From ca3cfbae742bc0c87632374bd8542cb467512692 Mon Sep 17 00:00:00 2001
From: Bert Belder <bertbelder@gmail.com>
Date: Tue, 19 Jul 2011 17:32:43 +0200
Subject: [PATCH] Windows: use low-res event loop clock.

For much better performance. Closes #88.
---
 src/win/core.c     |  3 ---
 src/win/internal.h |  3 ---
 src/win/timer.c    | 38 ++++++++++++++++++++------------------
 3 files changed, 20 insertions(+), 24 deletions(-)

diff --git a/src/win/core.c b/src/win/core.c
index 32009478..e2d5a32c 100644
--- a/src/win/core.c
+++ b/src/win/core.c
@@ -70,9 +70,6 @@ void uv_init() {
   /* Initialize winsock */
   uv_winsock_startup();
 
-  /* Initialize timers */
-  uv_timer_startup();
-
   /* Intialize event loop */
   uv_loop_init();
 }
diff --git a/src/win/internal.h b/src/win/internal.h
index 7c42a774..33783f6e 100644
--- a/src/win/internal.h
+++ b/src/win/internal.h
@@ -30,11 +30,8 @@
 /*
  * Timers
  */
-
 RB_HEAD(uv_timer_tree_s, uv_timer_s);
 
-void uv_timer_startup();
-
 void uv_timer_endgame(uv_timer_t* handle);
 
 DWORD uv_get_poll_timeout();
diff --git a/src/win/timer.c b/src/win/timer.c
index d2ab89e9..ea5e7195 100644
--- a/src/win/timer.c
+++ b/src/win/timer.c
@@ -37,12 +37,19 @@ static char uv_hrtime_initialized_ = 0;
 
 
 void uv_update_time() {
-  LARGE_INTEGER counter;
+  DWORD ticks = GetTickCount();
 
-  if (!QueryPerformanceCounter(&counter))
-    uv_fatal_error(GetLastError(), "QueryPerformanceCounter");
+  /* The assumption is made that LARGE_INTEGER.QuadPart has the same type */
+  /* LOOP->time, which happens to be. Is there any way to assert this? */
+  LARGE_INTEGER* time = (LARGE_INTEGER*) &LOOP->time;
 
-  LOOP->time = counter.QuadPart / uv_ticks_per_msec_;
+  /* If the timer has wrapped, add 1 to it's high-order dword. */
+  /* uv_poll must make sure that the timer can never overflow more than */
+  /* once between two subsequent uv_update_time calls. */
+  if (ticks < time->LowPart) {
+    time->HighPart += 1;
+  }
+  time->LowPart = ticks;
 }
 
 
@@ -88,16 +95,6 @@ uint64_t uv_hrtime(void) {
 }
 
 
-void uv_timer_startup() {
-  LARGE_INTEGER timer_frequency;
-
-  /* Initialize the event loop time */
-  if (!QueryPerformanceFrequency(&timer_frequency))
-    uv_fatal_error(GetLastError(), "QueryPerformanceFrequency");
-  uv_ticks_per_msec_ = timer_frequency.QuadPart / 1000;
-}
-
-
 static int uv_timer_compare(uv_timer_t* a, uv_timer_t* b) {
   if (a->due < b->due)
     return -1;
@@ -222,10 +219,15 @@ DWORD uv_get_poll_timeout() {
     uv_update_time();
 
     delta = timer->due - LOOP->time;
-    if (delta >= UINT_MAX) {
-      /* Can't have a timeout greater than UINT_MAX, and a timeout value of */
-      /* UINT_MAX means infinite, so that's no good either. */
-      return UINT_MAX - 1;
+    if (delta >= UINT_MAX >> 1) {
+      /* A timeout value of UINT_MAX means infinite, so that's no good. But */
+      /* more importantly, there's always the risk that GetTickCount wraps. */
+      /* uv_update_time can detect this, but we must make sure that the */
+      /* tick counter never overflows twice between two subsequent */
+      /* uv_update_time calls. We do this by never sleeping more than half */
+      /* the time it takes to wrap  the counter - which is huge overkill, */
+      /* but hey, it's not so bad to wake up every 25 days. */
+      return UINT_MAX >> 1;
     } else if (delta < 0) {
       /* Negative timeout values are not allowed */
       return 0;