
    /// let mut buffer = String::new();
    /// try!(io::stdin().read_to_string(&mut buffer));
    /// # Ok(buffer)
    /// # }
    /// ```
    ///
    /// Using explicit synchronization:
    ///
    /// ```
    /// use std::io::{self, Read};
    ///
    /// # fn foo() -> io::Result<String> {
    /// let mut buffer = String::new();
    /// let stdin = io::stdin();
    /// let mut handle = stdin.lock();
    ///
    /// try!(handle.read_to_string(&mut buffer));
    /// # Ok(buffer)
    /// # }
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn stdin() -> Stdin {
        static INSTANCE: Lazy<Mutex<BufReader<Maybe<StdinRaw>>>> = Lazy::new(stdin_init);
        return Stdin {
            inner: INSTANCE.get().expect("cannot access stdin during shutdown"),
        };

        fn stdin_init() -> Arc<Mutex<BufReader<Maybe<StdinRaw>>>> {
            let stdin = match stdin_raw() {
                Ok(stdin) => Maybe::Real(stdin),
                _ => Maybe::Fake
            };

            // The default buffer capacity is 64k, but apparently windows
            // doesn't like 64k reads on stdin. See #13304 for details, but the
            // idea is that on windows we use a slightly smaller buffer that's
            // been seen to be acceptable.
            Arc::new(Mutex::new(if cfg!(windows) {
                BufReader::with_capacity(8 * 1024, stdin)
            } else {
                BufReader::new(stdin)
            }))
        }
    }

    impl Stdin {
        /// Locks this handle to the standard input stream, returning a readable
        /// guard.
        ///
        /// The lock is released when the returned lock goes out of scope. The
        /// returned guard also implements the [`Read`] and [`BufRead`] traits for
        /// accessing the underlying data.
        ///
        /// [`Read`]: trait.Read.html
        /// [`BufRead`]: trait.BufRead.html
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn lock(&self) -> StdinLock {
            StdinLock { inner: self.inner.lock().unwrap_or_else(|e| e.into_inner()) }
        }

        /// Locks this handle and reads a line of input into the specified buffer.
        ///
        /// For detailed semantics of this method, see the documentation on
        /// [`BufRead::read_line`].
        ///
        /// [`BufRead::read_line`]: trait.BufRead.html#method.read_line
        ///
        /// # Examples
        ///
        /// ```no_run
        /// use std::io;
        ///
        /// let mut input = String::new();
        /// match io::stdin().read_line(&mut input) {
        ///     Ok(n) => {
        ///         println!("{} bytes read", n);
        ///         println!("{}", input);
        ///     }
        ///     Err(error) => println!("error: {}", error),
        /// }
        /// ```
        ///
        /// You can run the example one of two ways:
        ///
        /// - Pipe some text to it, e.g. `printf foo | path/to/executable`
        /// - Give it text interactively by running the executable directly,
        ///   in which case it will wait for the Enter key to be pressed before
        ///   continuing
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn read_line(&self, buf: &mut String) -> io::Result<usize> {
            self.lock().read_line(buf)
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl Read for Stdin {
        fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
            self.lock().read(buf)
        }
        fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
            self.lock().read_to_end(buf)
        }
        fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
            self.lock().read_to_string(buf)
        }
        fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
            self.lock().read_exact(buf)
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<'a> Read for StdinLock<'a> {
        fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
            self.inner.read(buf)
        }
        fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
            self.inner.read_to_end(buf)
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<'a> BufRead for StdinLock<'a> {
        fn fill_buf(&mut self) -> io::Result<&[u8]> { self.inner.fill_buf() }
        fn consume(&mut self, n: usize) { self.inner.consume(n) }
    }

    /// A handle to the global standard output stream of the current process.
    ///
    /// Each handle shares a global buffer of data to be written to the standard
    /// output stream. Access is also synchronized via a lock and explicit control
    /// over locking is available via the `lock` method.
    ///
    /// Created by the [`io::stdout`] method.
    ///
    /// [`io::stdout`]: fn.stdout.html
    #[stable(feature = "rust1", since = "1.0.0")]
    pub struct Stdout {
        // FIXME: this should be LineWriter or BufWriter depending on the state of
        //        stdout (tty or not). Note that if this is not line buffered it
        //        should also flush-on-panic or some form of flush-on-abort.
        inner: Arc<ReentrantMutex<RefCell<LineWriter<Maybe<StdoutRaw>>>>>,
    }

    /// A locked reference to the `Stdout` handle.
    ///
    /// This handle implements the [`Write`] trait, and is constructed via
    /// the [`Stdout::lock`] method.
    ///
    /// [`Write`]: trait.Write.html
    /// [`Stdout::lock`]: struct.Stdout.html#method.lock
    #[stable(feature = "rust1", since = "1.0.0")]
    pub struct StdoutLock<'a> {
        inner: ReentrantMutexGuard<'a, RefCell<LineWriter<Maybe<StdoutRaw>>>>,
    }

