Proof of concept how a real reload-handling with systemd could work.

Refs #6118

icinga-app/icinga.cpp

@@ -169,8 +169,11 @@ static bool Daemonize(const String& stderrFile)
 		return false;
 	}
 
-	if (pid)
+	if (pid) {
+		// TODO: do a real wait till the pidfile is written by the daemon
+		Utility::Sleep(5);
 		exit(0);
+	}
 
 	int fdnull = open("/dev/null", O_RDWR);
 	if (fdnull >= 0) {
@@ -483,7 +486,7 @@ int Main(void)
 		Log(LogInformation, "icinga-app", "Previous instance has ended, taking over now.");
 	}
 
-	if (g_AppParams.count("daemonize")) {
+	if (g_AppParams.count("daemonize") && !g_AppParams.count("reload-internal")) {
 		String errorLog;
 
 		if (g_AppParams.count("errorlog"))

lib/base/application.cpp

@@ -46,6 +46,7 @@ REGISTER_TYPE(Application);
 Application *Application::m_Instance = NULL;
 bool Application::m_ShuttingDown = false;
 bool Application::m_RequestRestart = false;
+pid_t Application::m_ReloadProcess = 0;
 static bool l_Restarting = false;
 bool Application::m_Debugging = false;
 int Application::m_ArgC;
@@ -91,6 +92,13 @@ void Application::Stop(void)
 	WSACleanup();
 #endif /* _WIN32 */
 
+	// Getting a shutdown-signal when a restart is in progress usually
+	// means that the restart succeeded and the new process wants to take
+	// over. Write the PID of the new process to the pidfile before this
+	// process exits to keep systemd happy.
+	if (l_Restarting)
+		UpdatePidFile(GetPidPath(),m_ReloadProcess);
+
 	ClosePidFile();
 
 	DynamicObject::Stop();
@@ -218,7 +226,7 @@ void Application::SetArgV(char **argv)
  * Processes events for registered sockets and timers and calls whatever
  * handlers have been set up for these events.
  */
-void Application::RunEventLoop(void) const
+void Application::RunEventLoop(void)
 {
 	Timer::Initialize();
 
@@ -254,7 +262,7 @@ mainloop:
 			goto mainloop;
 
 		l_Restarting = true;
-		StartReloadProcess();
+		m_ReloadProcess = StartReloadProcess();
 
 		goto mainloop;
 	}
@@ -285,7 +293,7 @@ static void ReloadProcessCallback(const ProcessResult& pr)
 	l_Restarting = false;
 }
 
-void Application::StartReloadProcess(void) const
+pid_t Application::StartReloadProcess(void)
 {
 	Log(LogInformation, "base", "Got reload command: Starting new instance.");
 
@@ -305,6 +313,8 @@ void Application::StartReloadProcess(void) const
 	Process::Ptr process = make_shared<Process>(Process::PrepareCommand(args));
 	process->SetTimeout(300);
 	process->Run(&ReloadProcessCallback);
+    
+	return process->GetHandle();
 }
 
 /**
@@ -619,8 +629,9 @@ int Application::Run(void)
  * if the PID file is already locked by another instance of the application.
  *
  * @param filename The name of the PID file.
+ * @param pid The PID to write; default is the current PID
  */
-void Application::UpdatePidFile(const String& filename)
+void Application::UpdatePidFile(const String& filename, pid_t pid)
 {
 	ASSERT(!OwnsLock());
 	ObjectLock olock(this);
@@ -663,7 +674,7 @@ void Application::UpdatePidFile(const String& filename)
 	}
 #endif /* _WIN32 */
 
-	fprintf(m_PidFile, "%d\n", Utility::GetPid());
+	fprintf(m_PidFile, "%d\n", pid);
 	fflush(m_PidFile);
 }
 

lib/base/application.h

@@ -23,6 +23,7 @@
 #include "base/i2-base.h"
 #include "base/application.th"
 #include "base/threadpool.h"
+#include "base/utility.h"
 
 namespace icinga
 {
@@ -67,7 +68,7 @@ public:
 	static void SetDebugging(bool debug);
 	static bool IsDebugging(void);
 
-	void UpdatePidFile(const String& filename);
+	void UpdatePidFile(const String& filename, pid_t pid = Utility::GetPid());
 	void ClosePidFile(void);
 	static pid_t ReadPidFile(const String& filename);
 
@@ -113,9 +114,9 @@ protected:
 	virtual void OnConfigLoaded(void);
 	virtual void Stop(void);
 
-	void RunEventLoop(void) const;
+	void RunEventLoop(void);
 
-	void StartReloadProcess(void) const;
+	pid_t StartReloadProcess(void);
 
 	virtual void OnShutdown(void);
 
@@ -124,7 +125,10 @@ private:
 
 	static bool m_ShuttingDown; /**< Whether the application is in the process of
 				  shutting down. */
-	static bool m_RequestRestart;
+	static bool m_RequestRestart; /**< A restart was requested through SIGHUP */
+	static pid_t m_ReloadProcess; /**< The PID of a subprocess doing a reload, 
+									only valid when l_Restarting==true */
+
 	static int m_ArgC; /**< The number of command-line arguments. */
 	static char **m_ArgV; /**< Command-line arguments. */
 	FILE *m_PidFile; /**< The PID file */

lib/base/process.cpp

@@ -636,6 +636,12 @@ bool Process::DoEvents(void)
 	return false;
 }
 
+Process::ProcessHandle Process::GetHandle(void) const
+{
+	return m_Process;
+}
+
+
 int Process::GetTID(void) const
 {
 	return (reinterpret_cast<uintptr_t>(this) / sizeof(void *)) % IOTHREADS;

lib/base/process.h

@@ -73,6 +73,8 @@ public:
 
 	void Run(const boost::function<void (const ProcessResult&)>& callback = boost::function<void (const ProcessResult&)>());
 
+	ProcessHandle GetHandle(void) const;
+
 	static Arguments PrepareCommand(const Value& command);
 
 	static void StaticInitialize(void);