change PBD::microseconds_t to a signed type and check for -1 in TimingStats::update

This may help a Windows issue with the return value of QueryPerformanceCounter

libs/ardour/ardour/plugin_insert.h

@@ -198,7 +198,7 @@ public:
 	bool load_preset (Plugin::PresetRecord);
 
 	bool provides_stats () const;
-	bool get_stats (uint64_t& min, uint64_t& max, double& avg, double& dev) const;
+	bool get_stats (PBD::microseconds_t& min, PBD::microseconds_t& max, double& avg, double& dev) const;
 	void clear_stats ();
 
 	/** A control that manipulates a plugin parameter (control port). */

libs/ardour/plugin_insert.cc

@@ -3383,7 +3383,7 @@ PluginInsert::provides_stats () const
 }
 
 bool
-PluginInsert::get_stats (uint64_t& min, uint64_t& max, double& avg, double& dev) const
+PluginInsert::get_stats (PBD::microseconds_t& min, PBD::microseconds_t& max, double& avg, double& dev) const
 {
 	/* TODO: consider taking a try/lock: Don't run concurrently with
 	 * TimingStats::update, TimingStats::reset.

libs/pbd/pbd/microseconds.h

@@ -26,7 +26,7 @@
 #include "pbd/libpbd_visibility.h"
 
 namespace PBD {
-	typedef uint64_t microseconds_t;
+	typedef int64_t microseconds_t;
 	LIBPBD_API microseconds_t get_microseconds();
 	void microsecond_timer_init ();
 }

libs/pbd/pbd/timing.h

@@ -116,8 +116,7 @@ public:
 		return elapsed () / 1000;
 	}
 
-private:
-
+  protected:
 	microseconds_t m_start_val;
 	microseconds_t m_last_val;
 
@@ -138,17 +137,18 @@ public:
 			reset ();
 		} else {
 			Timing::update ();
-			calc ();
-		}
-	}
 
-	/* interval computed externally */
-	void update (microseconds_t interval)
-	{
-		if (_queue_reset) {
-			reset ();
-		} else {
-			Timing::update (interval);
+			/* querying the performance counter can fail occasionally (-1).
+			 * Also on some multi-core systems, timers are CPU specific and not
+			 * synchronized. We assume they differ more than a few milliseconds
+			 * (4 * nominal cycle time) and simply ignore cases where the
+			 * execution switches cores.
+			 */
+
+			if (m_start_val < 0 || m_last_val < 0 || m_start_val > m_last_val) {
+				return;
+			}
+
 			calc ();
 		}
 	}

libs/pbd/timing.cc

@@ -26,17 +26,17 @@
 namespace PBD {
 
 bool
-get_min_max_avg_total (const std::vector<uint64_t>& values, uint64_t& min, uint64_t& max, uint64_t& avg, uint64_t& total)
+get_min_max_avg_total (const std::vector<microseconds_t>& values, microseconds_t& min, microseconds_t& max, microseconds_t& avg, microseconds_t& total)
 {
 	if (values.empty()) {
 		return false;
 	}
 
 	total = 0;
-	min = std::numeric_limits<uint64_t>::max();
+	min = std::numeric_limits<microseconds_t>::max();
 	max = 0; avg = 0;
 
-	for (std::vector<uint64_t>::const_iterator ci = values.begin(); ci != values.end(); ++ci) {
+	for (std::vector<microseconds_t>::const_iterator ci = values.begin(); ci != values.end(); ++ci) {
 		total += *ci;
 		min = std::min (min, *ci);
 		max = std::max (max, *ci);
@@ -47,11 +47,11 @@ get_min_max_avg_total (const std::vector<uint64_t>& values, uint64_t& min, uint6
 }
 
 std::string
-timing_summary (const std::vector<uint64_t>& values)
+timing_summary (const std::vector<microseconds_t>& values)
 {
 	std::ostringstream oss;
 
-	uint64_t min, max, avg, total;
+	microseconds_t min, max, avg, total;
 
 	if (get_min_max_avg_total (values, min, max, avg, total)) {
 		oss << "Count: " << values.size()

libs/surfaces/mackie/surface.cc

@@ -951,7 +951,7 @@ Surface::zero_controls ()
 }
 
 void
-Surface::periodic (uint64_t now_usecs)
+Surface::periodic (PBD::microseconds_t now_usecs)
 {
 	master_gain_changed();
 	for (Strips::iterator s = strips.begin(); s != strips.end(); ++s) {

libs/surfaces/us2400/surface.cc

@@ -909,7 +909,7 @@ Surface::zero_controls ()
 }
 
 void
-Surface::periodic (uint64_t now_usecs)
+Surface::periodic (PBD::microseconds_t now_usecs)
 {
 	if (_active) {
 		master_gain_changed();