/
rwlock.rs
288 lines (262 loc) · 8.82 KB
/
rwlock.rs
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#[cfg(not(test))]
use crate::alloc::{self, Layout};
use crate::num::NonZeroUsize;
#[cfg(not(test))]
use crate::slice;
#[cfg(not(test))]
use crate::str;
use super::waitqueue::{
try_lock_or_false, NotifiedTcs, SpinMutex, SpinMutexGuard, WaitQueue, WaitVariable,
};
use crate::mem;
pub struct RWLock {
readers: SpinMutex<WaitVariable<Option<NonZeroUsize>>>,
writer: SpinMutex<WaitVariable<bool>>,
}
// Below is to check at compile time, that RWLock has size of 128 bytes.
#[allow(dead_code)]
unsafe fn rw_lock_size_assert(r: RWLock) {
mem::transmute::<RWLock, [u8; 128]>(r);
}
impl RWLock {
pub const fn new() -> RWLock {
RWLock {
readers: SpinMutex::new(WaitVariable::new(None)),
writer: SpinMutex::new(WaitVariable::new(false)),
}
}
#[inline]
pub unsafe fn read(&self) {
let mut rguard = self.readers.lock();
let wguard = self.writer.lock();
if *wguard.lock_var() || !wguard.queue_empty() {
// Another thread has or is waiting for the write lock, wait
drop(wguard);
WaitQueue::wait(rguard);
// Another thread has passed the lock to us
} else {
// No waiting writers, acquire the read lock
*rguard.lock_var_mut() =
NonZeroUsize::new(rguard.lock_var().map_or(0, |n| n.get()) + 1);
}
}
#[inline]
pub unsafe fn try_read(&self) -> bool {
let mut rguard = try_lock_or_false!(self.readers);
let wguard = try_lock_or_false!(self.writer);
if *wguard.lock_var() || !wguard.queue_empty() {
// Another thread has or is waiting for the write lock
false
} else {
// No waiting writers, acquire the read lock
*rguard.lock_var_mut() =
NonZeroUsize::new(rguard.lock_var().map_or(0, |n| n.get()) + 1);
true
}
}
#[inline]
pub unsafe fn write(&self) {
let rguard = self.readers.lock();
let mut wguard = self.writer.lock();
if *wguard.lock_var() || rguard.lock_var().is_some() {
// Another thread has the lock, wait
drop(rguard);
WaitQueue::wait(wguard);
// Another thread has passed the lock to us
} else {
// We are just now obtaining the lock
*wguard.lock_var_mut() = true;
}
}
#[inline]
pub unsafe fn try_write(&self) -> bool {
let rguard = try_lock_or_false!(self.readers);
let mut wguard = try_lock_or_false!(self.writer);
if *wguard.lock_var() || rguard.lock_var().is_some() {
// Another thread has the lock
false
} else {
// We are just now obtaining the lock
*wguard.lock_var_mut() = true;
true
}
}
#[inline]
unsafe fn __read_unlock(
&self,
mut rguard: SpinMutexGuard<'_, WaitVariable<Option<NonZeroUsize>>>,
wguard: SpinMutexGuard<'_, WaitVariable<bool>>,
) {
*rguard.lock_var_mut() = NonZeroUsize::new(rguard.lock_var().unwrap().get() - 1);
if rguard.lock_var().is_some() {
// There are other active readers
} else {
if let Ok(mut wguard) = WaitQueue::notify_one(wguard) {
// A writer was waiting, pass the lock
*wguard.lock_var_mut() = true;
} else {
// No writers were waiting, the lock is released
assert!(rguard.queue_empty());
}
}
}
#[inline]
pub unsafe fn read_unlock(&self) {
let rguard = self.readers.lock();
let wguard = self.writer.lock();
self.__read_unlock(rguard, wguard);
}
#[inline]
unsafe fn __write_unlock(
&self,
rguard: SpinMutexGuard<'_, WaitVariable<Option<NonZeroUsize>>>,
wguard: SpinMutexGuard<'_, WaitVariable<bool>>,
) {
if let Err(mut wguard) = WaitQueue::notify_one(wguard) {
// No writers waiting, release the write lock
*wguard.lock_var_mut() = false;
if let Ok(mut rguard) = WaitQueue::notify_all(rguard) {
// One or more readers were waiting, pass the lock to them
