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Updated: Thursday, June 13, 2019
 
 

snmp_alarm_unregister (3)

Name

snmp_alarm_unregister - alarm functions

Synopsis

#include <net-snmp/utilities.h>

unsigned int
snmp_alarm_register(unsigned int seconds,
unsigned int flags,
SNMPAlarmCallback *f_callback,
void *clientarg);

unsigned int
snmp_alarm_register_hr(struct timeval t,
unsigned int flags,
SNMPAlarmCallback *f_callback,
void *clientarg);

void
snmp_alarm_unregister(unsigned int reg);

Description

SNMP_ALARM(3)                      Net-SNMP                      SNMP_ALARM(3)



NAME
       snmp_alarm_register,  snmp_alarm_register_hr,  snmp_alarm_unregister  -
       alarm functions

SYNOPSIS
       #include <net-snmp/utilities.h>

       unsigned int
       snmp_alarm_register(unsigned int seconds,
                           unsigned int flags,
                           SNMPAlarmCallback *f_callback,
                           void *clientarg);

       unsigned int
       snmp_alarm_register_hr(struct timeval t,
                              unsigned int flags,
                              SNMPAlarmCallback *f_callback,
                              void *clientarg);

       void
       snmp_alarm_unregister(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 my_callback(unsigned int reg, void *clientarg);

       Then, call snmp_alarm_register() to register your callback to be called
       seconds  from now.  The flags field should either be SA_REPEAT or NULL.
       If flags is set with SA_REPEAT, then the registered  callback  function
       will  be called every seconds.  If flags is NULL 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 snmp_alarm_register() 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   snmp_alarm_unregister()   function.    If    the
       snmp_alarm_register()  call fails it returns zero.  In particular, note
       that it is entirely permissible for an  alarm  function  to  unregister
       itself.

       The  snmp_alarm_register_hr() function is identical in operation to the
       snmp_alarm_register() 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 snmp_alarm_register() had been called
       with a first argument equal to the value of the  tv_sec  member  of  t.
       See, however, the notes below.

INITIALIZATION
       The  init_snmp() function initialises the snmp_alarm subsystem by call-
       ing init_snmp_alarm() and then init_alarm_post_config() to set  up  the
       first  timer  to initialise the callback function.  These two functions
       should not be used directly by applications.


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


       +---------------+-----------------------------------------------+
       |ATTRIBUTE TYPE |               ATTRIBUTE VALUE                 |
       +---------------+-----------------------------------------------+
       |Availability   | system/management/snmp/net-snmp/documentation |
       +---------------+-----------------------------------------------+
       |Stability      | Volatile                                      |
       +---------------+-----------------------------------------------+
NOTES
       The default behaviour of the snmp_alarm 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
       snmp_alarm 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  snmp_alarm  subsystem,  leaving  it
       available  for  other parts of the application.  This is done by making
       the following call:

       netsnmp_ds_set_boolean(NETSNMP_DS_LIBRARY_ID,
                              NETSNMP_DS_LIB_ALARM_DONT_USE_SIG, 1);

       before calling init_snmp().  Then, snmp_select_info() takes alarms into
       account  when  calculating  the timeout value to be used for select(2).
       All you need to do  is  call  run_alarms()  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
       netsnmp_session_api(3),   default_store(3),   alarm(2),   setitimer(2),
       select(2)


       This    software    was    built    from    source     available     at
       https://github.com/oracle/solaris-userland.    The  original  community
       source  was  downloaded  from   http://ftp.ntua.gr/mirror/net-snmp/net-
       snmp/5.7.3/net-snmp-5.7.3.tar.gz

       Further information about this software can be found on the open source
       community website at http://www.net-snmp.org/.



V5.7.3                            01 Aug 2002                    SNMP_ALARM(3)