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Rollup merge of #110543 - joboet:reentrant_lock, r=m-ou-se

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Make `ReentrantLock` public

Implements the ACP rust-lang/libs-team#193.

``@rustbot`` label +T-libs-api +S-waiting-on-ACP
This commit is contained in:
Matthias Krüger 2024-02-29 00:16:58 +01:00 • committed by GitHub
commit 332b9be7a1
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GPG key ID: B5690EEEBB952194
5 changed files with 375 additions and 207 deletions
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45
library/std/src/io/stdio.rs
View file

@ -11,8 +11,9 @@ use crate::fs::File;
use crate::io::{
self, BorrowedCursor, BufReader, IoSlice, IoSliceMut, LineWriter, Lines, SpecReadByte,
};
use crate::panic::{RefUnwindSafe, UnwindSafe};
use crate::sync::atomic::{AtomicBool, Ordering};
use crate::sync::{Arc, Mutex, MutexGuard, OnceLock, ReentrantMutex, ReentrantMutexGuard};
use crate::sync::{Arc, Mutex, MutexGuard, OnceLock, ReentrantLock, ReentrantLockGuard};
use crate::sys::stdio;
type LocalStream = Arc<Mutex<Vec<u8>>>;
@ -545,7 +546,7 @@ 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<RefCell<LineWriter<StdoutRaw>>>,
inner: &'static ReentrantLock<RefCell<LineWriter<StdoutRaw>>>,
}
/// A locked reference to the [`Stdout`] handle.
@ -567,10 +568,10 @@ pub struct Stdout {
#[must_use = "if unused stdout will immediately unlock"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct StdoutLock<'a> {
inner: ReentrantMutexGuard<'a, RefCell<LineWriter<StdoutRaw>>>,
inner: ReentrantLockGuard<'a, RefCell<LineWriter<StdoutRaw>>>,
}
static STDOUT: OnceLock<ReentrantMutex<RefCell<LineWriter<StdoutRaw>>>> = OnceLock::new();
static STDOUT: OnceLock<ReentrantLock<RefCell<LineWriter<StdoutRaw>>>> = OnceLock::new();
/// Constructs a new handle to the standard output of the current process.
///
@ -624,7 +625,7 @@ static STDOUT: OnceLock<ReentrantMutex<RefCell<LineWriter<StdoutRaw>>>> = OnceLo
pub fn stdout() -> Stdout {
Stdout {
inner: STDOUT
.get_or_init(|| ReentrantMutex::new(RefCell::new(LineWriter::new(stdout_raw())))),
.get_or_init(|| ReentrantLock::new(RefCell::new(LineWriter::new(stdout_raw())))),
}
}
@ -635,7 +636,7 @@ pub fn cleanup() {
let mut initialized = false;
let stdout = STDOUT.get_or_init(|| {
initialized = true;
ReentrantMutex::new(RefCell::new(LineWriter::with_capacity(0, stdout_raw())))
ReentrantLock::new(RefCell::new(LineWriter::with_capacity(0, stdout_raw())))
});
if !initialized {
@ -678,6 +679,12 @@ impl Stdout {
}
}
#[stable(feature = "catch_unwind", since = "1.9.0")]
impl UnwindSafe for Stdout {}
#[stable(feature = "catch_unwind", since = "1.9.0")]
impl RefUnwindSafe for Stdout {}
#[stable(feature = "std_debug", since = "1.16.0")]
impl fmt::Debug for Stdout {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
@ -737,6 +744,12 @@ impl Write for &Stdout {
}
}
#[stable(feature = "catch_unwind", since = "1.9.0")]
impl UnwindSafe for StdoutLock<'_> {}
#[stable(feature = "catch_unwind", since = "1.9.0")]
impl RefUnwindSafe for StdoutLock<'_> {}
#[stable(feature = "rust1", since = "1.0.0")]
impl Write for StdoutLock<'_> {
fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
@ -786,7 +799,7 @@ 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: &'static ReentrantMutex<RefCell<StderrRaw>>,
inner: &'static ReentrantLock<RefCell<StderrRaw>>,
}
/// A locked reference to the [`Stderr`] handle.
@ -808,7 +821,7 @@ pub struct Stderr {
#[must_use = "if unused stderr will immediately unlock"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct StderrLock<'a> {
inner: ReentrantMutexGuard<'a, RefCell<StderrRaw>>,
inner: ReentrantLockGuard<'a, RefCell<StderrRaw>>,
}
/// Constructs a new handle to the standard error of the current process.
@ -862,8 +875,8 @@ 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 for flushing the buffer
static INSTANCE: ReentrantMutex<RefCell<StderrRaw>> =
ReentrantMutex::new(RefCell::new(stderr_raw()));
static INSTANCE: ReentrantLock<RefCell<StderrRaw>> =
ReentrantLock::new(RefCell::new(stderr_raw()));
Stderr { inner: &INSTANCE }
}
@ -898,6 +911,12 @@ impl Stderr {
}
}
#[stable(feature = "catch_unwind", since = "1.9.0")]
impl UnwindSafe for Stderr {}
#[stable(feature = "catch_unwind", since = "1.9.0")]
impl RefUnwindSafe for Stderr {}
#[stable(feature = "std_debug", since = "1.16.0")]
impl fmt::Debug for Stderr {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
@ -957,6 +976,12 @@ impl Write for &Stderr {
}
}
#[stable(feature = "catch_unwind", since = "1.9.0")]
impl UnwindSafe for StderrLock<'_> {}
#[stable(feature = "catch_unwind", since = "1.9.0")]
impl RefUnwindSafe for StderrLock<'_> {}
#[stable(feature = "rust1", since = "1.0.0")]
impl Write for StderrLock<'_> {
fn write(&mut self, buf: &[u8]) -> io::Result<usize> {

