Linux Timer Timer "Turn"

Transferred from: https://www.jianshu.com/p/66b3c75cae81

TIMERFD is a timer interface provided by Linux for the user program, which is based on a file descriptor, which is timed out via a read-through event of the file descriptor and can be used for epoll/select. There are three main functions.

Header file: include <sys/timerfd.h>int timerfd_create (int clockid, int flags)

Function: Generate timer, return file descriptor.
Clockid:clock_monotonic or Clock_realtime, where clock_monotonic represents the time it takes for the system to restart to the present, and changing the system time has no effect on it. Clock_realtime represents the time from 1970.1.1 to the present, changing the system time changes the obtained value.
Flags:tfd_nonblock (non-blocking), tfd_cloexec (same as O_cloexec).
The file descriptor for the Return:timer.

int timerfd_settime (int tfd, int flags, const struct ITIMERSPEC *newvalue, struct itimerspec *oldvalue)

Function: Used to start or close the timer for the specified FD.
TFD:TIMERFD, returned by the Timerfd_create function.
Flags:1 indicates that the absolute time is set; 0 indicates the relative time.
NewValue: Specify a new time-out, or turn off the timer if Newvalue.it_value is not 0. If the Newvalue.it_interval is 0, the timer is timed only once, otherwise every set time expires once.
OldValue: NOT NULL returns the time-out before the timer is set.
Return: Failure returns-1.

struct TIMESPEC
{
time_t tv_sec; Seconds
Long tv_nsec; Na-Sec
}
struct ITIMERSPEC
{
struct Timespec it_interval; After the first timeout, every it_interval times out
struct Timespec it_value; First Time Out
}

int timerfd_gettime (int fd, struct itimerspec *curvalue)

Function: Used to get the time remaining from the next time-out. If the timer has expired (that is, more than It_value time) when called, and the timer is in loop mode (that is, It_interval is not 0), the timer starts again after the function is called.
FD:TIMERFD, returned by the Timerfd_create function.
Curvalue: Returns the remaining time from the next timeout.
Return: Failed return-1

Read TIMERFD

When the timer expires, TIMERFD is readable, returns an integer of type uint64_t, the number of timeouts (refers to how many timeouts are unread), if the timer does not have a timeout event, if the TIMERFD is blocked, read will block, if TIMERFD is non-blocking, return eagain error. If read is less than 8 bytes of data, the EINVAL error is returned.

Sample code

#Include<sys/timerfd.h>#Include<sys/epoll.h>#Include<unistd.h>#Include<stdint.h>#Include<iostream>UsingNamespaceStdConstint epoll_size =10;IntMain(int argc,char* argv[]) {int TfD, EPFD, Nfds;structEpoll_eventEventstructEpoll_eventevents[Epoll_size];Create TIMERFD, Clock_realtime for absolute time, tfd_nonblock for non-blocking TFD = Timerfd_create (Clock_realtime, Tfd_nonblock);if (TfD <0) {Cerr <<"Timerfd_create error!" <<EndlReturn-1; }structTimespecStartTime,IntervalTime; Starttime.tv_sec =0; Starttime.tv_nsec =1;Equivalent to immediate arrival time-out intervaltime.tv_sec =3;After the first timeout, the timeout is intervaltime.tv_nsec every three seconds =0;structItimerspecNewValue; Newvalue.it_value = StartTime; Newvalue.it_interval = IntervalTime;Set the time-out period and the relative timeif (Timerfd_settime (TFD,0, &newvalue,NULL) <0) {Cerr <<"Timerfd_settime error!" <<EndlReturn-1; }Use Epoll to monitor descriptor EPFD = epoll_create (epoll_size);if (EPFD <0) {Cerr <<"Epoll_create error!" <<EndlReturn-1; } EVENT.DATA.FD = tfd; Event.events = Epollin;if (Epoll_ctl (EPFD, Epoll_ctl_add, TfD, &event) <0) {Cerr <<"Epoll_ctl error!" <<EndlReturn-1; }uint64_t count =0;while (1) {//nonblocking wait Nfds = epoll_wait (EPFD, events, Epoll_size, 0); if (Nfds = 0) continue; for (int i = 0; i < Nfds; i++) {if (events[i].events & Epollin) {uint64_t data; Read (EVENTS[I].DATA.FD, &data, sizeof (uint64_t)); count + = data; cout << " read: "<< data << endl;}} return 0;}         

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Linux Timer Timer "Turn"