Simple Linux timer example crashes

[Josh]

Just making a simple timer is unbelievably complicated and the documentation example can't even run without crashing:

Quote

Unable to open 'sigprocmask.c': Unable to read file '/build/glibc-eX1tMB/glibc-2.31/sysdeps/unix/sysv/linux/sigprocmask.c' (Error: Unable to resolve non-existing file '/build/glibc-eX1tMB/glibc-2.31/sysdeps/unix/sysv/linux/sigprocmask.c').

#include <stdint.h>
       #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 orr;

           tidp = (timer_t*)si->si_value.sival_ptr;

           printf("    sival_ptr = %p; ", si->si_value.sival_ptr);
           printf("    *sival_ptr = %#jx\n", (uintmax_t) *tidp);

           orr = timer_getoverrun(*tidp);
           if (orr == -1)
               errExit("timer_getoverrun");
           else
               printf("    overrun count = %d\n", orr);
       }

       static void
       handler(int sig, siginfo_t *si, void *uc)
       {
           /* Note: calling printf() from a signal handler is not safe
              (and should not be done in production programs), since
              printf() is not async-signal-safe; see signal-safety(7).
              Nevertheless, we use printf() here as a simple way of
              showing that the handler was called. */

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

       int main(int argc, char *argv[])
       {
            long long msecs = 500;

           timer_t timerid;
           struct sigevent sev;
           struct itimerspec its;
           long long freq_nanosecs;
           sigset_t mask;
           struct sigaction sa;

           /* 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 %#jx\n", (uintmax_t) timerid);

           /* Start the timer. */

           freq_nanosecs = msecs * 1000000;
           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 5 seconds\n");
           sleep(5);

           /* 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);
       }

 

[Josh]

The problem is that GDB is stopping every time any signal is received. Very not wanted.

https://github.com/microsoft/vscode-cpptools/issues/7546

[Ma-Shell]

You can change GDB's behaviour: https://ftp.gnu.org/old-gnu/Manuals/gdb/html_node/gdb_38.html

Something like 

handle SIG33 nostop noprint pass

should do the trick (whereas SIG33 should correspond to SIGRTMIN). Just put any commands for disabling signals into your .gdbinit file.

Edited May 18, 2021 by Ma-Shell
formatting

[Josh]

Ah okay, the .gdbinit file has to be in the home directory, and then it will work. Thanks!

[Ma-Shell]

Yeah, basically every file starting with a dot belongs into the home directory because the starting dot is basically the Linux way of hiding files and that folder ist the only place where you would want to hide the files because otherwise they clutter your home directory (like on Windows your Documents-directory which is completely unusable for me because every program puts their data there)

[aiaf]

Home directory is the usual place to store program configurations for the user ( hidden .filename also .directoryname). Thats why gdb looks there.

Also every directory has this:

.  = current directory

.. = parent directory