4lDO2
71 lines
2.2 KiB
Rust
71 lines
2.2 KiB
Rust
use core::sync::atomic::{AtomicU32, Ordering};
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use crate::header::time::timespec;
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use crate::pthread::Pshared;
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pub struct Rwlock {
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state: AtomicU32,
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}
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// PTHREAD_RWLOCK_INITIALIZER is defined as "all zeroes".
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const EXCLUSIVE: u32 = (1 << (u32::BITS - 1)) - 1;
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// Separate "waiting for wrlocks" and "waiting for rdlocks"?
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//const WAITING: u32 = 1 << (u32::BITS - 1);
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// TODO: Optimize for short waits and long waits, using AtomicLock::wait_until, but still
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// supporting timeouts.
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// TODO: Add futex ops that use bitmasks.
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impl Rwlock {
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pub fn new(_pshared: Pshared) -> Self {
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Self {
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state: AtomicU32::new(0),
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}
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}
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pub fn acquire_write_lock(&self, _timeout: Option<×pec>) {
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// TODO: timeout
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while let Err(old) = self.try_acquire_read_lock() {
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crate::sync::futex_wait(&self.state, old, None);
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}
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}
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pub fn acquire_read_lock(&self, _timeout: Option<×pec>) {
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// TODO: timeout
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while let Err(old) = self.try_acquire_write_lock() {
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crate::sync::futex_wait(&self.state, old, None);
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}
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}
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pub fn try_acquire_read_lock(&self) -> Result<(), u32> {
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let mut cached = self.state.load(Ordering::Acquire);
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loop {
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let old = if cached == EXCLUSIVE { 0 } else { cached };
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let new = old + 1;
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// TODO: Return with error code instead?
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assert_ne!(new, EXCLUSIVE, "maximum number of rwlock readers reached");
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match self.state.compare_exchange_weak(cached, new, Ordering::Acquire, Ordering::Relaxed) {
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Ok(_) => return Ok(()),
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Err(value) if value == EXCLUSIVE => return Err(EXCLUSIVE),
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Err(value) => {
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cached = value;
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// TODO: SCHED_YIELD?
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core::hint::spin_loop();
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}
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}
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}
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}
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pub fn try_acquire_write_lock(&self) -> Result<(), u32> {
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self.state.compare_exchange(0, EXCLUSIVE, Ordering::Acquire, Ordering::Relaxed).map(|_| ())
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}
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pub fn unlock(&self) {
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let old = self.state.swap(0, Ordering::Release);
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if old == EXCLUSIVE {
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crate::sync::futex_wake(&self.state, i32::MAX);
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}
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}
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}
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