Merge pull request #140 from hussainnaqvee/patch-1
[awesomized/libmemcached] / libmemcached / memcached_callback.rst
1 Library callbacks
2 =================
3
4 SYNOPSIS
5 --------
6
7 #include <libmemcached/memcached.h>
8 Compile and link with -lmemcached
9
10 .. function:: memcached_return_t memcached_callback_set(memcached_st *ptr, memcached_callback_t flag, const void *data)
11
12 :param ptr: pointer to initialized `memcached_st` struct
13 :param flag: `memcached_callback_t` flag to set
14 :param data: data corresponding to `flag`
15 :returns: `memcached_return_t` indicating success
16
17 .. function:: void *memcached_callback_get(memcached_st *ptr, memcached_callback_t flag, memcached_return_t *error)
18
19 :param ptr: pointer to initialized `memcached_st` struct
20 :param flag: `memcached_callback_t` flag to query
21 :param error: pointer to `memcached_return_t` indicating success
22 :returns: the `data` previously set
23
24 .. c:type:: enum memcached_callback_t memcached_callback_t
25
26 .. enum:: memcached_callback_t
27
28 .. enumerator:: MEMCACHED_CALLBACK_CLEANUP_FUNCTION
29
30 When `memcached_free` or `memcached_reset` is called this function
31 will be executed. At the point of its execution all connections are closed.
32
33 Its signature is:
34
35 .. type:: memcached_return_t (*memcached_cleanup_fn)(const memcached_st *ptr)
36
37
38 .. enumerator:: MEMCACHED_CALLBACK_CLONE_FUNCTION
39
40 When `memcached_clone` is called this function will be executed.
41
42 Its signature is:
43
44 .. type:: memcached_return_t (*memcached_clone_fn)(memcached_st *destination, const memcached_st *source)
45
46 .. enumerator:: MEMCACHED_CALLBACK_PREFIX_KEY
47
48 See `MEMCACHED_CALLBACK_NAMESPACE`.
49
50 .. enumerator:: MEMCACHED_CALLBACK_NAMESPACE
51
52 You can set a value which will be used to create a domain for your keys.
53 The value specified here will be prefixed to each of your keys. The
54 value can not be greater then :c:macro:`MEMCACHED_MAX_NAMESPACE` - 1 and
55 will reduce :c:macro:`MEMCACHED_MAX_KEY` by the value of your key.
56
57 The prefix key is only applied to the primary key, not the master key.
58 `MEMCACHED_FAILURE` will be returned if no key is set. In the case of a
59 key which is too long, `MEMCACHED_BAD_KEY_PROVIDED` will be returned.
60
61 If you set a value with the value being NULL then the prefix key is
62 disabled.
63
64 .. enumerator:: MEMCACHED_CALLBACK_USER_DATA
65
66 This allows you to store a pointer to a specific piece of data. This can
67 be retrieved from inside of `memcached_fetch_execute`. Cloning a
68 `memcached_st` will copy the pointer to the clone.
69
70 .. enumerator:: MEMCACHED_CALLBACK_MALLOC_FUNCTION
71
72 .. deprecated:: <0.32
73 Use `memcached_set_memory_allocators` instead.
74
75 .. enumerator:: MEMCACHED_CALLBACK_REALLOC_FUNCTION
76
77 .. deprecated:: <0.32
78 Use `memcached_set_memory_allocators` instead.
79
80 .. enumerator:: MEMCACHED_CALLBACK_FREE_FUNCTION
81
82 .. deprecated:: <0.32
83 Use `memcached_set_memory_allocators` instead.
84
85 .. enumerator:: MEMCACHED_CALLBACK_GET_FAILURE
86
87 This function implements the read through cache behavior. On failure of
88 retrieval this callback will be called.
89
90 You are responsible for populating the result object provided. This
91 result object will then be stored in the server and returned to the
92 calling process.
93
94 You must clone the `memcached_st` in order to make use of it. The value
95 will be stored only if you return `MEMCACHED_SUCCESS` or
96 `MEMCACHED_BUFFERED`. Returning `MEMCACHED_BUFFERED` will cause the
97 object to be buffered and not sent immediately (if this is the default
98 behavior based on your connection setup this will happen automatically).
99
100 The prototype for this is:
101
102 .. type:: memcached_return_t (*memcached_trigger_key)(memcached_st *ptr, char *key, size_t key_length, memcached_result_st *result)
103
104 .. enumerator:: MEMCACHED_CALLBACK_DELETE_TRIGGER
105
106 This function implements a trigger upon successful deletion of a key.
107 The `memcached_st` structure will need to be cloned in order to make use
108 of it.
109
110 The prototype for this is:
111
112 .. type:: memcached_return_t (*memcached_trigger_delete_key)(memcached_st *ptr, char *key, size_t key_length)
113
114 DESCRIPTION
115 -----------
116
117 `libmemcached` can have callbacks set key execution points. These either provide
118 function calls at points in the code, or return pointers to structures for
119 particular usages.
120
121 `memcached_callback_get` takes a callback flag and returns the structure or
122 function set by `memcached_callback_set`.
123
124 `memcached_callback_set` changes the function/structure assigned by a callback
125 flag. No connections are reset.
126
127 You can use `MEMCACHED_CALLBACK_USER_DATA` to provide custom context if required
128 for any of the callbacks.
129
130 RETURN VALUE
131 ------------
132
133 `memcached_callback_get` returns the function or structure that was provided.
134 Upon error, nothing is set, NULL is returned, and the `memcached_return_t`
135 argument is set to `MEMCACHED_FAILURE`.
136
137 `memcached_callback_set` returns `MEMCACHED_SUCCESS` upon successful setting,
138 otherwise `MEMCACHED_FAILURE` on error.
139
140 SEE ALSO
141 --------
142
143 .. only:: man
144
145 :manpage:`memcached(1)`
146 :manpage:`libmemcached(3)`
147 :manpage:`memcached_strerror(3)`
148
149 .. only:: html
150
151 * :manpage:`memcached(1)`
152 * :doc:`../libmemcached`
153 * :doc:`memcached_strerror`