104 lines
2.6 KiB
Markdown
104 lines
2.6 KiB
Markdown
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---
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c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
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SPDX-License-Identifier: curl
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Title: CURLMOPT_TIMERFUNCTION
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Section: 3
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Source: libcurl
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See-also:
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- CURLMOPT_SOCKETFUNCTION (3)
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- CURLMOPT_TIMERDATA (3)
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---
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# NAME
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CURLMOPT_TIMERFUNCTION - callback to receive timeout values
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# SYNOPSIS
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~~~c
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#include <curl/curl.h>
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int timer_callback(CURLM *multi, /* multi handle */
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long timeout_ms, /* timeout in number of ms */
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void *clientp); /* private callback pointer */
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CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_TIMERFUNCTION, timer_callback);
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~~~
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# DESCRIPTION
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Pass a pointer to your callback function, which should match the prototype
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shown above.
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Certain features, such as timeouts and retries, require you to call libcurl
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even when there is no activity on the file descriptors.
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Your callback function **timer_callback** should install a non-repeating
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timer with an expire time of **timeout_ms** milliseconds. When that timer
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fires, call either curl_multi_socket_action(3) or
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curl_multi_perform(3), depending on which interface you use.
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A **timeout_ms** value of -1 passed to this callback means you should delete
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the timer. All other values are valid expire times in number of milliseconds.
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The **timer_callback** is called when the timeout expire time is changed.
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The **clientp** pointer is set with CURLMOPT_TIMERDATA(3).
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The timer callback should return 0 on success, and -1 on error. If this
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callback returns error, **all** transfers currently in progress in this
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multi handle are aborted and made to fail.
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This callback can be used instead of, or in addition to,
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curl_multi_timeout(3).
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**WARNING:** do not call libcurl directly from within the callback itself
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when the **timeout_ms** value is zero, since it risks triggering an
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unpleasant recursive behavior that immediately calls another call to the
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callback with a zero timeout...
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# DEFAULT
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NULL
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# PROTOCOLS
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All
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# EXAMPLE
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~~~c
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struct priv {
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void *custom;
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};
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static int timerfunc(CURLM *multi, long timeout_ms, void *clientp)
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{
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struct priv *mydata = clientp;
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printf("our ptr: %p\n", mydata->custom);
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if(timeout_ms) {
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/* this is the new single timeout to wait for */
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}
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else {
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/* delete the timeout, nothing to wait for now */
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}
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}
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int main(void)
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{
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struct priv mydata;
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CURLM *multi = curl_multi_init();
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curl_multi_setopt(multi, CURLMOPT_TIMERFUNCTION, timerfunc);
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curl_multi_setopt(multi, CURLMOPT_TIMERDATA, &mydata);
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}
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~~~
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# AVAILABILITY
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Added in 7.16.0
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# RETURN VALUE
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Returns CURLM_OK if the option is supported, and CURLM_UNKNOWN_OPTION if not.
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