RedBear-OS/src/sync/cond.rs

// Used design from https://www.remlab.net/op/futex-condvar.shtml

use crate::header::pthread::*;
use crate::header::bits_pthread::*;
use crate::header::time::timespec;
use crate::pthread::Errno;

use core::sync::atomic::{AtomicU32 as AtomicUint, Ordering};

pub struct Cond {
    cur: AtomicUint,
    prev: AtomicUint,
}

type Result<T, E = crate::pthread::Errno> = core::result::Result<T, E>;

impl Cond {
    pub fn new() -> Self {
        Self{
            cur: AtomicUint::new(0),
            prev: AtomicUint::new(0),
        }
    }
    fn wake(&self, count: i32) -> Result<(), Errno> {
        // This is formally correct as long as we don't have more than u32::MAX threads.
        let prev = self.prev.load(Ordering::Relaxed);
        self.cur.store(prev.wrapping_add(1), Ordering::Relaxed);

        crate::sync::futex_wake(&self.cur, count);
        Ok(())
    }
    pub fn broadcast(&self) -> Result<(), Errno> {
        self.wake(i32::MAX)
    }
    pub fn signal(&self) -> Result<(), Errno> {
        self.broadcast()
        //self.wake(1)
    }
    pub fn timedwait(&self, mutex: &RlctMutex, timeout: &timespec) -> Result<(), Errno> {
        self.wait_inner(mutex, Some(timeout))
    }
    fn wait_inner(&self, mutex: &RlctMutex, timeout: Option<&timespec>) -> Result<(), Errno> {
        self.wait_inner_generic(|| mutex.unlock(), || mutex.lock(), |timeout| mutex.lock_with_timeout(timeout), timeout)
    }
    pub fn wait_inner_typedmutex<'lock, T>(&self, guard: crate::sync::MutexGuard<'lock, T>) -> crate::sync::MutexGuard<'lock, T> {
        let mut newguard = None;
        let lock = guard.mutex;
        self.wait_inner_generic(move || {
            drop(guard);
            Ok(())
        }, || {
            newguard = Some(lock.lock());
            Ok(())
        }, |_| unreachable!(), None).unwrap();
        newguard.unwrap()
    }
    // TODO: FUTEX_REQUEUE
    fn wait_inner_generic(&self, unlock: impl FnOnce() -> Result<()>, lock: impl FnOnce() -> Result<()>, lock_with_timeout: impl FnOnce(&timespec) -> Result<()>, timeout: Option<&timespec>) -> Result<(), Errno> {
        // TODO: Error checking for certain types (i.e. robust and errorcheck) of mutexes, e.g. if the
        // mutex is not locked.
        let current = self.cur.load(Ordering::Relaxed);
        self.prev.store(current, Ordering::Relaxed);

        unlock();

        match timeout {
            Some(timeout) => {
                crate::sync::futex_wait(&self.cur, current, timespec::subtract(*timeout, crate::sync::rttime()).as_ref());
                lock_with_timeout(timeout);
            }
            None => {
                crate::sync::futex_wait(&self.cur, current, None);
                lock();
            }
        }
        Ok(())
    }
    pub fn wait(&self, mutex: &RlctMutex) -> Result<(), Errno> {
        self.wait_inner(mutex, None)
    }
}