5
library/std/src/sync/mod.rs
View file

@ -184,7 +184,8 @@ pub use self::lazy_lock::LazyLock;
#[stable(feature = "once_cell", since = "1.70.0")]
pub use self::once_lock::OnceLock;
pub(crate) use self::remutex::{ReentrantMutex, ReentrantMutexGuard};
#[unstable(feature = "reentrant_lock", issue = "121440")]
pub use self::reentrant_lock::{ReentrantLock, ReentrantLockGuard};
pub mod mpsc;
@ -196,5 +197,5 @@ mod mutex;
pub(crate) mod once;
mod once_lock;
mod poison;
mod remutex;
mod reentrant_lock;
mod rwlock;

320
library/std/src/sync/reentrant_lock.rs Normal file
View file

@ -0,0 +1,320 @@
#[cfg(all(test, not(target_os = "emscripten")))]
mod tests;
use crate::cell::UnsafeCell;
use crate::fmt;
use crate::ops::Deref;
use crate::panic::{RefUnwindSafe, UnwindSafe};
use crate::sync::atomic::{AtomicUsize, Ordering::Relaxed};
use crate::sys::locks as sys;
/// A re-entrant mutual exclusion lock
///
/// This lock will block *other* threads waiting for the lock to become
/// available. The thread which has already locked the mutex can lock it
/// multiple times without blocking, preventing a common source of deadlocks.
///
/// # Examples
///
/// Allow recursively calling a function needing synchronization from within
/// a callback (this is how [`StdoutLock`](crate::io::StdoutLock) is currently
/// implemented):
///
/// ```
/// #![feature(reentrant_lock)]
///
/// use std::cell::RefCell;
/// use std::sync::ReentrantLock;
///
/// pub struct Log {
/// data: RefCell<String>,
/// }
///
/// impl Log {
/// pub fn append(&self, msg: &str) {
/// self.data.borrow_mut().push_str(msg);
/// }
/// }
///
/// static LOG: ReentrantLock<Log> = ReentrantLock::new(Log { data: RefCell::new(String::new()) });
///
/// pub fn with_log<R>(f: impl FnOnce(&Log) -> R) -> R {
/// let log = LOG.lock();
/// f(&*log)
/// }
///
/// with_log(|log| {
/// log.append("Hello");
/// with_log(|log| log.append(" there!"));
/// });
/// ```
///
// # Implementation details
//
// The 'owner' field tracks which thread has locked the mutex.
//
// We use current_thread_unique_ptr() as the thread identifier,
// which is just the address of a thread local variable.
//
// If `owner` is set to the identifier of the current thread,
// we assume the mutex is already locked and instead of locking it again,
// we increment `lock_count`.
//
// When unlocking, we decrement `lock_count`, and only unlock the mutex when
// it reaches zero.
//
// `lock_count` is protected by the mutex and only accessed by the thread that has
// locked the mutex, so needs no synchronization.
//
// `owner` can be checked by other threads that want to see if they already
// hold the lock, so needs to be atomic. If it compares equal, we're on the
// same thread that holds the mutex and memory access can use relaxed ordering
// since we're not dealing with multiple threads. If it's not equal,
// synchronization is left to the mutex, making relaxed memory ordering for
// the `owner` field fine in all cases.
#[unstable(feature = "reentrant_lock", issue = "121440")]
pub struct ReentrantLock<T: ?Sized> {
mutex: sys::Mutex,
owner: AtomicUsize,
lock_count: UnsafeCell<u32>,
data: T,
}
#[unstable(feature = "reentrant_lock", issue = "121440")]
unsafe impl<T: Send + ?Sized> Send for ReentrantLock<T> {}
#[unstable(feature = "reentrant_lock", issue = "121440")]
