o3 0.26.4

shared-nothing primitives
Documentation 
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pub(in crate::buffer) use input::{Input, Measured};

use crate::buffer::{pool::owners, storage::regions};

mod input;

use std::{marker, mem, ptr};

use crate::{buffer, buffer::pool, mem::rc};

/// One exact live pool-slot edge with its backing and root mode preserved.
#[derive(Debug)]
#[repr(transparent)]
pub struct Edge<K: crate::buffer::raw::Backing = owners::Plain, M = pool::Owned> {
    ptr: Option<ptr::NonNull<regions::Prefix>>,
    mode: marker::PhantomData<(K, M)>,
}

impl<K: crate::buffer::raw::Backing, M> Edge<K, M> {
    pub(in crate::buffer) const NONE: Self = Self {
        ptr: None,
        mode: marker::PhantomData,
    };

    pub(in crate::buffer::pool) const fn new(ptr: ptr::NonNull<regions::Prefix>) -> Self {
        Self {
            ptr: Some(ptr),
            mode: marker::PhantomData,
        }
    }

    pub(in crate::buffer) fn into_raw(self) -> Option<ptr::NonNull<regions::Prefix>> {
        let this = mem::ManuallyDrop::new(self);
        this.ptr
    }

    pub(in crate::buffer) unsafe fn release_raw(ptr: ptr::NonNull<()>) {
        use crate::mem::raw::Edge;

        // SAFETY: callers transfer one live pool-slot prefix edge.
        if unsafe { ptr.cast::<regions::Prefix>().as_ref().release() } != rc::Release::Last {
            return;
        }
        // SAFETY: Last transfers the exact terminal slot edge into Retired.
        unsafe { owners::Retired::<K, owners::Any>::from_owner(ptr) }.finish();
    }
}

impl<L> Edge<owners::Plain<L>, pool::Borrowed<'_>> {
    pub(in crate::buffer) fn into_owned(self) -> Edge<owners::Plain<L>, pool::Owned> {
        let this = mem::ManuallyDrop::new(self);
        Edge {
            ptr: this.ptr,
            mode: marker::PhantomData,
        }
    }
}

impl<K: crate::buffer::raw::Backing, M> Drop for Edge<K, M> {
    fn drop(&mut self) {
        if let Some(ptr) = self.ptr {
            // SAFETY: Edge owns exactly one live pool-slot prefix edge.
            unsafe { Self::release_raw(ptr.cast()) };
        }
    }
}

// SAFETY: retaining Edge creates one edge for the same exact pool slot and
// preserves both its backing kind and root-mode lifetime.
unsafe impl<K: crate::buffer::raw::Backing, M> buffer::raw::Retain for Edge<K, M> {
    fn try_retain(&self) -> Result<Self, rc::Error> {
        use crate::mem::raw::Edge;

        let pointer = self.ptr;
        if let Some(ptr) = pointer {
            // SAFETY: the borrowed Edge proves this slot prefix is active.
            unsafe { ptr.as_ref().try_retain() }?;
        }
        Ok(Self {
            ptr: pointer,
            mode: marker::PhantomData,
        })
    }
}

const _: () = {
    assert!(size_of::<Edge>() == size_of::<usize>());
    assert!(size_of::<Edge<owners::Plain, pool::Borrowed<'static>>>() == size_of::<usize>());
    assert!(size_of::<Edge<owners::Resident<'static>>>() == size_of::<usize>());
};

impl<K: crate::buffer::raw::Backing, M> regions::End for Edge<K, M> {
    const EMPTY: Option<Self> = Some(Self::NONE);
}

impl<K: crate::buffer::raw::Backing, M> buffer::Residency for owners::Edge<K, M> {
    fn resident(&self) -> usize {
        self.ptr.map_or(0, |ptr| {
            // SAFETY: Edge retains this exact active pool-slot prefix.
            unsafe { owners::capacity_of(ptr.cast()) }.get() as usize
        })
    }
}