| // 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 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_eq!( |
| ptr.as_ptr().align_offset(std::mem::align_of::<T>()), |
| 0, |
| "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> {} |
| |
| #[cfg(test)] |
| mod tests { |
| use super::*; |
| |
| #[test] |
| #[should_panic(expected = "memory is not aligned")] |
| #[cfg_attr(miri, ignore)] // sometimes does not panic as expected |
| fn test_primitive_array_alignment() { |
| let bytes = vec![0u8, 1u8]; |
| unsafe { RawPtrBox::<u64>::new(bytes.as_ptr().offset(1)) }; |
| } |
| } |