jorgecarleitao commented on a change in pull request #1041: URL: https://github.com/apache/arrow-rs/pull/1041#discussion_r778440916
########## File path: parquet/src/arrow/record_reader/buffer.rs ########## @@ -0,0 +1,191 @@ +// 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::marker::PhantomData; +use std::ops::Range; + +use arrow::buffer::{Buffer, MutableBuffer}; + +/// A buffer that supports writing new data to the end, and removing data from the front +/// +/// Used by [RecordReader](`super::RecordReader`) to buffer up values before returning a +/// potentially smaller number of values, corresponding to a whole number of semantic records +pub trait BufferQueue: Sized { + type Output: Sized; + + type Slice: ?Sized; + + /// Split out the first `len` items + /// + /// # Panics + /// + /// Implementations must panic if `len` is beyond the length of [`BufferQueue`] + /// + fn split_off(&mut self, len: usize) -> Self::Output; + + /// Returns a [`Self::Slice`] with at least `batch_size` capacity that can be used + /// to append data to the end of this [`BufferQueue`] + /// + /// NB: writes to the returned slice will not update the length of [`BufferQueue`] + /// instead a subsequent call should be made to [`BufferQueue::set_len`] + fn spare_capacity_mut(&mut self, batch_size: usize) -> &mut Self::Slice; + + /// Sets the length of the [`BufferQueue`]. + /// + /// Intended to be used in combination with [`BufferQueue::spare_capacity_mut`] + /// + /// # Panics + /// + /// Implementations must panic if `len` is beyond the initialized length + /// + /// Implementations may panic if `set_len` is called with less than what has been written + /// + /// This distinction is to allow for implementations that return a default initialized + /// [BufferQueue::Slice`] which doesn't track capacity and length separately + /// + /// For example, [`TypedBuffer<T>`] returns a default-initialized `&mut [T]`, and does not + /// track how much of this slice is actually written to by the caller. This is still + /// safe as the slice is default-initialized. + /// + fn set_len(&mut self, len: usize); +} + +/// A typed buffer similar to [`Vec<T>`] but using [`MutableBuffer`] for storage +pub struct TypedBuffer<T> { + buffer: MutableBuffer, + + /// Length in elements of size T + len: usize, + + /// Placeholder to allow `T` as an invariant generic parameter + _phantom: PhantomData<*mut T>, +} + +impl<T> Default for TypedBuffer<T> { + fn default() -> Self { + Self::new() + } +} + +impl<T> TypedBuffer<T> { + pub fn new() -> Self { + Self { + buffer: MutableBuffer::new(0), + len: 0, + _phantom: Default::default(), + } + } + + pub fn len(&self) -> usize { + self.len + } + + pub fn is_empty(&self) -> bool { + self.len == 0 + } + + #[inline] + pub fn as_slice(&self) -> &[T] { + let (prefix, buf, suffix) = unsafe { self.buffer.as_slice().align_to::<T>() }; + assert!(prefix.is_empty() && suffix.is_empty()); + buf + } + + #[inline] + pub fn as_slice_mut(&mut self) -> &mut [T] { + let (prefix, buf, suffix) = + unsafe { self.buffer.as_slice_mut().align_to_mut::<T>() }; + assert!(prefix.is_empty() && suffix.is_empty()); + buf + } +} + +impl<T> BufferQueue for TypedBuffer<T> { + type Output = Buffer; + + type Slice = [T]; + + fn split_off(&mut self, len: usize) -> Self::Output { + assert!(len <= self.len); + + let num_bytes = len * std::mem::size_of::<T>(); + let remaining_bytes = self.buffer.len() - num_bytes; + // TODO: Optimize to reduce the copy + // create an empty buffer, as it will be resized below + let mut remaining = MutableBuffer::new(0); + remaining.resize(remaining_bytes, 0); + + let new_records = remaining.as_slice_mut(); + + new_records[0..remaining_bytes] + .copy_from_slice(&self.buffer.as_slice()[num_bytes..]); + + self.buffer.resize(num_bytes, 0); + self.len -= len; + + std::mem::replace(&mut self.buffer, remaining).into() + } + + fn spare_capacity_mut(&mut self, batch_size: usize) -> &mut Self::Slice { + self.buffer + .resize((self.len + batch_size) * std::mem::size_of::<T>(), 0); Review comment: `arrow2` no longer uses `MutableBuffer<T: NativeType>`: it recently migrated to `std::Vec<T: NativeType>`, for ease of use (and maintain). -- This is an automated message from the Apache Git Service. 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