Bugfix: Update state machine to use monotonic time for delay enforcement (#46)

This fixes error: "invalid execution delay error".
This could occur after NTP clock adjustments causing system clock to jump backwards.

Author: krixkrix

Implementation/Common/common_chrono.cpp

@@ -187,6 +187,11 @@ namespace AMCCommon {
 		return convertToISO8601TimeUTC(getUTCTimeStampInMicrosecondsSince1970());
 	}
 
+	uint64_t CChrono::getElapsedMicroseconds()
+	{
+		return m_pChronoImpl->getElapsedMicroseconds();
+	}
+
 	void CChrono::sleepSeconds(const uint64_t seconds)
 	{
 		sleepMicroseconds(seconds * 1000000ULL);

Implementation/Common/common_chrono.hpp

@@ -68,6 +68,11 @@ namespace AMCCommon {
 			// Returns Absolute UTC Time Stamp in ISO8601 formatting
 			std::string getUTCTimeInISO8601();
 
+			// Returns Monotonic Elapsed Time in microseconds since instance creation
+			// This time is NOT affected by system clock adjustments (NTP, manual changes)
+			// Use this for timing and delays, NOT for absolute timestamps
+			uint64_t getElapsedMicroseconds();
+
 			// Sleeps for some seconds
 			static void sleepSeconds(const uint64_t seconds);
 

Implementation/Core/amc_statemachinestate.cpp

@@ -85,7 +85,8 @@ namespace AMC {
 
 	void CStateMachineState::updateExecutionTime()
 	{
-		m_LastExecutionTimeStampInMicroseconds = m_pGlobalChrono->getUTCTimeStampInMicrosecondsSince1970 ();
+		// Use monotonic elapsed time to avoid issues with NTP clock adjustments
+		m_LastExecutionTimeStampInMicroseconds = m_pGlobalChrono->getElapsedMicroseconds();
 	}
 
 
@@ -161,8 +162,9 @@ namespace AMC {
 
 		if (chunkInMilliseconds < AMC_MINREPEATDELAY_MS)
 			throw ELibMCCustomException(LIBMC_ERROR_INVALIDREPEATDELAY, m_sInstanceName);
-		
-		uint64_t executionTimeInMicroSeconds = m_pGlobalChrono->getUTCTimeStampInMicrosecondsSince1970();
+
+		// Use monotonic elapsed time - not affected by NTP or system clock adjustments
+		uint64_t executionTimeInMicroSeconds = m_pGlobalChrono->getElapsedMicroseconds();
 		if (m_LastExecutionTimeStampInMicroseconds > executionTimeInMicroSeconds)
 			throw ELibMCCustomException(LIBMC_ERROR_INVALIDEXECUTIONDELAY, std::to_string (m_LastExecutionTimeStampInMicroseconds));
 
@@ -171,7 +173,7 @@ namespace AMC {
 		while (deltaExecutionTimeInMicroSeconds < (m_nRepeatDelay * 1000ULL)) {
 			m_pGlobalChrono->sleepMilliseconds(chunkInMilliseconds);
 
-			uint64_t newExecutionTimeInMicroSeconds = m_pGlobalChrono->getUTCTimeStampInMicrosecondsSince1970();
+			uint64_t newExecutionTimeInMicroSeconds = m_pGlobalChrono->getElapsedMicroseconds();
 			if (m_LastExecutionTimeStampInMicroseconds > newExecutionTimeInMicroSeconds)
 				throw ELibMCCustomException(LIBMC_ERROR_INVALIDEXECUTIONDELAY, std::to_string(m_LastExecutionTimeStampInMicroseconds));