arrow-buffer/src/alloc/mod.rs

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//! Defines the low-level [`Allocation`] API for shared memory regions

use std::alloc::Layout;
use std::fmt::{Debug, Formatter};
use std::panic::RefUnwindSafe;
use std::sync::Arc;

mod alignment;

pub use alignment::ALIGNMENT;

/// The owner of an allocation.
/// The trait implementation is responsible for dropping the allocations once no more references exist.
pub trait Allocation: RefUnwindSafe + Send + Sync {}

impl<T: RefUnwindSafe + Send + Sync> Allocation for T {}

/// Mode of deallocating memory regions
pub(crate) enum Deallocation {
    /// An allocation using [`std::alloc`]
    Standard(Layout),
    /// An allocation from an external source like the FFI interface
    /// Deallocation will happen on `Allocation::drop`
    /// The size of the allocation is tracked here separately only
    /// for memory usage reporting via `Array::get_buffer_memory_size`
    Custom(Arc<dyn Allocation>, usize),
}

impl Debug for Deallocation {
    fn fmt(&self, f: &mut Formatter) -> std::fmt::Result {
        match self {
            Deallocation::Standard(layout) => {
                write!(f, "Deallocation::Standard {layout:?}")
            }
            Deallocation::Custom(_, size) => {
                write!(f, "Deallocation::Custom {{ capacity: {size} }}")
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use crate::alloc::Deallocation;

    #[test]
    fn test_size_of_deallocation() {
        assert_eq!(
            std::mem::size_of::<Deallocation>(),
            3 * std::mem::size_of::<usize>()
        );
    }
}