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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)
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