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