compat/timer-resolution: use undocumented windows API

Unlike timeBeginPeriod in winmm, this one sets the timer
resolution for the calling process, only.

1 files changed, 103 insertions, 0 deletions

diff --git a/compat/timer-resolution.cpp b/compat/timer-resolution.cpp
new file mode 100644
index 00000000..597ee91e
--- /dev/null
+++ b/compat/timer-resolution.cpp
@@ -0,0 +1,103 @@
+/* Copyright (c) 2017 Stanislaw Halik <sthalik@misaki.pl>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ */
+
+#include "timer-resolution.hpp"
+
+#if defined _WIN32
+#   include <windows.h>
+
+#   include <QLibrary>
+#   include <QDebug>
+
+typedef LONG (__stdcall *funptr_NtSetTimerResolution) (ULONG, BOOLEAN, PULONG);
+static funptr_NtSetTimerResolution init_timer_resolution_funptr();
+static funptr_NtSetTimerResolution get_funptr();
+
+static funptr_NtSetTimerResolution init_timer_resolution_funptr()
+{
+    static QLibrary ntdll;
+    ntdll.setLoadHints(QLibrary::PreventUnloadHint);
+    ntdll.setFileName("ntdll.dll");
+    const bool load = ntdll.load();
+    if (!load)
+    {
+        qDebug() << "can't load ntdll:" << ntdll.errorString();
+        return nullptr;
+    }
+
+    auto ret = reinterpret_cast<funptr_NtSetTimerResolution>(ntdll.resolve("NtSetTimerResolution"));
+    if (ret == nullptr)
+    {
+        qDebug() << "can't find NtSetTimerResolution in ntdll:" << ntdll.errorString();
+        return nullptr;
+    }
+
+    return ret;
+}
+
+static funptr_NtSetTimerResolution get_funptr()
+{
+    static auto ret = init_timer_resolution_funptr();
+    return ret;
+}
+
+timer_resolution::timer_resolution(int msecs) : old_value(-1)
+{
+    if (msecs <= 0 || msecs > 30)
+    {
+        qDebug() << "can't set timer resolution to" << msecs << "ms";
+        return;
+    }
+
+    funptr_NtSetTimerResolution f = get_funptr();
+    if (f == nullptr)
+        return;
+
+    // hundredth of a nanosecond
+    const ULONG value = msecs * ULONG(10000);
+    NTSTATUS error = f(value, TRUE, &old_value);
+    ULONG old_value_ = -1;
+
+    if (error != 0)
+    {
+        old_value = -1;
+        qDebug() << "NtSetTimerResolution erred with" << error;
+        return;
+    }
+
+    // see if it stuck
+
+    error = f(value, TRUE, &old_value_);
+    if (error != 0)
+    {
+        old_value = -1;
+        qDebug() << "NtSetTimerResolution check erred with" << error;
+        return;
+    }
+
+    if (old_value_ != old_value)
+    {
+        qDebug() << "NtSetTimerResolution:"
+                 << "old value didn't stick"
+                 << "current resolution" << old_value_
+                 << "* 100 ns";
+        old_value = -1;
+        return;
+    }
+}
+
+timer_resolution::~timer_resolution()
+{
+    if (old_value != ULONG(-1))
+    {
+        funptr_NtSetTimerResolution f = get_funptr();
+        ULONG fuzz = -1;
+        (void) f(old_value, TRUE, &fuzz);
+    }
+}
+
+#endif