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getitimer(2)

getitimer(2)                     System Calls                     getitimer(2)



NAME
       getitimer, setitimer - get or set value of interval timer

SYNOPSIS
       #include <sys/time.h>

       int getitimer(int which, struct itimerval *value);


       int setitimer(int which, const struct itimerval *value,
            struct itimerval *ovalue);

DESCRIPTION
       The  system provides each process with four interval timers, defined in
       <sys/time.h>. The getitimer() function stores the current value of  the
       timer  specified  by  which into the structure pointed to by value. The
       setitimer() function call sets the value  of  the  timer  specified  by
       which  to the value specified in the structure pointed to by value, and
       if ovalue is not NULL, stores the previous value of the  timer  in  the
       structure pointed to by ovalue.


       A  timer  value  is  defined by the itimerval structure (see gettimeof‐
       day(3C) for the definition of timeval), which  includes  the  following
       members:



         struct timeval    it_interval;         /* timer interval */
         struct timeval    it_value;            /* current value */





       The  it_value  member  indicates the time to the next timer expiration.
       The it_interval member specifies  a  value  to  be  used  in  reloading
       it_value  when  the  timer  expires.  Setting  it_value to 0 disables a
       timer, regardless of the value of it_interval. Setting it_interval to 0
       disables  a  timer after its next expiration (assuming it_value is non-
       zero).


       Time values smaller than the resolution of the system clock are rounded
       up  to  the resolution of the system clock, except for ITIMER_REALPROF,
       whose values are rounded up to the resolution of the  profiling  clock.
       The four timers are as follows:

       ITIMER_REAL        Decrements  in real time. A SIGALRM signal is deliv‐
                          ered to the process when this timer expires.


       ITIMER_VIRTUAL     Decrements  in  lightweight  process  (lwp)  virtual
                          time.  It  runs only when the calling lwp is execut‐
                          ing. A SIGVTALRM signal is delivered to the  calling
                          lwp when it expires.


       ITIMER_PROF        Decrements both in lightweight process (lwp) virtual
                          time and when the system is running on behalf of the
                          lwp.  It  is  designed to be used by interpreters in
                          statistically profiling the execution of interpreted
                          programs.  Each  time the ITIMER_PROF timer expires,
                          the SIGPROF signal is delivered to the calling  lwp.
                          Because  this signal may interrupt in-progress func‐
                          tions, programs using this timer must be prepared to
                          restart interrupted functions.


       ITIMER_REALPROF    Decrements  in  real time. It is designed to be used
                          for real-time profiling of  multithreaded  programs.
                          Each  time  the  ITIMER_REALPROF  timer expires, one
                          counter in a set of counters maintained by the  sys‐
                          tem  for  each  lightweight  process (lwp) is incre‐
                          mented. The counter corresponds to the state of  the
                          lwp  at the time of the timer tick. All lwps execut‐
                          ing in user mode when the timer expires  are  inter‐
                          rupted  into system mode. When each lwp resumes exe‐
                          cution in user mode, if any of the elements  in  its
                          set  of counters are non-zero, the SIGPROF signal is
                          delivered to the lwp. The SIGPROF signal  is  deliv‐
                          ered  before  any  other signal except SIGKILL. This
                          signal does not interrupt any in-progress  function.
                          A  siginfo structure, defined in <sys/siginfo.h>, is
                          associated with the delivery of the SIGPROF  signal,
                          and includes the following members:


                            si_tstamp;      /* high resolution timestamp */
                            si_syscall;     /* current syscall */
                            si_nsysarg;     /* number of syscall arguments */
                            si_sysarg[];     /* actual syscall arguments */
                            si_fault;       /* last fault type */
                            si_faddr;       /* last fault address */
                            si_mstate[];     /* ticks in each microstate */



                          The   enumeration   of   microstates  (indices  into
                          si_mstate) is defined in <sys/msacct.h>.

                          Unlike the other interval timers,  the  ITIMER_REAL‐
                          PROF  interval  timer is not inherited across a call
                          to one of the exec(2) family of functions.


RETURN VALUES
       Upon successful completion, 0 is returned. Otherwise,  −1  is  returned
       and errno is set to indicate the error.

ERRORS
       The getitimer() and setitimer() functions will fail if:

       EINVAL    The  specified number of seconds is greater than 100,000,000,
                 the number of  microseconds  is  greater  than  or  equal  to
                 1,000,000, or the which argument is unrecognized.


ATTRIBUTES
       See attributes(7) for descriptions of the following attributes:


       tab()  box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
       TRIBUTE VALUE _ Interface StabilityCommitted (Obsolete)  _  MT-LevelMT-
       Safe _ StandardSee standards(7).


SEE ALSO
       alarm(2),    exec(2),    gettimeofday(3C),    sleep(3C),   sysconf(3C),
       attributes(7), standards(7)

NOTES
       The setitimer() function is independent of the alarm(2)  and  sleep(3C)
       functions.


       The  ITIMER_PROF and ITIMER_REALPROF timers deliver the same signal and
       have different semantics. They cannot be used together.


       The granularity of the resolution of alarm time is platform-dependent.



Oracle Solaris 11.4               15 Aug 2012                     getitimer(2)
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