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+=================
+Setting callbacks
+=================
+
+
+Get and set a callback
+
+.. index:: object: memcached_st
+
+
+--------
+SYNOPSIS
+--------
+
+#include <libmemcached/memcached.h>
+
+.. c:type:: memcached_callback_t
+ 
+.. c:function:: memcached_return_t memcached_callback_set (memcached_st *ptr, memcached_callback_t flag, const void *data)
+ 
+.. c:function:: void * memcached_callback_get (memcached_st *ptr, memcached_callback_t flag, memcached_return_t *error)
+
+Compile and link with -lmemcached
+
+
+-----------
+DESCRIPTION
+-----------
+
+
+libmemcached(3) 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.
+
+:c:func:`memcached_callback_get` takes a callback flag and returns the 
+structure or function set by :c:func:`memcached_callback_set`.
+
+:c:func:`memcached_callback_set` changes the function/structure assigned by a
+callback flag. No connections are reset.
+
+You can use :c:type:`MEMCACHED_CALLBACK_USER_DATA` to provide custom context 
+if required for any of the callbacks.
+
+
+.. c:type:: MEMCACHED_CALLBACK_CLEANUP_FUNCTION
+ 
+When :c:func:`memcached_delete` is called this function will be excuted. At 
+the point of its execution all connections are closed.
+ 
+
+
+.. c:type:: MEMCACHED_CALLBACK_CLONE_FUNCTION
+ 
+When :c:func:`memcached_delete` is called this function will be excuted. 
+At the point of its execution all connections are closed.
+
+.. c:type:: MEMCACHED_CALLBACK_PREFIX_KEY
+
+   See :c:type:`MEMCACHED_CALLBACK_NAMESPACE`
+
+.. c:type:: 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 :c:macro:`MEMCACHED_PREFIX_KEY_MAX_SIZE` - 1 and will
+reduce :c:macro:`MEMCACHED_MAX_KEY` by the value of your key. 
+
+The prefix key is only applied to the primary key, not the master key. 
+:c:type:`MEMCACHED_FAILURE` will be returned if no key is set. In the case of 
+a key which is too long, :c:type:`MEMCACHED_BAD_KEY_PROVIDED` will be returned.
+ 
+If you set a value with the value being NULL then the prefix key is disabled.
+
+.. c:type:: MEMCACHED_CALLBACK_USER_DATA
+ 
+This allows you to store a pointer to a specifc piece of data. This can be
+retrieved from inside of :c:func:`memcached_fetch_execute`. Cloning a 
+:c:type:`memcached_st` will copy the pointer to the clone.
+ 
+.. c:type:: MEMCACHED_CALLBACK_MALLOC_FUNCTION
+.. deprecated:: <0.32
+   Use :c:type:`memcached_set_memory_allocators` instead.
+
+.. c:type:: MEMCACHED_CALLBACK_REALLOC_FUNCTION
+.. deprecated:: <0.32
+   Use :c:type:`memcached_set_memory_allocators` instead.
+ 
+.. c:type:: MEMCACHED_CALLBACK_FREE_FUNCTION
+.. deprecated:: <0.32
+   Use :c:type:`memcached_set_memory_allocators` instead.
+
+.. c:type:: 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 :c:type:`memcached_st` in order to
+make use of it. The value will be stored only if you return
+:c:type:`MEMCACHED_SUCCESS` or :c:type:`MEMCACHED_BUFFERED`. Returning 
+:c:type:`MEMCACHED_BUFFERED` will cause the object to be buffered and not sent 
+immediatly (if this is the default behavior based on your connection setup 
+this will happen automatically).
+ 
+The prototype for this is:
+
+.. c:function:: memcached_return_t (\*memcached_trigger_key)(memcached_st \*ptr, char \*key, size_t key_length, memcached_result_st \*result);
+ 
+
+
+.. c:type:: 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: 
+
+.. c:function:: typedef memcached_return_t (\*memcached_trigger_delete_key)(memcached_st \*ptr, char \*key, size_t key_length);
+ 
+
+
+
+------
+RETURN
+------
+
+
+:c:func:`memcached_callback_get` return the function or structure that was 
+provided. Upon error, nothing is set, null is returned, and the 
+:c:type:`memcached_return_t` argument is set to :c:type:`MEMCACHED_FAILURE`.
+
+:c:func:`memcached_callback_set` returns :c:type:`MEMCACHED_SUCCESS` upon 
+successful setting, otherwise :c:type:`MEMCACHED_FAILURE` on error.
+
+
+----
+HOME
+----
+
+
+To find out more information please check:
+`http://libmemcached.org/ <http://libmemcached.org/>`_
+
+
+------
+AUTHOR
+------
+
+
+Brian Aker, <brian@tangent.org>
+
+
+--------
+SEE ALSO
+--------
+
+
+:manpage:`memcached(1)` :manpage:`libmemcached(3)` :manpage:`memcached_strerror(3)`