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|
use crate::cell::UnsafeCell;
use crate::mem;
use crate::mem::MaybeUninit;
use crate::sync::atomic::{AtomicU32, Ordering};
use crate::sys::cloudabi::abi;
use crate::sys::rwlock::{self, RWLock};
extern "C" {
#[thread_local]
static __pthread_thread_id: abi::tid;
}
// Implement Mutex using an RWLock. This doesn't introduce any
// performance overhead in this environment, as the operations would be
// implemented identically.
pub struct Mutex(RWLock);
pub unsafe fn raw(m: &Mutex) -> *mut AtomicU32 {
rwlock::raw(&m.0)
}
impl Mutex {
pub const fn new() -> Mutex {
Mutex(RWLock::new())
}
pub unsafe fn init(&mut self) {
// This function should normally reinitialize the mutex after
// moving it to a different memory address. This implementation
// does not require adjustments after moving.
}
pub unsafe fn try_lock(&self) -> bool {
self.0.try_write()
}
pub unsafe fn lock(&self) {
self.0.write()
}
pub unsafe fn unlock(&self) {
self.0.write_unlock()
}
pub unsafe fn destroy(&self) {
self.0.destroy()
}
}
pub struct ReentrantMutex {
lock: UnsafeCell<MaybeUninit<AtomicU32>>,
recursion: UnsafeCell<MaybeUninit<u32>>,
}
impl ReentrantMutex {
pub unsafe fn uninitialized() -> ReentrantMutex {
ReentrantMutex {
lock: UnsafeCell::new(MaybeUninit::uninit()),
recursion: UnsafeCell::new(MaybeUninit::uninit()),
}
}
pub unsafe fn init(&mut self) {
self.lock = UnsafeCell::new(MaybeUninit::new(AtomicU32::new(abi::LOCK_UNLOCKED.0)));
self.recursion = UnsafeCell::new(MaybeUninit::new(0));
}
pub unsafe fn try_lock(&self) -> bool {
// Attempt to acquire the lock.
let lock = (*self.lock.get()).as_mut_ptr();
let recursion = (*self.recursion.get()).as_mut_ptr();
if let Err(old) = (*lock).compare_exchange(
abi::LOCK_UNLOCKED.0,
__pthread_thread_id.0 | abi::LOCK_WRLOCKED.0,
Ordering::Acquire,
Ordering::Relaxed,
) {
// If we fail to acquire the lock, it may be the case
// that we've already acquired it and may need to recurse.
if old & !abi::LOCK_KERNEL_MANAGED.0 == __pthread_thread_id.0 | abi::LOCK_WRLOCKED.0 {
*recursion += 1;
true
} else {
false
}
} else {
// Success.
assert_eq!(*recursion, 0, "Mutex has invalid recursion count");
true
}
}
pub unsafe fn lock(&self) {
if !self.try_lock() {
// Call into the kernel to acquire a write lock.
let lock = self.lock.get();
let subscription = abi::subscription {
type_: abi::eventtype::LOCK_WRLOCK,
union: abi::subscription_union {
lock: abi::subscription_lock {
lock: lock as *mut abi::lock,
lock_scope: abi::scope::PRIVATE,
},
},
..mem::zeroed()
};
let mut event = MaybeUninit::<abi::event>::uninit();
let mut nevents = MaybeUninit::<usize>::uninit();
let ret = abi::poll(&subscription, event.as_mut_ptr(), 1, nevents.as_mut_ptr());
assert_eq!(ret, abi::errno::SUCCESS, "Failed to acquire mutex");
let event = event.assume_init();
assert_eq!(event.error, abi::errno::SUCCESS, "Failed to acquire mutex");
}
}
pub unsafe fn unlock(&self) {
let lock = (*self.lock.get()).as_mut_ptr();
let recursion = (*self.recursion.get()).as_mut_ptr();
assert_eq!(
(*lock).load(Ordering::Relaxed) & !abi::LOCK_KERNEL_MANAGED.0,
__pthread_thread_id.0 | abi::LOCK_WRLOCKED.0,
"This mutex is locked by a different thread"
);
if *recursion > 0 {
*recursion -= 1;
} else if !(*lock)
.compare_exchange(
__pthread_thread_id.0 | abi::LOCK_WRLOCKED.0,
abi::LOCK_UNLOCKED.0,
Ordering::Release,
Ordering::Relaxed,
)
.is_ok()
{
// Lock is managed by kernelspace. Call into the kernel
// to unblock waiting threads.
let ret = abi::lock_unlock(lock as *mut abi::lock, abi::scope::PRIVATE);
assert_eq!(ret, abi::errno::SUCCESS, "Failed to unlock a mutex");
}
}
pub unsafe fn destroy(&self) {
let lock = (*self.lock.get()).as_mut_ptr();
let recursion = (*self.recursion.get()).as_mut_ptr();
assert_eq!(
(*lock).load(Ordering::Relaxed),
abi::LOCK_UNLOCKED.0,
"Attempted to destroy locked mutex"
);
assert_eq!(*recursion, 0, "Recursion counter invalid");
}
}
|
