[Vm-dev] [OpenSmalltalk/opensmalltalk-vm] Heart defect on Windows since October (#531)

[Eliot Miranda]

Hi Christoph,

   first it's not true that Time is broken on Windows:

Smalltalk os platformName 'Win32'
Smalltalk getSystemAttribute: 1007 'CoInterpreter VMMaker.oscog-eem.2850 uuid: 4d7fc8a4-2c7d-4bad-8aeb-5f8c5766e12a Oct 21 2020'
DateAndTime now 2020-10-22T23:06:29.983933-07:00
Time utcMicrosecondClock 3780886299961528

It is true that unless you have 8.1 or later and have GetSystemTimePreciseAsFileTime in kernel32 then Time will not work.  Here:

```
$ git diff 712cfe6c3e29667b56e668d7641daced18efb666 platforms/win32/vm/sqWin32Heartbeat.c | more
diff --git a/platforms/win32/vm/sqWin32Heartbeat.c b/platforms/win32/vm/sqWin32H
eartbeat.c
old mode 100644
new mode 100755
index 85d27674a..70c430889
--- a/platforms/win32/vm/sqWin32Heartbeat.c
+++ b/platforms/win32/vm/sqWin32Heartbeat.c
@@ -14,6 +14,7 @@
 #include <mmsystem.h>

 #include "sq.h"
+#undef EXPORT
 #include "sqAssert.h"
 #include "sqMemoryFence.h"

@@ -76,19 +77,41 @@ sqLong ioHighResClock(void) {
   return value;
 }

+#if (_WIN32_WINNT >= _WIN32_WINNT_WIN8)
+
+/* Compute the current VM time basis, the number of microseconds from 1901.
+ *
+ * As of Windows 8 there is a FILETIME wall clock interface which is high
+ * precision and so does not have to be combined with the millisecond clock.
+ */
+# define currentUTCMicroseconds(a,b,c) currentUTCMicrosecondsImplementation()
+static inline unsigned __int64
+currentUTCMicrosecondsImplementation(void)
+{
+       union { // got to love little-endian architectures...
+               FILETIME         utcNowFiletime;
+               unsigned __int64 utcNow;
+       } un;
+
+       // cannot fail...
+       GetSystemTimePreciseAsFileTime(&un.utcNowFiletime);
+       return un.utcNow / TocksPerMicrosecond - MicrosecondsFrom1601To1901;
+}
+#else // _WIN32_WINNT >= _WIN32_WINNT_WIN8
+
```


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