rt 0.19.0

A real-time operating system capable of full preemption
Documentation 
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use core::{
    cell::UnsafeCell,
    marker::PhantomData,
    mem::MaybeUninit,
    ops::{Deref, DerefMut},
    panic::{RefUnwindSafe, UnwindSafe},
    ptr::null_mut,
    sync::atomic::AtomicPtr,
};

use crate::{
    bindings::{rt_mutex, rt_pool, rt_pool_get, rt_pool_put},
    cell::SyncUnsafeCell,
    list::list_init,
    ptr_macros::{ptr_to_field, ptr_to_field_mut},
    sync::condvar::c_cond_init,
};

pub struct Pool<T: ?Sized> {
    pool: UnsafeCell<rt_pool>,
    _phantom_data: PhantomData<T>,
}

unsafe impl<T: ?Sized + Send> Send for Pool<T> {}
unsafe impl<T: ?Sized + Send> Sync for Pool<T> {}
impl<T: ?Sized> UnwindSafe for Pool<T> {}
impl<T: ?Sized> RefUnwindSafe for Pool<T> {}

impl<T> Pool<T> {
    /// Initialize a new `Pool` with the given pointers.
    ///
    /// # Safety
    ///
    /// This must be called with a pointer to a `static` `Pool` and be used to initialize that
    /// same `Pool`. Users should use the `rt::sync::pool!` macro to create a `Pool` rather than
    /// call `Pool::init` directly.
    #[must_use]
    pub const unsafe fn init<const N: usize>(
        this: *const Self,
        ptrs: &'static [AtomicPtr<T>; N],
    ) -> Pool<T> {
        let pool = UnsafeCell::raw_get(ptr_to_field!(this, pool));
        Pool {
            pool: UnsafeCell::new(rt_pool {
                mutex: rt_mutex {
                    holder: 0,
                    wait_list: list_init(ptr_to_field_mut!(pool, mutex, wait_list)),
                    list: list_init(ptr_to_field_mut!(pool, mutex, list)),
                    level: -1,
                },
                cond: c_cond_init(ptr_to_field_mut!(pool, cond)),
                ptrs: ptrs.as_ptr().cast_mut().cast(),
                avail: N,
            }),
            _phantom_data: PhantomData,
        }
    }

    #[must_use]
    pub const fn make_ptrs<const N: usize>(
        data: &'static [SyncUnsafeCell<MaybeUninit<T>>; N],
    ) -> [AtomicPtr<T>; N] {
        let mut ptrs = [const { AtomicPtr::new(null_mut()) }; N];
        let mut i = 0;
        while i < N {
            ptrs[i] = AtomicPtr::new(data[i].get().cast());
            i += 1;
        }
        ptrs
    }

    /// Adds an element to the queue, blocking until there is space in the queue.
    #[inline]
    pub fn alloc(&self, val: T) -> PoolBox<'_, T> {
        let pool_ptr = self.pool.get();
        let ptr: *mut T = unsafe { rt_pool_get(pool_ptr) }.cast();
        unsafe { ptr.write(val) }
        PoolBox { ptr, pool: self }
    }
}

pub struct PoolBox<'a, T: ?Sized> {
    ptr: *mut T,
    pool: &'a Pool<T>,
}

impl<T: ?Sized> Deref for PoolBox<'_, T> {
    type Target = T;
    fn deref(&self) -> &T {
        unsafe { &*self.ptr }
    }
}

impl<T: ?Sized> DerefMut for PoolBox<'_, T> {
    fn deref_mut(&mut self) -> &mut T {
        unsafe { &mut *self.ptr }
    }
}

impl<T: ?Sized> Drop for PoolBox<'_, T> {
    #[inline]
    fn drop(&mut self) {
        unsafe { self.ptr.drop_in_place() }
        let pool_ptr = self.pool.pool.get();
        let ptr = self.ptr.cast();
        unsafe { rt_pool_put(pool_ptr, ptr) }
    }
}

unsafe impl<T: Send> Send for PoolBox<'_, T> {}
unsafe impl<T: Sync> Sync for PoolBox<'_, T> {}
impl<T> UnwindSafe for PoolBox<'_, T> {}
impl<T> RefUnwindSafe for PoolBox<'_, T> {}

#[macro_export]
macro_rules! pool {
    ($name: ident, $type: ty, $num: expr) => {
        static $name: $crate::sync::Pool<$type> = {
            use core::{mem::MaybeUninit, sync::atomic::AtomicPtr};

            use $crate::cell::SyncUnsafeCell;

            let ptr = &raw const $name;
            static DATA: [SyncUnsafeCell<MaybeUninit<$type>>; $num] =
                [const { SyncUnsafeCell::new(MaybeUninit::zeroed()) }; $num];
            static PTRS: [AtomicPtr<$type>; $num] = $crate::sync::Pool::make_ptrs(&DATA);
            unsafe { $crate::sync::Pool::init(ptr, &PTRS) }
        };
    };
}

#[cfg(test)]
mod tests {
    crate::pool!(POOL, i32, 10);

    #[test]
    fn fast_path() {
        let mut x = POOL.alloc(0);
        *x += 1;
    }
}