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Auto merge of #100576 - joboet:movable_const_remutex, r=Mark-Simulacrum

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Make `ReentrantMutex` movable and `const`

As `MovableMutex` is now `const`, it can be used to simplify the implementation and interface of the internal reentrant mutex type. Consequently, the standard error stream does not need to be wrapped in `OnceLock` and `OnceLock::get_or_init_pin()` can be removed.
This commit is contained in:
bors 2022-09-04 22:53:58 +00:00
commit e7cdd4c090
12 changed files with 39 additions and 165 deletions
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41
library/std/src/io/stdio.rs
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@ -8,7 +8,6 @@ use crate::io::prelude::*;
use crate::cell::{Cell, RefCell};
use crate::fmt;
use crate::io::{self, BufReader, IoSlice, IoSliceMut, LineWriter, Lines};
use crate::pin::Pin;
use crate::sync::atomic::{AtomicBool, Ordering};
use crate::sync::{Arc, Mutex, MutexGuard, OnceLock};
use crate::sys::stdio;
@ -526,7 +525,7 @@ 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: Pin<&'static ReentrantMutex<RefCell<LineWriter<StdoutRaw>>>>,
inner: &'static ReentrantMutex<RefCell<LineWriter<StdoutRaw>>>,
}
/// A locked reference to the [`Stdout`] handle.
@ -603,24 +602,20 @@ static STDOUT: OnceLock<ReentrantMutex<RefCell<LineWriter<StdoutRaw>>>> = OnceLo
#[stable(feature = "rust1", since = "1.0.0")]
pub fn stdout() -> Stdout {
Stdout {
inner: Pin::static_ref(&STDOUT).get_or_init_pin(
|| unsafe { ReentrantMutex::new(RefCell::new(LineWriter::new(stdout_raw()))) },
|mutex| unsafe { mutex.init() },
),
inner: STDOUT
.get_or_init(|| ReentrantMutex::new(RefCell::new(LineWriter::new(stdout_raw())))),
}
}
pub fn cleanup() {
if let Some(instance) = STDOUT.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());
}
// 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) = STDOUT.get().and_then(ReentrantMutex::try_lock) {
*lock.borrow_mut() = LineWriter::with_capacity(0, stdout_raw());
}
}
@ -761,7 +756,7 @@ impl fmt::Debug for StdoutLock<'_> {
/// standard library or via raw Windows API calls, will fail.
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Stderr {
inner: Pin<&'static ReentrantMutex<RefCell<StderrRaw>>>,
inner: &'static ReentrantMutex<RefCell<StderrRaw>>,
}
/// A locked reference to the [`Stderr`] handle.
@ -834,16 +829,12 @@ pub struct StderrLock<'a> {
#[stable(feature = "rust1", since = "1.0.0")]
pub fn stderr() -> Stderr {
// 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. Stderr is not buffered, so there's no need to run a
// destructor for flushing the buffer
static INSTANCE: OnceLock<ReentrantMutex<RefCell<StderrRaw>>> = OnceLock::new();
static INSTANCE: ReentrantMutex<RefCell<StderrRaw>> =
ReentrantMutex::new(RefCell::new(stderr_raw()));
Stderr {
inner: Pin::static_ref(&INSTANCE).get_or_init_pin(
|| unsafe { ReentrantMutex::new(RefCell::new(stderr_raw())) },
|mutex| unsafe { mutex.init() },
),
}
Stderr { inner: &INSTANCE }
}
impl Stderr {

55
library/std/src/sync/once_lock.rs
View File

@ -3,7 +3,6 @@ use crate::fmt;
use crate::marker::PhantomData;
use crate::mem::MaybeUninit;
use crate::panic::{RefUnwindSafe, UnwindSafe};
use crate::pin::Pin;
use crate::sync::Once;
/// A synchronization primitive which can be written to only once.
@ -223,60 +222,6 @@ impl<T> OnceLock<T> {
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<F, G>(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 `OnceLock`, returning the wrapped value. Returns
/// `None` if the cell was empty.
///

3
library/std/src/sys/hermit/mutex.rs
View File

@ -174,9 +174,6 @@ impl Mutex {
Mutex { inner: Spinlock::new(MutexInner::new()) }
}
#[inline]
pub unsafe fn init(&mut self) {}
#[inline]
pub unsafe fn lock(&self) {
loop {

