MEMCACHED_CALLBACK_GET(3)

📦
version 1.1.4 · 13 versions
, in fedora 43

💖 MEMCACHED_CALLBACK_GET 💖

okay bestie, sit down, hydrate, because we're about to talk about the libmemcached-awesome callback system and it is lowkey iconic. this is the memcached_callback_get page from the libmemcached docs, and yes, the setter function is here too, because they're a package deal. 🫶

✨ NAME ✨

memcached_callback_get — libmemcached Documentation. that's the whole vibe. it gets callbacks. no cap. 💅

🌸 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

  • MEMCACHED_CALLBACK_CLEANUP_FUNCTION — when memcached_free() or memcached_reset gets called, this function runs. and at the exact moment it runs? all connections are closed. bye bestie, doors shut. ✌️

its signature is:

typedef memcached_return_t (*memcached_cleanup_fn)(const
memcached_st *ptr)
  • MEMCACHED_CALLBACK_CLONE_FUNCTION — when memcached_clone() gets called, this function runs. main character moment for cloning, fr fr.

its signature is:

typedef memcached_return_t (*memcached_clone_fn)(
memcached_st *destination, const memcached_st *source)
  • MEMCACHED_CALLBACK_PREFIX_KEY — go look at MEMCACHED_CALLBACK_NAMESPACE, they're the same situation. it's giving "see also: my sister". 👯
  • MEMCACHED_CALLBACK_NAMESPACE — you can set a value that gets used to build a domain for your keys. that value gets prefixed onto every single one of your keys. the value can not be greater then MEMCACHED_MAX_NAMESPACE - 1 and it 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. if no key is set, MEMCACHED_FAILURE gets returned. and if your key is too long? MEMCACHED_BAD_KEY_PROVIDED comes back at you. 😭

and if you set the value to NULL, the prefix key gets disabled. periodt.

  • MEMCACHED_CALLBACK_USER_DATA — this lets you stash a pointer to a specific lil piece of data. you can grab it back from inside memcached_fetch_execute(). and cloning a memcached_st will copy that pointer over to the clone. 🎀
  • MEMCACHED_CALLBACK_MALLOC_FUNCTION — deprecated since version <0.32: use memcached_set_memory_allocators() instead. it's over, bestie, move on. 💀
  • MEMCACHED_CALLBACK_REALLOC_FUNCTION — deprecated since version <0.32: use memcached_set_memory_allocators() instead. same energy, same replacement. 🙈
  • MEMCACHED_CALLBACK_FREE_FUNCTION — deprecated since version <0.32: use memcached_set_memory_allocators() instead. third one, still deprecated, still the same answer. 💅
  • MEMCACHED_CALLBACK_GET_FAILURE — this one implements the read through cache behavior. when a retrieval fails, this callback gets called. ✨

you are responsible for populating the result object that's provided. that 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 only be stored if you return MEMCACHED_SUCCESS or MEMCACHED_BUFFERED. returning MEMCACHED_BUFFERED will cause the object to be buffered and not sent immediately — and if that's the default behavior based on your connection setup, it'll happen automatically anyway. slay. 🌈

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)
  • MEMCACHED_CALLBACK_DELETE_TRIGGER — this one 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 at key execution points. these either provide function calls at points in the code, or return pointers to structures for particular usages. it's giving "hooks, but make it fancy". 🧚

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. like, zero. none. chill.

you can use MEMCACHED_CALLBACK_USER_DATA to provide custom context if you require it for any of the callbacks. very much the "bring your own vibes" option. 🍓

⭐ 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.

ngl, MEMCACHED_FAILURE is the vibe check nobody wants to fail. check your return values, bestie. 🙏

🔥 SEE ALSO 🔥

that's the whole page, bestie, no notes. this was libmemcached-awesome version 1.1, dated Jul 24, 2025 — go forth and set your callbacks responsibly, ily, mwah 💖🦋👑

📦 where this page comes from