Restart thread pool after freezing Configuration

The user (-D) or we could have changed Configuration.Concurrency,
so correct the thread pool's thread amount.

icinga-app/icinga.cpp

@@ -451,6 +451,8 @@ static int Main()
 		Configuration::Concurrency = std::thread::hardware_concurrency();
 	}
 
+	Application::GetTP().Restart();
+
 	/* Ensure that all defined constants work in the way we expect them. */
 	HandleLegacyDefines();
 

lib/base/threadpool.cpp

@@ -20,10 +20,15 @@ void ThreadPool::Start()
 	boost::unique_lock<decltype(m_Mutex)> lock (m_Mutex);
 
 	if (!m_Pool) {
-		m_Pool = decltype(m_Pool)(new boost::asio::thread_pool(Configuration::Concurrency * 2u));
+		InitializePool();
 	}
 }
 
+void ThreadPool::InitializePool()
+{
+	m_Pool = decltype(m_Pool)(new boost::asio::thread_pool(Configuration::Concurrency * 2u));
+}
+
 void ThreadPool::Stop()
 {
 	boost::unique_lock<decltype(m_Mutex)> lock (m_Mutex);
@@ -33,3 +38,14 @@ void ThreadPool::Stop()
 		m_Pool = nullptr;
 	}
 }
+
+void ThreadPool::Restart()
+{
+	boost::unique_lock<decltype(m_Mutex)> lock (m_Mutex);
+
+	if (m_Pool) {
+		m_Pool->join();
+	}
+
+	InitializePool();
+}

lib/base/threadpool.hpp

@@ -42,6 +42,7 @@ public:
 
 	void Start();
 	void Stop();
+	void Restart();
 
 	/**
 	 * Appends a work item to the work queue. Work items will be processed in FIFO order.
@@ -91,6 +92,8 @@ private:
 	boost::shared_mutex m_Mutex;
 	std::unique_ptr<boost::asio::thread_pool> m_Pool;
 	Atomic<uint_fast64_t> m_Pending;
+
+	void InitializePool();
 };
 
 }