[glib: 1/2] win32: make g_cond_wait_until() wait at least until end_time before returning with a timeout. See #1

[Philip Withnall <pwithnall src gnome org>]

commit 583fb1a397023257ea3d2ee81f88b360007f07a2
Author: Christoph Reiter <reiter christoph gmail com>
Date:   Thu May 10 13:28:49 2018 +0200

    win32: make g_cond_wait_until() wait at least until end_time before returning with a timeout. See #1371
    
    The tests in test_async_queue_timed() assume that g_async_queue_timeout_pop()
    and in turn g_cond_wait_until() wait at least until end_time
    before returning, i.e. calling g_get_monotonic_time() after the timeout should result
    in a value equal or larger than the timeout end time.
    
    For the win32 implementation of g_cond_wait_until() this isn't the case which
    makes those tests fail.
    
    There are three reasons why the function returns early:
    
    1) The underlying API works with milliseconds and the timeout gets rounded
       down, resulting in a too small timeout value.
    2) In case the timeout is too large to be passed to the API it gets limited
       (there is also a bug because it converts INFINITE to milliseconds while
       they already are, but using INFINITE would be wrong as well, as passing
       a large timeout is not the same as blocking forever really)
    3) Even with the rounding changed the underlying API still returns a bit early
       sometimes on my machine (relative to g_get_monotonic_time())
    
    This changes the implementation to round up to the next millisecond (fixing 1)
    and to wait again in case a timeout occurs but the end time hasn't been
    reached yet (fixing 2 and 3).
    
    This makes the test_async_queue_timed() tests pass.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=795569

 glib/gthread-win32.c | 35 ++++++++++++++++++++++++++++-------
 1 file changed, 28 insertions(+), 7 deletions(-)
---
diff --git a/glib/gthread-win32.c b/glib/gthread-win32.c
index 938ed5f3c..a81f00a5c 100644
--- a/glib/gthread-win32.c
+++ b/glib/gthread-win32.c
@@ -305,17 +305,38 @@ g_cond_wait_until (GCond  *cond,
                    GMutex *entered_mutex,
                    gint64  end_time)
 {
-  gint64 span;
+  gint64 span, start_time;
+  DWORD span_millis;
+  gboolean signalled;
 
-  span = end_time - g_get_monotonic_time ();
+  start_time = g_get_monotonic_time ();
+  do
+    {
+      span = end_time - start_time;
+
+      if G_UNLIKELY (span < 0)
+        span_millis = 0;
+      else if G_UNLIKELY (span > G_GINT64_CONSTANT (1000) * (DWORD) INFINITE)
+        span_millis = INFINITE;
+      else
+        /* Round up so we don't time out too early */
+        span_millis = (span + 1000 - 1) / 1000;
+
+      /* We never want to wait infinitely */
+      if (span_millis >= INFINITE)
+        span_millis = INFINITE - 1;
 
-  if G_UNLIKELY (span < 0)
-    span = 0;
+      signalled = g_thread_impl_vtable.SleepConditionVariableSRW (cond, entered_mutex, span_millis, 0);
+      if (signalled)
+        break;
 
-  if G_UNLIKELY (span > G_GINT64_CONSTANT (1000) * G_MAXINT32)
-    span = INFINITE;
+      /* In case we didn't wait long enough after a timeout, wait again for the
+       * remaining time */
+      start_time = g_get_monotonic_time ();
+    }
+  while (start_time < end_time);
 
-  return g_thread_impl_vtable.SleepConditionVariableSRW (cond, entered_mutex, span / 1000, 0);
+  return signalled;
 }
 
 /* {{{1 GPrivate */