Add PBD::QPC::initialize to initialize timer and call it from PBD::init

Check timer for invalid frequency
Precalculate timer tick rate to save a few instructions
Don't use static variables inside functions to avoid checking for initialization
Use static functions inside anonymous namespace for internal linkage

libs/pbd/pbd.cc

@@ -109,6 +109,7 @@ PBD::init ()
 		return false;
 	}
 
+	QPC::initialize();
 	test_timers_from_env ();
 
 	if (!PBD::MMCSS::initialize()) {

libs/pbd/pbd/windows_timer_utils.h

@@ -59,20 +59,29 @@ bool reset_resolution();
 
 namespace QPC {
 
+/**
+ * Initialize the QPC timer, must be called before QPC::get_microseconds will
+ * return a valid value.
+ * @return true if QPC timer is usable, use check_timer_valid to try to check
+ * if it is monotonic.
+ */
+bool initialize ();
+
 /**
  * @return true if QueryPerformanceCounter is usable as a timer source
  * This should always return true for systems > XP as those versions of windows
  * have there own tests to check timer validity and will select an appropriate
- * timer source.
+ * timer source. This check is not conclusive and there are probably conditions
+ * under which this check will return true but the timer is not monotonic.
  */
 bool check_timer_valid ();
 
 /**
  * @return the value of the performance counter converted to microseconds
  *
- * If get_counter_valid returns true then get_microseconds will always
- * return a positive value. If QPC is not supported(OS < XP) then -1 is
- * returned but the MS docs say that this won't occur for systems >= XP.
+ * If initialize returns true then get_microseconds will always return a
+ * positive value. If QPC is not supported(OS < XP) then -1 is returned but the
+ * MS docs say that this won't occur for systems >= XP.
  */
 int64_t get_microseconds ();
 

libs/pbd/windows_timer_utils.cc

@@ -23,11 +23,15 @@
 
 #include "pbd/compose.h"
 #include "pbd/debug.h"
+#include "pbd/error.h"
+
+#include "i18n.h"
 
 #define DEBUG_TIMING(msg) DEBUG_TRACE (PBD::DEBUG::Timing, msg);
 
 namespace {
 
+static
 UINT&
 timer_resolution ()
 {
@@ -35,7 +39,7 @@ timer_resolution ()
 	return timer_res_ms;
 }
 
-}
+} // namespace
 
 namespace PBD {
 
@@ -100,6 +104,7 @@ reset_resolution ()
 		DEBUG_TIMING("Could not reset the Timer resolution.\n");
 		return false;
 	}
+	DEBUG_TIMING("Reset the Timer resolution.\n");
 	timer_resolution() = 0;
 	return true;
 }
@@ -108,34 +113,9 @@ reset_resolution ()
 
 namespace {
 
-bool&
-qpc_frequency_success ()
-{
-	static bool success = false;
-	return success;
-}
-
-LARGE_INTEGER
-qpc_frequency ()
-{
-	LARGE_INTEGER freq;
-	if (QueryPerformanceFrequency(&freq) == 0) {
-		DEBUG_TIMING ("Failed to determine frequency of QPC\n");
-		qpc_frequency_success() = false;
-	} else {
-		qpc_frequency_success() = true;
-	}
-
-	return freq;
-}
-
-LARGE_INTEGER
-qpc_frequency_cached ()
-{
-	static LARGE_INTEGER frequency = qpc_frequency ();
-	return frequency;
-}
+static double timer_rate_us = 0.0;
 
+static
 bool
 test_qpc_validity ()
 {
@@ -159,25 +139,37 @@ namespace QPC {
 bool
 check_timer_valid ()
 {
-	// setup caching the timer frequency
-	qpc_frequency_cached ();
-	if (!qpc_frequency_success ()) {
+	if (!timer_rate_us) {
 		return false;
 	}
 	return test_qpc_validity ();
 }
 
+bool
+initialize ()
+{
+	LARGE_INTEGER freq;
+	if (!QueryPerformanceFrequency(&freq) || freq.QuadPart < 1) {
+		info << X_("Failed to determine frequency of QPC\n") << endmsg;
+		timer_rate_us = 0;
+	} else {
+		timer_rate_us = 1000000.0 / freq.QuadPart;
+	}
+	info << string_compose(X_("QPC timer microseconds per tick: %1\n"),
+	                       timer_rate_us) << endmsg;
+	return !timer_rate_us;
+}
+
 int64_t
 get_microseconds ()
 {
 	LARGE_INTEGER current_val;
 
-	if (qpc_frequency_success()) {
+	if (timer_rate_us) {
 		// MS docs say this will always succeed for systems >= XP but it may
 		// not return a monotonic value with non-invariant TSC's etc
 		if (QueryPerformanceCounter(&current_val) != 0) {
-			return (int64_t)(((double)current_val.QuadPart) /
-			                 ((double)qpc_frequency_cached().QuadPart) * 1000000.0);
+			return (int64_t)(current_val.QuadPart * timer_rate_us);
 		}
 	}
 	DEBUG_TIMING ("Could not get QPC timer\n");
@@ -189,8 +181,7 @@ get_microseconds ()
 int64_t
 get_microseconds ()
 {
-	qpc_frequency_cached();
-	if (qpc_frequency_success()) {
+	if (timer_rate_us) {
 		return QPC::get_microseconds ();
 	}
 	// For XP systems that don't support a high-res performance counter