// Copyright 2018 Amanieu d'Antras
//
// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
// http://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 core::cell::{Cell, UnsafeCell};
use core::fmt;
use core::marker::PhantomData;
use core::mem;
use core::ops::Deref;
use core::sync::atomic::{AtomicUsize, Ordering};
use mutex::{RawMutex, RawMutexFair, RawMutexTimed};
use GuardNoSend;
#[cfg(feature = "owning_ref")]
use owning_ref::StableAddress;
/// Helper trait which returns a non-zero thread ID.
///
/// The simplest way to implement this trait is to return the address of a
/// thread-local variable.
///
/// # Safety
///
/// Implementations of this trait must ensure that no two active threads share
/// the same thread ID. However the ID of a thread that has exited can be
/// re-used since that thread is no longer active.
pub unsafe trait GetThreadId {
/// Initial value.
const INIT: Self;
/// Returns a non-zero thread ID which identifies the current thread of
/// execution.
fn nonzero_thread_id(&self) -> usize;
}
struct RawReentrantMutex<R: RawMutex, G: GetThreadId> {
owner: AtomicUsize,
lock_count: Cell<usize>,
mutex: R,
get_thread_id: G,
}
impl<R: RawMutex, G: GetThreadId> RawReentrantMutex<R, G> {
#[inline]
fn lock_internal<F: FnOnce() -> bool>(&self, try_lock: F) -> bool {
let id = self.get_thread_id.nonzero_thread_id();
if self.owner.load(Ordering::Relaxed) == id {
self.lock_count.set(
self.lock_count
.get()
.checked_add(1)
.expect("ReentrantMutex lock count overflow"),
);
} else {
if !try_lock() {
return false;
}
self.owner.store(id, Ordering::Relaxed);
self.lock_count.set(1);
}
true
}
#[inline]
fn lock(&self) {
self.lock_internal(|| {
self.mutex.lock();
true
});
}
#[inline]
fn try_lock(&self) -> bool {
self.lock_internal(|| self.mutex.try_lock())
}
#[inline]
fn unlock(&self) {
let lock_count = self.lock_count.get() - 1;
if lock_count == 0 {
self.owner.store(0, Ordering::Relaxed);
self.mutex.unlock();
} else {
self.lock_count.set(lock_count);
}
}
}
impl<R: RawMutexFair, G: GetThreadId> RawReentrantMutex<R, G> {
#[inline]
fn unlock_fair(&self) {
let lock_count = self.lock_count.get() - 1;
if lock_count == 0 {
self.owner.store(0, Ordering::Relaxed);
self.mutex.unlock_fair();
} else {
self.lock_count.set(lock_count);
}
}
#[inline]
fn bump(&self) {
if self.lock_count.get() == 1 {
let id = self.owner.load(Ordering::Relaxed);
self.owner.store(0, Ordering::Relaxed);
self.mutex.bump();
self.owner.store(id, Ordering::Relaxed);
}
}
}
impl<R: RawMutexTimed, G: GetThreadId> RawReentrantMutex<R, G> {
#[inline]
fn try_lock_until(&self, timeout: R::Instant) -> bool {
self.lock_internal(|| self.mutex.try_lock_until(timeout))
}
#[inline]
fn try_lock_for(&self, timeout: R::Duration) -> bool {
self.lock_internal(|| self.mutex.try_lock_for(timeout))
}
}
/// A mutex which can be recursively locked by a single thread.
///
/// This type is identical to `Mutex` except for the following points:
///
/// - Locking multiple times from the same thread will work correctly instead of
/// deadlocking.
/// - `ReentrantMutexGuard` does not give mutable references to the locked data.
/// Use a `RefCell` if you need this.
///
/// See [`Mutex`](struct.Mutex.html) for more details about the underlying mutex
/// primitive.
pub struct ReentrantMutex<R: RawMutex, G: GetThreadId, T: ?Sized> {
raw: RawReentrantMutex<R, G>,
data: UnsafeCell<T>,
}
unsafe impl<R: RawMutex + Send, G: GetThreadId + Send, T: ?Sized + Send> Send
for ReentrantMutex<R, G, T>
{}
unsafe impl<R: RawMutex + Sync, G: GetThreadId + Sync, T: ?Sized + Send> Sync
for ReentrantMutex<R, G, T>
{}
impl<R: RawMutex, G: GetThreadId, T> ReentrantMutex<R, G, T> {
/// Creates a new reentrant mutex in an unlocked state ready for use.
