Introduce RAII style `ObjectNameLock` class

lib/remote/configobjectslock.cpp

@@ -1,13 +1,16 @@
 /* Icinga 2 | (c) 2022 Icinga GmbH | GPLv2+ */
 
-#ifndef _WIN32
-
-#include "base/shared-memory.hpp"
 #include "remote/configobjectslock.hpp"
+
+#ifndef _WIN32
+#include "base/shared-memory.hpp"
 #include <boost/interprocess/sync/lock_options.hpp>
+#endif /* _WIN32 */
 
 using namespace icinga;
 
+#ifndef _WIN32
+
 // On *nix one process may write config objects while another is loading the config, so this uses IPC.
 static SharedMemory<boost::interprocess::interprocess_sharable_mutex> l_ConfigObjectsMutex;
 
@@ -22,3 +25,37 @@ ConfigObjectsSharedLock::ConfigObjectsSharedLock(std::try_to_lock_t)
 }
 
 #endif /* _WIN32 */
+
+std::mutex ObjectNameLock::m_Mutex;
+std::condition_variable ObjectNameLock::m_CV;
+std::map<Type*, std::set<String>> ObjectNameLock::m_LockedObjectNames;
+
+/**
+ * Locks the specified object name of the given type and unlocks it upon destruction of the instance of this class.
+ *
+ * If it is already locked, the call blocks until the lock is released.
+ *
+ * @param Type::Ptr ptype The type of the object you want to lock
+ * @param String objName The object name you want to lock
+ */
+ObjectNameLock::ObjectNameLock(const Type::Ptr& ptype, const String& objName): m_ObjectName{objName}, m_Type{ptype}
+{
+	std::unique_lock<std::mutex> lock(m_Mutex);
+	m_CV.wait(lock, [this]{
+		auto& locked = m_LockedObjectNames[m_Type.get()];
+		return locked.find(m_ObjectName) == locked.end();
+	});
+
+	// Add the object name to the locked list to block all other threads that try
+	// to process a message affecting the same object.
+	m_LockedObjectNames[ptype.get()].emplace(objName);
+}
+
+ObjectNameLock::~ObjectNameLock()
+{
+	{
+		std::unique_lock<std::mutex> lock(m_Mutex);
+		m_LockedObjectNames[m_Type.get()].erase(m_ObjectName);
+	}
+	m_CV.notify_all();
+}

lib/remote/configobjectslock.hpp

@@ -2,7 +2,12 @@
 
 #pragma once
 
+#include "base/type.hpp"
+#include "base/string.hpp"
+#include <condition_variable>
+#include <map>
 #include <mutex>
+#include <set>
 
 #ifndef _WIN32
 #include <boost/interprocess/sync/interprocess_sharable_mutex.hpp>
@@ -69,4 +74,29 @@ private:
 
 #endif /* _WIN32 */
 
+
+/**
+ * Allows you to easily lock/unlock a specific object of a given type by its name.
+ *
+ * That way, locking an object "this" of type Host does not affect an object "this" of
+ * type "Service" nor an object "other" of type "Host".
+ *
+ * @ingroup remote
+ */
+class ObjectNameLock
+{
+public:
+	ObjectNameLock(const Type::Ptr& ptype, const String& objName);
+
+	~ObjectNameLock();
+
+private:
+	String m_ObjectName;
+	Type::Ptr m_Type;
+
+	static std::mutex m_Mutex;
+	static std::condition_variable m_CV;
+	static std::map<Type*, std::set<String>> m_LockedObjectNames;
+};
+
 }