mtfse/src/ext/sync.rs

//! Sync utils
use super::*;
use std::{
    ptr::NonNull,
    sync::atomic::{AtomicBool, Ordering},
};
use std::ops::Drop;
use crossbeam_utils::atomic::AtomicCell;

struct InitData<T>
{
    data: AtomicCell<Option<T>>,
    drop: AtomicBool,
}

#[derive(Debug)]
struct InitInner<T>
{
    boxed: NonNull<InitData<T>>,
}

impl<T> InitInner<T>
{
    #[inline] pub fn new() -> Self
    {
	let from = Box::new(InitData {
	    data: AtomicCell::new(None),
	    drop: false.into(),
	});
	Self {
	    boxed: unsafe{NonNull::new_unchecked(Box::into_raw(from))},
	}
    }
}

impl<T> Clone for InitInner<T>
{
    fn clone(&self) -> Self {
	Self {
	    boxed: unsafe{NonNull::new_unchecked(self.boxed.as_ptr())}
	}
    }
}

impl<T> InitInner<T>
{
    #[inline(always)] fn should_drop(&self) -> &AtomicBool
    {
	&unsafe {&*self.boxed.as_ptr()}.drop
    }
    
    #[inline(always)] fn data_ref(&self) -> &InitData<T>
    {
	unsafe{&*self.boxed.as_ptr()}
    }
}

unsafe impl<T> Send for InitInner<T>{}
unsafe impl<T> Sync for InitInner<T>{}

impl<T> Drop for InitInner<T>
{
    fn drop(&mut self) {
	if let Err(true) = self.should_drop().compare_exchange(false, true, Ordering::SeqCst, Ordering::SeqCst) {
	    unsafe {
		drop(Box::from_raw(self.boxed.as_ptr()))
	    }
	}
    }
}

#[derive(Debug)]
pub struct InitHalf<T>(InitInner<T>);
#[derive(Debug)]
pub struct UninitHalf<T>(InitInner<T>);

impl<T> InitHalf<T>
{
    /// Set the value
    pub fn set(&mut self, value: T)
    {
	self.0.data_ref().data.store(Some(value));
    }
    /// Set the value, returning the previous one if it was set
    pub fn swap(&mut self, value: T) -> Option<T>
    {
	self.0.data_ref().data.swap(Some(value))
    }
}

impl<T> UninitHalf<T>
{
    /// Take the initialised value
    ///
    /// # Panics
    /// If the value hasn't yet been initialised.
    pub fn take(&mut self) -> T
    {
	self.0.data_ref().data.take().unwrap()
    }
    /// Take the value if it is set, if not, returns `None`.
    pub fn try_take(&mut self) -> Option<T>
    {
	self.0.data_ref().data.take()
    }
}

/// Create a pair of atomic initialser-receivers.
pub fn shared_uninit<T>() -> (InitHalf<T>, UninitHalf<T>)
{
    let inner = InitInner::<T>::new();

    (InitHalf(inner.clone()),
     UninitHalf(inner))
}

/*
/// Type to allow for a seperate thread or task to initialise a value.
#[derive(Debug)]
pub struct SharedUninit<T>(oneshot::Receiver<T>);

/// Type to initialise a value for a `SharedUninit`.
#[derive(Debug)]
pub struct SharedInitialiser<T>(oneshot::Sender<T>);

impl<'a, T> SharedUninit<T>
where T: 'a
{
/// Create an uninit/initialiser pair.
pub fn pair() -> (SharedInitialiser<T>, Self)
{
let (tx, rx) = oneshot::channel();
(SharedInitialiser(tx), Self(rx))
    }

    /// Try to receive the initialised value.
    ///
    /// Returns `None` if the initialiser was dropped before setting a value.
    #[inline] pub fn try_get(self) -> impl Future<Output = Option<T>> + 'a
    {
	self.0.map(|x| x.ok())
    }

    /// Receive the initialised value.
    ///
    /// # Panics
    /// If the initialiser was dropped without setting a value.
    #[inline] pub fn get(self) -> impl Future<Output = T> + 'a
    {
	self.try_get().map(|x| x.unwrap())
    }
}

impl<'a, T> SharedInitialiser<T>
    where T: 'a
{
    /// Set the value for the `SharedUninit`.
    #[inline] pub fn init(self, value: T)
    {
	let _ = self.0.send(value);
    }
}
*/
// This was a failure. Just use `tokio::sync::oneshot`...

/*
#[derive(Debug)]
struct SharedInitialiser<T>
{
    data: Arc<(UnsafeCell<MaybeUninit<T>>, AtomicBool)>,
}

impl<T> Clone for SharedInitialiser<T>
{
    #[inline] fn clone(&self) -> Self {
	Self { data: Arc::clone(&self.data) }
    }
}

#[derive(Debug)]
pub struct SharedInitRx<T>(SharedInitialiser<T>);

/// Permits initialising across a thread.
// Do we even need this? No.. We can just use `tokio::sync::oneshot`....
#[derive(Debug)]
pub struct SharedInitTx<T>(SharedInitialiser<T>);

impl<T> SharedInitTx<T>
{
    /// Consume this instance and initialise it.
    ///
    /// # Panics
    /// If there is already a value set (this should never happen).
    pub fn initialise(self, value: T)
    {
	todo!()
    }
}

impl<T> SharedInitRx<T>
{
    /// Create a sender and receiver pair
    pub fn pair() -> (SharedInitTx<T>, Self)
    {
	let this = Self::new();
	(this.create_tx(), this)
    }
    /// Create a new, uninitialised receiver.
    #[inline] fn new() -> Self
    {
	Self(SharedInitialiser{data: Arc::new((UnsafeCell::new(MaybeUninit::uninit()), false.into()))})
    }
    /// Create an initialiser
    ///
    /// # Panics (debug)
    /// If an initialiser already exists
    #[inline] fn create_tx(&self) -> SharedInitTx<T>
    {
	debug_assert_eq!(Arc::strong_count(&self.0.data), 1, "Sender already exists");

	SharedInitTx(self.0.clone())
    }

    /// Checks if there is a value present, or if it is possible for a value to be present.
    pub fn is_pending(&self) -> bool
    {
	todo!("Either self.0.data.1 == true, OR, strong_count() == 2")
    }

    /// Has a value already been set
    pub fn has_value(&self) -> bool
    {
	todo!("self.0.data.1 == true")
    }
    
    /// Try to consume into the initialised value.
    pub fn try_into_value(self) -> Result<T, Self>
    {
	todo!()
    }

    /// Consume into the initialised value
    ///
    /// # Panics
    /// If the value hasn't been initialised
    #[inline] pub fn into_value(self) -> T
    {
	self.try_into_value().map_err(|_| "No initialised value present").unwrap()
    }

    /// Does this receiver have an initialser that hasn't yet produced a value?
    pub fn has_initialiser(&self) -> bool
    {
	Arc::strong_count(&self.0.data) == 2
    }
}
*/