direct_io.cc

#include <iostream>
#include <unistd.h>
#include <cstring>
#include <sys/mman.h>
#include <vector>
#include <thread>
#include <sys/stat.h> 
#include <fcntl.h>


#define likely(x)      __builtin_expect(!!(x), 1)
#define unlikely(x)    __builtin_expect(!!(x), 0)

static char data[4096] __attribute__((aligned(4096))) = {'a'};

void writer(int index) {
  std::string fname = "data" + std::to_string(index);

  int data_fd = ::open(fname.c_str(), O_RDWR | O_CREAT | O_APPEND | O_DIRECT, 0645);

  for (int32_t i = 0; i < 1000000; i++) {
    ::write(data_fd, data, 4096);
  }

  close(data_fd);
}

int main() {
  std::vector<std::thread> threads;
  for(int i = 0; i < 64; i++) {
    std::thread worker(writer, i);
    threads.push_back(std::move(worker));
  }
  for (int i = 0; i < 64; i++) {
    threads[i].join();
  }
  return 0;
}

// g++ -std=c++11 -O2 -pthread direct_io.cc -o benchmark