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cache_handler(3)                   net-snmp                   cache_handler(3)



NAME
       cache_handler -

       Maintains a cache of data for use by lower level handlers.


   Functions
       netsnmp_cache * netsnmp_cache_get_head (void)
           get cache head
       netsnmp_cache * netsnmp_cache_find_by_oid (const oid *rootoid, int rootoid_len)
           find existing cache
       netsnmp_cache * netsnmp_cache_create (int timeout, NetsnmpCacheLoad *load_hook, NetsnmpCacheFree *free_hook,
           const oid *rootoid, int rootoid_len)
           returns a cache
       int netsnmp_cache_free (netsnmp_cache *cache)
           frees a cache
       unsigned int netsnmp_cache_timer_start (netsnmp_cache *cache)
           starts the recurring cache_load callback
       void netsnmp_cache_timer_stop (netsnmp_cache *cache)
           stops the recurring cache_load callback
       netsnmp_mib_handler * netsnmp_cache_handler_get (netsnmp_cache *cache)
           returns a cache handler that can be injected into a given handler chain.
       netsnmp_mib_handler * netsnmp_get_cache_handler (int timeout, NetsnmpCacheLoad *load_hook, NetsnmpCacheFree
           *free_hook, const oid *rootoid, int rootoid_len)
           returns a cache handler that can be injected into a given handler chain.
       int netsnmp_cache_handler_register (netsnmp_handler_registration *reginfo, netsnmp_cache *cache)
           functionally the same as calling netsnmp_register_handler() but also injects a cache handler at the same
           time for you.
       int netsnmp_register_cache_handler (netsnmp_handler_registration *reginfo, int timeout, NetsnmpCacheLoad
           *load_hook, NetsnmpCacheFree *free_hook)
           functionally the same as calling netsnmp_register_handler() but also injects a cache handler at the same
           time for you.
       NETSNMP_STATIC_INLINE char * _build_cache_name (const char *name)
       void netsnmp_cache_reqinfo_insert (netsnmp_cache *cache, netsnmp_agent_request_info *reqinfo, const char *name)
           Insert the cache information for a given request (PDU).
       netsnmp_cache * netsnmp_cache_reqinfo_extract (netsnmp_agent_request_info *reqinfo, const char *name)
           Extract the cache information for a given request (PDU).
       netsnmp_cache * netsnmp_extract_cache_info (netsnmp_agent_request_info *reqinfo)
           Extract the cache information for a given request (PDU).
       int netsnmp_cache_check_expired (netsnmp_cache *cache)
           Check if the cache timeout has passed.
       int netsnmp_cache_check_and_reload (netsnmp_cache *cache)
           Reload the cache if required.
       int netsnmp_cache_is_valid (netsnmp_agent_request_info *reqinfo, const char *name)
           Is the cache valid for a given request?
       int netsnmp_is_cache_valid (netsnmp_agent_request_info *reqinfo)
           Is the cache valid for a given request? for backwards compatability.
       int netsnmp_cache_helper_handler (netsnmp_mib_handler *handler, netsnmp_handler_registration *reginfo,
           netsnmp_agent_request_info *reqinfo, netsnmp_request_info *requests)
           Implements the cache handler.
       void release_cached_resources (unsigned int regNo, void *clientargs)
           run regularly to automatically release cached resources.

Detailed Description
       Maintains a cache of data for use by lower level handlers.

       This helper checks to see whether the data has been loaded 'recently' (according to the timeout for that
       particular cache) and calls the registered 'load_cache' routine if necessary. The lower handlers can then work
       with this local cached data.

       A timeout value of -1 will cause netsnmp_cache_check_expired() to always return true, and thus the cache will
       be reloaded for every request.

       To minimze resource use by the agent, a periodic callback checks for expired caches, and will call the
       free_cache function for any expired cache.

       The load_cache route should return a negative number if the cache was not successfully loaded. 0 or any
       positive number indicates successs.

       Several flags can be set to affect the operations on the cache.

       If NETSNMP_CACHE_DONT_INVALIDATE_ON_SET is set, the free_cache method will not be called after a set request
       has processed. It is assumed that the lower mib handler using the cache has maintained cache consistency.

       If NETSNMP_CACHE_DONT_FREE_BEFORE_LOAD is set, the free_cache method will not be called before the load_cache
       method is called. It is assumed that the load_cache routine will properly deal with being called with a valid
       cache.

       If NETSNMP_CACHE_DONT_FREE_EXPIRED is set, the free_cache method will not be called with the cache expires. The
       expired flag will be set, but the valid flag will not be cleared. It is assumed that the load_cache routine
       will properly deal with being called with a valid cache.

       If NETSNMP_CACHE_PRELOAD is set when a the cache handler is created, the cache load routine will be called
       immediately.

       If NETSNMP_CACHE_DONT_AUTO_RELEASE is set, the periodic callback that checks for expired caches will skip the
       cache. The cache will only be checked for expiration when a request triggers the cache handler. This is useful
       if the cache has it's own periodic callback to keep the cache fresh.

       If NETSNMP_CACHE_AUTO_RELOAD is set, a timer will be set up to reload the cache when it expires. This is useful
       for keeping the cache fresh, even in the absence of incoming snmp requests.

       Here are some suggestions for some common situations.

