>From c3c9f38379dca3f6f59520c5ceafce34ee8c8d90 Mon Sep 17 00:00:00 2001
From: Craig Ringer <craig@2ndquadrant.com>
Date: Thu, 18 Sep 2014 23:02:14 +0800
Subject: [PATCH 2/2] Use GetSystemTimePreciseAsFileTime when available

This will cause PostgreSQL on Windows 8 or Windows Server 2012 to
obtain high-resolution timestamps while allowing the same binaries
to run without problems on older releases.
---
 src/backend/main/main.c |  6 ++++++
 src/include/port.h      |  2 ++
 src/port/gettimeofday.c | 56 +++++++++++++++++++++++++++++++++++++++++++++++--
 3 files changed, 62 insertions(+), 2 deletions(-)

diff --git a/src/backend/main/main.c b/src/backend/main/main.c
index c51b391..73c30c5 100644
--- a/src/backend/main/main.c
+++ b/src/backend/main/main.c
@@ -260,6 +260,12 @@ startup_hacks(const char *progname)
 
 		/* In case of general protection fault, don't show GUI popup box */
 		SetErrorMode(SEM_FAILCRITICALERRORS | SEM_NOGPFAULTERRORBOX);
+
+#ifndef HAVE_GETTIMEOFDAY
+		/* Figure out which syscall to use to capture timestamp information */
+		init_win32_gettimeofday();
+#endif
+
 	}
 #endif   /* WIN32 */
 
diff --git a/src/include/port.h b/src/include/port.h
index 94a0e2f..58677ec 100644
--- a/src/include/port.h
+++ b/src/include/port.h
@@ -328,6 +328,8 @@ extern FILE *pgwin32_popen(const char *command, const char *type);
 #ifndef HAVE_GETTIMEOFDAY
 /* Last parameter not used */
 extern int	gettimeofday(struct timeval * tp, struct timezone * tzp);
+/* On windows we need to call some backend start setup for accurate timing */
+extern void init_win32_gettimeofday(void);
 #endif
 #else							/* !WIN32 */
 
diff --git a/src/port/gettimeofday.c b/src/port/gettimeofday.c
index 73ec406..a82a1a4 100644
--- a/src/port/gettimeofday.c
+++ b/src/port/gettimeofday.c
@@ -30,14 +30,66 @@
 
 #include <sys/time.h>
 
+#ifndef FRONTEND
+#include <utils/elog.h>
+#endif
+
 
 /* FILETIME of Jan 1 1970 00:00:00. */
 static const unsigned __int64 epoch = UINT64CONST(116444736000000000);
 
 /*
+ * Both GetSystemTimeAsFileTime and GetSystemTimePreciseAsFileTime share a
+ * signature, so we can just store a pointer to whichever we find. This
+ * is the pointer's type.
+ */
+typedef VOID (WINAPI *PgGetSystemTimeFn)(LPFILETIME);
+/* Storage for the function we pick at runtime */
+static PgGetSystemTimeFn pg_get_system_time = NULL;
+
+/*
+ * During backend startup, determine if GetSystemTimePreciseAsFileTime is
+ * available and use it; if not, fall back to GetSystemTimeAsFileTime.
+ */
+void
+init_win32_gettimeofday(void)
+{
+	/*
+	 * Because it's guaranteed that kernel32.dll will be linked into our
+	 * address space already, we don't need to LoadLibrary it and worry about
+	 * closing it afterwards, so we're not using Pg's dlopen/dlsym() wrapper.
+	 *
+	 * We'll just look up the address of GetSystemTimePreciseAsFileTime if
+	 * present.
+	 *
+	 * While we could look up the Windows version and skip this on Windows
+	 * versions below Windows 8 / Windows Server 2012 there isn't much point,
+	 * and determining the windows version is its self somewhat Windows version
+	 * and development SDK specific...
+	 */
+	pg_get_system_time = (PgGetSystemTimeFn) GetProcAddress(
+			GetModuleHandle(TEXT("kernel32.dll")),
+				"GetSystemTimePreciseAsFileTime");
+	if (pg_get_system_time == NULL)
+	{
+		/*
+		 * The expected error from GetLastError() is ERROR_PROC_NOT_FOUND, if
+		 * the function isn't present. No other error should occur.
+		 *
+		 * It's too early in startup to elog(...) if we get some unexpected
+		 * error, and not serious enough to warrant a fprintf to stderr about
+		 * it or save the error and report it later. So silently fall back to
+		 * GetSystemTimeAsFileTime irrespective of why the failure occurred.
+		 */
+		pg_get_system_time = &GetSystemTimeAsFileTime;
+	}
+
+}
+
+/*
  * timezone information is stored outside the kernel so tzp isn't used anymore.
  *
- * Note: this function is not for Win32 high precision timing purpose. See
+ * Note: this function is not for Win32 high precision timing purposes. See
  * elapsed_time().
  */
 int
@@ -46,7 +98,7 @@ gettimeofday(struct timeval * tp, struct timezone * tzp)
 	FILETIME	file_time;
 	ULARGE_INTEGER ularge;
 
-	GetSystemTimeAsFileTime(&file_time);
+	(*pg_get_system_time)(&file_time);
 	ularge.LowPart = file_time.dwLowDateTime;
 	ularge.HighPart = file_time.dwHighDateTime;
 
-- 
1.9.3