unsafe impl<T: Send + ?Sized> Sync for ReentrantLock<T> {}
// Because of the `UnsafeCell`, these traits are not implemented automatically
#[unstable(feature = "reentrant_lock", issue = "121440")]
impl<T: UnwindSafe + ?Sized> UnwindSafe for ReentrantLock<T> {}
#[unstable(feature = "reentrant_lock", issue = "121440")]
impl<T: RefUnwindSafe + ?Sized> RefUnwindSafe for ReentrantLock<T> {}
/// An RAII implementation of a "scoped lock" of a re-entrant lock. When this
/// structure is dropped (falls out of scope), the lock will be unlocked.
///
/// The data protected by the mutex can be accessed through this guard via its
/// [`Deref`] implementation.
///
/// This structure is created by the [`lock`](ReentrantLock::lock) method on
/// [`ReentrantLock`].
///
/// # Mutability
///
/// Unlike [`MutexGuard`](super::MutexGuard), `ReentrantLockGuard` does not
/// implement [`DerefMut`](crate::ops::DerefMut), because implementation of
/// the trait would violate Rust’s reference aliasing rules. Use interior
/// mutability (usually [`RefCell`](crate::cell::RefCell)) in order to mutate
/// the guarded data.
#[must_use = "if unused the ReentrantLock will immediately unlock"]
#[unstable(feature = "reentrant_lock", issue = "121440")]
pub struct ReentrantLockGuard<'a, T: ?Sized + 'a> {
lock: &'a ReentrantLock<T>,
}
#[unstable(feature = "reentrant_lock", issue = "121440")]
impl<T: ?Sized> !Send for ReentrantLockGuard<'_, T> {}
#[unstable(feature = "reentrant_lock", issue = "121440")]
impl<T> ReentrantLock<T> {
/// Creates a new re-entrant lock in an unlocked state ready for use.
///
/// # Examples
///
/// ```
/// #![feature(reentrant_lock)]
/// use std::sync::ReentrantLock;
///
/// let lock = ReentrantLock::new(0);
/// ```
pub const fn new(t: T) -> ReentrantLock<T> {
ReentrantLock {
mutex: sys::Mutex::new(),
owner: AtomicUsize::new(0),
lock_count: UnsafeCell::new(0),
data: t,
}
}
/// Consumes this lock, returning the underlying data.
///
/// # Examples
///
/// ```
/// #![feature(reentrant_lock)]
///
/// use std::sync::ReentrantLock;
///
/// let lock = ReentrantLock::new(0);
/// assert_eq!(lock.into_inner(), 0);
/// ```
pub fn into_inner(self) -> T {
self.data
}
}
#[unstable(feature = "reentrant_lock", issue = "121440")]
impl<T: ?Sized> ReentrantLock<T> {
/// Acquires the lock, blocking the current thread until it is able to do
/// so.
///
/// This function will block the caller until it is available to acquire
/// the lock. Upon returning, the thread is the only thread with the lock
/// held. When the thread calling this method already holds the lock, the
/// call succeeds without blocking.
///
/// # Examples
///
/// ```
/// #![feature(reentrant_lock)]
/// use std::cell::Cell;
/// use std::sync::{Arc, ReentrantLock};
/// use std::thread;
///
/// let lock = Arc::new(ReentrantLock::new(Cell::new(0)));
/// let c_lock = Arc::clone(&lock);
///
/// thread::spawn(move || {
/// c_lock.lock().set(10);
/// }).join().expect("thread::spawn failed");
/// assert_eq!(lock.lock().get(), 10);
/// ```
pub fn lock(&self) -> ReentrantLockGuard<'_, T> {
let this_thread = current_thread_unique_ptr();
// Safety: We only touch lock_count when we own the lock.
unsafe {
if self.owner.load(Relaxed) == this_thread {
self.increment_lock_count().expect("lock count overflow in reentrant mutex");
