diff --git a/library/std/src/io/stdio.rs b/library/std/src/io/stdio.rs index 6ea7704d42213..1160011f35287 100644 --- a/library/std/src/io/stdio.rs +++ b/library/std/src/io/stdio.rs @@ -9,6 +9,7 @@ use crate::cell::{Cell, RefCell}; use crate::fmt; use crate::io::{self, BufReader, Initializer, IoSlice, IoSliceMut, LineWriter}; use crate::lazy::SyncOnceCell; +use crate::pin::Pin; use crate::sync::atomic::{AtomicBool, Ordering}; use crate::sync::{Arc, Mutex, MutexGuard}; use crate::sys::stdio; @@ -490,7 +491,7 @@ 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: &'static ReentrantMutex>>, + inner: Pin<&'static ReentrantMutex>>>, } /// A locked reference to the `Stdout` handle. @@ -550,25 +551,29 @@ pub struct StdoutLock<'a> { pub fn stdout() -> Stdout { static INSTANCE: SyncOnceCell>>> = SyncOnceCell::new(); + + fn cleanup() { + if let Some(instance) = INSTANCE.get() { + // Flush the data and disable buffering during shutdown + // by replacing the line writer by one with zero + // buffering capacity. + // We use try_lock() instead of lock(), because someone + // might have leaked a StdoutLock, which would + // otherwise cause a deadlock here. + if let Some(lock) = Pin::static_ref(instance).try_lock() { + *lock.borrow_mut() = LineWriter::with_capacity(0, stdout_raw()); + } + } + } + Stdout { - inner: INSTANCE.get_or_init(|| unsafe { - let _ = sys_common::at_exit(|| { - if let Some(instance) = INSTANCE.get() { - // Flush the data and disable buffering during shutdown - // by replacing the line writer by one with zero - // buffering capacity. - // We use try_lock() instead of lock(), because someone - // might have leaked a StdoutLock, which would - // otherwise cause a deadlock here. - if let Some(lock) = instance.try_lock() { - *lock.borrow_mut() = LineWriter::with_capacity(0, stdout_raw()); - } - } - }); - let r = ReentrantMutex::new(RefCell::new(LineWriter::new(stdout_raw()))); - r.init(); - r - }), + inner: Pin::static_ref(&INSTANCE).get_or_init_pin( + || unsafe { + let _ = sys_common::at_exit(cleanup); + ReentrantMutex::new(RefCell::new(LineWriter::new(stdout_raw()))) + }, + |mutex| unsafe { mutex.init() }, + ), } } @@ -700,7 +705,7 @@ impl fmt::Debug for StdoutLock<'_> { /// an error. #[stable(feature = "rust1", since = "1.0.0")] pub struct Stderr { - inner: &'static ReentrantMutex>, + inner: Pin<&'static ReentrantMutex>>, } /// A locked reference to the `Stderr` handle. @@ -756,21 +761,16 @@ pub struct StderrLock<'a> { /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn stderr() -> Stderr { - // Note that unlike `stdout()` we don't use `Lazy` here which registers a - // destructor. Stderr is not buffered nor does the `stderr_raw` type consume - // any owned resources, so there's no need to run any destructors at some - // point in the future. - // - // This has the added benefit of allowing `stderr` to be usable during - // process shutdown as well! + // Note that unlike `stdout()` we don't use `at_exit` here to register a + // destructor. Stderr is not buffered , so there's no need to run a + // destructor for flushing the buffer static INSTANCE: SyncOnceCell>> = SyncOnceCell::new(); Stderr { - inner: INSTANCE.get_or_init(|| unsafe { - let r = ReentrantMutex::new(RefCell::new(stderr_raw())); - r.init(); - r - }), + inner: Pin::static_ref(&INSTANCE).get_or_init_pin( + || unsafe { ReentrantMutex::new(RefCell::new(stderr_raw())) }, + |mutex| unsafe { mutex.init() }, + ), } } diff --git a/library/std/src/lazy.rs b/library/std/src/lazy.rs index e0095e64faf31..68f57958bb233 100644 --- a/library/std/src/lazy.rs +++ b/library/std/src/lazy.rs @@ -10,6 +10,7 @@ use crate::{ mem::MaybeUninit, ops::{Deref, Drop}, panic::{RefUnwindSafe, UnwindSafe}, + pin::Pin, sync::Once, }; @@ -297,6 +298,60 @@ impl SyncOnceCell { Ok(unsafe { self.get_unchecked() }) } + /// Internal-only API that gets the contents of the cell, initializing it + /// in two steps with `f` and `g` if the cell was empty. + /// + /// `f` is called to construct the value, which is then moved into the cell + /// and given as a (pinned) mutable reference to `g` to