#[cfg(feature = "nightly")]
#[inline]
pub const fn new(val: T) -> ReentrantMutex<R, G, T> {
ReentrantMutex {
data: UnsafeCell::new(val),
raw: RawReentrantMutex {
owner: AtomicUsize::new(0),
lock_count: Cell::new(0),
mutex: R::INIT,
get_thread_id: G::INIT,
},
}
}
/// Creates a new reentrant mutex in an unlocked state ready for use.
#[cfg(not(feature = "nightly"))]
#[inline]
pub fn new(val: T) -> ReentrantMutex<R, G, T> {
ReentrantMutex {
data: UnsafeCell::new(val),
raw: RawReentrantMutex {
owner: AtomicUsize::new(0),
lock_count: Cell::new(0),
mutex: R::INIT,
get_thread_id: G::INIT,
},
}
}
/// Consumes this mutex, returning the underlying data.
#[inline]
#[allow(unused_unsafe)]
pub fn into_inner(self) -> T {
unsafe { self.data.into_inner() }
}
}
impl<R: RawMutex, G: GetThreadId, T: ?Sized> ReentrantMutex<R, G, T> {
#[inline]
fn guard(&self) -> ReentrantMutexGuard<R, G, T> {
ReentrantMutexGuard {
remutex: &self,
marker: PhantomData,
}
}
/// Acquires a reentrant mutex, blocking the current thread until it is able
/// to do so.
///
/// If the mutex is held by another thread then this function will block the
/// local thread until it is available to acquire the mutex. If the mutex is
/// already held by the current thread then this function will increment the
/// lock reference count and return immediately. Upon returning,
/// the thread is the only thread with the mutex held. An RAII guard is
/// returned to allow scoped unlock of the lock. When the guard goes out of
/// scope, the mutex will be unlocked.
#[inline]
pub fn lock(&self) -> ReentrantMutexGuard<R, G, T> {
self.raw.lock();
self.guard()
}
/// 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. The lock will be unlocked when the
/// guard is dropped.
///
/// This function does not block.
#[inline]
pub fn try_lock(&self) -> Option<ReentrantMutexGuard<R, G, T>> {
if self.raw.try_lock() {
Some(self.guard())
} else {
None
}
}
/// Returns a mutable reference to the underlying data.
///
/// Since this call borrows the `ReentrantMutex` mutably, no actual locking needs to
/// take place---the mutable borrow statically guarantees no locks exist.
#[inline]
pub fn get_mut(&mut self) -> &mut T {
unsafe { &mut *self.data.get() }
}
/// Forcibly unlocks the mutex.
///
/// This is useful when combined with `mem::forget` to hold a lock without
/// the need to maintain a `ReentrantMutexGuard` object alive, for example when
/// dealing with FFI.
///
/// # Safety
///
/// This method must only be called if the current thread logically owns a
/// `ReentrantMutexGuard` but that guard has be discarded using `mem::forget`.
/// Behavior is undefined if a mutex is unlocked when not locked.
#[inline]
pub unsafe fn force_unlock(&self) {
self.raw.unlock();
}
/// Returns the underlying raw mutex object.
///
/// Note that you will most likely need to import the `RawMutex` trait from
/// `lock_api` to be able to call functions on the raw mutex.
///
/// # Safety
///
/// This method is unsafe because it allows unlocking a mutex while
/// still holding a reference to a `ReentrantMutexGuard`.
#[inline]
pub unsafe fn raw(&self) -> &R {
&self.raw.mutex
}
}
impl<R: RawMutexFair, G: GetThreadId, T: ?Sized> ReentrantMutex<R, G, T> {
/// Forcibly unlocks the mutex using a fair unlock procotol.
///
/// This is useful when combined with `mem::forget` to hold a lock without
/// the need to maintain a `ReentrantMutexGuard` object alive, for example when
/// dealing with FFI.
///
/// # Safety
///
/// This method must only be called if the current thread logically owns a
/// `ReentrantMutexGuard` but that guard has be discarded using `mem::forget`.
/// Behavior is undefined if a mutex is unlocked when not locked.
#[inline]
pub unsafe fn force_unlock_fair(&self) {
self.raw.unlock_fair();
}
}
impl<R: RawMutexTimed, G: GetThreadId, T: ?Sized> ReentrantMutex<R, G, T> {
/// Attempts to acquire this lock until a timeout is reached.