} else {
self.mutex.lock();
self.owner.store(this_thread, Relaxed);
debug_assert_eq!(*self.lock_count.get(), 0);
*self.lock_count.get() = 1;
}
}
ReentrantLockGuard { lock: self }
}
/// Returns a mutable reference to the underlying data.
///
/// Since this call borrows the `ReentrantLock` mutably, no actual locking
/// needs to take place -- the mutable borrow statically guarantees no locks
/// exist.
///
/// # Examples
///
/// ```
/// #![feature(reentrant_lock)]
/// use std::sync::ReentrantLock;
///
/// let mut lock = ReentrantLock::new(0);
/// *lock.get_mut() = 10;
/// assert_eq!(*lock.lock(), 10);
/// ```
pub fn get_mut(&mut self) -> &mut T {
&mut self.data
}
/// Attempts to acquire this lock.
///
/// If the lock could not be acquired at this time, then `None` is returned.
/// Otherwise, an RAII guard is returned.
///
/// This function does not block.
pub(crate) fn try_lock(&self) -> Option<ReentrantLockGuard<'_, T>> {
let this_thread = current_thread_unique_ptr();
// Safety: We only touch lock_count when we own the lock.
unsafe {
if self.owner.load(Relaxed) == this_thread {
self.increment_lock_count()?;
Some(ReentrantLockGuard { lock: self })
} else if self.mutex.try_lock() {
self.owner.store(this_thread, Relaxed);
debug_assert_eq!(*self.lock_count.get(), 0);
*self.lock_count.get() = 1;
Some(ReentrantLockGuard { lock: self })
} else {
None
}
}
}
unsafe fn increment_lock_count(&self) -> Option<()> {
*self.lock_count.get() = (*self.lock_count.get()).checked_add(1)?;
Some(())
}
}
#[unstable(feature = "reentrant_lock", issue = "121440")]
impl<T: fmt::Debug + ?Sized> fmt::Debug for ReentrantLock<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let mut d = f.debug_struct("ReentrantLock");
match self.try_lock() {
Some(v) => d.field("data", &&*v),
None => d.field("data", &format_args!("<locked>")),
};
d.finish_non_exhaustive()
}
}
#[unstable(feature = "reentrant_lock", issue = "121440")]
impl<T: Default> Default for ReentrantLock<T> {
fn default() -> Self {
Self::new(T::default())
}
}
#[unstable(feature = "reentrant_lock", issue = "121440")]
impl<T> From<T> for ReentrantLock<T> {
fn from(t: T) -> Self {
Self::new(t)
}
}
#[unstable(feature = "reentrant_lock", issue = "121440")]
impl<T: ?Sized> Deref for ReentrantLockGuard<'_, T> {
type Target = T;
fn deref(&self) -> &T {
&self.lock.data
}
}
#[unstable(feature = "reentrant_lock", issue = "121440")]
impl<T: fmt::Debug + ?Sized> fmt::Debug for ReentrantLockGuard<'_, T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
(**self).fmt(f)
}
}
#[unstable(feature = "reentrant_lock", issue = "121440")]
impl<T: fmt::Display + ?Sized> fmt::Display for ReentrantLockGuard<'_, T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
(**self).fmt(f)
}
}
#[unstable(feature = "reentrant_lock", issue = "121440")]
impl<T: ?Sized> Drop for ReentrantLockGuard<'_, T> {
#[inline]
fn drop(&mut self) {
// 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();
}
}
}
}
/// Get an address that is unique per running thread.
///
/// This can be used as a non-null usize-sized ID.
pub(crate) fn current_thread_unique_ptr() -> usize {
// Use a non-drop type to make sure it's still available during thread destruction.
thread_local! { static X: u8 = const { 0 } }
X.with(|x| <*const _>::addr(x))
}

