arrow 3.0.0

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

use crate::memory;
use std::ptr::NonNull;

/// This struct is highly `unsafe` and offers the possibility to self-reference a [arrow::Buffer] from [arrow::array::ArrayData].
/// as a pointer to the beginning of its contents.
pub(super) struct RawPtrBox<T> {
    ptr: NonNull<T>,
}

impl<T> RawPtrBox<T> {
    /// # Safety
    /// The user must guarantee that:
    /// * the contents where `ptr` points to are never `moved`. This is guaranteed when they are Pinned.
    /// * the lifetime of this struct does not outlive the lifetime of `ptr`.
    /// Failure to fulfill any the above conditions results in undefined behavior.
    /// # Panic
    /// This function panics if:
    /// * `ptr` is null
    /// * `ptr` is not aligned to a slice of type `T`. This is guaranteed if it was built from a slice of type `T`.
    pub(super) unsafe fn new(ptr: *const u8) -> Self {
        let ptr = NonNull::new(ptr as *mut u8).expect("Pointer cannot be null");
        assert!(
            memory::is_aligned(ptr, std::mem::align_of::<T>()),
            "memory is not aligned"
        );
        Self { ptr: ptr.cast() }
    }

    pub(super) fn as_ptr(&self) -> *const T {
        self.ptr.as_ptr()
    }
}

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