auronandace
86 lines
2.3 KiB
Rust
86 lines
2.3 KiB
Rust
// From https://www.remlab.net/op/futex-misc.shtml
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//TODO: improve implementation
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use crate::{
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header::{
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bits_time::timespec,
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time::{CLOCK_MONOTONIC, CLOCK_REALTIME, timespec_realtime_to_monotonic},
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},
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platform::types::{c_uint, clockid_t},
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};
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use core::sync::atomic::{AtomicU32, Ordering};
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pub struct Semaphore {
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count: AtomicU32,
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}
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impl Semaphore {
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pub const fn new(value: c_uint) -> Self {
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Self {
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count: AtomicU32::new(value),
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}
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}
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// TODO: Acquire-Release ordering?
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pub fn post(&self, count: c_uint) {
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self.count.fetch_add(count, Ordering::SeqCst);
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// TODO: notify one?
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crate::sync::futex_wake(&self.count, i32::MAX);
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}
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pub fn try_wait(&self) -> u32 {
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loop {
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let value = self.count.load(Ordering::SeqCst);
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if value == 0 {
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return 0;
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}
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match self.count.compare_exchange_weak(
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value,
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value - 1,
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Ordering::SeqCst,
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Ordering::SeqCst,
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) {
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Ok(_) => {
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// Acquired
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return value;
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}
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Err(_) => (),
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}
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// Try again (as long as value > 0)
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}
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}
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pub fn wait(&self, timeout_opt: Option<×pec>, clock_id: clockid_t) -> Result<(), ()> {
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loop {
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let value = self.try_wait();
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if value == 0 {
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return Ok(());
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}
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if let Some(timeout) = timeout_opt {
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let relative = match clock_id {
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// FUTEX expect monotonic clock
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CLOCK_MONOTONIC => timeout.clone(),
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CLOCK_REALTIME => match timespec_realtime_to_monotonic(timeout.clone()) {
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Ok(relative) => relative,
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Err(_) => return Err(()),
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},
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_ => return Err(()),
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};
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crate::sync::futex_wait(&self.count, value, Some(&relative));
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} else {
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// Use futex to wait for the next change, without a timeout
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crate::sync::futex_wait(&self.count, value, None);
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}
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}
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}
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pub fn value(&self) -> c_uint {
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self.count.load(Ordering::SeqCst)
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}
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}
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