6
library/std/src/sys/itron/mutex.rs
View File

@ -31,12 +31,6 @@ impl Mutex {
Mutex { mtx: SpinIdOnceCell::new() }
}
pub unsafe fn init(&mut self) {
// Initialize `self.mtx` eagerly
let id = new_mtx().unwrap_or_else(|e| fail(e, &"acre_mtx"));
unsafe { self.mtx.set_unchecked((id, ())) };
}
/// Get the inner mutex's ID, which is lazily created.
fn raw(&self) -> abi::ID {
match self.mtx.get_or_try_init(|| new_mtx().map(|id| (id, ()))) {

3
library/std/src/sys/sgx/mutex.rs
View File

@ -20,9 +20,6 @@ impl Mutex {
Mutex { inner: SpinMutex::new(WaitVariable::new(false)) }
}
#[inline]
pub unsafe fn init(&mut self) {}
#[inline]
pub unsafe fn lock(&self) {
let mut guard = self.inner.lock();

3
library/std/src/sys/unix/locks/fuchsia_mutex.rs
View File

@ -85,9 +85,6 @@ impl Mutex {
Mutex { futex: AtomicU32::new(UNLOCKED) }
}
#[inline]
pub unsafe fn init(&mut self) {}
#[inline]
pub unsafe fn try_lock(&self) -> bool {
let thread_self = zx_thread_self();

3
library/std/src/sys/unix/locks/futex_mutex.rs
View File

@ -19,9 +19,6 @@ impl Mutex {
Self { futex: AtomicU32::new(0) }
}
#[inline]
pub unsafe fn init(&mut self) {}
#[inline]
pub unsafe fn try_lock(&self) -> bool {
self.futex.compare_exchange(0, 1, Acquire, Relaxed).is_ok()

2
library/std/src/sys/unix/locks/pthread_mutex.rs
View File

@ -52,7 +52,7 @@ impl Mutex {
Mutex { inner: UnsafeCell::new(libc::PTHREAD_MUTEX_INITIALIZER) }
}
#[inline]
pub unsafe fn init(&mut self) {
unsafe fn init(&mut self) {
// Issue #33770
//
// A pthread mutex initialized with PTHREAD_MUTEX_INITIALIZER will have

3
library/std/src/sys/unsupported/locks/mutex.rs
View File

@ -16,9 +16,6 @@ impl Mutex {
Mutex { locked: Cell::new(false) }
}
#[inline]
pub unsafe fn init(&mut self) {}
#[inline]
pub unsafe fn lock(&self) {
assert_eq!(self.locked.replace(true), false, "cannot recursively acquire mutex");

2
library/std/src/sys/windows/locks/mutex.rs
View File

@ -37,8 +37,6 @@ impl Mutex {
pub const fn new() -> Mutex {
Mutex { srwlock: UnsafeCell::new(c::SRWLOCK_INIT) }
}
#[inline]
pub unsafe fn init(&mut self) {}
#[inline]
pub unsafe fn lock(&self) {

