8.16 process times

8.16 process times

讲了怎么给一个process计时，这个计时包括：

1. Clock time及程序总共从启动到结束的时间差

2. user time，即在用户层使用的时间

3. system time即，在system层使用的时间。

当然要求在启动时和退出时两个时间点作两次记录，然后两次的结果做减法来得到。

单位都是ticks，一般CPU在一秒钟都有几十个ticks，这个可以通过sysconf获得。

接口：

#include

 

clock_t times(struct tms *buf);

 

Returns: elapsed wall clock time in clock ticks if OK, 1 on error

 

struct tms {

     clock_t  tms_utime;  /* user CPU time */

     clock_t  tms_stime;  /* system CPU time */

     clock_t  tms_cutime; /* user CPU time, terminated children */

     clock_t  tms_cstime; /* system CPU time, terminated children */

   };

 

例子：

Figure 8.30. Time and execute all command-line arguments

#include "apue.h"

#include 

static void pr_times(clock_t, struct tms *, struct tms *);

static void do_cmd(char *);

int

main(int argc, char *argv[])

{

    int     i;

    setbuf(stdout, NULL);

    for (i = 1; i < argc; i++)

        do_cmd(argv[i]);    /* once for each command-line arg */

    exit(0);

}

static void

do_cmd(char *cmd)        /* execute and time the "cmd" */

{

     struct tms  tmsstart, tmsend;

     clock_t     start, end;

     int         status;

     printf("\ncommand: %s\n", cmd);

     if ((start = times(&tmsstart)) == -1)    /* starting values */

         err_sys("times error");

     if ((status = system(cmd)) < 0)     /* execute command */

         err_sys("system() error");

     if ((end = times(&tmsend)) == -1)       /* ending values */

         err_sys("times error");

     pr_times(end-start, &tmsstart, &tmsend);

     pr_exit(status);

}

static void

pr_times(clock_t real, struct tms *tmsstart, struct tms *tmsend)

{

    static long     clktck = 0;

    if (clktck == 0)    /* fetch clock ticks per second first time */

        if ((clktck = sysconf(_SC_CLK_TCK)) < 0)

            err_sys("sysconf error");

     printf(" real:  %7.2f\n", real / (double) clktck);

     printf(" user:  %7.2f\n",

       (tmsend->tms_utime - tmsstart->tms_utime) / (double) clktck);

     printf(" sys:   %7.2f\n",

       (tmsend->tms_stime - tmsstart->tms_stime) / (double) clktck);

     printf(" child user:   %7.2f\n",

       (tmsend->tms_cutime - tmsstart->tms_cutime) / (double) clktck);

     printf(" child sys:    %7.2f\n",

       (tmsend->tms_cstime - tmsstart->tms_cstime) / (double) clktck);

}

结果：

$ ./a.out "sleep 5" "date"

   command: sleep 5

     real:     5.02

     user:     0.00

     sys:      0.00

     child user:     0.01

     child sys:      0.00

   normal termination, exit status = 0

   command: date

   Mon Mar 22 00:43:58 EST 2004

     real:     0.01

     user:     0.00

     sys:      0.00

     child user:     0.01

     child sys:      0.00

 normal termination, exit status = 0