ApiListener: Process cluster config updates sequentially

lib/remote/apilistener-configsync.cpp

@@ -7,6 +7,7 @@
 #include "base/configtype.hpp"
 #include "base/json.hpp"
 #include "base/convert.hpp"
+#include "base/defer.hpp"
 #include "config/vmops.hpp"
 #include <fstream>
 
@@ -104,6 +105,15 @@ Value ApiListener::ConfigUpdateObjectAPIHandler(const MessageOrigin::Ptr& origin
 		return Empty;
 	}
 
+	// Wait for the object name to become available for processing and block it immediately.
+	// Doing so guarantees that only one cluster event (create/update/delete) of a given
+	// object is being processed at any given time.
+	listener->m_ObjectConfigChangeLock.Lock(ptype, objName);
+
+	Defer unlockAndNotify([&listener, &ptype, &objName]{
+		listener->m_ObjectConfigChangeLock.Unlock(ptype, objName);
+	});
+
 	ConfigObject::Ptr object = ctype->GetObject(objName);
 
 	String config = params->Get("config");
@@ -258,6 +268,15 @@ Value ApiListener::ConfigDeleteObjectAPIHandler(const MessageOrigin::Ptr& origin
 		return Empty;
 	}
 
+	// Wait for the object name to become available for processing and block it immediately.
+	// Doing so guarantees that only one cluster event (create/update/delete) of a given
+	// object is being processed at any given time.
+	listener->m_ObjectConfigChangeLock.Lock(ptype, objName);
+
+	Defer unlockAndNotify([&listener, &ptype, &objName]{
+		listener->m_ObjectConfigChangeLock.Unlock(ptype, objName);
+	});
+
 	ConfigObject::Ptr object = ctype->GetObject(objName);
 
 	if (!object) {

lib/remote/apilistener.hpp

@@ -277,6 +277,9 @@ private:
 	mutable std::mutex m_ActivePackageStagesLock;
 	std::map<String, String> m_ActivePackageStages;
 
+	/* ensures that at most one create/update/delete is being processed per object at each time */
+	mutable ObjectNameMutex m_ObjectConfigChangeLock;
+
 	void UpdateActivePackageStagesCache();
 };