///
/// If the lock could not be acquired before the timeout expired, then
/// `None` is returned. Otherwise, an RAII guard is returned. The lock will
/// be unlocked when the guard is dropped.
#[inline]
pub fn try_lock_for(&self, timeout: R::Duration) -> Option<ReentrantMutexGuard<R, G, T>> {
if self.raw.try_lock_for(timeout) {
Some(self.guard())
} else {
None
}
}
/// Attempts to acquire this lock until a timeout is reached.
///
/// If the lock could not be acquired before the timeout expired, then
/// `None` is returned. Otherwise, an RAII guard is returned. The lock will
/// be unlocked when the guard is dropped.
#[inline]
pub fn try_lock_until(&self, timeout: R::Instant) -> Option<ReentrantMutexGuard<R, G, T>> {
if self.raw.try_lock_until(timeout) {
Some(self.guard())
} else {
None
}
}
}
impl<R: RawMutex, G: GetThreadId, T: ?Sized + Default> Default for ReentrantMutex<R, G, T> {
#[inline]
fn default() -> ReentrantMutex<R, G, T> {
ReentrantMutex::new(Default::default())
}
}
impl<R: RawMutex, G: GetThreadId, T> From<T> for ReentrantMutex<R, G, T> {
#[inline]
fn from(t: T) -> ReentrantMutex<R, G, T> {
ReentrantMutex::new(t)
}
}
impl<R: RawMutex, G: GetThreadId, T: ?Sized + fmt::Debug> fmt::Debug for ReentrantMutex<R, G, T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
match self.try_lock() {
Some(guard) => f
.debug_struct("ReentrantMutex")
.field("data", &&*guard)
.finish(),
None => f.pad("ReentrantMutex { <locked> }"),
}
}
}
/// An RAII implementation of a "scoped lock" of a reentrant 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.
#[must_use]
pub struct ReentrantMutexGuard<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> {
remutex: &'a ReentrantMutex<R, G, T>,
marker: PhantomData<(&'a T, GuardNoSend)>,
}
unsafe impl<'a, R: RawMutex + Sync + 'a, G: GetThreadId + Sync + 'a, T: ?Sized + Sync + 'a> Sync
for ReentrantMutexGuard<'a, R, G, T>
{}
impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> ReentrantMutexGuard<'a, R, G, T> {
/// Returns a reference to the original `ReentrantMutex` object.
pub fn remutex(s: &Self) -> &'a ReentrantMutex<R, G, T> {
s.remutex
}
/// Makes a new `MappedReentrantMutexGuard` for a component of the locked data.
///
/// This operation cannot fail as the `ReentrantMutexGuard` passed
/// in already locked the mutex.
///
/// This is an associated function that needs to be
/// used as `ReentrantMutexGuard::map(...)`. A method would interfere with methods of
/// the same name on the contents of the locked data.
#[inline]
pub fn map<U: ?Sized, F>(s: Self, f: F) -> MappedReentrantMutexGuard<'a, R, G, U>
where
F: FnOnce(&T) -> &U,
{
let raw = &s.remutex.raw;
let data = f(unsafe { &*s.remutex.data.get() });
mem::forget(s);
MappedReentrantMutexGuard {
raw,
data,
marker: PhantomData,
}
}
/// Temporarily unlocks the mutex to execute the given function.
///
/// This is safe because `&mut` guarantees that there exist no other
/// references to the data protected by the mutex.
#[inline]
pub fn unlocked<F, U>(s: &mut Self, f: F) -> U
where
F: FnOnce() -> U,
{
s.remutex.raw.unlock();
defer!(s.remutex.raw.lock());
f()
}
}
impl<'a, R: RawMutexFair + 'a, G: GetThreadId + 'a, T: ?Sized + 'a>
ReentrantMutexGuard<'a, R, G, T>
{
/// Unlocks the mutex using a fair unlock protocol.
///
/// By default, mutexes are unfair and allow the current thread to re-lock
/// the mutex before another has the chance to acquire the lock, even if
/// that thread has been blocked on the mutex for a long time. This is the
/// default because it allows much higher throughput as it avoids forcing a
/// context switch on every mutex unlock. This can result in one thread
/// acquiring a mutex many more times than other threads.
///
/// However in some cases it can be beneficial to ensure fairness by forcing
/// the lock to pass on to a waiting thread if there is one. This is done by
/// using this method instead of dropping the `ReentrantMutexGuard` normally.
