4thr.cpp

#include <thread>
#include <sys/time.h>
#include <stdio.h>


void Thr1(){
    float num;
    for(unsigned int i=0;i<25000U;i++){
        num=1.00001f;
        for(unsigned int j=0;j<1000000U;j++){
            num*=1.00001f;
        }
    }
}
void Thr2(){
    float num;
    for(unsigned int i=0;i<25000U;i++){
        num=1.00001f;
        for(unsigned int j=0;j<1000000U;j++){
            num*=1.00001f;
        }
    }
}
void Thr3(){
    float num;
    for(unsigned int i=0;i<25000U;i++){
        num=1.00001f;
        for(unsigned int j=0;j<1000000U;j++){
            num*=1.00001f;
        }
    }
}
void Thr4(){
    float num;
    for(unsigned int i=0;i<25000U;i++){
        num=1.00001f;
        for(unsigned int j=0;j<1000000U;j++){
            num*=1.00001f;
        }
    }
}
int main(){
    timeval n,e;
    double exec_time=0;
    float num;
    std::thread thr1,thr2,thr3,thr4;
    gettimeofday(&n,NULL);

    thr1=std::thread(Thr1);
    thr2=std::thread(Thr2);
    thr3=std::thread(Thr3);
    thr4=std::thread(Thr4);

    thr1.join();
    thr2.join();
    thr3.join();
    thr4.join();

    gettimeofday(&e,NULL);
    exec_time=((double)e.tv_sec-n.tv_sec)*1000.0f+((double)e.tv_usec-n.tv_usec)/1000.0f;
    printf("%f\n",exec_time);
    return 0;
}