finish + /// initialization. + /// + /// This allows `g` to inspect an manipulate the value after it has been + /// moved into its final place in the cell, but before the cell is + /// considered initialized. + /// + /// # Panics + /// + /// If `f` or `g` panics, the panic is propagated to the caller, and the + /// cell remains uninitialized. + /// + /// With the current implementation, if `g` panics, the value from `f` will + /// not be dropped. This should probably be fixed if this is ever used for + /// a type where this matters. + /// + /// It is an error to reentrantly initialize the cell from `f`. The exact + /// outcome is unspecified. Current implementation deadlocks, but this may + /// be changed to a panic in the future. + pub(crate) fn get_or_init_pin(self: Pin<&Self>, f: F, g: G) -> Pin<&T> + where + F: FnOnce() -> T, + G: FnOnce(Pin<&mut T>), + { + if let Some(value) = self.get_ref().get() { + // SAFETY: The inner value was already initialized, and will not be + // moved anymore. + return unsafe { Pin::new_unchecked(value) }; + } + + let slot = &self.value; + + // Ignore poisoning from other threads + // If another thread panics, then we'll be able to run our closure + self.once.call_once_force(|_| { + let value = f(); + // SAFETY: We use the Once (self.once) to guarantee unique access + // to the UnsafeCell (slot). + let value: &mut T = unsafe { (&mut *slot.get()).write(value) }; + // SAFETY: The value has been written to its final place in + // self.value. We do not to move it anymore, which we promise here + // with a Pin<&mut T>. + g(unsafe { Pin::new_unchecked(value) }); + }); + + // SAFETY: The inner value has been initialized, and will not be moved + // anymore. + unsafe { Pin::new_unchecked(self.get_ref().get_unchecked()) } + } + /// Consumes the `SyncOnceCell`, returning the wrapped value. Returns /// `None` if the cell was empty. /// diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs index 6c240cb4c3ed9..def8db1f45c37 100644 --- a/library/std/src/lib.rs +++ b/library/std/src/lib.rs @@ -266,6 +266,7 @@ #![feature(format_args_nl)] #![feature(gen_future)] #![feature(generator_trait)] +#![feature(get_mut_unchecked)] #![feature(global_asm)] #![feature(hashmap_internals)] #![feature(int_error_internals)] @@ -293,6 +294,7 @@ #![feature(panic_info_message)] #![feature(panic_internals)] #![feature(panic_unwind)] +#![feature(pin_static_ref)] #![feature(prelude_import)] #![feature(ptr_internals)] #![feature(raw)] diff --git a/library/std/src/sys_common/remutex.rs b/library/std/src/sys_common/remutex.rs index 162eab2388d55..475bfca9b6dcc 100644 --- a/library/std/src/sys_common/remutex.rs +++ b/library/std/src/sys_common/remutex.rs @@ -1,10 +1,10 @@ #[cfg(all(test, not(target_os = "emscripten")))] mod tests; -use crate::fmt; -use crate::marker; +use crate::marker::PhantomPinned; use crate::ops::Deref; use crate::panic::{RefUnwindSafe, UnwindSafe}; +use crate::pin::Pin; use crate::sys::mutex as sys; /// A re-entrant mutual exclusion @@ -15,6 +15,7 @@ use crate::sys::mutex as sys; pub struct ReentrantMutex { inner: sys::ReentrantMutex, data: T, + _pinned: PhantomPinned, } unsafe impl Send for ReentrantMutex {} @@ -37,10 +38,10 @@ impl RefUnwindSafe for ReentrantMutex {} /// guarded data. #[must_use = "if unused the ReentrantMutex will immediately unlock"] pub struct ReentrantMutexGuard<'a, T: 'a> { - lock: &'a ReentrantMutex, + lock: Pin<&'a ReentrantMutex>, } -impl !marker::Send for ReentrantMutexGuard<'_, T> {} +impl !Send for ReentrantMutexGuard<'_, T> {} impl ReentrantMutex { /// Creates a new reentrant mutex in an unlocked state. @@ -51,7 +52,11 @@ impl ReentrantMutex { /// once this mutex is in its final resting place, and only then are the /// lock/unlock methods safe. pub const unsafe fn new(t: T) -> ReentrantMutex { - ReentrantMutex { inner: sys::ReentrantMutex::uninitialized(), data: t } + ReentrantMutex { + inner: sys::ReentrantMutex::uninitialized(), + data: t, + _pinned: PhantomPinned, + } } /// Initializes this mutex so it's ready for use. @@ -60,8 +65,8 @@ impl ReentrantMutex { /// /// Unsafe