multi_socket: handles timer inaccuracy better for timeouts

Igor Novoseltsev reported a problem with the multi socket API and
using timeouts and timers. It boiled down to a problem with
libcurl's use of GetTickCount() interally to figure out the
current time, while Igor's own application code used another
function call.

It made his app call the socket API timeout function a bit
_before_ libcurl would consider the timeout to trigger, and that
could easily lead to timeouts or stalls in the app. It seems
GetTickCount() in general often has no better resolution than
16ms and switching to the alternative function
QueryPerformanceCounter has its share of problems:
http://www.virtualdub.org/blog/pivot/entry.php?id=106

We address this problem by simply having libcurl treat timers
that already has occured or will occur within 40ms subject for
treatment. I'm confident that there are other implementations and
operating systems with similarly in accurate timer functions so
it makes sense to have applied generically and I don't believe we
sacrifice much by adding a 40ms inaccuracy on these timeouts.

1 files changed, 3 insertions, 1 deletions

diff --git a/RELEASE-NOTES b/RELEASE-NOTES
index 86260d14f..7639afe28 100644
--- a/RELEASE-NOTES
+++ b/RELEASE-NOTES
@@ -33,6 +33,7 @@ This release includes the following bugfixes:
  o OpenSSL handshake state-machine for multi interface
  o TFTP timeout option sent correctly
  o TFTP block id wrap
+ o curl_multi_socket_action() timeout handles inaccuracy in timers better
 
 This release includes the following known bugs:
 
@@ -43,6 +44,7 @@ advice from friends like these:
 
  Rainer Canavan, Paul Howarth, Jerome Vouillon, Ruslan Gazizov, Yang Tse,
  Kamil Dudka, Alex Bligh, Ben Greear, Hoi-Ho Chan, Howard Chu, Dirk Manske,
- Pavel Raiskup, John-Mark Bell, Eric Mertens, Tor Arntsen, Douglas Kilpatrick
+ Pavel Raiskup, John-Mark Bell, Eric Mertens, Tor Arntsen, Douglas Kilpatrick,
+ Igor Novoseltsev
 
         Thanks! (and sorry if I forgot to mention someone)