CURLMOPT_TIMERFUNCTION.m: emphasize that only a single timer should run

Closes #14886

diff --git a/docs/libcurl/opts/CURLMOPT_TIMERFUNCTION.md b/docs/libcurl/opts/CURLMOPT_TIMERFUNCTION.md
index 40ec76eb945ee8f62ca4e8d5982746a670601169..35fabdc7b3dad2a67bc6005e36f3445202ea4320 100644 (file)
--- a/docs/libcurl/opts/CURLMOPT_TIMERFUNCTION.md
+++ b/docs/libcurl/opts/CURLMOPT_TIMERFUNCTION.md
@@ -23,7 +23,7 @@ CURLMOPT_TIMERFUNCTION - callback to receive timeout values
 
 int timer_callback(CURLM *multi,    /* multi handle */
                    long timeout_ms, /* timeout in number of ms */
-                   void *clientp);    /* private callback pointer */
+                   void *clientp);  /* private callback pointer */
 
 CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_TIMERFUNCTION, timer_callback);
 ~~~
@@ -36,11 +36,15 @@ shown above.
 Certain features, such as timeouts and retries, require you to call libcurl
 even when there is no activity on the file descriptors.
 
-Your callback function **timer_callback** should install a non-repeating
-timer with an expire time of **timeout_ms** milliseconds. When that timer
-fires, call either curl_multi_socket_action(3) or
+Your callback function **timer_callback** should install a single
+non-repeating timer with an expire time of **timeout_ms** milliseconds. When
+that timer fires, call either curl_multi_socket_action(3) or
 curl_multi_perform(3), depending on which interface you use.
 
+If this callback is called when a timer is already running, this new expire
+time *replaces* the former timeout. The application should then effectively
+cancel the old timeout and set a new timeout using this new expire time.
+
 A **timeout_ms** value of -1 passed to this callback means you should delete
 the timer. All other values are valid expire times in number of milliseconds.
 
@@ -49,16 +53,16 @@ The **timer_callback** is called when the timeout expire time is changed.
 The **clientp** pointer is set with CURLMOPT_TIMERDATA(3).
 
 The timer callback should return 0 on success, and -1 on error. If this
-callback returns error, **all** transfers currently in progress in this
-multi handle are aborted and made to fail.
+callback returns error, **all** transfers currently in progress in this multi
+handle are aborted and made to fail.
 
 This callback can be used instead of, or in addition to,
 curl_multi_timeout(3).
 
-**WARNING:** do not call libcurl directly from within the callback itself
-when the **timeout_ms** value is zero, since it risks triggering an
-unpleasant recursive behavior that immediately calls another call to the
-callback with a zero timeout...
+**WARNING:** do not call libcurl directly from within the callback itself when
+the **timeout_ms** value is zero, since it risks triggering an unpleasant
+recursive behavior that immediately calls another call to the callback with a
+zero timeout...
 
 # DEFAULT
 
@@ -75,15 +79,15 @@ struct priv {
 
 static int timerfunc(CURLM *multi, long timeout_ms, void *clientp)
 {
- struct priv *mydata = clientp;
- printf("our ptr: %p\n", mydata->custom);
-
- if(timeout_ms) {
-   /* this is the new single timeout to wait for */
- }
- else {
-   /* delete the timeout, nothing to wait for now */
- }
+  struct priv *mydata = clientp;
+  printf("our ptr: %p\n", mydata->custom);
+
+  if(timeout_ms) {
+    /* this is the new single timeout to wait for */
+  }
+  else {
+    /* delete the timeout, nothing to wait for now */
+  }
 }
 
 int main(void)