Commit 0feeab78 authored by Daniel Stenberg's avatar Daniel Stenberg
Browse files

curl_easy_perform: avoid busy-looping 

When curl_multi_wait() finds no file descriptor to wait for, it returns
instantly and this must be handled gracefully within curl_easy_perform()
or cause a busy-loop. Starting now, repeated fast returns without any
file descriptors is detected and a gradually increasing sleep will be
used (up to a max of 1000 milliseconds) before continuing the loop.

Bug: http://curl.haxx.se/bug/view.cgi?id=1238
Reported-by: Miguel Angel
parent f24dc09d

lib/easy.c

+25 −0
Original line number Original line Diff line number Diff line
@@ -420,6 +420,9 @@ CURLcode curl_easy_perform(CURL *easy) 
  bool done = FALSE;

  bool done = FALSE;

  int rc;

  int rc;

  struct SessionHandle *data = easy;

  struct SessionHandle *data = easy;

  int without_fds = 0;  /* count number of consecutive returns from

                           curl_multi_wait() without any filedescriptors */

  struct timeval before;





  if(!easy)

  if(!easy)

    return CURLE_BAD_FUNCTION_ARGUMENT;

    return CURLE_BAD_FUNCTION_ARGUMENT;
@@ -460,6 +463,7 @@ CURLcode curl_easy_perform(CURL *easy) 
    int still_running;

    int still_running;

    int ret;

    int ret;





    before = curlx_tvnow();

    mcode = curl_multi_wait(multi, NULL, 0, 1000, &ret);

    mcode = curl_multi_wait(multi, NULL, 0, 1000, &ret);





    if(mcode == CURLM_OK) {

    if(mcode == CURLM_OK) {
@@ -468,6 +472,27 @@ CURLcode curl_easy_perform(CURL *easy) 
        code = CURLE_RECV_ERROR;

        code = CURLE_RECV_ERROR;

        break;

        break;

      }

      }

      else if(ret == 0) {

        struct timeval after = curlx_tvnow();

        /* If it returns without any filedescriptor instantly, we need to

           avoid busy-looping during periods where it has nothing particular

           to wait for */

        if(curlx_tvdiff(after, before) <= 10) {

          without_fds++;

          if(without_fds > 2) {

            int sleep_ms = without_fds * 50;

            if(sleep_ms > 1000)

              sleep_ms = 1000;

            Curl_wait_ms(sleep_ms);

          }

        }

        else

          /* it wasn't "instant", restart counter */

          without_fds = 0;

      }

      else

        /* got file descriptor, restart counter */

        without_fds = 0;





      mcode = curl_multi_perform(multi, &still_running);

      mcode = curl_multi_perform(multi, &still_running);

    }

    }