usleep: implement with millisecond resolution on native Windows

[Bruno Haible]

The usleep() emulation on MSVC has a resolution of 1 second only.
This patch improves it, to have a resolution of 15 milliseconds.


2019-07-02  Bruno Haible  <br...@clisp.org>

        usleep: Implement with millisecond resolution on native Windows.
        * lib/usleep.c (usleep): On native Windows, implement using Sleep().
        * doc/pastposix-functions/usleep.texi: Update accordingly.

diff --git a/doc/pastposix-functions/usleep.texi 
b/doc/pastposix-functions/usleep.texi
index 440a00e..14de4b2 100644
--- a/doc/pastposix-functions/usleep.texi
+++ b/doc/pastposix-functions/usleep.texi
@@ -16,7 +16,7 @@ mingw.
 This function is missing on some platforms.  However, the replacement
 is designed to be lightweight, and may round to the nearest second;
 use @code{select} or @code{nanosleep} if better resolution is needed:
-IRIX 5.3, Solaris 2.4, older mingw, MSVC 14, BeOS.
+IRIX 5.3, Solaris 2.4, BeOS.
 @end itemize
 
 Portability problems not fixed by Gnulib:
diff --git a/lib/usleep.c b/lib/usleep.c
index f7e2480..480605f 100644
--- a/lib/usleep.c
+++ b/lib/usleep.c
@@ -28,6 +28,11 @@
 
 #include <errno.h>
 
+#if defined _WIN32 && ! defined __CYGWIN__
+# define WIN32_LEAN_AND_MEAN  /* avoid including junk */
+# include <windows.h>
+#endif
+
 #ifndef HAVE_USLEEP
 # define HAVE_USLEEP 0
 #endif
@@ -39,7 +44,20 @@
 
 int
 usleep (useconds_t micro)
+#undef usleep
 {
+#if defined _WIN32 && ! defined __CYGWIN__
+  unsigned int milliseconds = micro / 1000;
+  if (sizeof milliseconds < sizeof micro && micro / 1000 != milliseconds)
+    {
+      errno = EINVAL;
+      return -1;
+    }
+  if (micro % 1000)
+    milliseconds++;
+  Sleep (milliseconds);
+  return 0;
+#else
   unsigned int seconds = micro / 1000000;
   if (sizeof seconds < sizeof micro && micro / 1000000 != seconds)
     {
@@ -50,9 +68,9 @@ usleep (useconds_t micro)
     seconds++;
   while ((seconds = sleep (seconds)) != 0);
 
-#undef usleep
-#if !HAVE_USLEEP
-# define usleep(x) 0
-#endif
+# if !HAVE_USLEEP
+#  define usleep(x) 0
+# endif
   return usleep (micro % 1000000);
+#endif
 }