RedBear-OS/src/sync/mod.rs

//! Synchronization primitives.

pub mod barrier;
pub mod cond;
// TODO: Merge with pthread_mutex
pub mod mutex;

pub mod once;
pub mod pthread_mutex;
pub mod rwlock;
pub mod semaphore;
pub mod waitval;

pub use self::{
    mutex::{Mutex, MutexGuard},
    once::Once,
    semaphore::Semaphore,
};

use crate::{
    error::Errno,
    header::{
        bits_timespec::timespec,
        errno::{EAGAIN, EINTR, ETIMEDOUT},
    },
    out::Out,
    platform::{Pal, Sys, types::c_int},
};
use core::{
    hint,
    mem::MaybeUninit,
    ops::Deref,
    ptr,
    sync::atomic::{AtomicI32, AtomicI32 as AtomicInt, AtomicU32},
};

const FUTEX_WAIT: c_int = 0;
const FUTEX_WAKE: c_int = 1;

#[derive(Clone, Copy, PartialEq, Eq)]
pub enum AttemptStatus {
    Desired,
    Waiting,
    Other,
}

pub trait FutexTy {
    fn conv(self) -> u32;
}
pub trait FutexAtomicTy {
    type Ty: FutexTy;

    fn ptr(&self) -> *mut Self::Ty;
}
impl FutexTy for u32 {
    fn conv(self) -> u32 {
        self
    }
}
impl FutexTy for i32 {
    fn conv(self) -> u32 {
        self as u32
    }
}
impl FutexAtomicTy for AtomicU32 {
    type Ty = u32;

    fn ptr(&self) -> *mut u32 {
        // TODO: Change when Redox's toolchain is updated. This is not about targets, but compiler
        // versions!
        /*

        #[cfg(target_os = "redox")]
        return AtomicU32::as_ptr(self);

        #[cfg(target_os = "linux")]
        return AtomicU32::as_mut_ptr(self);

        */

        // AtomicU32::as_mut_ptr internally calls UnsafeCell::get, which itself simply does (&self
        // as *const Self as *mut Self).
        ptr::from_ref::<AtomicU32>(self) as *mut u32
    }
}
impl FutexAtomicTy for AtomicI32 {
    type Ty = i32;

    fn ptr(&self) -> *mut i32 {
        // TODO
        /*#[cfg(target_os = "redox")]
        return AtomicI32::as_ptr(self);

        #[cfg(target_os = "linux")]
        return AtomicI32::as_mut_ptr(self);*/

        ptr::from_ref::<AtomicI32>(self) as *mut i32
    }
}

pub unsafe fn futex_wake_ptr(ptr: *mut impl FutexTy, n: i32) -> usize {
    // TODO: unwrap_unchecked?
    unsafe { Sys::futex_wake(ptr.cast(), n as u32) }.unwrap() as usize
}
pub unsafe fn futex_wait_ptr<T: FutexTy>(
    ptr: *mut T,
    value: T,
    deadline_opt: Option<&timespec>,
) -> FutexWaitResult {
    match unsafe { Sys::futex_wait(ptr.cast(), value.conv(), deadline_opt) } {
        Ok(()) | Err(Errno(EINTR)) => FutexWaitResult::Waited,
        Err(Errno(EAGAIN)) => FutexWaitResult::Stale,
        Err(Errno(ETIMEDOUT)) if deadline_opt.is_some() => FutexWaitResult::TimedOut,
        Err(err) => {
            todo_error!(0, err, "futex failed");
            FutexWaitResult::Waited
        }
    }
}
pub fn futex_wake(atomic: &impl FutexAtomicTy, n: i32) -> usize {
    unsafe { futex_wake_ptr(atomic.ptr(), n) }
}
pub fn futex_wait<T: FutexAtomicTy>(
    atomic: &T,
    value: T::Ty,
    deadline_opt: Option<&timespec>,
) -> FutexWaitResult {
    unsafe { futex_wait_ptr(atomic.ptr(), value, deadline_opt) }
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum FutexWaitResult {
    Waited, // possibly spurious
    Stale,  // outdated value
    TimedOut,
}

pub fn rttime() -> timespec {
    unsafe {
        let mut time = MaybeUninit::uninit();

        if let Ok(()) = Sys::clock_gettime(
            crate::header::time::CLOCK_REALTIME,
            Out::from_uninit_mut(&mut time),
        ) {}; // TODO handle error

        time.assume_init()
    }
}

pub fn wait_until_generic<F1, F2>(word: &AtomicInt, attempt: F1, mark_long: F2, long: c_int)
where
    F1: Fn(&AtomicInt) -> AttemptStatus,
    F2: Fn(&AtomicInt) -> AttemptStatus,
{
    // First, try spinning for really short durations
    for _ in 0..999 {
        hint::spin_loop();
        if attempt(word) == AttemptStatus::Desired {
            return;
        }
    }

    // One last attempt, to initiate "previous"
    let mut previous = attempt(word);

    // Ok, that seems to take quite some time. Let's go into a
    // longer, more patient, wait.
    loop {
        if previous == AttemptStatus::Desired {
            return;
        }

        if
        // If we or somebody else already initiated a long
        // wait, OR
        previous == AttemptStatus::Waiting ||
            // Otherwise, unless our attempt to initiate a long
            // wait informed us that we might be done waiting
            mark_long(word) != AttemptStatus::Desired
        {
            futex_wait(word, long, None);
        }

        previous = attempt(word);
    }
}

/// Convenient wrapper around the "futex" system call for
/// synchronization implementations
#[repr(C)]
pub(crate) struct AtomicLock {
    pub(crate) atomic: AtomicInt,
}
impl AtomicLock {
    pub const fn new(value: c_int) -> Self {
        Self {
            atomic: AtomicInt::new(value),
        }
    }
    pub fn notify_one(&self) {
        futex_wake(&self.atomic, 1);
    }
    pub fn notify_all(&self) {
        futex_wake(&self.atomic, i32::MAX);
    }
    pub fn wait_if(&self, value: c_int, timeout_opt: Option<&timespec>) {
        self.wait_if_raw(value, timeout_opt);
    }
    pub fn wait_if_raw(&self, value: c_int, timeout_opt: Option<&timespec>) -> FutexWaitResult {
        futex_wait(&self.atomic, value, timeout_opt)
    }

    /// A general way to efficiently wait for what might be a long time, using two closures:
    ///
    /// - `attempt` = Attempt to modify the atomic value to any
    ///   desired state.
    /// - `mark_long` = Attempt to modify the atomic value to sign
    ///   that it want's to get notified when waiting is done.
    ///
    /// Both of these closures are allowed to spuriously give a
    /// non-success return value, they are used only as optimization
    /// hints. However, what counts as a "desired value" may differ
    /// per closure. Therefore, `mark_long` can notify a value as
    /// "desired" in order to get `attempt` retried immediately.
    ///
    /// The `long` parameter is the only one which actually cares
    /// about the specific value of your atomics. This is needed
    /// because it needs to pass this to the futex system call in
    /// order to avoid race conditions where the atomic could be
    /// modified to the desired value before the call is complete and
    /// we receive the wakeup notification.
    pub fn wait_until<F1, F2>(&self, attempt: F1, mark_long: F2, long: c_int)
    where
        F1: Fn(&AtomicInt) -> AttemptStatus,
        F2: Fn(&AtomicInt) -> AttemptStatus,
    {
        wait_until_generic(&self.atomic, attempt, mark_long, long)
    }
}
impl Deref for AtomicLock {
    type Target = AtomicInt;

    fn deref(&self) -> &Self::Target {
        &self.atomic
    }
}