if let NotifiedTcs::All { count } = rguard.notified_tcs() {
*rguard.lock_var_mut() = Some(count)
} else {
unreachable!() // called notify_all
}
} else {
// No readers waiting, the lock is released
}
} else {
// There was a thread waiting for write, just pass the lock
}
}
#[inline]
pub unsafe fn write_unlock(&self) {
let rguard = self.readers.lock();
let wguard = self.writer.lock();
self.__write_unlock(rguard, wguard);
}
// only used by __rust_rwlock_unlock below
#[inline]
#[cfg_attr(test, allow(dead_code))]
unsafe fn unlock(&self) {
let rguard = self.readers.lock();
let wguard = self.writer.lock();
if *wguard.lock_var() == true {
self.__write_unlock(rguard, wguard);
} else {
self.__read_unlock(rguard, wguard);
}
}
#[inline]
pub unsafe fn destroy(&self) {}
}
#[cfg(not(test))]
const EINVAL: i32 = 22;
// used by libunwind port
#[cfg(not(test))]
#[no_mangle]
pub unsafe extern "C" fn __rust_rwlock_rdlock(p: *mut RWLock) -> i32 {
if p.is_null() {
return EINVAL;
}
(*p).read();
return 0;
}
#[cfg(not(test))]
#[no_mangle]
pub unsafe extern "C" fn __rust_rwlock_wrlock(p: *mut RWLock) -> i32 {
if p.is_null() {
return EINVAL;
}
(*p).write();
return 0;
}
#[cfg(not(test))]
#[no_mangle]
pub unsafe extern "C" fn __rust_rwlock_unlock(p: *mut RWLock) -> i32 {
if p.is_null() {
return EINVAL;
}
(*p).unlock();
return 0;
}
// the following functions are also used by the libunwind port. They're
// included here to make sure parallel codegen and LTO don't mess things up.
#[cfg(not(test))]
#[no_mangle]
pub unsafe extern "C" fn __rust_print_err(m: *mut u8, s: i32) {
if s < 0 {
return;
}
let buf = slice::from_raw_parts(m as *const u8, s as _);
if let Ok(s) = str::from_utf8(&buf[..buf.iter().position(|&b| b == 0).unwrap_or(buf.len())]) {
eprint!("{}", s);
}
}
#[cfg(not(test))]
#[no_mangle]
// NB. used by both libunwind and libpanic_abort
pub unsafe extern "C" fn __rust_abort() {
crate::sys::abort_internal();
}
#[cfg(not(test))]
#[no_mangle]
pub unsafe extern "C" fn __rust_c_alloc(size: usize, align: usize) -> *mut u8 {
alloc::alloc(Layout::from_size_align_unchecked(size, align))
}
#[cfg(not(test))]
#[no_mangle]
pub unsafe extern "C" fn __rust_c_dealloc(ptr: *mut u8, size: usize, align: usize) {
alloc::dealloc(ptr, Layout::from_size_align_unchecked(size, align))
}
#[cfg(test)]
mod tests {
use super::*;
use core::array::FixedSizeArray;
use crate::mem::{self, MaybeUninit};
// Verify that the bytes of initialized RWLock are the same as in
// libunwind. If they change, `src/UnwindRustSgx.h` in libunwind needs to
// be changed too.
#[test]
fn test_c_rwlock_initializer() {
const RWLOCK_INIT: &[u8] = &[
0x1, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x3, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x1, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x3, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
];
#[inline(never)]
fn zero_stack() {
test::black_box(MaybeUninit::<[RWLock; 16]>::zeroed());
}
#[inline(never)]
unsafe fn rwlock_new(init: &mut MaybeUninit<RWLock>) {
init.write(RWLock::new());
}
unsafe {
// try hard to make sure that the padding/unused bytes in RWLock
// get initialized as 0. If the assertion below fails, that might
// just be an issue with the test code and not with the value of
// RWLOCK_INIT.
zero_stack();
let mut init = MaybeUninit::<RWLock>::zeroed();
rwlock_new(&mut init);
assert_eq!(
mem::transmute::<_, [u8; 128]>(init.assume_init()).as_slice(),
RWLOCK_INIT
)
};
}
}