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// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use cell::UnsafeCell;
use super::mutex::Mutex;
use super::condvar::Condvar;
// A simple read-preferring RWLock implementation that I found on wikipedia <.<
pub struct RWLock {
mutex: Mutex,
cvar: Condvar,
reader_count: UnsafeCell<u32>,
writer_active: UnsafeCell<bool>,
}
unsafe impl Send for RWLock {}
unsafe impl Sync for RWLock {}
impl RWLock {
pub const fn new() -> RWLock {
RWLock {
mutex: Mutex::new(),
cvar: Condvar::new(),
reader_count: UnsafeCell::new(0),
writer_active: UnsafeCell::new(false),
}
}
#[inline]
pub unsafe fn read(&self) {
self.mutex.lock();
while *self.writer_active.get() {
self.cvar.wait(&self.mutex);
}
assert!(*self.reader_count.get() != u32::max_value());
*self.reader_count.get() += 1;
self.mutex.unlock();
}
#[inline]
pub unsafe fn try_read(&self) -> bool {
if !self.mutex.try_lock() {
return false
}
while *self.writer_active.get() {
self.cvar.wait(&self.mutex);
}
assert!(*self.reader_count.get() != u32::max_value());
*self.reader_count.get() += 1;
self.mutex.unlock();
true
}
#[inline]
pub unsafe fn write(&self) {
self.mutex.lock();
while *self.writer_active.get() || *self.reader_count.get() > 0 {
self.cvar.wait(&self.mutex);
}
*self.writer_active.get() = true;
self.mutex.unlock();
}
#[inline]
pub unsafe fn try_write(&self) -> bool {
if !self.mutex.try_lock() {
return false;
}
while *self.writer_active.get() || *self.reader_count.get() > 0 {
self.cvar.wait(&self.mutex);
}
*self.writer_active.get() = true;
self.mutex.unlock();
true
}
#[inline]
pub unsafe fn read_unlock(&self) {
self.mutex.lock();
*self.reader_count.get() -= 1;
if *self.reader_count.get() == 0 {
self.cvar.notify_one()
}
self.mutex.unlock();
}
#[inline]
pub unsafe fn write_unlock(&self) {
self.mutex.lock();
*self.writer_active.get() = false;
self.cvar.notify_all();
self.mutex.unlock();
}
#[inline]
pub unsafe fn destroy(&self) {
self.mutex.destroy();
self.cvar.destroy();
*self.reader_count.get() = 0;
*self.writer_active.get() = false;
}
}
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