    /// Constructs a new handle to the standard output of the current process.
    ///
    /// Each handle returned is a reference to a shared global buffer whose access
    /// is synchronized via a mutex. If you need more explicit control over
    /// locking, see the [Stdout::lock] method.
    ///
    /// [Stdout::lock]: struct.Stdout.html#method.lock
    ///
    /// # Examples
    ///
    /// Using implicit synchronization:
    ///
    /// ```
    /// use std::io::{self, Write};
    ///
    /// # fn foo() -> io::Result<()> {
    /// try!(io::stdout().write(b"hello world"));
    ///
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// Using explicit synchronization:
    ///
    /// ```
    /// use std::io::{self, Write};
    ///
    /// # fn foo() -> io::Result<()> {
    /// let stdout = io::stdout();
    /// let mut handle = stdout.lock();
    ///
    /// try!(handle.write(b"hello world"));
    ///
    /// # Ok(())
    /// # }
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn stdout() -> Stdout {
        static INSTANCE: Lazy<ReentrantMutex<RefCell<LineWriter<Maybe<StdoutRaw>>>>>
            = Lazy::new(stdout_init);
        return Stdout {
            inner: INSTANCE.get().expect("cannot access stdout during shutdown"),
        };

        fn stdout_init() -> Arc<ReentrantMutex<RefCell<LineWriter<Maybe<StdoutRaw>>>>> {
            let stdout = match stdout_raw() {
                Ok(stdout) => Maybe::Real(stdout),
                _ => Maybe::Fake,
            };
            Arc::new(ReentrantMutex::new(RefCell::new(LineWriter::new(stdout))))
        }
    }

    impl Stdout {
        /// Locks this handle to the standard output stream, returning a writable
        /// guard.
        ///
        /// The lock is released when the returned lock goes out of scope. The
        /// returned guard also implements the `Write` trait for writing data.
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn lock(&self) -> StdoutLock {
            StdoutLock { inner: self.inner.lock().unwrap_or_else(|e| e.into_inner()) }
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl Write for Stdout {
        fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
            self.lock().write(buf)
        }
        fn flush(&mut self) -> io::Result<()> {
            self.lock().flush()
        }
        fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
            self.lock().write_all(buf)
        }
        fn write_fmt(&mut self, args: fmt::Arguments) -> io::Result<()> {
            self.lock().write_fmt(args)
        }
    }
    #[stable(feature = "rust1", since = "1.0.0")]
    impl<'a> Write for StdoutLock<'a> {
        fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
            self.inner.borrow_mut().write(buf)
        }
        fn flush(&mut self) -> io::Result<()> {
            self.inner.borrow_mut().flush()
        }
    }

    /// A handle to the standard error stream of a process.
    ///
    /// For more information, see the [`io::stderr`] method.
    ///
    /// [`io::stderr`]: fn.stderr.html
    #[stable(feature = "rust1", since = "1.0.0")]
    pub struct Stderr {
        inner: Arc<ReentrantMutex<RefCell<Maybe<StderrRaw>>>>,
    }

    /// A locked reference to the `Stderr` handle.
    ///
    /// This handle implements the `Write` trait and is constructed via
    /// the [`Stderr::lock`] method.
    ///
    /// [`Stderr::lock`]: struct.Stderr.html#method.lock
    #[stable(feature = "rust1", since = "1.0.0")]
    pub struct StderrLock<'a> {
        inner: ReentrantMutexGuard<'a, RefCell<Maybe<StderrRaw>>>,
    }

    /// Constructs a new handle to the standard error of the current process.
    ///
    /// This handle is not buffered.
    ///
    /// # Examples
    ///
    /// Using implicit synchronization:
    ///
    /// ```
    /// use std::io::{self, Write};
    ///
    /// # fn foo() -> io::Result<()> {
    /// try!(io::stderr().write(b"hello world"));
    ///
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// Using explicit synchronization:
    ///
    /// ```
    /// use std::io::{self, Write};
    ///
    /// # fn foo() -> io::Result<()> {
    /// let stderr = io::stderr();
    /// let mut handle = stderr.lock();
    ///
    /// try!(handle.write(b"hello world"));
    ///
    /// # Ok(())
    /// # }
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn stderr() -> Stderr {
        static INSTANCE: Lazy<ReentrantMutex<RefCell<Maybe<StderrRaw>>>> = Lazy::new(stderr_init);
        return Stderr {
            inner: INSTANCE.get().expect("cannot access stderr during shutdown"),
        };

