Timothée Leclaire-Fournier
7f58269866
A benchmark with 50 objects with and without false sharing mitigations gives these values (for the initArray() function) on Windows: - With mitigations: ~5500 microseconds - Without mitigations: ~9000 microseconds On Linux: - With mitigations: ~600 microseconds - Without mitigations: ~700 microseconds
109 lines
2.9 KiB
C++
109 lines
2.9 KiB
C++
#pragma once
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#include <algorithm>
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#include <cassert>
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#include <concepts>
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#include <cstddef>
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#include <cstring>
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#include <mutex>
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#include <new>
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#include <thread>
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#include <unordered_map>
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#include <vector>
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template<class T>
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concept resetable = requires(T val) {
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val.reset();
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};
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template<class T>
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requires std::default_initializable<T> && resetable<T>
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class allocPool {
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public:
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explicit allocPool(size_t allocNumbers)
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: vec(allocNumbers), pivot{allocNumbers} {
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memset(&(vec[0]), 0, sizeof(vec[0]) * vec.size());
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initArray(allocNumbers);
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}
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~allocPool() {
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for (auto i: vec)
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delete i;
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}
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T *getPtr() {
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if (pivot == 0)
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resizeVec();
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auto *ptrToReturn{vec[0]};
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std::swap(vec[0], vec[pivot - 1]);
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positionMap[vec[0]] = 0;
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positionMap[vec[pivot - 1]] = pivot - 1;
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pivot--;
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return ptrToReturn;
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}
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void returnPtr(T *ptr) {
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size_t pos = positionMap[ptr];
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ptr->reset();
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std::swap(vec[pos], vec[pivot]);
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positionMap[vec[pos]] = pos;
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positionMap[vec[pivot]] = pivot;
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pivot++;
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}
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private:
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std::vector<T *> vec;
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std::mutex positionMapMutex;
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std::unordered_map<T *, size_t> positionMap;
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size_t pivot;
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void initArray(size_t arrSize) {
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size_t amountOfThreads{std::thread::hardware_concurrency()};
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assert(amountOfThreads);
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size_t amountPerThread{arrSize / amountOfThreads};
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size_t minObjPerThread{std::hardware_destructive_interference_size / sizeof(void *)};
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std::vector<std::thread> threads;
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threads.reserve(amountOfThreads);
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// We try to avoid false sharing by defining a minimum size.
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amountPerThread = minObjPerThread > amountPerThread ? minObjPerThread : amountPerThread;
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amountOfThreads = arrSize / amountPerThread;
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for (size_t i{}; i < amountOfThreads; i++)
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threads.emplace_back(&allocPool::initObjects, this, i * amountPerThread, amountPerThread);
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for (auto &t: threads)
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t.join();
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// Remainder
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initObjects(arrSize - (arrSize % amountOfThreads), arrSize % amountOfThreads);
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}
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void initObjects(size_t startIdx, size_t amount) {
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for (size_t i{}; i < amount; i++) {
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vec[startIdx + i] = new T;
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}
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// In the future, it should be possible to write a custom hashmap with sections
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// with independent locks, or use a data structure which would be contiguous.
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std::lock_guard<std::mutex> guard(positionMapMutex);
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for (size_t i{}; i < amount; i++) {
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positionMap[vec[startIdx + i]] = i;
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}
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}
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void resizeVec() {
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size_t size{vec.size()};
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vec.resize(2 * size);
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pivot = size;
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memcpy(&(vec[size]), &(vec[0]), sizeof(vec[0]) * size);
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for (size_t i{}; i < size; i++)
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positionMap[vec[size + i]] = size + i;
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initArray(size);
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}
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};
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