From 67c18fdec59cf313818b8606c3847a8af6bcf684 Mon Sep 17 00:00:00 2001 From: Mara Bos Date: Sat, 10 Oct 2020 20:20:14 +0200 Subject: [PATCH] Use Pin for the 'don't move' requirement of ReentrantMutex. The code in io::stdio before this change misused the ReentrantMutexes, by calling init() on them and moving them afterwards. Now that ReentrantMutex requires Pin for init(), this mistake is no longer easy to make. --- library/std/src/io/stdio.rs | 54 +++++++++++---------- library/std/src/lib.rs | 2 + library/std/src/sys_common/remutex.rs | 52 ++++++++------------ library/std/src/sys_common/remutex/tests.rs | 35 +++++++------ 4 files changed, 70 insertions(+), 73 deletions(-) diff --git a/library/std/src/io/stdio.rs b/library/std/src/io/stdio.rs index b5594c8e093..1160011f352 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. @@ -762,11 +767,10 @@ pub fn stderr() -> Stderr { 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/lib.rs b/library/std/src/lib.rs index 6c240cb4c3e..def8db1f45c 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 35d6701efd0..475bfca9b6d 100644 --- a/library/std/src/sys_common/remutex.rs +++ b/library/std/src/sys_common/remutex.rs @@ -1,9 +1,10 @@ #[cfg(all(test, not(target_os = "emscripten")))] mod tests; -use crate::fmt; +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 @@ -14,6 +15,7 @@ use crate::sys::mutex as sys; pub struct ReentrantMutex { inner: sys::ReentrantMutex, data: T, + _pinned: PhantomPinned, } unsafe impl Send for ReentrantMutex {} @@ -36,7 +38,7 @@ 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 !Send for ReentrantMutexGuard<'_, T> {} @@ -50,7 +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. @@ -59,8 +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. @@ -75,9 +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. @@ -92,8 +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 + } } } @@ -106,30 +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 9c686e579d7..88453ded2f9 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>);