#[inline]
pub fn unlock_fair(s: Self) {
s.remutex.raw.unlock_fair();
mem::forget(s);
}
/// Temporarily unlocks the mutex to execute the given function.
///
/// The mutex is unlocked a fair unlock protocol.
///
/// This is safe because `&mut` guarantees that there exist no other
/// references to the data protected by the mutex.
#[inline]
pub fn unlocked_fair<F, U>(s: &mut Self, f: F) -> U
where
F: FnOnce() -> U,
{
s.remutex.raw.unlock_fair();
defer!(s.remutex.raw.lock());
f()
}
/// Temporarily yields the mutex to a waiting thread if there is one.
///
/// This method is functionally equivalent to calling `unlock_fair` followed
/// by `lock`, however it can be much more efficient in the case where there
/// are no waiting threads.
#[inline]
pub fn bump(s: &mut Self) {
s.remutex.raw.bump();
}
}
impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> Deref
for ReentrantMutexGuard<'a, R, G, T>
{
type Target = T;
#[inline]
fn deref(&self) -> &T {
unsafe { &*self.remutex.data.get() }
}
}
impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> Drop
for ReentrantMutexGuard<'a, R, G, T>
{
#[inline]
fn drop(&mut self) {
self.remutex.raw.unlock();
}
}
#[cfg(feature = "owning_ref")]
unsafe impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> StableAddress
for ReentrantMutexGuard<'a, R, G, T>
{}
/// An RAII mutex guard returned by `ReentrantMutexGuard::map`, which can point to a
/// subfield of the protected data.
///
/// The main difference between `MappedReentrantMutexGuard` and `ReentrantMutexGuard` is that the
/// former doesn't support temporarily unlocking and re-locking, since that
/// could introduce soundness issues if the locked object is modified by another
/// thread.
#[must_use]
pub struct MappedReentrantMutexGuard<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> {
raw: &'a RawReentrantMutex<R, G>,
data: *const T,
marker: PhantomData<&'a T>,
}
unsafe impl<'a, R: RawMutex + Sync + 'a, G: GetThreadId + Sync + 'a, T: ?Sized + Sync + 'a> Sync
for MappedReentrantMutexGuard<'a, R, G, T>
{}
impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a>
MappedReentrantMutexGuard<'a, R, G, T>
{
/// Makes a new `MappedReentrantMutexGuard` for a component of the locked data.
///
/// This operation cannot fail as the `ReentrantMutexGuard` passed
/// in already locked the mutex.
///
/// This is an associated function that needs to be
/// used as `ReentrantMutexGuard::map(...)`. A method would interfere with methods of
/// the same name on the contents of the locked data.
#[inline]
pub fn map<U: ?Sized, F>(s: Self, f: F) -> MappedReentrantMutexGuard<'a, R, G, U>
where
F: FnOnce(&T) -> &U,
{
let raw = s.raw;
let data = f(unsafe { &*s.data });
mem::forget(s);
MappedReentrantMutexGuard {
raw,
data,
marker: PhantomData,
}
}
}
impl<'a, R: RawMutexFair + 'a, G: GetThreadId + 'a, T: ?Sized + 'a>
MappedReentrantMutexGuard<'a, R, G, T>
{
/// Unlocks the mutex using a fair unlock protocol.
///
/// By default, mutexes are unfair and allow the current thread to re-lock
/// the mutex before another has the chance to acquire the lock, even if
/// that thread has been blocked on the mutex for a long time. This is the
/// default because it allows much higher throughput as it avoids forcing a
/// context switch on every mutex unlock. This can result in one thread
/// acquiring a mutex many more times than other threads.
///
/// However in some cases it can be beneficial to ensure fairness by forcing
/// the lock to pass on to a waiting thread if there is one. This is done by
/// using this method instead of dropping the `ReentrantMutexGuard` normally.
#[inline]
pub fn unlock_fair(s: Self) {
s.raw.unlock_fair();
mem::forget(s);
}
}
impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> Deref
for MappedReentrantMutexGuard<'a, R, G, T>
{
type Target = T;
#[inline]
fn deref(&self) -> &T {
unsafe { &*self.data }
}
}
impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> Drop
for MappedReentrantMutexGuard<'a, R, G, T>
{
#[inline]
fn drop(&mut self) {
self.raw.unlock();
}
}
#[cfg(feature = "owning_ref")]
unsafe impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> StableAddress
for MappedReentrantMutexGuard<'a, R, G, T>
{}