       Cached File: If your table is based on a file that may periodically change, you can test the modification date
       to see if the file has changed since the last cache load. To get the cache helper to call the load function for
       every request, set the timeout to -1, which will cause the cache to always report that it is expired. This
       means that you will want to prevent the agent from flushing the cache when it has expired, and you will have to
       flush it manually if you detect that the file has changed. To accomplish this, set the following flags:

       NETSNMP_CACHE_DONT_FREE_EXPIRED NETSNMP_CACHE_DONT_AUTO_RELEASE

       Constant (periodic) reload: If you want the cache kept up to date regularly, even if no requests for the table
       are received, you can have your cache load routine called periodically. This is very useful if you need to
       monitor the data for changes (eg a LastChanged object). You will need to prevent the agent from flushing the
       cache when it expires. Set the cache timeout to the frequency, in seconds, that you wish to reload your cache,
       and set the following flags:

       NETSNMP_CACHE_DONT_FREE_EXPIRED NETSNMP_CACHE_DONT_AUTO_RELEASE NETSNMP_CACHE_AUTO_RELOAD

Function Documentation
   int netsnmp_cache_check_and_reload (netsnmp_cache * cache)
       Reload the cache if required.

       Definition at line 420 of file cache_handler.c.

   int netsnmp_cache_check_expired (netsnmp_cache * cache)
       Check if the cache timeout has passed. Sets and return the expired flag.

       Definition at line 405 of file cache_handler.c.

   netsnmp_cache* netsnmp_cache_create (int timeout, NetsnmpCacheLoad * load_hook, NetsnmpCacheFree * free_hook, const
       oid * rootoid, int rootoid_len)
       returns a cache

       Definition at line 146 of file cache_handler.c.

   netsnmp_cache* netsnmp_cache_find_by_oid (const oid * rootoid, int rootoid_len)
       find existing cache

       Definition at line 130 of file cache_handler.c.

   int netsnmp_cache_free (netsnmp_cache * cache)
       frees a cache

       Definition at line 189 of file cache_handler.c.

   netsnmp_cache* netsnmp_cache_get_head (void)
       get cache head

       Definition at line 122 of file cache_handler.c.

   netsnmp_mib_handler* netsnmp_cache_handler_get (netsnmp_cache * cache)
       returns a cache handler that can be injected into a given handler chain.

       Definition at line 282 of file cache_handler.c.

   int netsnmp_cache_handler_register (netsnmp_handler_registration * reginfo, netsnmp_cache * cache)
       functionally the same as calling netsnmp_register_handler() but also injects a cache handler at the same time
       for you.

       Definition at line 330 of file cache_handler.c.

   int netsnmp_cache_helper_handler (netsnmp_mib_handler * handler, netsnmp_handler_registration * reginfo,
       netsnmp_agent_request_info * reqinfo, netsnmp_request_info * requests)
       Implements the cache handler.

       next handler called automatically - 'AUTO_NEXT'

       next handler called automatically - 'AUTO_NEXT'

       next handler called automatically - 'AUTO_NEXT'

       Definition at line 455 of file cache_handler.c.

   int netsnmp_cache_is_valid (netsnmp_agent_request_info * reqinfo, const char * name)
       Is the cache valid for a given request?

       Definition at line 437 of file cache_handler.c.

   netsnmp_cache* netsnmp_cache_reqinfo_extract (netsnmp_agent_request_info * reqinfo, const char * name)
       Extract the cache information for a given request (PDU).

       Definition at line 385 of file cache_handler.c.

   void netsnmp_cache_reqinfo_insert (netsnmp_cache * cache, netsnmp_agent_request_info * reqinfo, const char * name)
       Insert the cache information for a given request (PDU).

       Definition at line 368 of file cache_handler.c.

   unsigned int netsnmp_cache_timer_start (netsnmp_cache * cache)
       starts the recurring cache_load callback

       Definition at line 226 of file cache_handler.c.

   void netsnmp_cache_timer_stop (netsnmp_cache * cache)
       stops the recurring cache_load callback

       Definition at line 261 of file cache_handler.c.

   netsnmp_cache* netsnmp_extract_cache_info (netsnmp_agent_request_info * reqinfo)
       Extract the cache information for a given request (PDU).

       Definition at line 397 of file cache_handler.c.

   netsnmp_mib_handler* netsnmp_get_cache_handler (int timeout, NetsnmpCacheLoad * load_hook, NetsnmpCacheFree *
       free_hook, const oid * rootoid, int rootoid_len)
       returns a cache handler that can be injected into a given handler chain.

       Definition at line 311 of file cache_handler.c.

   int netsnmp_is_cache_valid (netsnmp_agent_request_info * reqinfo)
       Is the cache valid for a given request? for backwards compatability. for backwards compat

       netsnmp_cache_is_valid() is preferred.

       Definition at line 448 of file cache_handler.c.

   int netsnmp_register_cache_handler (netsnmp_handler_registration * reginfo, int timeout, NetsnmpCacheLoad *
       load_hook, NetsnmpCacheFree * free_hook)
       functionally the same as calling netsnmp_register_handler() but also injects a cache handler at the same time
       for you.

       Definition at line 343 of file cache_handler.c.

   void release_cached_resources (unsigned int regNo, void * clientargs)
       run regularly to automatically release cached resources. xxx - method to prevent cache from expiring while a
       request is being processed (e.g. delegated request). proposal: set a flag, which would be cleared when request
       finished (which could be acomplished by a dummy data list item in agent req info & custom free function).

       Definition at line 608 of file cache_handler.c.

Author
       Generated automatically by Doxygen for net-snmp from the source code.



Version 5.5                       23 Sep 2009                 cache_handler(3)