1MEMCACHED_CALLBACK(3)        libmemcached-awesome        MEMCACHED_CALLBACK(3)
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NAME

6       memcached_callback - libmemcached Documentation
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SYNOPSIS

9       #include <libmemcached/memcached.h>
10              Compile and link with -lmemcached
11
12       memcached_return_t       memcached_callback_set(memcached_st      *ptr,
13       memcached_callback_t flag, const void *data)
14
15              Parameters
16
17                     • ptr -- pointer to initialized memcached_st struct
18
19                     • flag -- memcached_callback_t flag to set
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21                     • data -- data corresponding to flag
22
23              Returns
24                     memcached_return_t indicating success
25
26       void  *memcached_callback_get(memcached_st  *ptr,  memcached_callback_t
27       flag, memcached_return_t *error)
28
29              Parameters
30
31                     • ptr -- pointer to initialized memcached_st struct
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33                     • flag -- memcached_callback_t flag to query
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35                     • error  -- pointer to memcached_return_t indicating suc‐
36                       cess
37
38              Returns
39                     the data previously set
40
41       typedef enum memcached_callback_t memcached_callback_t
42
43       enum memcached_callback_t
44
45              enumerator MEMCACHED_CALLBACK_CLEANUP_FUNCTION
46                     When memcached_free() or memcached_reset is  called  this
47                     function  will be executed. At the point of its execution
48                     all connections are closed.
49
50                     Its signature is:
51
52                     typedef memcached_return_t  (*memcached_cleanup_fn)(const
53                     memcached_st *ptr)
54
55              enumerator MEMCACHED_CALLBACK_CLONE_FUNCTION
56                     When  memcached_clone()  is  called this function will be
57                     executed.
58
59                     Its signature is:
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61                     typedef   memcached_return_t   (*memcached_clone_fn)(mem‐
62                     cached_st *destination, const memcached_st *source)
63
64              enumerator MEMCACHED_CALLBACK_PREFIX_KEY
65                     See MEMCACHED_CALLBACK_NAMESPACE.
66
67              enumerator MEMCACHED_CALLBACK_NAMESPACE
68                     You can set a value which will be used to create a domain
69                     for your keys.  The value specified here will be prefixed
70                     to  each  of your keys. The value can not be greater then
71                     MEMCACHED_MAX_NAMESPACE  -  1  and   will   reduce   MEM‐
72                     CACHED_MAX_KEY by the value of your key.
73
74                     The  prefix  key  is only applied to the primary key, not
75                     the master key.  MEMCACHED_FAILURE will be returned if no
76                     key  is set. In the case of a key which is too long, MEM‐
77                     CACHED_BAD_KEY_PROVIDED will be returned.
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79                     If you set a value with the value  being  NULL  then  the
80                     prefix key is disabled.
81
82              enumerator MEMCACHED_CALLBACK_USER_DATA
83                     This allows you to store a pointer to a specific piece of
84                     data.  This  can  be  retrieved  from  inside   of   mem‐
85                     cached_fetch_execute().  Cloning a memcached_st will copy
86                     the pointer to the clone.
87
88              enumerator MEMCACHED_CALLBACK_MALLOC_FUNCTION
89                     Deprecated since version  <0.32:  Use  memcached_set_mem‐
90                     ory_allocators() instead.
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92
93              enumerator MEMCACHED_CALLBACK_REALLOC_FUNCTION
94                     Deprecated  since  version  <0.32: Use memcached_set_mem‐
95                     ory_allocators() instead.
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97
98              enumerator MEMCACHED_CALLBACK_FREE_FUNCTION
99                     Deprecated since version  <0.32:  Use  memcached_set_mem‐
100                     ory_allocators() instead.
101
102
103              enumerator MEMCACHED_CALLBACK_GET_FAILURE
104                     This function implements the read through cache behavior.
105                     On failure of retrieval this callback will be called.
106
107                     You are responsible for populating the result object pro‐
108                     vided.  This  result  object  will  then be stored in the
109                     server and returned to the calling process.
110
111                     You must clone the memcached_st in order to make  use  of
112                     it.  The  value  will  be  stored only if you return MEM‐
113                     CACHED_SUCCESS  or  MEMCACHED_BUFFERED.  Returning   MEM‐
114                     CACHED_BUFFERED  will cause the object to be buffered and
115                     not sent immediately (if this  is  the  default  behavior
116                     based on your connection setup this will happen automati‐
117                     cally).
118
119                     The prototype for this is:
120
121                     typedef memcached_return_t  (*memcached_trigger_key)(mem‐
122                     cached_st   *ptr,  char  *key,  size_t  key_length,  mem‐
123                     cached_result_st *result)
124
125              enumerator MEMCACHED_CALLBACK_DELETE_TRIGGER
126                     This function implements a trigger upon successful  dele‐
127                     tion  of  a key.  The memcached_st structure will need to
128                     be cloned in order to make use of it.
129
130                     The prototype for this is:
131
132                     typedef       memcached_return_t        (*memcached_trig‐
133                     ger_delete_key)(memcached_st   *ptr,  char  *key,  size_t
134                     key_length)
135

DESCRIPTION

137       libmemcached can have callbacks set key execution points. These  either
138       provide  function  calls  at  points in the code, or return pointers to
139       structures for particular usages.
140
141       memcached_callback_get() takes a callback flag and returns  the  struc‐
142       ture or function set by memcached_callback_set().
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144       memcached_callback_set()  changes  the function/structure assigned by a
145       callback flag. No connections are reset.
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147       You can use MEMCACHED_CALLBACK_USER_DATA to provide custom  context  if
148       required for any of the callbacks.
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RETURN VALUE

151       memcached_callback_get()  returns  the  function  or structure that was
152       provided.  Upon error, nothing is set, NULL is returned, and  the  mem‐
153       cached_return_t argument is set to MEMCACHED_FAILURE.
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155       memcached_callback_set() returns MEMCACHED_SUCCESS upon successful set‐
156       ting, otherwise MEMCACHED_FAILURE on error.
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SEE ALSO

159       memcached(1) libmemcached(3) memcached_strerror(3)
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1641.1                              Sep 20, 2021            MEMCACHED_CALLBACK(3)