通过man手册可以查看详细的用法 见文末
#include
int getitimer(int which, struct itimerval *curr_value);
int setitimer(int which, const struct itimerval *new_value,
struct itimerval *old_value);
(1)which
which参数表示类型,可选的值有:
ITIMER_REAL:以系统真实的时间来计算,它送出SIGALRM信号。
ITIMER_VIRTUAL:以该进程在用户态下花费的时间来计算,它送出SIGVTALRM信号。
ITIMER_PROF:以该进程在用户态下和内核态下所费的时间来计算,它送出SIGPROF信号
(2)时间结构体
struct itimerval
{
/* Interval for periodic timer */
struct timeval it_interval;
/* Time until next expiration */
struct timeval it_value;
};
struct timeval
{
time_t tv_sec; /* seconds */
suseconds_t tv_usec; /* microseconds 1/1000000 seconds */
};
new_value: 参数用来对计时器进行设置,it_interval为计时间隔,it_value为延时时长,下面例子中表示的是在setitimer方法调用成功后,延时it_value后触发一次SIGALRM信号,以后每隔it_interval触发一次SIGALRM信号。
settimer工作机制是,先对it_value倒计时,当it_value为零时触发信号,然后重置为it_interval,继续对it_value倒计时,一直这样循环下去。
基于此机制,setitimer既可以用来延时执行,也可定时执行。
假如it_value为0是不会触发信号的,所以要能触发信号,it_value得大于0;如果it_interval为零,只会延时,不会定时(也就是说只会触发一次信号)。
old_value: 参数,通常用不上,设置为NULL,它是用来存储上一次setitimer调用时设置的new_value值。
以下是简单的定时器实现
#ifndef _LINUX_TIMER_H_
#define _LINUX_TIMER_H_
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
//定时器精度 100ms
typedef struct TimerEvent
{
unsigned long long periodic_time;
void (*ExecuFunc)(void *);
}TimerEvent;
int InitTimer();
int AddTimer(TimerEvent * _pst_timer_event);
int DeleteTimer(TimerEvent * _pst_timer_target);
#endif
#include "linux_timer.h"
using namespace std;
static std::list <TimerEvent> list_timer_event;
static unsigned long long g_timer_expires = 0;
static void TimerSchedule(int signo);
int InitTimer()
{
struct itimerval value_new;
signal(SIGALRM,TimerSchedule);
value_new.it_value.tv_sec = 1; // 一秒之后启动定时器
value_new.it_value.tv_usec = 0;
value_new.it_interval.tv_sec = 0;
value_new.it_interval.tv_usec = 100000;
setitimer(ITIMER_REAL, &value_new, NULL);
}
int AddTimer(TimerEvent * _pst_timer_event)
{
if(_pst_timer_event != nullptr)
{
list_timer_event.push_back(* _pst_timer_event);
}
}
int DeleteTimer(TimerEvent * _pst_timer_target)
{
for(auto it_timer_event = list_timer_event.begin();
it_timer_event != list_timer_event.end();it_timer_event++)
{
if(it_timer_event->periodic_time == _pst_timer_target->periodic_time &&
it_timer_event->ExecuFunc == _pst_timer_target->ExecuFunc)
{
list_timer_event.erase(it_timer_event);
}
}
}
static void ThrExecuFunc(std::list<TimerEvent>::iterator _it_timer_event)
{
_it_timer_event->ExecuFunc(NULL);
}
static void TimerSchedule(int signo)
{
g_timer_expires++;
for(auto it_timer_event = list_timer_event.begin();it_timer_event != list_timer_event.end();it_timer_event++)
{
if(it_timer_event->periodic_time && (g_timer_expires % it_timer_event->periodic_time) == 0
&& it_timer_event->ExecuFunc)
{
thread thr_execu_func(ThrExecuFunc,it_timer_event);
thr_execu_func.detach();
}
}
}
http://man7.org/linux/man-pages/
GETITIMER(2) Linux Programmer's Manual GETITIMER(2)
NAME
getitimer, setitimer - get or set value of an interval timer
SYNOPSIS
#include
int getitimer(int which, struct itimerval *curr_value);
int setitimer(int which, const struct itimerval *new_value,
struct itimerval *old_value);
DESCRIPTION
These system calls provide access to interval timers, that is, timers that initially expire at some point in the future,
and (optionally) at regular intervals after that. When a timer expires, a signal is generated for the calling process,
and the timer is reset to the specified interval (if the interval is nonzero).
Three types of timers—specified via the which argument—are provided, each of which counts against a different clock and
generates a different signal on timer expiration:
ITIMER_REAL This timer counts down in real (i.e., wall clock) time. At each expiration, a SIGALRM signal is gener‐
ated.
ITIMER_VIRTUAL This timer counts down against the user-mode CPU time consumed by the process. (The measurement includes
CPU time consumed by all threads in the process.) At each expiration, a SIGVTALRM signal is generated.
