我试图在C方案拟订中履行(......)职能。

I m using the struct tms structure which consists of the fields: tms_utime, tms_cutime, tms_stime and tms_cstime.

为了在我的节目中履行职能,我确实:

1. Before I fork and create a child, I call the times function (in the parent process).

   times(&start_tms);
   

2. I create a pipe and I pass the times of start structure to the pipe when I m in the child process.
3. The child executes a simple ls -l command

4. 当儿童完成处决时,父亲第二次要求履行(或)职能。

   times(&end_tms);
   

   不幸的是,末端的时代是零! 我不知道为什么。

我在方案中不理解的是:

1) In the first printfs the times of the struct start are negative. Why is that? 2) When I run the program, why do I get zeros for times? What am i doing wrong?

我的方案如下:

提前感谢

#include <sys/times.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

int main() {

printf("test
");

int     fd[2]; //two pointers
int nbytes;
char    string[] = "Hello, world!
";
char    readbuffer[80];
struct tms start_tms;
struct tms end_tms;
clock_t start, end;
double cpu_time_used;

pipe(fd);

//once we have established the pipeline we fork the child
pid_t   childpid;
pid_t pid_waitpid;

//NEW MODIFICATION!!! call times before fork()!!!
times(&start_tms);

//they return negative values, but why???
printf("Test start_tms.tms_utime = %f

",start_tms.tms_utime);
printf("Test start_tms.tms_cutime = %f

",start_tms.tms_cutime);
printf("Test start_tms.tms_stime = %f

",start_tms.tms_stime);


if((childpid = fork()) == -1)
            {
                    perror("fork");
                    exit(1);
            }

if(childpid == 0)
            {

                    /* Child process closes up input side of pipe */
                     close(fd[0]);

                   /* call times function */ 
                   /*times(&start_tms);*/


                      //REMOVED!!!!
                    //write(fd[1], string, (strlen(string)+1));
                    write(fd[1], &start_tms.tms_cutime, sizeof(clock_t));
                    write(fd[1], &start_tms.tms_utime, sizeof(clock_t));
                    write(fd[1], &start_tms.tms_stime, sizeof(clock_t));

                     //execute /bin/ls
                    execl("/bin/ls", "/bin/ls", "-r", "-t", "-l", (char *) 0);

                    exit(0);


            }
else
            {
                    /* Parent process closes up output side of pipe */
                    close(fd[1]);

                    /* NEW MODIFICATION, wait for the child!!! */
                     if( (pid_waitpid  = waitpid(childpid,NULL,0) ) == -1)
                    {
                             perror("waitpid");
                             exit(1);
                     }



                    /* call times for capturing end times */
                    times(&end_tms);

                    /* define t1, t2, variables */
                    clock_t t1,t2,t3;


                     //REMOVED!!!!
                    //nbytes = read(fd[0], readbuffer, sizeof(readbuffer));
                    read(fd[0], &t1, sizeof(clock_t));
                    read(fd[0], &t2, sizeof(clock_t));
                    read(fd[0], &t3, sizeof(clock_t));

                    printf("Received string: %s

", readbuffer);
                    printf("Test t1 = %f

",t1);
                    printf("Test end_tms.tms_utime = %f

",end_tms.tms_utime);
                    printf("Test end_tms.tms_cutime = %f

",end_tms.tms_cutime);
                    printf("Test end_tms.tms_stime = %f

",end_tms.tms_stime);

                    /* Calculate times, unfortunately return zero, but why??? */
                    double cpu_time = end_tms.tms_cutime - t1;
                    double utime = end_tms.tms_utime - t2;
                    double stime = end_tms.tms_stime - t3;

                    //Unfortunately printfs return zero, but why???
                    printf("cpu time %f

",cpu_time);
                    printf("cpu Utime %f

",utime);
                    printf("cpu Stime %f

",stime);


}

}