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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;
use crate::mem::MaybeUninit; use crate::mem::MaybeUninit;
use crate::sync::atomic::{AtomicU32, Ordering}; use crate::sync::atomic::{AtomicU32, Ordering};
@ -13,28 +12,25 @@ extern "C" {
static mut RDLOCKS_ACQUIRED: u32 = 0; static mut RDLOCKS_ACQUIRED: u32 = 0;
pub struct RWLock { pub struct RWLock {
lock: UnsafeCell<AtomicU32>, lock: AtomicU32,
} }
pub unsafe fn raw(r: &RWLock) -> *mut 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 Send for RWLock {}
unsafe impl Sync for RWLock {} unsafe impl Sync for RWLock {}
const NEW: RWLock = RWLock { lock: UnsafeCell::new(AtomicU32::new(abi::LOCK_UNLOCKED.0)) };
impl RWLock { impl RWLock {
pub const fn new() -> RWLock { pub const fn new() -> RWLock {
NEW RWLock { lock: AtomicU32::new(abi::LOCK_UNLOCKED.0) }
} }
pub unsafe fn try_read(&self) -> bool { pub unsafe fn try_read(&self) -> bool {
let lock = self.lock.get();
let mut old = abi::LOCK_UNLOCKED.0; let mut old = abi::LOCK_UNLOCKED.0;
while let Err(cur) = 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 { if (cur & abi::LOCK_WRLOCKED.0) != 0 {
// Another thread already has a write lock. // Another thread already has a write lock.
@ -61,12 +57,11 @@ impl RWLock {
pub unsafe fn read(&self) { pub unsafe fn read(&self) {
if !self.try_read() { if !self.try_read() {
// Call into the kernel to acquire a read lock. // Call into the kernel to acquire a read lock.
let lock = self.lock.get();
let subscription = abi::subscription { let subscription = abi::subscription {
type_: abi::eventtype::LOCK_RDLOCK, type_: abi::eventtype::LOCK_RDLOCK,
union: abi::subscription_union { union: abi::subscription_union {
lock: abi::subscription_lock { 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, lock_scope: abi::scope::PRIVATE,
}, },
}, },
@ -96,11 +91,10 @@ impl RWLock {
assert!(RDLOCKS_ACQUIRED > 0, "Bad lock count"); assert!(RDLOCKS_ACQUIRED > 0, "Bad lock count");
let mut old = 1; let mut old = 1;
loop { loop {
let lock = self.lock.get();
if old == 1 | abi::LOCK_KERNEL_MANAGED.0 { if old == 1 | abi::LOCK_KERNEL_MANAGED.0 {
// Last read lock while threads are waiting. Attempt to upgrade // Last read lock while threads are waiting. Attempt to upgrade
// to a write lock before calling into the kernel to unlock. // 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, old,
__pthread_thread_id.0 | abi::LOCK_WRLOCKED.0 | abi::LOCK_KERNEL_MANAGED.0, __pthread_thread_id.0 | abi::LOCK_WRLOCKED.0 | abi::LOCK_KERNEL_MANAGED.0,
Ordering::Acquire, Ordering::Acquire,
@ -109,7 +103,10 @@ impl RWLock {
old = cur; old = cur;
} else { } else {
// Call into the kernel to unlock. // 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"); assert_eq!(ret, abi::errno::SUCCESS, "Failed to write unlock a rwlock");
break; break;
} }
@ -122,7 +119,7 @@ impl RWLock {
0, 0,
"Attempted to read-unlock a write-locked rwlock" "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,
old - 1, old - 1,
Ordering::Acquire, Ordering::Acquire,
@ -140,8 +137,7 @@ impl RWLock {
pub unsafe fn try_write(&self) -> bool { pub unsafe fn try_write(&self) -> bool {
// Attempt to acquire the lock. // Attempt to acquire the lock.
let lock = self.lock.get(); if let Err(old) = self.lock.compare_exchange(
if let Err(old) = (*lock).compare_exchange(
abi::LOCK_UNLOCKED.0, abi::LOCK_UNLOCKED.0,
__pthread_thread_id.0 | abi::LOCK_WRLOCKED.0, __pthread_thread_id.0 | abi::LOCK_WRLOCKED.0,
Ordering::Acquire, Ordering::Acquire,
@ -163,12 +159,11 @@ impl RWLock {
pub unsafe fn write(&self) { pub unsafe fn write(&self) {
if !self.try_write() { if !self.try_write() {
// Call into the kernel to acquire a write lock. // Call into the kernel to acquire a write lock.
let lock = self.lock.get();
let subscription = abi::subscription { let subscription = abi::subscription {
type_: abi::eventtype::LOCK_WRLOCK, type_: abi::eventtype::LOCK_WRLOCK,
union: abi::subscription_union { union: abi::subscription_union {
lock: abi::subscription_lock { 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, lock_scope: abi::scope::PRIVATE,
}, },
}, },
@ -184,14 +179,14 @@ impl RWLock {
} }
pub unsafe fn write_unlock(&self) { pub unsafe fn write_unlock(&self) {
let lock = self.lock.get();
assert_eq!( 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, __pthread_thread_id.0 | abi::LOCK_WRLOCKED.0,
"This rwlock is not write-locked by this thread" "This rwlock is not write-locked by this thread"
); );
if !(*lock) if !self
.lock
.compare_exchange( .compare_exchange(
__pthread_thread_id.0 | abi::LOCK_WRLOCKED.0, __pthread_thread_id.0 | abi::LOCK_WRLOCKED.0,
abi::LOCK_UNLOCKED.0, abi::LOCK_UNLOCKED.0,
@ -202,15 +197,17 @@ impl RWLock {
{ {
// Lock is managed by kernelspace. Call into the kernel // Lock is managed by kernelspace. Call into the kernel
// to unblock waiting threads. // 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"); assert_eq!(ret, abi::errno::SUCCESS, "Failed to write unlock a rwlock");
} }
} }
pub unsafe fn destroy(&self) { pub unsafe fn destroy(&self) {
let lock = self.lock.get();
assert_eq!( assert_eq!(
(*lock).load(Ordering::Relaxed), self.lock.load(Ordering::Relaxed),
abi::LOCK_UNLOCKED.0, abi::LOCK_UNLOCKED.0,
"Attempted to destroy locked rwlock" "Attempted to destroy locked rwlock"
); );