ITIMER_PROF This timer counts down against the total (i.e., both user and system) CPU time consumed by the process.
(The measurement includes CPU time consumed by all threads in the process.) At each expiration, a SIGPROF
signal is generated.
In conjunction with ITIMER_VIRTUAL, this timer can be used to profile user and system CPU time consumed by
the process.
A process has only one of each of the three types of timers.
Timer values are defined by the following structures:
struct itimerval {
struct timeval it_interval; /* Interval for periodic timer */
struct timeval it_value; /* Time until next expiration */
};
struct timeval {
time_t tv_sec; /* seconds */
suseconds_t tv_usec; /* microseconds */
};
getitimer()
The function getitimer() places the current value of the timer specified by which in the buffer pointed to by curr_value.
The it_value substructure is populated with the amount of time remaining until the next expiration of the specified
timer. This value changes as the timer counts down, and will be reset to it_interval when the timer expires. If both
fields of it_value are zero, then this timer is currently disarmed (inactive).
The it_interval substructure is populated with the timer interval. If both fields of it_interval are zero, then this is
a single-shot timer (i.e., it expires just once).
setitimer()
The function setitimer() arms or disarms the timer specified by which, by setting the timer to the value specified by
new_value. If old_value is non-NULL, the buffer it points to is used to return the previous value of the timer (i.e.,
the same information that is returned by getitimer()).
If either field in new_value.it_value is nonzero, then the timer is armed to initially expire at the specified time. If
both fields in new_value.it_value are zero, then the timer is disarmed.
The new_value.it_interval field specifies the new interval for the timer; if both of its subfields are zero, the timer is
single-shot.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
ERRORS
EFAULT new_value, old_value, or curr_value is not valid a pointer.
EINVAL which is not one of ITIMER_REAL, ITIMER_VIRTUAL, or ITIMER_PROF; or (since Linux 2.6.22) one of the tv_usec fields
in the structure pointed to by new_value contains a value outside the range 0 to 999999.
CONFORMING TO
POSIX.1-2001, SVr4, 4.4BSD (this call first appeared in 4.2BSD). POSIX.1-2008 marks getitimer() and setitimer() obso‐
lete, recommending the use of the POSIX timers API (timer_gettime(2), timer_settime(2), etc.) instead.
NOTES
Timers will never expire before the requested time, but may expire some (short) time afterward, which depends on the sys‐
tem timer resolution and on the system load; see time(7). (But see BUGS below.) If the timer expires while the process
is active (always true for ITIMER_VIRTUAL), the signal will be delivered immediately when generated.
A child created via fork(2) does not inherit its parent's interval timers. Interval timers are preserved across an
execve(2).
POSIX.1 leaves the interaction between setitimer() and the three interfaces alarm(2), sleep(3), and usleep(3) unspeci‐
fied.
The standards are silent on the meaning of the call:
setitimer(which, NULL, &old_value);
Many systems (Solaris, the BSDs, and perhaps others) treat this as equivalent to:
getitimer(which, &old_value);
In Linux, this is treated as being equivalent to a call in which the new_value fields are zero; that is, the timer is
disabled. Don't use this Linux misfeature: it is nonportable and unnecessary.
BUGS
The generation and delivery of a signal are distinct, and only one instance of each of the signals listed above may be
pending for a process. Under very heavy loading, an ITIMER_REAL timer may expire before the signal from a previous expi‐
ration has been delivered. The second signal in such an event will be lost.
On Linux kernels before 2.6.16, timer values are represented in jiffies. If a request is made set a timer with a value
whose jiffies representation exceeds MAX_SEC_IN_JIFFIES (defined in include/linux/jiffies.h), then the timer is silently
truncated to this ceiling value. On Linux/i386 (where, since Linux 2.6.13, the default jiffy is 0.004 seconds), this
means that the ceiling value for a timer is approximately 99.42 days. Since Linux 2.6.16, the kernel uses a different
internal representation for times, and this ceiling is removed.
On certain systems (including i386), Linux kernels before version 2.6.12 have a bug which will produce premature timer
expirations of up to one jiffy under some circumstances. This bug is fixed in kernel 2.6.12.
POSIX.1-2001 says that setitimer() should fail if a tv_usec value is specified that is outside of the range 0 to 999999.
However, in kernels up to and including 2.6.21, Linux does not give an error, but instead silently adjusts the corre‐
sponding seconds value for the timer. From kernel 2.6.22 onward, this nonconformance has been repaired: an improper
tv_usec value results in an EINVAL error.
SEE ALSO
gettimeofday(2), sigaction(2), signal(2), timer_create(2), timerfd_create(2), time(7)
COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about
reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
Linux 2017-09-15 GETITIMER(2)
参考博文 https://blog.csdn.net/lixianlin/article/details/25604779