timers/demo_timerfd.c

+/* demo_timerfd.c
+
+   Demonstrate the use of the timerfd API, which creates timers whose
+   expirations can be read via a file descriptor.
+
+   This program is Linux-specific. The timerfd API is supported since kernel
+   2.6.25. Library support is provided since glibc 2.8.
+*/
 #include <sys/timerfd.h>
 #include <time.h>
 #include <stdint.h>                     /* Definition of uint64_t */
 #include "itimerspec_from_str.h"        /* Declares itimerspecFromStr() */
 #include "tlpi_hdr.h"
 
 int
 main(int argc, char *argv[])
 {
     struct itimerspec ts;
     struct timespec start, now;
     int maxExp, fd, secs, nanosecs;
     uint64_t numExp, totalExp;
     ssize_t s;
 
     if (argc < 2 || strcmp(argv[1], "--help") == 0)
         usageErr("%s secs[/nsecs][:int-secs[/int-nsecs]] [max-exp]\n", argv[0]);
 
     itimerspecFromStr(argv[1], &ts);
     maxExp = (argc > 2) ? getInt(argv[2], GN_GT_0, "max-exp") : 1;
 
     fd = timerfd_create(CLOCK_REALTIME, 0);
     if (fd == -1)
         errExit("timerfd_create");
 
     if (timerfd_settime(fd, 0, &ts, NULL) == -1)
         errExit("timerfd_settime");
 
     if (clock_gettime(CLOCK_MONOTONIC, &start) == -1)
         errExit("clock_gettime");
 
     for (totalExp = 0; totalExp < maxExp;) {
 
         /* Read number of expirations on the timer, and then display
            time elapsed since timer was started, followed by number
            of expirations read and total expirations so far. */
 
         s = read(fd, &numExp, sizeof(uint64_t));
         if (s != sizeof(uint64_t))
             errExit("read");
 
         totalExp += numExp;
 
         if (clock_gettime(CLOCK_MONOTONIC, &now) == -1)
             errExit("clock_gettime");
 
         secs = now.tv_sec - start.tv_sec;
         nanosecs = now.tv_nsec - start.tv_nsec;
         if (nanosecs < 0) {
             secs--;
             nanosecs += 1000000000;
         }
 
         printf("%d.%03d: expirations read: %llu; total=%llu\n",
                 secs, (nanosecs + 500000) / 1000000,
                 (unsigned long long) numExp, (unsigned long long) totalExp);
     }
 
     exit(EXIT_SUCCESS);
 }