应用层timer_libc

Posted 2020-11-08 yuxi_o

应用层除了通过setitimer/getitimer设置获取timer外，还可通过timer_create()等一系列函数实现应用层timer功能。

应用流程

The timers created by timer_create() are commonly known as "POSIX (interval) timers". The POSIX timers API consists of the following interfaces:

* timer_create(): Create a timer.

* timer_settime(2): Arm (start) or disarm (stop) a timer.

* timer_gettime(2): Fetch the time remaining until the next expiration of a timer, along with the interval setting of the timer.

* timer_getoverrun(2): Return the overrun count for the last timer expiration.

* timer_delete(2): Disarm and delete a timer.

timer_create

#include <signal.h>
#include <time.h>
int timer_create(clockid_t clockid, struct sigevent *sevp, timer_t *timerid);

 

timer_create() creates a new per-process interval timer. The ID of the new timer is returned in the buffer pointed to by timerid, which must be a non-null pointer.
This ID is unique within the process, until the timer is deleted. The new timer is initially disarmed（初始化时timer未安装）.

参数clockid

The clockid argument specifies the clock that the new timer uses to measure time. It can be specified as one of the following values:

CLOCK_REALTIME      A settable system-wide real-time clock.（一般采用此id）

CLOCK_MONOTONIC
A nonsettable monotonically increasing clock that measures time from some unspecified point in the past that does not change after system startup.

CLOCK_PROCESS_CPUTIME_ID (since Linux 2.6.12)
A clock that measures (user and system) CPU time consumed by (all of the threads in) the calling process.

CLOCK_THREAD_CPUTIME_ID (since Linux 2.6.12)
A clock that measures (user and system) CPU time consumed by the calling thread.

参数sevp

sigevent指定当timer到期时的动作。

sevp.sigev_notify可以是SIGEV_NONE（时间到期时不通知），SIGEV_SIGNAL（产生信号），SIGEV_THREAD（invoke新进程），SIGEV_THREAD_ID（指定线程处理）。

详细内容可man sigevent。

返回值
成功返回0，timeid保存到*timerid。 失败返回-1。

manpage示例：

　　　　#include <stdlib.h>
       #include <unistd.h>
       #include <stdio.h>
       #include <signal.h>
       #include <time.h>

       #define CLOCKID CLOCK_REALTIME
       #define SIG SIGRTMIN

       #define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \
                               } while (0)

       static void
       print_siginfo(siginfo_t *si)
       {
           timer_t *tidp;
           int or;

           tidp = si->si_value.sival_ptr;

           printf("    sival_ptr = %p; ", si->si_value.sival_ptr);
           printf("    *sival_ptr = 0x%lx\n", (long) *tidp);

           or = timer_getoverrun(*tidp);
           if (or == -1)
               errExit("timer_getoverrun");
           else
               printf("    overrun count = %d\n", or);
       }
static void
       handler(int sig, siginfo_t *si, void *uc)
       {
           /* Note: calling printf() from a signal handler is not
              strictly correct, since printf() is not async-signal-safe;
              see signal(7) */

           printf("Caught signal %d\n", sig);
           print_siginfo(si);
           signal(sig, SIG_IGN);
       }

       int
       main(int argc, char *argv[])
       {
           timer_t timerid;
           struct sigevent sev;
           struct itimerspec its;
           long long freq_nanosecs;
           sigset_t mask;
           struct sigaction sa;

           if (argc != 3) {
               fprintf(stderr, "Usage: %s <sleep-secs> <freq-nanosecs>\n",
                       argv[0]);
               exit(EXIT_FAILURE);
           }

           /* Establish handler for timer signal */

           printf("Establishing handler for signal %d\n", SIG);
           sa.sa_flags = SA_SIGINFO;
           sa.sa_sigaction = handler;
           sigemptyset(&sa.sa_mask);
           if (sigaction(SIG, &sa, NULL) == -1)
               errExit("sigaction");

           /* Block timer signal temporarily */
           printf("Blocking signal %d\n", SIG);
           sigemptyset(&mask);
           sigaddset(&mask, SIG);
           if (sigprocmask(SIG_SETMASK, &mask, NULL) == -1)
               errExit("sigprocmask");

           /* Create the timer */

           sev.sigev_notify = SIGEV_SIGNAL;
           sev.sigev_signo = SIG;
           sev.sigev_value.sival_ptr = &timerid;
           if (timer_create(CLOCKID, &sev, &timerid) == -1)
               errExit("timer_create");

           printf("timer ID is 0x%lx\n", (long) timerid);

           /* Start the timer */

           freq_nanosecs = atoll(argv[2]);
           its.it_value.tv_sec = freq_nanosecs / 1000000000;
           its.it_value.tv_nsec = freq_nanosecs % 1000000000;
           its.it_interval.tv_sec = its.it_value.tv_sec;
           its.it_interval.tv_nsec = its.it_value.tv_nsec;

           if (timer_settime(timerid, 0, &its, NULL) == -1)
                errExit("timer_settime");

           /* Sleep for a while; meanwhile, the timer may expire
              multiple times */

           printf("Sleeping for %d seconds\n", atoi(argv[1]));
           sleep(atoi(argv[1]));

           /* Unlock the timer signal, so that timer notification
              can be delivered */

           printf("Unblocking signal %d\n", SIG);
           if (sigprocmask(SIG_UNBLOCK, &mask, NULL) == -1)
               errExit("sigprocmask");

           exit(EXIT_SUCCESS);
       }