Linux System Programming Learning Notes (11) Time

1. The kernel provides three different ways to record time:

Wall Time(or real time): actual time and date in the real worldProcess Time: The time, a process spends executing on a processor includes user times and system time themonotonic Time: Use the system ' suptime (time since boot)For this purpose,guarantee, the time source is strictly linearly increasing UNIX represents absolute timing: the number of elapsed seconds s Ince the epoch, which is defined as00:00:00UTC on the morning of 1 January 1970On Linux, the frequency of the system timer is called HZ,The value of HZ is Architecture-specificPOSIX functions that return time in terms of the clock ticks use clocks_per_sec To represent the fixed frequency 2. The original representation of the data structure of the time representation:

long time_t;

That's won ' t last long before Overflowing! Microsecond precision means:

 #include <sys/time.h> Timeval {time_t tv_sec;  /*   seconds   suseconds_t Tv_usec;  /*   microseconds  Span style= "Color:rgb (0, 128, 0); >*/ };  

<time.h>struct  timespec {        time_t  tv_sec;        /*  */        long    tv_nsec;      /* */};

3. Get the current time

#include <time.h>*t);

Time () returns the current time represented as the number of seconds elapsed since the epoch

#include <sys/time.h>int gettimeofday(structstruct timezone *tz);

Gettimeofday () places the current time of the timeval structure pointed at by TV and returns 0 parameter TZ is always null

 struct   Timeval TV;  int   Ret;ret  = gettimeofday (&tv, NULL ); if   (ret) perror (  gettimeofday   "  else   printf (  seconds=%ld useconds=%ld\n  " , ( long ) Tv.sec, (long ) tv.tv_usec); 

#include <sys/times.h>structTMS {clock_t tms_utime; /*User Time consumed*/clock_t Tms_stime; /*system time consumed*/clock_t Tms_cutime; /*user time consumed by children*/clock_t Tms_cstime; /*system time consumed by children*/};clock_t Times (structTMS *buf);

User time is the time spent executing code in user space.  System time is the time spent executing code in kernel space. 4. Set the current time

#include <time.h>int stime (time_t *<sys/time.h>int settimeofday (const  structconststruct timezone *tz);

Parameter TZ is always null

struct 31415926 27182818  }; int  = Settimeofday (&TV, NULL); if (ret)        perror ("settimeofday");

5. Sleep hibernation

/*   puts the invoking process to  sleepfor the number of seconds*/<unistd.h> /c6>intint seconds);

/*  */#define _xopen_source<unistd.h>int  int usec);

#include <sys/Select.h>intSelect (intstruct timeval *timeout);

The Select function sets the parameter n to 0, and the three detection event set is set to null, when the select is equivalent to a sleep function of the exact time, and this usage is most portable

struct 0 757  }; Select (0, NULL, NULL, NULL, &TV);

6. Timer timers provide a mechanism for notifying a process when a given amount of time elapses simple timer:

#include <unistd.h>intint seconds);

Schedules the delivery of a SIGALRM signal to the invoking process after seconds of real time has elapsed

void alarm_handler (int  signum) {        printf ("Five seconds passed!\n " );} void func (void) {        signal (SIGALRM, alarm_handler);        Alarm (5);        Pause ();}

Interval Timer:

#include <sys/time.h>intGetitimer (intWhich,structItimerval *value);intSetitimer (intWhich,Const structItimerval *value,structItimerval *ovalue);structItimerval {structTimeval It_interval;/*Next Value*/        structTimeval It_value;/*Current value*/};structTimeval {LongTv_sec;/*seconds*/        LongTv_usec;/*microseconds*/};

voidAlarm_handler (intSigno) {printf ("Timer hit!\n");}voidFoo (void){        structitimerval delay; intret;        Signal (SIGALRM, Alarm_handler); Delay.it_value.tv_sec=5; Delay.it_value.tv_usec=0; Delay.it_interval.tv_sec=1; Delay.it_interval.tv_usec=0; RET= Setitimer (Itimer_real, &delay, NULL); if(ret) {perror ("Setitimer"); return; } pause ();}