NAME

       memcached_callback_get - libmemcached Documentation

SYNOPSIS

       #include <libmemcached/memcached.h>
              Compile and link with -lmemcached

       memcached_return_t memcached_callback_set(memcached_st *ptr, memcached_callback_t flag, const void *data)

              Parameters

                     • ptr -- pointer to initialized memcached_st struct

                     • flag -- memcached_callback_t flag to set

                     • data -- data corresponding to flag

              Returns
                     memcached_return_t indicating success

       void *memcached_callback_get(memcached_st *ptr, memcached_callback_t flag, memcached_return_t *error)

              Parameters

                     • ptr -- pointer to initialized memcached_st struct

                     • flag -- memcached_callback_t flag to query

                     • error -- pointer to memcached_return_t indicating success

              Returns
                     the data previously set

       typedef enum memcached_callback_t memcached_callback_t

       enum memcached_callback_t

              enumerator MEMCACHED_CALLBACK_CLEANUP_FUNCTION
                     When  memcached_free()  or memcached_reset is called this function will be executed. At the
                     point of its execution all connections are closed.

                     Its signature is:

                     typedef memcached_return_t (*memcached_cleanup_fn)(const memcached_st *ptr)

              enumerator MEMCACHED_CALLBACK_CLONE_FUNCTION
                     When memcached_clone() is called this function will be executed.

                     Its signature is:

                     typedef memcached_return_t (*memcached_clone_fn)(memcached_st *destination, const
                     memcached_st *source)

              enumerator MEMCACHED_CALLBACK_PREFIX_KEY
                     See MEMCACHED_CALLBACK_NAMESPACE.

              enumerator MEMCACHED_CALLBACK_NAMESPACE
                     You can set a value which will be used to  create  a  domain  for  your  keys.   The  value
                     specified  here  will  be  prefixed to each of your keys. The value can not be greater then
                     MEMCACHED_MAX_NAMESPACE - 1 and will reduce MEMCACHED_MAX_KEY by the value of your key.

                     The prefix key is only applied to the primary key, not the master  key.   MEMCACHED_FAILURE
                     will  be  returned  if  no  key  is  set.  In  the  case  of  a  key  which  is  too  long,
                     MEMCACHED_BAD_KEY_PROVIDED will be returned.

                     If you set a value with the value being NULL then the prefix key is disabled.

              enumerator MEMCACHED_CALLBACK_USER_DATA
                     This allows you to store a pointer to a specific piece of data. This can be retrieved  from
                     inside  of  memcached_fetch_execute().  Cloning a memcached_st will copy the pointer to the
                     clone.

              enumerator MEMCACHED_CALLBACK_MALLOC_FUNCTION
                     Deprecated since version <0.32: Use memcached_set_memory_allocators() instead.

              enumerator MEMCACHED_CALLBACK_REALLOC_FUNCTION
                     Deprecated since version <0.32: Use memcached_set_memory_allocators() instead.

              enumerator MEMCACHED_CALLBACK_FREE_FUNCTION
                     Deprecated since version <0.32: Use memcached_set_memory_allocators() instead.

              enumerator MEMCACHED_CALLBACK_GET_FAILURE
                     This function implements the read through cache behavior.  On  failure  of  retrieval  this
                     callback will be called.

                     You are responsible for populating the result object provided. This result object will then
                     be stored in the server and returned to the calling process.

                     You  must  clone the memcached_st in order to make use of it. The value will be stored only
                     if you return MEMCACHED_SUCCESS or MEMCACHED_BUFFERED.  Returning  MEMCACHED_BUFFERED  will
                     cause  the  object to be buffered and not sent immediately (if this is the default behavior
                     based on your connection setup this will happen automatically).

                     The prototype for this is:

                     typedef memcached_return_t (*memcached_trigger_key)(memcached_st *ptr, char *key, size_t
                     key_length, memcached_result_st *result)

              enumerator MEMCACHED_CALLBACK_DELETE_TRIGGER
                     This function implements a trigger upon successful deletion of  a  key.   The  memcached_st
                     structure will need to be cloned in order to make use of it.

                     The prototype for this is:

                     typedef memcached_return_t (*memcached_trigger_delete_key)(memcached_st *ptr, char *key,
                     size_t key_length)

DESCRIPTION

       libmemcached  can  have callbacks set key execution points. These either provide function calls at points
       in the code, or return pointers to structures for particular usages.

       memcached_callback_get()  takes  a  callback  flag  and  returns  the  structure  or  function   set   by
       memcached_callback_set().

       memcached_callback_set()  changes  the function/structure assigned by a callback flag. No connections are
       reset.

       You can use MEMCACHED_CALLBACK_USER_DATA to provide custom context if required for any of the callbacks.

RETURN VALUE

       memcached_callback_get() returns the function or structure that was provided.   Upon  error,  nothing  is
       set, NULL is returned, and the memcached_return_t argument is set to MEMCACHED_FAILURE.

       memcached_callback_set()  returns  MEMCACHED_SUCCESS upon successful setting, otherwise MEMCACHED_FAILURE
       on error.

SEE ALSO

       memcached(1) libmemcached(3) memcached_strerror(3)

1.1                                               Mar 31, 2024                         MEMCACHED_CALLBACK_GET(3)