starlark 0.14.0

An implementation of the Starlark language in Rust.
Documentation 
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/*
 * Copyright 2019 The Starlark in Rust Authors.
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * Licensed 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
 *
 *     https://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::mem::MaybeUninit;
use std::ptr::NonNull;

use crate::values::layout::value_alloc_size::ValueAllocSize;

pub(crate) enum ChunkAllocationDirection {
    /// Next allocation in the chunk has higher address than the previous one.
    Up,
    /// Next allocation in the chunk has lower address than the previous one.
    Down,
}

/// Fast memory allocator for the heap.
pub(crate) trait ArenaAllocator {
    /// Number of bytes allocated by this allocator.
    ///
    /// That is:
    /// * space occupied by allocated values
    /// * padding
    /// * reserved but not yet allocated space
    /// * does not include metadata
    fn allocated_bytes(&self) -> usize;
    /// Number of bytes reserved but not yet allocated by this allocator.
    fn remaining_capacity(&self) -> usize;
    /// Estimate the size of allocated metadata.
    fn allocation_overhead(&self) -> usize;
    /// Allocate given number of words.
    fn alloc(&self, size: ValueAllocSize) -> NonNull<u8>;

    /// This allocator chunk allocation direction.
    const CHUNK_ALLOCATION_DIRECTION: ChunkAllocationDirection;

    type ChunkRevIterator<'a>: Iterator<Item = &'a [MaybeUninit<u8>]>
    where
        Self: 'a;

    /// Iterate allocated chunks in the reverse order.
    unsafe fn iter_allocated_chunks_rev(&self) -> Self::ChunkRevIterator<'_>;

    /// No more allocation, reclaim memory if possible.
    fn finish(&mut self);
}