新增了rust实现的信号量 (#181)

* 新增了rust实现的信号量

---------

Co-authored-by: longjin <longjin@RinGoTek.cn>
This commit is contained in:
Gou Ngai 2023-03-04 17:47:17 +08:00 committed by GitHub
parent 83b9512c1c
commit f1284c3571
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@ -9,3 +9,5 @@ pub mod lockref;
pub mod mutex;
pub mod semaphore;
pub mod wait_queue;
pub mod rwlock;

447
kernel/src/libs/rwlock.rs Normal file
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@ -0,0 +1,447 @@
#![allow(dead_code)]
use core::{
cell::UnsafeCell,
hint::spin_loop,
mem::{self, ManuallyDrop},
ops::{Deref, DerefMut},
sync::atomic::{AtomicU32, Ordering},
};
use crate::include::bindings::bindings::EOVERFLOW;
///RwLock读写锁
/// @brief READER位占据从右往左数第三个比特位
const READER: u32 = 1 << 2;
/// @brief UPGRADED位占据从右到左数第二个比特位
const UPGRADED: u32 = 1 << 1;
/// @brief WRITER位占据最右边的比特位
const WRITER: u32 = 1;
const READER_BIT: u32 = 2;
/// @brief 读写锁的基本数据结构
/// @param lock 32位原子变量,最右边的两位从左到右分别是UPGRADED,WRITER (标志位)
/// 剩下的bit位存储READER数量(除了MSB)
/// 对于标志位,0代表无, 1代表有
/// 对于剩下的比特位表征READER的数量的多少
/// lock的MSB必须为0,否则溢出
#[derive(Debug)]
pub struct RwLock<T> {
lock: AtomicU32,
data: UnsafeCell<T>,
}
/// @brief READER守卫的数据结构
/// @param lock 是对RwLock的lock属性值的只读引用
pub struct RwLockReadGuard<'a, T: 'a> {
data: *const T,
lock: &'a AtomicU32,
}
/// @brief UPGRADED是介于READER和WRITER之间的一种锁,它可以升级为WRITER,
/// UPGRADED守卫的数据结构,注册UPGRADED锁只需要查看UPGRADED和WRITER的比特位
/// 但是当UPGRADED守卫注册后,不允许有新的读者锁注册
/// @param inner 是对RwLock数据结构的只读引用
pub struct RwLockUpgradableGuard<'a, T: 'a> {
data: *const T,
inner: &'a RwLock<T>,
}
/// @brief WRITER守卫的数据结构
/// @param data RwLock的data的可变引用
/// @param inner 是对RwLock数据结构的只读引用
pub struct RwLockWriteGuard<'a, T: 'a> {
data: *mut T,
inner: &'a RwLock<T>,
}
unsafe impl<T: Send> Send for RwLock<T> {}
unsafe impl<T: Send + Sync> Sync for RwLock<T> {}
/// @brief RwLock的API
impl<T> RwLock<T> {
#[inline]
/// @brief RwLock的初始化
pub const fn new(data: T) -> Self {
return RwLock {
lock: AtomicU32::new(0),
data: UnsafeCell::new(data),
};
}
#[allow(dead_code)]
#[inline]
/// @brief 将读写锁的皮扒掉,返回内在的data,返回的是一个真身而非引用
pub fn into_inner(self) -> T {
let RwLock { data, .. } = self;
return data.into_inner();
}
#[allow(dead_code)]
#[inline]
/// @brief 返回data的raw pointer,
/// unsafe
pub fn as_mut_ptr(&self) -> *mut T {
return self.data.get();
}
#[allow(dead_code)]
#[inline]
/// @brief 获取实时的读者数并尝试加1,如果增加值成功则返回增加1后的读者数,否则panic
fn current_reader(&self) -> Result<u32, i32> {
const MAX_READERS: u32 = core::u32::MAX >> READER_BIT >> 1; //右移3位
let value = self.lock.fetch_add(READER, Ordering::Acquire);
//value二进制形式的MSB不能为1, 否则导致溢出
if value > MAX_READERS << READER_BIT {
self.lock.fetch_sub(READER, Ordering::Release);
//panic!("Too many lock readers, cannot safely proceed");
return Err(-(EOVERFLOW as i32));
} else {
return Ok(value);
}
}
#[allow(dead_code)]
#[inline]
/// @brief 尝试获取READER守卫
pub fn try_read(&self) -> Option<RwLockReadGuard<T>> {
let reader_value = self.current_reader();
//得到自增后的reader_value, 包括了尝试获得READER守卫的进程
let value;
if reader_value.is_err() {
return None; //获取失败
} else {
value = reader_value.unwrap();
}
//判断有没有writer和upgrader
//注意, 若upgrader存在,已经存在的读者继续占有锁,但新读者不允许获得锁
if value & (WRITER | UPGRADED) != 0 {