to call more than once, and must be called after this will no /// longer move in memory. - pub unsafe fn init(&self) { - self.inner.init(); + pub unsafe fn init(self: Pin<&mut Self>) { + self.get_unchecked_mut().inner.init() } /// Acquires a mutex, blocking the current thread until it is able to do so. @@ -76,9 +81,9 @@ impl ReentrantMutex { /// If another user of this mutex panicked while holding the mutex, then /// this call will return failure if the mutex would otherwise be /// acquired. - pub fn lock(&self) -> ReentrantMutexGuard<'_, T> { + pub fn lock(self: Pin<&Self>) -> ReentrantMutexGuard<'_, T> { unsafe { self.inner.lock() } - ReentrantMutexGuard::new(&self) + ReentrantMutexGuard { lock: self } } /// Attempts to acquire this lock. @@ -93,8 +98,12 @@ impl ReentrantMutex { /// If another user of this mutex panicked while holding the mutex, then /// this call will return failure if the mutex would otherwise be /// acquired. - pub fn try_lock(&self) -> Option> { - if unsafe { self.inner.try_lock() } { Some(ReentrantMutexGuard::new(&self)) } else { None } + pub fn try_lock(self: Pin<&Self>) -> Option> { + if unsafe { self.inner.try_lock() } { + Some(ReentrantMutexGuard { lock: self }) + } else { + None + } } } @@ -107,30 +116,6 @@ impl Drop for ReentrantMutex { } } -impl fmt::Debug for ReentrantMutex { - fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - match self.try_lock() { - Some(guard) => f.debug_struct("ReentrantMutex").field("data", &*guard).finish(), - None => { - struct LockedPlaceholder; - impl fmt::Debug for LockedPlaceholder { - fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - f.write_str("") - } - } - - f.debug_struct("ReentrantMutex").field("data", &LockedPlaceholder).finish() - } - } - } -} - -impl<'mutex, T> ReentrantMutexGuard<'mutex, T> { - fn new(lock: &'mutex ReentrantMutex) -> ReentrantMutexGuard<'mutex, T> { - ReentrantMutexGuard { lock } - } -} - impl Deref for ReentrantMutexGuard<'_, T> { type Target = T; diff --git a/library/std/src/sys_common/remutex/tests.rs b/library/std/src/sys_common/remutex/tests.rs index 9c686e579d735..88453ded2f9fb 100644 --- a/library/std/src/sys_common/remutex/tests.rs +++ b/library/std/src/sys_common/remutex/tests.rs @@ -1,4 +1,6 @@ +use crate::boxed::Box; use crate::cell::RefCell; +use crate::pin::Pin; use crate::sync::Arc; use crate::sys_common::remutex::{ReentrantMutex, ReentrantMutexGuard}; use crate::thread; @@ -6,10 +8,11 @@ use crate::thread; #[test] fn smoke() { let m = unsafe { - let m = ReentrantMutex::new(()); - m.init(); + let mut m = Box::pin(ReentrantMutex::new(())); + m.as_mut().init(); m }; + let m = m.as_ref(); { let a = m.lock(); { @@ -27,18 +30,19 @@ fn smoke() { #[test] fn is_mutex() { let m = unsafe { - let m = Arc::new(ReentrantMutex::new(RefCell::new(0))); - m.init(); - m + // FIXME: Simplify this if Arc gets a Arc::get_pin_mut. + let mut m = Arc::new(ReentrantMutex::new(RefCell::new(0))); + Pin::new_unchecked(Arc::get_mut_unchecked(&mut m)).init(); + Pin::new_unchecked(m) }; let m2 = m.clone(); - let lock = m.lock(); + let lock = m.as_ref().lock(); let child = thread::spawn(move || { - let lock = m2.lock(); + let lock = m2.as_ref().lock(); assert_eq!(*lock.borrow(), 4950); }); for i in 0..100 { - let lock = m.lock(); + let lock = m.as_ref().lock(); *lock.borrow_mut() += i; } drop(lock); @@ -48,20 +52,21 @@ fn is_mutex() { #[test] fn trylock_works() { let m = unsafe { - let m = Arc::new(ReentrantMutex::new(())); - m.init(); - m + // FIXME: Simplify this if Arc gets a Arc::get_pin_mut. + let mut m = Arc::new(ReentrantMutex::new(())); + Pin::new_unchecked(Arc::get_mut_unchecked(&mut m)).init(); + Pin::new_unchecked(m) }; let m2 = m.clone(); - let _lock = m.try_lock(); - let _lock2 = m.try_lock(); + let _lock = m.as_ref().try_lock(); + let _lock2 = m.as_ref().try_lock(); thread::spawn(move || { - let lock = m2.try_lock(); + let lock = m2.as_ref().try_lock(); assert!(lock.is_none()); }) .join() .unwrap(); - let _lock3 = m.try_lock(); + let _lock3 = m.as_ref().try_lock(); } pub struct Answer<'a>(pub ReentrantMutexGuard<'a, RefCell>);