C++11特性原子类型——多原子类型并行访问的串行化测试
/*C++11 原子类型测试
问题：如果有多个原子需要操作，如何保障并行的序列化
*/
#include <thread>
#include <stdlib.h>
#include <atomic>
#include <iostream>
#include <time.h>
#include <vector>
#include "mytimer.h"
using namespace std;
//用原子数据类型作为共享资源的数据类型
atomic_long total(0);
atomic_int i(0);
//long total = 0;
TimeVal a, b;
void click()
{
//由于有两个原子类型，必须保证更新的顺序性
while (i++ < 10000000) //原子操作，保障了顺序操作
total += 1; //
/*错误
while(i < 1000000) //一次读取
{
i++; //上次读取i到这里未防止再次读取i的值
total++;
}
*/
}
//如果用单线程计算的话
long commonclick()
{
long total = 0;
for(int i = 0; i < 10000000; i++)
total++;
return total;
}
int main(int argc, char* argv[])
{
int N = 16;
double time0, time1;
if (argc == 2)
N = atoi(argv[1]);
//主线程测试
get_current_time( a );
long val = commonclick();
get_current_time( b );
cout << "Main thread" << endl;
cout<<"result:"<<val<<endl;
time0 = getDeltaTime(b, a) * 1e3;
cout<<"duration:"<< time0 <<"ms"<<endl;
cout << "Single thread" << endl;
//单线程测试
get_current_time( a );
thread t1(commonclick);
t1.join();
get_current_time( b );
cout<<"duration:"<< getDeltaTime(b, a) * 1e3 <<"ms"<<endl;
cout << "Multi thread " << N << endl;
// 计时开始
get_current_time( a );
// 创建N个线程模拟点击统计
vector<thread> threads(N);
for(int i=0; i<N;++i)
{
threads[i] = thread(click);
}
for(int i=0; i<N;++i)
threads[i].join();
// 计时结束
get_current_time( b );
// 输出结果
cout<<"result:"<<total<<endl;
time1 = getDeltaTime(b, a) * 1e3;
cout<<"duration:"<< time1 <<"ms"<<endl;
cout << "Delay for each thread: " << time1 / N - time0 << "ms, about " << time1/N / time0 << " time of main thread." << endl;
return 0;
}
mytimer.h文件
#ifndef __MYGLIB_H__
#define __MYGLIB_H__
#include <windows.h>
typedef LARGE_INTEGER TimeVal;
LARGE_INTEGER freq;
void get_current_time(TimeVal& s)
{
QueryPerformanceFrequency(&freq);
QueryPerformanceCounter(&s);
}
double getDeltaTime(TimeVal t2, TimeVal t1)
{
double time = (double)(t2.QuadPart-t1.QuadPart)/(double)freq.QuadPart;
return time;
}
#endif
编译：
g++ -std=c++11 atomic_par.cpp
运行结果：
运行a 2
Main thread
result:10000000
duration:25.7743ms
Single thread
duration:29.4485ms
Multi thread 2
result:10000000
duration:372.861ms
Delay for each thread: 160.656ms, about 7.23319 time of main thread.
运行a 4
Main thread
result:10000000
duration:22.2332ms
Single thread
duration:23.3911ms
Multi thread 4
result:10000000
duration:472.065ms
Delay for each thread: 95.783ms, about 5.3081 time of main thread.
运行a 8
Main thread
result:10000000
duration:22.2252ms
Single thread
duration:22.7899ms
Multi thread 8
result:10000000
duration:468.485ms
Delay for each thread: 36.3355ms, about 2.63488 time of main thread.
运行a 16
Main thread
result:10000000
duration:22.399ms
Single thread
duration:23.7603ms
Multi thread 16
result:10000000
duration:489.68ms
Delay for each thread: 8.20599ms, about 1.36636 time of main thread.
从最后结果看，每个线程由于任务少了，所用时间短了，但总的系统用于线程调度的时间多了。