1---
2c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
3SPDX-License-Identifier: curl
4Title: CURLMOPT_TIMERFUNCTION
5Section: 3
6Source: libcurl
7See-also:
8  - CURLMOPT_SOCKETFUNCTION (3)
9  - CURLMOPT_TIMERDATA (3)
10Protocol:
11  - All
12Added-in: 7.16.0
13---
14
15# NAME
16
17CURLMOPT_TIMERFUNCTION - callback to receive timeout values
18
19# SYNOPSIS
20
21~~~c
22#include <curl/curl.h>
23
24int timer_callback(CURLM *multi,    /* multi handle */
25                   long timeout_ms, /* timeout in number of ms */
26                   void *clientp);    /* private callback pointer */
27
28CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_TIMERFUNCTION, timer_callback);
29~~~
30
31# DESCRIPTION
32
33Pass a pointer to your callback function, which should match the prototype
34shown above.
35
36Certain features, such as timeouts and retries, require you to call libcurl
37even when there is no activity on the file descriptors.
38
39Your callback function **timer_callback** should install a non-repeating
40timer with an expire time of **timeout_ms** milliseconds. When that timer
41fires, call either curl_multi_socket_action(3) or
42curl_multi_perform(3), depending on which interface you use.
43
44A **timeout_ms** value of -1 passed to this callback means you should delete
45the timer. All other values are valid expire times in number of milliseconds.
46
47The **timer_callback** is called when the timeout expire time is changed.
48
49The **clientp** pointer is set with CURLMOPT_TIMERDATA(3).
50
51The timer callback should return 0 on success, and -1 on error. If this
52callback returns error, **all** transfers currently in progress in this
53multi handle are aborted and made to fail.
54
55This callback can be used instead of, or in addition to,
56curl_multi_timeout(3).
57
58**WARNING:** do not call libcurl directly from within the callback itself
59when the **timeout_ms** value is zero, since it risks triggering an
60unpleasant recursive behavior that immediately calls another call to the
61callback with a zero timeout...
62
63# DEFAULT
64
65NULL
66
67# %PROTOCOLS%
68
69# EXAMPLE
70
71~~~c
72struct priv {
73  void *custom;
74};
75
76static int timerfunc(CURLM *multi, long timeout_ms, void *clientp)
77{
78 struct priv *mydata = clientp;
79 printf("our ptr: %p\n", mydata->custom);
80
81 if(timeout_ms) {
82   /* this is the new single timeout to wait for */
83 }
84 else {
85   /* delete the timeout, nothing to wait for now */
86 }
87}
88
89int main(void)
90{
91  struct priv mydata;
92  CURLM *multi = curl_multi_init();
93  curl_multi_setopt(multi, CURLMOPT_TIMERFUNCTION, timerfunc);
94  curl_multi_setopt(multi, CURLMOPT_TIMERDATA, &mydata);
95}
96~~~
97
98# %AVAILABILITY%
99
100# RETURN VALUE
101
102Returns CURLM_OK if the option is supported, and CURLM_UNKNOWN_OPTION if not.
103