        fn stderr_init() -> Arc<ReentrantMutex<RefCell<Maybe<StderrRaw>>>> {
            let stderr = match stderr_raw() {
                Ok(stderr) => Maybe::Real(stderr),
                _ => Maybe::Fake,
            };
            Arc::new(ReentrantMutex::new(RefCell::new(stderr)))
        }
    }

    impl Stderr {
        /// Locks this handle to the standard error stream, returning a writable
        /// guard.
        ///
        /// The lock is released when the returned lock goes out of scope. The
        /// returned guard also implements the `Write` trait for writing data.
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn lock(&self) -> StderrLock {
            StderrLock { inner: self.inner.lock().unwrap_or_else(|e| e.into_inner()) }
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl Write for Stderr {
        fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
            self.lock().write(buf)
        }
        fn flush(&mut self) -> io::Result<()> {
            self.lock().flush()
        }
        fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
            self.lock().write_all(buf)
        }
        fn write_fmt(&mut self, args: fmt::Arguments) -> io::Result<()> {
            self.lock().write_fmt(args)
        }
    }
    #[stable(feature = "rust1", since = "1.0.0")]
    impl<'a> Write for StderrLock<'a> {
        fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
            self.inner.borrow_mut().write(buf)
        }
        fn flush(&mut self) -> io::Result<()> {
            self.inner.borrow_mut().flush()
        }
    }

    /// Resets the thread-local stderr handle to the specified writer
    ///
    /// This will replace the current thread's stderr handle, returning the old
    /// handle. All future calls to `panic!` and friends will emit their output to
    /// this specified handle.
    ///
    /// Note that this does not need to be called for all new threads; the default
    /// output handle is to the process's stderr stream.
    #[unstable(feature = "set_stdio",
               reason = "this function may disappear completely or be replaced \
                         with a more general mechanism",
               issue = "0")]
    #[doc(hidden)]
    pub fn set_panic(sink: Box<Write + Send>) -> Option<Box<Write + Send>> {
        use panicking::LOCAL_STDERR;
        use mem;
        LOCAL_STDERR.with(move |slot| {
            mem::replace(&mut *slot.borrow_mut(), Some(sink))
        }).and_then(|mut s| {
            let _ = s.flush();
            Some(s)
        })
    }

    /// Resets the thread-local stdout handle to the specified writer
    ///
    /// This will replace the current thread's stdout handle, returning the old
    /// handle. All future calls to `print!` and friends will emit their output to
    /// this specified handle.
    ///
    /// Note that this does not need to be called for all new threads; the default
    /// output handle is to the process's stdout stream.
    #[unstable(feature = "set_stdio",
               reason = "this function may disappear completely or be replaced \
                         with a more general mechanism",
               issue = "0")]
    #[doc(hidden)]
    pub fn set_print(sink: Box<Write + Send>) -> Option<Box<Write + Send>> {
        use mem;
        LOCAL_STDOUT.with(move |slot| {
            mem::replace(&mut *slot.borrow_mut(), Some(sink))
        }).and_then(|mut s| {
            let _ = s.flush();
            Some(s)
        })
    }

    #[unstable(feature = "print",
               reason = "implementation detail which may disappear or be replaced at any time",
               issue = "0")]
    #[doc(hidden)]
    pub fn _print(args: fmt::Arguments) {
        // As an implementation of the `println!` macro, we want to try our best to
        // not panic wherever possible and get the output somewhere. There are
        // currently two possible vectors for panics we take care of here:
        //
        // 1. If the TLS key for the local stdout has been destroyed, accessing it
        //    would cause a panic. Note that we just lump in the uninitialized case
        //    here for convenience, we're not trying to avoid a panic.
        // 2. If the local stdout is currently in use (e.g. we're in the middle of
        //    already printing) then accessing again would cause a panic.
        //
        // If, however, the actual I/O causes an error, we do indeed panic.
        let result = match LOCAL_STDOUT.state() {
            LocalKeyState::Uninitialized |
            LocalKeyState::Destroyed => stdout().write_fmt(args),
            LocalKeyState::Valid => {
                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);
        }
    }

    #[cfg(test)]
    mod tests {
        use thread;
        use super::*;

        #[test]
        fn panic_doesnt_poison() {
            thread::spawn(|| {
                let _a = stdin();
                let _a = _a.lock();
                let _a = stdout();
                let _a = _a.lock();
                let _a = stderr();
                let _a = _a.lock();
                panic!();
            }).join().unwrap_err();

            let _a = stdin();
            let _a = _a.lock();
            let _a = stdout();
            let _a = _a.lock();
            let _a = stderr();
            let _a = _a.lock();
        }
    }

# Help

## Keyboard Shortcuts

?
  Show this help dialog
S
  Focus the search field
⇤
  Move up in search results
⇥
  Move down in search results
⏎
  Go to active search result

## Search Tricks

Prefix searches with a type followed by a colon (e.g. `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g. `vec -> usize` or `* -> vec`)