34
library/std/src/sync/remutex/tests.rs → library/std/src/sync/reentrant_lock/tests.rs
View file

@ -1,17 +1,17 @@
use super::{ReentrantMutex, ReentrantMutexGuard};
use super::{ReentrantLock, ReentrantLockGuard};
use crate::cell::RefCell;
use crate::sync::Arc;
use crate::thread;
#[test]
fn smoke() {
let m = ReentrantMutex::new(());
let l = ReentrantLock::new(());
{
let a = m.lock();
let a = l.lock();
{
let b = m.lock();
let b = l.lock();
{
let c = m.lock();
let c = l.lock();
assert_eq!(*c, ());
}
assert_eq!(*b, ());
@ -22,15 +22,15 @@ fn smoke() {
#[test]
fn is_mutex() {
let m = Arc::new(ReentrantMutex::new(RefCell::new(0)));
let m2 = m.clone();
let lock = m.lock();
let l = Arc::new(ReentrantLock::new(RefCell::new(0)));
let l2 = l.clone();
let lock = l.lock();
let child = thread::spawn(move || {
let lock = m2.lock();
let lock = l2.lock();
assert_eq!(*lock.borrow(), 4950);
});
for i in 0..100 {
let lock = m.lock();
let lock = l.lock();
*lock.borrow_mut() += i;
}
drop(lock);
@ -39,20 +39,20 @@ fn is_mutex() {
#[test]
fn trylock_works() {
let m = Arc::new(ReentrantMutex::new(()));
let m2 = m.clone();
let _lock = m.try_lock();
let _lock2 = m.try_lock();
let l = Arc::new(ReentrantLock::new(()));
let l2 = l.clone();
let _lock = l.try_lock();
let _lock2 = l.try_lock();
thread::spawn(move || {
let lock = m2.try_lock();
let lock = l2.try_lock();
assert!(lock.is_none());
})
.join()
.unwrap();
let _lock3 = m.try_lock();
let _lock3 = l.try_lock();
}
pub struct Answer<'a>(pub ReentrantMutexGuard<'a, RefCell<u32>>);
pub struct Answer<'a>(pub ReentrantLockGuard<'a, RefCell<u32>>);
impl Drop for Answer<'_> {
fn drop(&mut self) {
*self.0.borrow_mut() = 42;

