added shared_uninit

src/ext/sync.rs

@@ -1,8 +1,120 @@
 //! Sync utils
 use super::*;
-use tokio::sync::oneshot;
-use futures::prelude::*;
+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>);
@@ -48,7 +160,7 @@ impl<'a, T> SharedInitialiser<T>
 	let _ = self.0.send(value);
     }
 }
-
+*/
 // This was a failure. Just use `tokio::sync::oneshot`...
 
 /*