SNMPALARM(3)                      Net-SNMP                      SNMPALARM(3)



NAME
       snmpalarmregister,  snmpalarmregisterhr,  snmpalarmunregister  -
       alarm functions

SYNOPSIS
       ##include <>

       unsigned int
       snmpalarmregister(unsigned int seconds,,
                           unsigned int flags,,
                           SNMPAlarmCallback **fcallback,,
                           void **clientarg);;

       unsigned int
       snmpalarmregisterhr(struct timeval t,,
                              unsigned int flags,,
                              SNMPAlarmCallback **fcallback,,
                              void **clientarg);;

       void
       snmpalarmunregister(unsigned int reg);;

DESCRIPTION
       These functions implement support for a generic timer  handling  mecha-
       nism  for  multiple  parts of an application to register function call-
       backs to happen at a particular time in the future.

USAGE
       The usage is fairly simple and straight-forward:  Simply create a func-
       tion  you  want  called back at some point in the future.  The function
       definition should be similar to:

           void mycallback(unsigned int reg,, void **clientarg);;

       Then, call snmpalarmregister() to register your callback to be called
       seconds  from now.  The flags field should either be SAREPEAT or NUL.
       If flags is set with SAREPEAT, then the registered  callback  function
       will  be called every seconds.  If flags is NUL then the function will
       only be called once and then removed from the  alarm  system  registra-
       tion.

       The  clientarg  parameter  in the registration function is used only by
       the client function and is stored and passed back directly to  them  on
       every call to the system.

       The snmpalarmregister() function returns a unique unsigned int (which
       is also passed as the first argument of each callback), which can  then
       be  used  to remove the callback from the queue at a later point in the
       future   using   the   snmpalarmunregister()   function.    If    the
       snmpalarmregister()  call fails it returns zero.  In particular, note
       that it is entirely permissible for an  alarm  function  to  unregister
       itself.

       The  snmpalarmregisterhr() function is identical in operation to the
       snmpalarmregister() function, but takes a struct timeval as  a  first
       parameter, and schedules the callback after the period represented by t
       (the letters hr stand for "high resolution").  The  operation  of  this
       function  is dependent on the provision of the setitimer(2) system call
       by the operating system.  If this system call  is  not  available,  the
       alarm  will  be  scheduled  as if snmpalarmregister() had been called
       with a first argument equal to the value of the  tvsec  member  of  t.
       See, however, the notes below.

INITIALIZATION
       The  initsnmp() function initialises the snmpalarm subsystem by call-
       ing initsnmpalarm() and then initalarmpostconfig() to set  up  the
       first  timer  to initialise the callback function.  These two functions
       should not be used directly by applications.

NOTES
       The default behaviour of the snmpalarm subsystem is to request SIGALRM
       signals from the operating system via the alarm(2) or setitimer(2) sys-
       tem calls.  This has the disadvantage, however, that no other  part  of
       the  application  can  use the SIGLARM functionality (or, if some other
       part of  the  application  does  use  the  SIGALRM  functionality,  the
       snmpalarm subsystem will not work correctly).

       If  your  application runs a select(2)-based event loop, however, there
       is no need to use SIGALRM for  the  snmpalarm  subsystem,  leaving  it
       available  for  other parts of the application.  This is done by making
       the following call:

       netsnmpdssetboolean(NETSNMPDSLIBRARYID,
                              NETSNMPDSLIBALARMDONTUSESIG, 1);

       before calling initsnmp().  Then, snmpselectinfo() takes alarms into
       account  when  calculating  the timeout value to be used for select(2).
       All you need to do  is  call  runalarms()  when  select(2)  times  out
       (return  value  of zero).  This is the approach taken in the agent; see
       snmpd.c.  Furthermore, when using this method, high  resolution  alarms
       do not depend on the presence of the setitimer(2) system call, although
       overall precision is of course still determined by the underlying oper-
       ating system.  Recommended.

SEE ALSO
       snmpapi(3),     defaultstore(3),    snmpselectinfo(3),    alarm(2),
       setitimer(2), select(2)



4.2 Berkeley Distribution         07 Mar 2002                    SNMPALARM(3)