self.lock.fetch_sub(READER, Ordering::Release);
return None;
} else {
return Some(RwLockReadGuard {
data: unsafe { &*self.data.get() },
lock: &self.lock,
});
}
}
#[allow(dead_code)]
#[inline]
/// @brief 获得READER的守卫
pub fn read(&self) -> RwLockReadGuard<T> {
loop {
match self.try_read() {
Some(guard) => return guard,
None => spin_loop(),
}
} //忙等待
}
#[allow(dead_code)]
#[inline]
/// @brief 获取读者+UPGRADER的数量, 不能保证能否获得同步值
pub fn reader_count(&self) -> u32 {
let state = self.lock.load(Ordering::Relaxed);
return state / READER + (state & UPGRADED) / UPGRADED;
}
#[allow(dead_code)]
#[inline]
/// @brief 获取写者数量,不能保证能否获得同步值
pub fn writer_count(&self) -> u32 {
return (self.lock.load(Ordering::Relaxed) & WRITER) / WRITER;
}
#[cfg(target_arch = "x86_64")]
#[allow(dead_code)]
#[inline]
/// @brief 尝试获得WRITER守卫
pub fn try_write(&self) -> Option<RwLockWriteGuard<T>> {
let res:bool = self
.lock
.compare_exchange(0, WRITER, Ordering::Acquire, Ordering::Relaxed).is_ok();
//只有lock大小为0的时候能获得写者守卫
if res {
return Some(RwLockWriteGuard {
data: unsafe { &mut *self.data.get() },
inner: self,
});
} else {
return None;
}
} //当架构为arm时,有些代码需要作出调整compare_exchange=>compare_exchange_weak
#[allow(dead_code)]
#[inline]
/// @brief 获得WRITER守卫
pub fn write(&self) -> RwLockWriteGuard<T> {
loop {
match self.try_write() {
Some(guard) => return guard,
None => spin_loop(),
}
}
}
#[allow(dead_code)]
#[inline]
/// @brief 尝试获得UPGRADER守卫
pub fn try_upgradeable_read(&self) -> Option<RwLockUpgradableGuard<T>> {
//获得UPGRADER守卫不需要查看读者位
//如果获得读者锁失败,不需要撤回fetch_or的原子操作
if self.lock.fetch_or(UPGRADED, Ordering::Acquire) & (WRITER | UPGRADED) == 0 {
return Some(RwLockUpgradableGuard {
inner: self,
data: unsafe { &mut *self.data.get() },
});
} else {
return None;
}
}
#[allow(dead_code)]
#[inline]
/// @brief 获得UPGRADER守卫
pub fn upgradeable_read(&self) -> RwLockUpgradableGuard<T> {
loop {
match self.try_upgradeable_read() {
Some(guard) => return guard,
None => spin_loop(),
}
}
}
#[allow(dead_code)]
#[inline]
//extremely unsafe behavior
/// @brief 强制减少READER数
pub unsafe fn force_read_decrement(&self) {
debug_assert!(self.lock.load(Ordering::Relaxed) & !WRITER > 0);
self.lock.fetch_sub(READER, Ordering::Release);
}
#[allow(dead_code)]
#[inline]
//extremely unsafe behavior
/// @brief 强制给WRITER解锁
pub unsafe fn force_write_unlock(&self) {
debug_assert_eq!(self.lock.load(Ordering::Relaxed) & !(WRITER | UPGRADED), 0);
self.lock.fetch_and(!(WRITER | UPGRADED), Ordering::Release);
}
#[allow(dead_code)]
pub fn get_mut(&mut self) -> &mut T {
unsafe { &mut *self.data.get() }
}
}
impl<T: Default> Default for RwLock<T> {
fn default() -> Self {
Self::new(Default::default())
}
}
/// @brief 由原有的值创建新的锁
impl<T> From<T> for RwLock<T> {
fn from(data: T) -> Self {
return Self::new(data);
}
}
impl<'rwlock, T> RwLockReadGuard<'rwlock, T> {
#[allow(dead_code)]
#[inline]
/// @brief 释放守卫,获得保护的值的不可变引用
pub fn leak(this: Self) -> &'rwlock T {
let Self { data, .. } = this;
return unsafe { &*data };
}
}
impl<'rwlock, T> RwLockUpgradableGuard<'rwlock, T> {
#[allow(dead_code)]
#[inline]
/// @brief 尝试将UPGRADER守卫升级为WRITER守卫
pub fn try_upgrade(self) -> Result<RwLockWriteGuard<'rwlock, T>, Self> {
let res = self.inner.lock.compare_exchange(
