Re: Problem where timer callback keeps setting a 0 timer

Hi,

On Wed, Dec 4, 2019 at 3:37 PM Jeff Mears via curl-library <
curl-library_at_cool.haxx.se> wrote:

> I have a background thread that starts and stops libcurl downloads using
> the "multi" interface. It has a poll() loop that waits for something to
> happen on either one of libcurl's sockets or on a loopback socket that is
> used to interrupt poll().
>
> After running for a bit, there is a periodic HTTP request we send. When
> these start, libcurl calls our CURLMOPT_TIMERFUNCTION with a timeout of 0.
> So the poll() loop starts polling with hot CPU.
>

Reading the man page
<https://curl.haxx.se/libcurl/c/CURLMOPT_TIMERFUNCTION.html>, it looks like
calls to the timer function request a single shot timer. Your description
makes it sound like you set up a periodic timer that fires every timeout_ms
milliseconds. It shouldn't be necessary for curl to provide a -1
cancellation because the timer was meant to be a single shot, it's only
specified to fire once.

The example on the man page may be a source of confusion. The example uses
g_timeout_add() to set up a periodic timer that is cancelled when the timer
callback returns false. However the example timer callback always returns
false, making this a single shot timer. If you didn't notice the timer
callback return value (at the end of timeout_cb in the example) you might
assume that the timer is meant to be periodic.

The download then completes. We curl_multi_remove_handle() then
> curl_easy_cleanup() in our handling of the curl_multi_info_read() messages.
>
> However, at this point, even though libcurl has no active downloads on the
> multi handle, we never get a timer callback to set the timeout back to -1,
> so our poll() loop continues running hot.
>
> Am I doing something wrong? For now, I'm going to set the timeout to -1
> when curl_multi_socket_action(CURL_SOCKET_TIMEOUT) returns 0 running
> handles to stop the thread running hot.
>

Thanks,
Sean

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Received on 2019-12-04