NAME

       memcached_callback - 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)