Multithreading fstream
Archived 2 years ago
F
Fabian Hofmann
Playing Custom Status
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I'm trying to write simulaniously into a file using fstreams on multiple threads. But for some reason I always get the fastest results when only using one thread. Does anyone know why?
```#pragma once
#include <atomic>
#include <thread>
#include "TestWriter.h"
#include "../ut_General/Random.hpp"
#include "../ut_General/Test.hpp"
template <uintmax_t ThreadCount>
class TestWriterMultiThreadManualChunkBuffer : public TestWriter {
public:
TestWriterMultiThreadManualChunkBuffer() = default;
virtual ~TestWriterMultiThreadManualChunkBuffer() = default;
virtual void WriteToFile(std::filesystem::path path, uintmax_t fileSize, uintmax_t chunkSize, char* data) {
std::error_code err;
std::filesystem::resize_file(path, fileSize, err);
if (err) {
std::cout << err.message() << std::endl;
return;
}
std::thread* threads[ThreadCount];
for (int x = 0; x < ThreadCount; x++) {
threads[x] = new std::thread(&WriteThread, path, fileSize, chunkSize, data, this);
}
for (int x = 0; x < ThreadCount; x++) {
threads[x]->join();
delete threads[x];
}
}
virtual std::string ToString() {
return "Multi Thread <" + std::to_string(ThreadCount) + "> : Manual Chunk Buffer";
}
private:
static void WriteThread(std::filesystem::path path, uintmax_t fileSize, uintmax_t chunkSize, char* data, TestWriterMultiThreadManualChunkBuffer* that) {
std::fstream stream(path, std::fstream::out | std::fstream::in | std::fstream::binary);
while (true) {
uintmax_t c = that->counter.fetch_add(1);
if (c >= fileSize / chunkSize) {
return;
}
stream.write(data + c * chunkSize, chunkSize);
}
}
std::atomic<uintmax_t> counter = 0;
};```
