Commit 21091549 authored by Daniel Stenberg's avatar Daniel Stenberg
Browse files

multi_socket: reduce timeout inaccuracy margin 

Allow less room for "triggered too early" mistakes by applications /
timers on non-windows platforms. Starting now, we assume that a timeout
call is never made earlier than 3 milliseconds before the actual
timeout. This greatly improves timeout accuracy on Linux.

Bug: http://curl.haxx.se/bug/view.cgi?id=1228
Reported-by: Hang Su
parent 7b97f03f

lib/multi.c

+24 −2
Original line number Diff line number Diff line
@@ -2106,6 +2106,11 @@ static CURLMcode add_next_timeout(struct timeval now, 
  return CURLM_OK;

}



#ifdef WIN32

#define TIMEOUT_INACCURACY 40000

#else

#define TIMEOUT_INACCURACY 3000

#endif



static CURLMcode multi_socket(struct Curl_multi *multi,

                              bool checkall,
@@ -2195,8 +2200,25 @@ static CURLMcode multi_socket(struct Curl_multi *multi, 
    }

  }



  now.tv_usec += 40000; /* compensate for bad precision timers that might've

                           triggered too early */

  /* Compensate for bad precision timers that might've triggered too early.



     This precaution was added in commit 2c72732ebf3da5e as a result of bad

     resolution in the windows function use(d).



     The problematic case here is when using the multi_socket API and libcurl

     has told the application about a timeout, and that timeout is what fires

     off a bit early. As we don't have any IDs associated with the timeout we

     can't tell which timeout that fired off but we only have the times to use

     to check what to do. If it fires off too early, we don't run the correct

     actions and we don't tell the application again about the same timeout as

     was already first in the queue...



     Originally we made the timeouts run 40 milliseconds early on all systems,

     but now we have an #ifdef setup to provide a decent precaution inaccuracy

     margin.

  */



  now.tv_usec += TIMEOUT_INACCURACY;

  if(now.tv_usec >= 1000000) {

    now.tv_sec++;

    now.tv_usec -= 1000000;