[host] windows: add delayExecution function for more accurate sleeps

This change not only exposes and allows use of NtDelayExecution, but
also moves the code to set the system timer resolution.

host/platform/Windows/src/delay.c

@@ -0,0 +1,49 @@
+/**
+ * Looking Glass
+ * Copyright (C) 2017-2021 The Looking Glass Authors
+ * https://looking-glass.io
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc., 59
+ * Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#include "windows/delay.h"
+#include "common/debug.h"
+
+NtDelayExecution_t NtDelayExecution;
+ZwSetTimerResolution_t ZwSetTimerResolution;
+
+void delayInit(void)
+{
+  HMODULE ntdll = GetModuleHandle("ntdll.dll");
+  NtDelayExecution = (NtDelayExecution_t)
+    GetProcAddress(ntdll, "NtDelayExecution");
+
+  // Increase the timer resolution
+  ZwSetTimerResolution = (ZwSetTimerResolution_t)
+    GetProcAddress(ntdll, "ZwSetTimerResolution");
+
+  if (ZwSetTimerResolution)
+  {
+    ULONG actualResolution;
+    ZwSetTimerResolution(1, true, &actualResolution);
+    DEBUG_INFO("System timer resolution: %lu ns", actualResolution * 100);
+  }
+}
+
+void delayExecution(float ms)
+{
+  LARGE_INTEGER interval = { .QuadPart = -1 * (int)(ms * 1000.0f) };
+  NtDelayExecution(FALSE, &interval);
+}

host/platform/Windows/src/mousehook.c

@@ -19,6 +19,7 @@
  */
 
 #include "windows/mousehook.h"
+#include "windows/delay.h"
 #include "common/windebug.h"
 #include "platform.h"
 
@@ -104,7 +105,7 @@ static DWORD WINAPI updateThreadProc(LPVOID lParam)
         mouseHook.callback(mouseHook.x, mouseHook.y);
 
         // limit this to 1000Hz, who has a mouse that updates faster anyway?
-        Sleep(1);
+        delayExecution(1.0f);
         break;
     }
   }

host/platform/Windows/src/platform.c

@@ -20,6 +20,7 @@
 
 #include "platform.h"
 #include "service.h"
+#include "windows/delay.h"
 #include "windows/mousehook.h"
 
 #include <windows.h>
@@ -61,10 +62,6 @@ struct AppState
 static struct AppState app = {0};
 HWND MessageHWND;
 
-// undocumented API to adjust the system timer resolution (yes, its a nasty hack)
-typedef NTSTATUS (__stdcall *ZwSetTimerResolution_t)(ULONG RequestedResolution, BOOLEAN Set, PULONG ActualResolution);
-static ZwSetTimerResolution_t ZwSetTimerResolution = NULL;
-
 // linux mingw64 is missing this
 #ifndef MSGFLT_RESET
   #define MSGFLT_RESET (0)
@@ -504,7 +501,7 @@ void boostPriority(void)
 
 bool app_init(void)
 {
-  const char * logFile   = option_get_string("os", "logFile"  );
+  const char * logFile = option_get_string("os", "logFile");
 
   // redirect stderr to a file
   if (logFile && strcmp(logFile, "stderr") != 0)
@@ -513,14 +510,7 @@ bool app_init(void)
   // always flush stderr
   setbuf(stderr, NULL);
 
-  // Increase the timer resolution
-  ZwSetTimerResolution = (ZwSetTimerResolution_t)GetProcAddress(GetModuleHandle("ntdll.dll"), "ZwSetTimerResolution");
-  if (ZwSetTimerResolution)
-  {
-    ULONG actualResolution;
-    ZwSetTimerResolution(1, true, &actualResolution);
-    DEBUG_INFO("System timer resolution: %lu ns", actualResolution * 100);
-  }
+  delayInit();
 
   // get the performance frequency for spinlocks
   QueryPerformanceFrequency(&app.perfFreq);