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Get rid of UnsafeCell in cloudabi rwlock.

This commit is contained in:
Mara Bos 2020-10-07 18:17:16 +02:00
parent 0f26578f2e
commit 41066beb4d
1 changed files with 21 additions and 24 deletions
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45
library/std/src/sys/cloudabi/rwlock.rs
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@ -1,4 +1,3 @@
use crate::cell::UnsafeCell;
use crate::mem;
use crate::mem::MaybeUninit;
use crate::sync::atomic::{AtomicU32, Ordering};
@ -13,28 +12,25 @@ extern "C" {
static mut RDLOCKS_ACQUIRED: u32 = 0;
pub struct RWLock {
lock: UnsafeCell<AtomicU32>,
lock: AtomicU32,
}
pub unsafe fn raw(r: &RWLock) -> *mut AtomicU32 {
r.lock.get()
&r.lock as *const AtomicU32 as *mut AtomicU32
}
unsafe impl Send for RWLock {}
unsafe impl Sync for RWLock {}
const NEW: RWLock = RWLock { lock: UnsafeCell::new(AtomicU32::new(abi::LOCK_UNLOCKED.0)) };
impl RWLock {
pub const fn new() -> RWLock {
NEW
RWLock { lock: AtomicU32::new(abi::LOCK_UNLOCKED.0) }
}
pub unsafe fn try_read(&self) -> bool {
let lock = self.lock.get();
let mut old = abi::LOCK_UNLOCKED.0;
while let Err(cur) =
(*lock).compare_exchange_weak(old, old + 1, Ordering::Acquire, Ordering::Relaxed)
self.lock.compare_exchange_weak(old, old + 1, Ordering::Acquire, Ordering::Relaxed)
{
if (cur & abi::LOCK_WRLOCKED.0) != 0 {
// Another thread already has a write lock.
@ -61,12 +57,11 @@ impl RWLock {
pub unsafe fn read(&self) {
if !self.try_read() {
// Call into the kernel to acquire a read lock.
let lock = self.lock.get();
let subscription = abi::subscription {
type_: abi::eventtype::LOCK_RDLOCK,
union: abi::subscription_union {
lock: abi::subscription_lock {
lock: lock as *mut abi::lock,
lock: &self.lock as *const AtomicU32 as *mut abi::lock,
lock_scope: abi::scope::PRIVATE,
},
},
@ -96,11 +91,10 @@ impl RWLock {
assert!(RDLOCKS_ACQUIRED > 0, "Bad lock count");
let mut old = 1;
loop {
let lock = self.lock.get();
if old == 1 | abi::LOCK_KERNEL_MANAGED.0 {
// Last read lock while threads are waiting. Attempt to upgrade
// to a write lock before calling into the kernel to unlock.
if let Err(cur) = (*lock).compare_exchange_weak(
if let Err(cur) = self.lock.compare_exchange_weak(
old,
__pthread_thread_id.0 | abi::LOCK_WRLOCKED.0 | abi::LOCK_KERNEL_MANAGED.0,
Ordering::Acquire,
@ -109,7 +103,10 @@ impl RWLock {
old = cur;
} else {
// Call into the kernel to unlock.
let ret = abi::lock_unlock(lock as *mut abi::lock, abi::scope::PRIVATE);
let ret = abi::lock_unlock(
&self.lock as *const AtomicU32 as *mut abi::lock,
abi::scope::PRIVATE,
);
assert_eq!(ret, abi::errno::SUCCESS, "Failed to write unlock a rwlock");
break;
}
@ -122,7 +119,7 @@ impl RWLock {
0,
"Attempted to read-unlock a write-locked rwlock"
);
if let Err(cur) = (*lock).compare_exchange_weak(
if let Err(cur) = self.lock.compare_exchange_weak(
old,
old - 1,
Ordering::Acquire,
@ -140,8 +137,7 @@ impl RWLock {
pub unsafe fn try_write(&self) -> bool {
// Attempt to acquire the lock.
let lock = self.lock.get();
if let Err(old) = (*lock).compare_exchange(
if let Err(old) = self.lock.compare_exchange(
abi::LOCK_UNLOCKED.0,
__pthread_thread_id.0 | abi::LOCK_WRLOCKED.0,
Ordering::Acquire,
@ -163,12 +159,11 @@ impl RWLock {
pub unsafe fn write(&self) {
if !self.try_write() {
// 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: &self.lock as *const AtomicU32 as *mut abi::lock,
lock_scope: abi::scope::PRIVATE,
},
},
@ -184,14 +179,14 @@ impl RWLock {
}
pub unsafe fn write_unlock(&self) {
let lock = self.lock.get();
assert_eq!(
(*lock).load(Ordering::Relaxed) & !abi::LOCK_KERNEL_MANAGED.0,
self.lock.load(Ordering::Relaxed) & !abi::LOCK_KERNEL_MANAGED.0,
__pthread_thread_id.0 | abi::LOCK_WRLOCKED.0,
"This rwlock is not write-locked by this thread"
);
if !(*lock)
if !self
.lock
.compare_exchange(
__pthread_thread_id.0 | abi::LOCK_WRLOCKED.0,
abi::LOCK_UNLOCKED.0,
@ -202,15 +197,17 @@ impl RWLock {
{
// 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);
let ret = abi::lock_unlock(
&self.lock as *const AtomicU32 as *mut abi::lock,
abi::scope::PRIVATE,
);
assert_eq!(ret, abi::errno::SUCCESS, "Failed to write unlock a rwlock");
}
}
pub unsafe fn destroy(&self) {
let lock = self.lock.get();
assert_eq!(
(*lock).load(Ordering::Relaxed),
self.lock.load(Ordering::Relaxed),
abi::LOCK_UNLOCKED.0,
"Attempted to destroy locked rwlock"
);