foundationdb/flow/Deque.h

/*
 * Deque.h
 *
 * This source file is part of the FoundationDB open source project
 *
 * Copyright 2013-2018 Apple Inc. and the FoundationDB project authors
 *
 * 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
 *
 *     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.
 */

#ifndef FLOW_DEQUE_H
#define FLOW_DEQUE_H
#pragma once

#include "flow/Platform.h"
#include <stdexcept>

template <class T>
class Deque {
	// Double ended queue implemented using circular array (and on-demand reallocation, like std::vector)
	// Interface similar to std::deque, but incomplete (also reallocation invalidates all iterators like std::vector)
	// Capacity is limited to 2^32-1 items even in 64 bit

public:
	typedef T value_type;
	typedef T& reference;
	typedef T const& const_reference;
	typedef int32_t difference_type;
	typedef uint32_t size_type;

	Deque() : arr(0), begin(0), end(0), mask(-1) {}

	// TODO: iterator construction, other constructors
	Deque(Deque const& r) : arr(0), begin(0), end(r.size()), mask(r.mask) {
		if(r.capacity() > 0)
			arr = (T*)aligned_alloc(__alignof(T), capacity()*sizeof(T));
		ASSERT(capacity() >= end || end == 0);
		for(int i=0; i<end; i++)
			new (&arr[i]) T(r[i]);
		// FIXME: Specialization for POD types using memcpy?
	}

	void operator=(Deque const& r) {
		cleanup();

		arr = 0;
		begin = 0;
		end = r.size();
		mask = r.mask;
		if(r.capacity() > 0)
			arr = (T*)aligned_alloc(__alignof(T), capacity()*sizeof(T));
		ASSERT(capacity() >= end || end == 0);
		for(int i=0; i<end; i++)
			new (&arr[i]) T(r[i]);
		// FIXME: Specialization for POD types using memcpy?
	}

	Deque(Deque&& r) BOOST_NOEXCEPT : begin(r.begin), end(r.end), mask(r.mask), arr(r.arr) {
		r.arr = 0;
		r.begin = r.end = 0;
		r.mask = -1;
	}

	void operator=(Deque&& r) BOOST_NOEXCEPT {
		cleanup();

		begin = r.begin;
		end = r.end;
		mask = r.mask;
		arr = r.arr;
		
		r.arr = 0;
		r.begin = r.end = 0;
		r.mask = -1;
	}

	bool operator == (const Deque& r) const { 
		if(size() != r.size())
			return false;
		for(int i=0; i<size(); i++)
			if((*this)[i] != r[i])
				return false;
		return true;
	}

	~Deque() {
		cleanup();
	}

	void push_back(const T& val) {
		if (full()) grow();
		new (&arr[end&mask]) T(val);
		end++;
	}

	template<class... U>
	reference emplace_back(U&&... val) {
		if (full()) grow();
		new (&arr[end&mask]) T(std::forward<U>(val)...);
		reference result = arr[end & mask];
		end++;
		return result;
	}

	void pop_back() {
		ASSERT(!empty());
		end--;
		arr[end&mask].~T();
	}

	void pop_front() {
		ASSERT(!empty());
		arr[begin].~T();
		if (begin == mask) {
			begin -= mask;
			end -= mask + 1;
		}
		else
			begin++;
	}

	void clear() {
		for (int i = begin; i != end; i++)
			arr[i&mask].~T();
		begin = end = 0;
	}

	size_type size() const { return end - begin; }
	bool empty() const { return end == begin; }
	size_type capacity() const { return mask+1; }
	size_type max_size() const { return 1 << 30; }  // All the logic should work at size 2^32, but size() can't return it, and callers might break, and there might be bugs...

	T& front() { return arr[begin]; }
	T const& front() const { return arr[begin]; }
	T& back() { return arr[(end - 1)&mask]; }
	T const& back() const { return arr[(end - 1)&mask]; }

	T& operator[](int i) { return arr[(begin + i)&mask]; }
	T const& operator[](int i) const { return arr[(begin + i)&mask]; }

	T& at(int i) { if (i<0 || i>=end - begin) throw std::out_of_range("requires 0 <= i < size"); return (*this)[i]; }
	T const& at(int i) const { if (i<0 || i>=end - begin) throw std::out_of_range("requires 0 <= i < size"); return (*this)[i]; }

private:
	T *arr;
	uint32_t begin, end, mask;

	bool full() const { return end == begin + mask + 1; }
	void grow() {
		// This doubles capacity (or makes it at least 8), and arbitrarily moves begin to be 0

		size_t mp1 = arr ? size_t(mask) + 1 : 4;
		size_t newSize = mp1 * 2;
		if (newSize > max_size()) throw std::bad_alloc();
		//printf("Growing to %lld (%u-%u mask %u)\n", (long long)newSize, begin, end, mask);
		T *newArr = (T*)aligned_alloc(__alignof(T), newSize*sizeof(T));   // SOMEDAY: FastAllocator, exception safety
		for (int i = begin; i != end; i++) {
			new (&newArr[i - begin]) T(std::move(arr[i&mask]));
			arr[i&mask].~T();
		}
		aligned_free(arr);
		arr = newArr;
		end -= begin;
		begin = 0;
		mask = uint32_t(newSize - 1);
	}

	void cleanup() {
		for (int i = begin; i != end; i++)
			arr[i&mask].~T();
		if(arr)
			aligned_free(arr);
	}
};

#endif