Linux signal Practice (5)--Time and timer

three different kinds of sleep accuracy

1.sleep

#include <unistd.h>unsigned int sleep (unsigned int seconds);

RETURN VALUE

Zero If the requested time has a elapsed, or the number of seconds left to sleep,

If the call is interrupted by a signal handler.

Example int sleeptime = 5;do{    sleeptime = Sleep (sleeptime);} while (Sleeptime > 0);

2.usleep (in microseconds)

int Usleep (useconds_t usec);

The type useconds_t is a unsigned integer type capable of holding integers in the range [0,1000000].

Programs'll is more portable if they never mention this type explicitly.

3.nanosleep (in nanoseconds)

#include <time.h>int nanosleep (const struct TIMESPEC *req, struct timespec *rem);

REQ Specifies the time of sleep, REM returns the remaining sleep time

struct timespec{    time_t tv_sec;        /* Seconds: SEC */    long   tv_nsec;       /* nanoseconds: nanoseconds */};

Three time Structures

time_t

struct Timeval {long    tv_sec;         /* seconds */long    tv_usec;        /* microseconds microseconds */};

struct Timespec {time_t tv_sec;        /* seconds */long   tv_nsec;       /* nanoseconds */};

Setitimer

#include <sys/time.h>int setitimer (int which, const struct itimerval *value, struct itimerval *ovalue));

Setitimer () is powerful than alarm and supports 3 types of timers

Parameters

The first parameter which specifies the type of timer

The second parameter is the requested time

The third parameter is the value that the timer originally associated

struct itimerval{    struct timeval it_interval;/* Next value: The interval between the time the signal is generated */    struct timeval it_value;    /* Current value: The first time the signal is generated */};struct timeval{    time_t      tv_sec;         /* Seconds: SEC */    suseconds_t tv_usec;        /* Microseconds: microseconds */};

which value

itimer_real: After a specified amount of time, the kernel sends a SIGALRM signal to the process (with more)

itimer_virtual : After the program executes the specified time in the user space, the kernel sends a SIGVTALRM signal to the process

itimer_prof : When the process executes in kernel space, the time count is reduced, usually shared with itimer_virtual, and the kernel sends a SIGPROF signal to the process after the specified time has elapsed between user space and kernel space.

/** example 1:1. Generates a signal after 5 seconds of starting the process 2. Then generate a signal every 1 seconds **/int main () {    if (signal (SIGALRM, signalaction) = = Sig_err)        err_exit ("Signal error");    struct Itimerval it;    struct Timeval it_interval = {1, 0};    struct Timeval It_value = {5, 0};    It.it_interval = It_interval;    It.it_value = It_value;    if (Setitimer (Itimer_real, &it, NULL) = =-1)        err_exit ("Setitimer error");    while (true)        pause ();}

/** Example 2: Get the Itimerval struct **/int main () {    struct itimerval it;    struct Timeval it_interval = {1, 0};    struct Timeval It_value = {5, 0};    It.it_interval = It_interval;    It.it_value = It_value;    if (Setitimer (Itimer_real, &it, NULL) = =-1)        err_exit ("Setitimer error");    for (int i = 0; i < 100000; ++i)        ;    struct Itimerval oldit;//    if (Setitimer (Itimer_real, &it, &oldit) = =-1)//        err_exit ("Setitimer error ");    Get the remaining time without re-setting the clock    if (Getitimer (itimer_real, &oldit) = =-1)        err_exit ("Getitimer error");    cout << oldIt.it_interval.tv_sec << ' << oldIt.it_interval.tv_usec         << ' << oldit.i T_value.tv_sec << ' << oldIt.it_value.tv_usec << Endl;}

Attached: seconds-microseconds-conversion of nanoseconds

s (seconds), MS (MS), μs (microseconds), NS (nanoseconds), Where: 1s=1000ms,1 ms=1000μs,1μs=1000ns

Linux signal Practice (5)--Time and timer