atomic

#include <atomic>
#include <fcntl.h> /* For O_* constants */
#include <fstream>
#include <iostream>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/stat.h> /* For mode constants */
#include <sys/wait.h>
#include <thread>
#include <unistd.h>/* For fork*/
#include <vector>

#define FILE_MODE (S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)
#define SVSHM_MODE (SHM_R | SHM_W | SHM_R >> 3 | SHM_R >> 6)

std::atomic<int> acnt = ATOMIC_VAR_INIT(0);
int cnt;

void fun() {
  for (int n = 0; n < 1000; ++n) {
    std::atomic_fetch_add(&acnt, 1); // 原子的
    ++cnt; // 未定义行为，实际上会失去一些更新
  }
  return;
}

int main(void) {
  std::vector<std::thread> v;
  for (int n = 0; n < 10; ++n) {
    v.emplace_back(fun);
  }
  for (auto &t : v) {
    t.join();
  }

  printf("The atomic counter is %u\n", acnt.load());
  printf("The non-atomic counter is %u\n", cnt);
  int shmid =
      shmget(IPC_PRIVATE, sizeof(std::atomic<int>), SVSHM_MODE | IPC_CREAT);
  std::atomic<int> *pAtomic = (std::atomic<int> *)shmat(shmid, NULL, 0);
  std::cout << "share addr:" << pAtomic << std::endl;
  std::vector<pid_t> pidList;
  int processId = 0;
  int thNum = 3;

  std::ofstream test_case_ofs;
  for (; processId < thNum; processId++) {
    pid_t pid = fork();
    if (pid == 0 || pid == -1) {
      // pAtomic = (std::atomic<int> *)shmat(shmid, NULL, 0); /*not must*/
      std::cout << "share addr:" << pAtomic << std::endl;
      std::string file = "group" + std::to_string(processId);
      test_case_ofs.open(file);
      break;
    } else {
      pidList.push_back(pid);
    }
  }
  if (processId < thNum) {
    int test_index;
    while (test_index = std::atomic_fetch_add(pAtomic, 1), test_index < 1000) {
      test_case_ofs << "index:" << test_index << std::endl;
    }
  } else {
    int wstatus = 0;
    for (auto &cpid : pidList) {
      waitpid(cpid, &wstatus, 0);
    }
    std::cout << "The share mem atomic counter is " << pAtomic->load() << std::endl;
  }
}

atomic

原文：https://www.cnblogs.com/ims-/p/13902693.html