testwrite.c

/***** testwrite.c *******/
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/time.h>
#include <fcntl.h>

double my_get_time() {
        struct timeval tv;
        gettimeofday(&tv,NULL);
        return ((double)tv.tv_sec+(double)tv.tv_usec/1000000);
}
int main(int argc, char** argv)
{
        int shm_id,i;
        key_t key;
        char temp;
        char *p_map;

        shm_id=shmget(1234567,100,IPC_CREAT|0660);
        if(shm_id==-1)
        {
                perror("shmget error");
                return;
        }
        p_map=(char*)shmat(shm_id,NULL,0);
        temp='a';
        double time_start,time_end;
        int fd = open("status",O_CREAT|O_RDONLY);
        
        for(i = 0;i<2;i++)
        {
               time_start = my_get_time();
                flock(fd,LOCK_EX);
                memset(p_map,temp,1);
                flock(fd,LOCK_UN);
                time_end = my_get_time();
                printf("%f\n",(time_end-time_start));
        }
         
        if(shmdt(p_map)==-1)
                perror(" detach error ");
}