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use crate::cell::{Cell, UnsafeCell};
use crate::mem::{self, MaybeUninit};
use crate::sync::atomic::{AtomicUsize, Ordering};
use crate::sys::c;
pub struct Mutex {
lock: AtomicUsize,
}
pub type MovableMutex = Mutex;
unsafe impl Send for Mutex {}
unsafe impl Sync for Mutex {}
struct Inner {
remutex: ReentrantMutex,
held: Cell<bool>,
}
#[derive(Clone, Copy)]
enum Kind {
SRWLock,
CriticalSection,
}
#[inline]
pub unsafe fn raw(m: &Mutex) -> c::PSRWLOCK {
debug_assert!(mem::size_of::<c::SRWLOCK>() <= mem::size_of_val(&m.lock));
&m.lock as *const _ as *mut _
}
impl Mutex {
pub const fn new() -> Mutex {
Mutex {
lock: AtomicUsize::new(0),
}
}
#[inline]
pub unsafe fn init(&mut self) {}
pub unsafe fn lock(&self) {
match kind() {
Kind::SRWLock => c::AcquireSRWLockExclusive(raw(self)),
Kind::CriticalSection => {
let inner = &*self.inner();
inner.remutex.lock();
if inner.held.replace(true) {
inner.remutex.unlock();
panic!("cannot recursively lock a mutex");
}
}
}
}
pub unsafe fn try_lock(&self) -> bool {
match kind() {
Kind::SRWLock => c::TryAcquireSRWLockExclusive(raw(self)) != 0,
Kind::CriticalSection => {
let inner = &*self.inner();
if !inner.remutex.try_lock() {
false
} else if inner.held.replace(true) {
inner.remutex.unlock();
false
} else {
true
}
}
}
}
pub unsafe fn unlock(&self) {
match kind() {
Kind::SRWLock => c::ReleaseSRWLockExclusive(raw(self)),
Kind::CriticalSection => {
let inner = &*(self.lock.load(Ordering::SeqCst) as *const Inner);
inner.held.set(false);
inner.remutex.unlock();
}
}
}
pub unsafe fn destroy(&self) {
match kind() {
Kind::SRWLock => {}
Kind::CriticalSection => match self.lock.load(Ordering::SeqCst) {
0 => {}
n => Box::from_raw(n as *mut Inner).remutex.destroy(),
},
}
}
unsafe fn inner(&self) -> *const Inner {
match self.lock.load(Ordering::SeqCst) {
0 => {}
n => return n as *const _,
}
let inner = box Inner { remutex: ReentrantMutex::uninitialized(), held: Cell::new(false) };
inner.remutex.init();
let inner = Box::into_raw(inner);
match self.lock.compare_and_swap(0, inner as usize, Ordering::SeqCst) {
0 => inner,
n => {
Box::from_raw(inner).remutex.destroy();
n as *const _
}
}
}
}
fn kind() -> Kind {
if c::AcquireSRWLockExclusive::is_available() { Kind::SRWLock } else { Kind::CriticalSection }
}
pub struct ReentrantMutex {
inner: MaybeUninit<UnsafeCell<c::CRITICAL_SECTION>>,
}
unsafe impl Send for ReentrantMutex {}
unsafe impl Sync for ReentrantMutex {}
impl ReentrantMutex {
pub const fn uninitialized() -> ReentrantMutex {
ReentrantMutex { inner: MaybeUninit::uninit() }
}
pub unsafe fn init(&self) {
c::InitializeCriticalSection(UnsafeCell::raw_get(self.inner.as_ptr()));
}
pub unsafe fn lock(&self) {
c::EnterCriticalSection(UnsafeCell::raw_get(self.inner.as_ptr()));
}
#[inline]
pub unsafe fn try_lock(&self) -> bool {
c::TryEnterCriticalSection(UnsafeCell::raw_get(self.inner.as_ptr())) != 0
}
pub unsafe fn unlock(&self) {
c::LeaveCriticalSection(UnsafeCell::raw_get(self.inner.as_ptr()));
}
pub unsafe fn destroy(&self) {
c::DeleteCriticalSection(UnsafeCell::raw_get(self.inner.as_ptr()));
}
}