allocPool/allocPool.hpp

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#pragma once
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <cstring>
#include <exception>
#include <thread>
#include <unordered_map>
#include <vector>
template<class T>
concept resetable = requires(T val) {
val.reset();
};
template<class T>
requires std::default_initializable<T> && resetable<T>
class allocPool {
public:
explicit allocPool(size_t defaultAllocNumbers = 1000)
: vec(defaultAllocNumbers), pivot{defaultAllocNumbers} {
memset(&(vec[0]), 0, sizeof(vec[0]) * vec.size());
initArray(defaultAllocNumbers);
}
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T *getPtr() {
if (pivot == 0)
resizeVec();
auto *ptrToReturn{vec[0]};
std::swap(vec[0], vec[pivot - 1]);
positionMap[vec[0]] = 0;
positionMap[vec[pivot - 1]] = pivot - 1;
pivot--;
return ptrToReturn;
}
void returnPtr(T *ptr) {
size_t pos = positionMap[ptr];
(vec[pos])->reset();
std::swap(vec[pos], vec[pivot]);
positionMap[vec[pos]] = pos;
positionMap[vec[pivot]] = pivot;
pivot++;
}
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private:
std::vector<T *> vec;
std::unordered_map<T *, size_t> positionMap;
size_t pivot;
void initArray(size_t amount) {
const auto amountOfThreads{std::thread::hardware_concurrency()};
assert(amountOfThreads);
const auto amountPerThreads{amount / amountOfThreads};
std::vector<std::thread> threads;
threads.reserve(amountOfThreads);
for (size_t i{}; i < amountOfThreads; i++)
threads.emplace_back(&allocPool::initObjects, this, i, amountPerThreads);
for (auto &t: threads)
t.join();
// Remainder
initObjects(amount - (amount % amountOfThreads), amount % amountOfThreads);
}
void initObjects(size_t startIdx, size_t amount) {
for (size_t i{}; i < amount; i++) {
// TODO: Be more cache friendly by making a vector per thread, then doing memcpy into the original vector.
vec[startIdx + i] = new T;
positionMap[vec[startIdx + i]] = i;
}
}
void resizeVec() {
size_t size{vec.size()};
vec.resize(2 * size);
pivot = size;
memcpy(&(vec[size]), &(vec[0]), sizeof(vec[0]) * size);
for (size_t i{}; i < size; i++)
positionMap[vec[size + i]] = size + i;
initArray(size);
}
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};