UPGRADED,
WRITER,
Ordering::Acquire,
Ordering::Relaxed,
);
//当且仅当只有UPGRADED守卫时可以升级
if res.is_ok() {
let inner = self.inner;
mem::forget(self);
Ok(RwLockWriteGuard {
data: unsafe { &mut *inner.data.get() },
inner,
})
} else {
Err(self)
}
}
#[allow(dead_code)]
#[inline]
/// @brief 将upgrader升级成writer
pub fn upgrade(mut self) -> RwLockWriteGuard<'rwlock, T> {
loop {
self = match self.try_upgrade() {
Ok(writeguard) => return writeguard,
Err(former) => former,
};
spin_loop();
}
}
#[allow(dead_code)]
#[inline]
/// @brief UPGRADER降级为READER
pub fn downgrade(self) -> RwLockReadGuard<'rwlock, T> {
while self.inner.current_reader().is_err() {
spin_loop();
}
let inner: &RwLock<T> = self.inner;
//自动移去UPGRADED比特位
mem::drop(self);
RwLockReadGuard {
data: unsafe { &*inner.data.get() },
lock: &inner.lock,
}
}
#[allow(dead_code)]
#[inline]
/// @brief 返回内部数据的引用,消除锁
pub fn leak(this: Self) -> &'rwlock T {
let this = ManuallyDrop::new(this);
unsafe { &*this.data }
}
}
impl<'rwlock, T> RwLockWriteGuard<'rwlock, T> {
#[allow(dead_code)]
#[inline]
/// @brief 返回内部数据的引用,消除锁
pub fn leak(this: Self) -> &'rwlock T {
let this = ManuallyDrop::new(this);
return unsafe { &*this.data };
}
#[allow(dead_code)]
#[inline]
/// @brief 将WRITER降级为READER
pub fn downgrade(self) -> RwLockReadGuard<'rwlock, T> {
while self.inner.current_reader().is_err() {
spin_loop();
}
//本质上来说绝对保证没有任何读者
let inner = self.inner;
mem::drop(self);
return RwLockReadGuard {
data: unsafe { &*inner.data.get() },
lock: &inner.lock,
};
}
#[allow(dead_code)]
#[inline]
/// @brief 将WRITER降级为UPGRADER
pub fn downgrade_to_upgradeable(self) -> RwLockUpgradableGuard<'rwlock, T> {
debug_assert_eq!(
self.inner.lock.load(Ordering::Acquire) & (WRITER | UPGRADED),
WRITER
);
self.inner.lock.store(UPGRADED, Ordering::Release);
let inner = self.inner;
mem::forget(self);
return RwLockUpgradableGuard {
inner,
data: unsafe { &*inner.data.get() },
};
}
}
impl<'rwlock, T> Deref for RwLockReadGuard<'rwlock, T> {
type Target = T;
fn deref(&self) -> &Self::Target {
return unsafe { &*self.data };
}
}
impl<'rwlock, T> Deref for RwLockUpgradableGuard<'rwlock, T> {
type Target = T;
fn deref(&self) -> &Self::Target {
return unsafe { &*self.data };
}
}
impl<'rwlock, T> Deref for RwLockWriteGuard<'rwlock, T> {
type Target = T;
fn deref(&self) -> &Self::Target {
return unsafe { &*self.data };
}
}
impl<'rwlock, T> DerefMut for RwLockWriteGuard<'rwlock, T> {
fn deref_mut(&mut self) -> &mut Self::Target {
return unsafe { &mut *self.data };
}
}
impl<'rwlock, T> Drop for RwLockReadGuard<'rwlock, T> {
fn drop(&mut self) {
debug_assert!(self.lock.load(Ordering::Relaxed) & !(WRITER | UPGRADED) > 0);
self.lock.fetch_sub(READER, Ordering::Release);
}
}
impl<'rwlock, T> Drop for RwLockUpgradableGuard<'rwlock, T> {
fn drop(&mut self) {
debug_assert_eq!(
self.inner.lock.load(Ordering::Relaxed) & (WRITER | UPGRADED),
UPGRADED
);
self.inner.lock.fetch_sub(UPGRADED, Ordering::AcqRel);
//这里为啥要AcqRel? Release应该就行了?
}
}
impl<'rwlock, T> Drop for RwLockWriteGuard<'rwlock, T> {
fn drop(&mut self) {
debug_assert_eq!(self.inner.lock.load(Ordering::Relaxed) & WRITER, WRITER);
self.inner
.lock
.fetch_and(!(WRITER | UPGRADED), Ordering::Release);
}
}