From 1badbab0023ba19dc7e76a53dd00a027f7316038 Mon Sep 17 00:00:00 2001
From: "Alexander A. Klimov" <alexander.klimov@icinga.com>
Date: Tue, 21 Mar 2023 11:45:47 +0100
Subject: [PATCH] Timer::TimerThreadProc(): keep a Timer alive while it's
 running

to prevent the case: Timer callback destroys parent object -> destroys
Timer -> ~Timer() -> Stop(true) -> waits for the Timer callback to finish
-> deadlock.
---
 lib/base/timer.cpp | 19 ++++++++++++++++++-
 lib/base/timer.hpp |  7 ++-----
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/lib/base/timer.cpp b/lib/base/timer.cpp
index 4de5d7e0e..bdeb0f277 100644
--- a/lib/base/timer.cpp
+++ b/lib/base/timer.cpp
@@ -12,6 +12,7 @@
 #include <condition_variable>
 #include <mutex>
 #include <thread>
+#include <utility>
 
 using namespace icinga;
 
@@ -61,6 +62,15 @@ static int l_AliveTimers = 0;
 
 static Defer l_ShutdownTimersCleanlyOnExit (&Timer::Uninitialize);
 
+Timer::Ptr Timer::Create()
+{
+	Ptr t (new Timer());
+
+	t->m_Self = t;
+
+	return t;
+}
+
 /**
  * Destructor for the Timer class.
  */
@@ -316,11 +326,18 @@ void Timer::TimerThreadProc()
 		 * until the current call is completed. */
 		l_Timers.erase(timer);
 
+		auto keepAlive (timer->m_Self.lock());
+
+		if (!keepAlive) {
+			// The last std::shared_ptr is gone, let ~Timer() proceed
+			continue;
+		}
+
 		timer->m_Running = true;
 
 		lock.unlock();
 
 		/* Asynchronously call the timer. */
-		Utility::QueueAsyncCallback([timer]() { timer->Call(); });
+		Utility::QueueAsyncCallback([timer=std::move(keepAlive)]() { timer->Call(); });
 	}
 }
diff --git a/lib/base/timer.hpp b/lib/base/timer.hpp
index 29625a358..a90963509 100644
--- a/lib/base/timer.hpp
+++ b/lib/base/timer.hpp
@@ -21,11 +21,7 @@ class Timer final
 public:
 	typedef std::shared_ptr<Timer> Ptr;
 
-	static inline
-	Ptr Create()
-	{
-		return Ptr(new Timer());
-	}
+	static Ptr Create();
 
 	~Timer();
 
@@ -52,6 +48,7 @@ private:
 	double m_Next{0}; /**< When the next event should happen. */
 	bool m_Started{false}; /**< Whether the timer is enabled. */
 	bool m_Running{false}; /**< Whether the timer proc is currently running. */
+	std::weak_ptr<Timer> m_Self;
 
 	Timer() = default;
 	void Call();