46
library/std/src/sys_common/remutex.rs
View File

@ -1,13 +1,11 @@
#[cfg(all(test, not(target_os = "emscripten")))]
mod tests;
use super::mutex as sys;
use crate::cell::UnsafeCell;
use crate::marker::PhantomPinned;
use crate::ops::Deref;
use crate::panic::{RefUnwindSafe, UnwindSafe};
use crate::pin::Pin;
use crate::sync::atomic::{AtomicUsize, Ordering::Relaxed};
use crate::sys::locks as sys;
/// A re-entrant mutual exclusion
///
@ -41,11 +39,10 @@ use crate::sys::locks as sys;
/// synchronization is left to the mutex, making relaxed memory ordering for
/// the `owner` field fine in all cases.
pub struct ReentrantMutex<T> {
mutex: sys::Mutex,
mutex: sys::MovableMutex,
owner: AtomicUsize,
lock_count: UnsafeCell<u32>,
data: T,
_pinned: PhantomPinned,
}
unsafe impl<T: Send> Send for ReentrantMutex<T> {}
@ -68,39 +65,22 @@ impl<T> RefUnwindSafe for ReentrantMutex<T> {}
/// guarded data.
#[must_use = "if unused the ReentrantMutex will immediately unlock"]
pub struct ReentrantMutexGuard<'a, T: 'a> {
lock: Pin<&'a ReentrantMutex<T>>,
lock: &'a ReentrantMutex<T>,
}
impl<T> !Send for ReentrantMutexGuard<'_, T> {}
impl<T> ReentrantMutex<T> {
/// Creates a new reentrant mutex in an unlocked state.
///
/// # Unsafety
///
/// This function is unsafe because it is required that `init` is called
/// 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<T> {
pub const fn new(t: T) -> ReentrantMutex<T> {
ReentrantMutex {
mutex: sys::Mutex::new(),
mutex: sys::MovableMutex::new(),
owner: AtomicUsize::new(0),
lock_count: UnsafeCell::new(0),
data: t,
_pinned: PhantomPinned,
}
}
/// Initializes this mutex so it's ready for use.
///
/// # Unsafety
///
/// Unsafe to call more than once, and must be called after this will no
/// longer move in memory.
pub unsafe fn init(self: Pin<&mut Self>) {
self.get_unchecked_mut().mutex.init()
}
/// Acquires a mutex, blocking the current thread until it is able to do so.
///
/// This function will block the caller until it is available to acquire the mutex.
@ -113,15 +93,14 @@ impl<T> ReentrantMutex<T> {
/// 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: Pin<&Self>) -> ReentrantMutexGuard<'_, T> {
pub fn lock(&self) -> ReentrantMutexGuard<'_, T> {
let this_thread = current_thread_unique_ptr();
// Safety: We only touch lock_count when we own the lock,
// and since self is pinned we can safely call the lock() on the mutex.
// Safety: We only touch lock_count when we own the lock.
unsafe {
if self.owner.load(Relaxed) == this_thread {
self.increment_lock_count();
} else {
self.mutex.lock();
self.mutex.raw_lock();
self.owner.store(this_thread, Relaxed);
debug_assert_eq!(*self.lock_count.get(), 0);
*self.lock_count.get() = 1;
@ -142,10 +121,9 @@ impl<T> ReentrantMutex<T> {
/// 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: Pin<&Self>) -> Option<ReentrantMutexGuard<'_, T>> {
pub fn try_lock(&self) -> Option<ReentrantMutexGuard<'_, T>> {
let this_thread = current_thread_unique_ptr();
// Safety: We only touch lock_count when we own the lock,
// and since self is pinned we can safely call the try_lock on the mutex.
// Safety: We only touch lock_count when we own the lock.
unsafe {
if self.owner.load(Relaxed) == this_thread {
self.increment_lock_count();
@ -179,12 +157,12 @@ impl<T> Deref for ReentrantMutexGuard<'_, T> {
impl<T> Drop for ReentrantMutexGuard<'_, T> {
#[inline]
fn drop(&mut self) {
// Safety: We own the lock, and the lock is pinned.
// Safety: We own the lock.
unsafe {
*self.lock.lock_count.get() -= 1;
if *self.lock.lock_count.get() == 0 {
self.lock.owner.store(0, Relaxed);
self.lock.mutex.unlock();
self.lock.mutex.raw_unlock();
}
}
}

37
library/std/src/sys_common/remutex/tests.rs
View File

@ -1,18 +1,11 @@
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;
#[test]
fn smoke() {
let m = unsafe {
let mut m = Box::pin(ReentrantMutex::new(()));
m.as_mut().init();
m
};
let m = m.as_ref();
let m = ReentrantMutex::new(());
{
let a = m.lock();
{
@ -29,20 +22,15 @@ fn smoke() {
#[test]
fn is_mutex() {
let m = unsafe {
// FIXME: Simplify this if Arc gets an 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 m = Arc::new(ReentrantMutex::new(RefCell::new(0)));
let m2 = m.clone();
let lock = m.as_ref().lock();
let lock = m.lock();
let child = thread::spawn(move || {
let lock = m2.as_ref().lock();
let lock = m2.lock();
assert_eq!(*lock.borrow(), 4950);
});
for i in 0..100 {
let lock = m.as_ref().lock();
let lock = m.lock();
*lock.borrow_mut() += i;
}
drop(lock);
@ -51,22 +39,17 @@ fn is_mutex() {
#[test]
fn trylock_works() {
let m = unsafe {
// FIXME: Simplify this if Arc gets an 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 m = Arc::new(ReentrantMutex::new(()));
let m2 = m.clone();
let _lock = m.as_ref().try_lock();
let _lock2 = m.as_ref().try_lock();
let _lock = m.try_lock();
let _lock2 = m.try_lock();
thread::spawn(move || {
let lock = m2.as_ref().try_lock();
let lock = m2.try_lock();
assert!(lock.is_none());
})
.join()
.unwrap();
let _lock3 = m.as_ref().try_lock();
let _lock3 = m.try_lock();
}
pub struct Answer<'a>(pub ReentrantMutexGuard<'a, RefCell<u32>>);