jhorstmann commented on a change in pull request #8401: URL: https://github.com/apache/arrow/pull/8401#discussion_r530350708
########## File path: rust/arrow/src/bytes.rs ########## @@ -0,0 +1,166 @@ +// 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. + +//! This module contains an implementation of a contiguous immutable memory region that knows +//! how to de-allocate itself, [`Bytes`]. +//! Note that this is a low-level functionality of this crate. + +use core::slice; +use std::sync::Arc; +use std::{fmt::Debug, fmt::Formatter}; + +use crate::{ffi, memory}; + +/// Mode of deallocating memory regions +pub enum Deallocation { + /// Native deallocation, using Rust deallocator with Arrow-specific memory aligment + Native(usize), + /// Foreign interface, via a callback + Foreign(Arc<ffi::FFI_ArrowArray>), +} + +impl Debug for Deallocation { + fn fmt(&self, f: &mut Formatter) -> std::fmt::Result { + match self { + Deallocation::Native(capacity) => { + write!(f, "Deallocation::Native {{ capacity: {} }}", capacity) + } + Deallocation::Foreign(_) => { + write!(f, "Deallocation::Foreign {{ capacity: unknown }}") + } + } + } +} + +/// A continuous, fixed-size, immutable memory region that knows how to de-allocate itself. +/// This structs' API is inspired by the `bytes::Bytes`, but it is not limited to using rust's +/// global allocator nor u8 aligmnent. +/// +/// In the most common case, this buffer is allocated using [`allocate_aligned`](memory::allocate_aligned) +/// and deallocated accordingly [`free_aligned`](memory::free_aligned). +/// When the region is allocated by an foreign allocator, [Deallocation::Foreign], this calls the +/// foreign deallocator to deallocate the region when it is no longer needed. +pub struct Bytes { + /// The raw pointer to be begining of the region + ptr: *const u8, + + /// The number of bytes visible to this region. This is always smaller than its capacity (when avaliable). + len: usize, + + /// how to deallocate this region + deallocation: Deallocation, +} + +impl Bytes { + /// Takes ownership of an allocated memory region, + /// + /// # Arguments + /// + /// * `ptr` - Pointer to raw parts + /// * `len` - Length of raw parts in **bytes** + /// * `capacity` - Total allocated memory for the pointer `ptr`, in **bytes** + /// + /// # Safety + /// + /// This function is unsafe as there is no guarantee that the given pointer is valid for `len` + /// bytes. If the `ptr` and `capacity` come from a `Buffer`, then this is guaranteed. + pub unsafe fn new(ptr: *const u8, len: usize, deallocation: Deallocation) -> Bytes { + Bytes { + ptr, + len, + deallocation, + } + } + + #[inline] + pub fn as_slice(&self) -> &[u8] { + unsafe { slice::from_raw_parts(self.ptr, self.len) } + } + + #[inline] + pub fn len(&self) -> usize { + self.len + } + + #[inline] + pub fn is_empty(&self) -> bool { + self.len == 0 + } + + #[inline] + pub fn raw_data(&self) -> *const u8 { + self.ptr + } + + #[inline] + pub fn raw_data_mut(&mut self) -> *mut u8 { + self.ptr as *mut u8 + } + + pub fn capacity(&self) -> usize { + match self.deallocation { + Deallocation::Native(capacity) => capacity, + // we cannot determine this in general, + // and thus we state that this is externally-owned memory + Deallocation::Foreign(_) => 0, Review comment: Also a good point. Seems it is only used for reporting memory usage of arrays and you could argue that does not need to include foreign memory. For that usecase the method could have a better name like `memory_usage`, with the current name I think returning `len` sounds more logical. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org