178
library/std/src/sync/remutex.rs
View file

@ -1,178 +0,0 @@
#[cfg(all(test, not(target_os = "emscripten")))]
mod tests;
use crate::cell::UnsafeCell;
use crate::ops::Deref;
use crate::panic::{RefUnwindSafe, UnwindSafe};
use crate::sync::atomic::{AtomicUsize, Ordering::Relaxed};
use crate::sys::locks as sys;
/// A reentrant mutual exclusion
///
/// This mutex will block *other* threads waiting for the lock to become
/// available. The thread which has already locked the mutex can lock it
/// multiple times without blocking, preventing a common source of deadlocks.
///
/// This is used by stdout().lock() and friends.
///
/// ## Implementation details
///
/// The 'owner' field tracks which thread has locked the mutex.
///
/// We use current_thread_unique_ptr() as the thread identifier,
/// which is just the address of a thread local variable.
///
/// If `owner` is set to the identifier of the current thread,
/// we assume the mutex is already locked and instead of locking it again,
/// we increment `lock_count`.
///
/// When unlocking, we decrement `lock_count`, and only unlock the mutex when
/// it reaches zero.
///
/// `lock_count` is protected by the mutex and only accessed by the thread that has
/// locked the mutex, so needs no synchronization.
///
/// `owner` can be checked by other threads that want to see if they already
/// hold the lock, so needs to be atomic. If it compares equal, we're on the
/// same thread that holds the mutex and memory access can use relaxed ordering
/// since we're not dealing with multiple threads. If it's not equal,
/// 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,
owner: AtomicUsize,
lock_count: UnsafeCell<u32>,
data: T,
}
unsafe impl<T: Send> Send for ReentrantMutex<T> {}
unsafe impl<T: Send> Sync for ReentrantMutex<T> {}
impl<T> UnwindSafe for ReentrantMutex<T> {}
impl<T> RefUnwindSafe for ReentrantMutex<T> {}
/// An RAII implementation of a "scoped lock" of a mutex. When this structure is
/// dropped (falls out of scope), the lock will be unlocked.
///
/// The data protected by the mutex can be accessed through this guard via its
/// Deref implementation.
///
/// # Mutability
///
/// Unlike `MutexGuard`, `ReentrantMutexGuard` does not implement `DerefMut`,
/// because implementation of the trait would violate Rust’s reference aliasing
/// rules. Use interior mutability (usually `RefCell`) in order to mutate the
/// guarded data.
#[must_use = "if unused the ReentrantMutex will immediately unlock"]
pub struct ReentrantMutexGuard<'a, T: 'a> {
lock: &'a ReentrantMutex<T>,
}
impl<T> !Send for ReentrantMutexGuard<'_, T> {}
impl<T> ReentrantMutex<T> {
/// Creates a new reentrant mutex in an unlocked state.
pub const fn new(t: T) -> ReentrantMutex<T> {
ReentrantMutex {
mutex: sys::Mutex::new(),
owner: AtomicUsize::new(0),
lock_count: UnsafeCell::new(0),
data: t,
}
}
/// 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.
/// Upon returning, the thread is the only thread with the mutex held. When the thread
/// calling this method already holds the lock, the call shall succeed without
/// blocking.
///
/// # Errors
///
/// 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> {
let this_thread = current_thread_unique_ptr();
// 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.owner.store(this_thread, Relaxed);
debug_assert_eq!(*self.lock_count.get(), 0);
*self.lock_count.get() = 1;
}
}
ReentrantMutexGuard { lock: self }
}
/// Attempts to acquire this lock.
///
/// If the lock could not be acquired at this time, then `Err` is returned.
/// Otherwise, an RAII guard is returned.
///
/// This function does not block.
///
/// # Errors
///
/// 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<ReentrantMutexGuard<'_, T>> {
let this_thread = current_thread_unique_ptr();
// Safety: We only touch lock_count when we own the lock.
unsafe {
if self.owner.load(Relaxed) == this_thread {
self.increment_lock_count();
Some(ReentrantMutexGuard { lock: self })
} else if self.mutex.try_lock() {
self.owner.store(this_thread, Relaxed);
debug_assert_eq!(*self.lock_count.get(), 0);
*self.lock_count.get() = 1;
Some(ReentrantMutexGuard { lock: self })
} else {
None
}
}
}
unsafe fn increment_lock_count(&self) {
*self.lock_count.get() = (*self.lock_count.get())
.checked_add(1)
.expect("lock count overflow in reentrant mutex");
}
}
impl<T> Deref for ReentrantMutexGuard<'_, T> {
type Target = T;
fn deref(&self) -> &T {
&self.lock.data
}
}
impl<T> Drop for ReentrantMutexGuard<'_, T> {
#[inline]
fn drop(&mut self) {
// 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();
}
}
}
}
/// Get an address that is unique per running thread.
///
/// This can be used as a non-null usize-sized ID.
pub fn current_thread_unique_ptr() -> usize {
// Use a non-drop type to make sure it's still available during thread destruction.
thread_local! { static X: u8 = const { 0 } }
X.with(|x| <*const _>::addr(x))
}