fix(TCPServer): continues to accept connections after stop() #4892 (#4896)

* fix(TCPServer): continues to accept connections after stop() #4892

* fix(TCPServer): first attempt to silence TSAN #4892

* fix(TCPServer): check stopped status after poll; add TCPServerFactory::stop() and allow factory to return nullptr on connection creation request #4892

* fix(TCPServer): initialize factory stopped flag #4892

* revert(SocketImpl): atomic sock fd

Net/include/Poco/Net/SocketImpl.h

@@ -295,11 +295,11 @@ public:
 		/// If count is != 0, sends the given number of bytes, otherwise
 		/// sends all bytes, starting from the given offset.
 		///
-		/// On Linux, macOS and FreeBSD systems, the implementation 
+		/// On Linux, macOS and FreeBSD systems, the implementation
 		/// uses sendfile() or sendfile64().
 		/// On Windows, the implementation uses TransmitFile().
 		///
-		/// If neither sendfile() nor TransmitFile() is available, 
+		/// If neither sendfile() nor TransmitFile() is available,
 		/// or the socket is a secure one (secure() returne true),
 		/// falls back to reading the file block by block and calling sendBytes().
 		///
@@ -307,7 +307,7 @@ public:
 		/// as count, unless count is 0.
 		///
 		/// Throws NetException (or a subclass) in case of any errors.
-		/// Also throws a NetException if the socket has been set to 
+		/// Also throws a NetException if the socket has been set to
 		/// non-blocking.
 
 	virtual int available();
@@ -636,7 +636,7 @@ inline bool SocketImpl::getBlocking() const
 
 
 #if defined(POCO_OS_FAMILY_WINDOWS)
-	#pragma comment(lib, "mswsock.lib") 
-#endif 
+	#pragma comment(lib, "mswsock.lib")
+#endif
 
 #endif // Net_SocketImpl_INCLUDED

Net/include/Poco/Net/TCPServerConnectionFactory.h

@@ -35,7 +35,13 @@ class Net_API TCPServerConnectionFactory
 	/// it accepts.
 	///
 	/// Subclasses must override the createConnection()
-	/// method.
+	/// method, which can refuse connections by returning nullptr.
+	/// Some examples when an implementation may refuse new connections:
+	///
+	///  - number of connections exceeded a limit
+	///  - a connection from unwanted client attempted
+	///  - too many connection attempts in a short timespan
+	///  - etc.
 	///
 	/// The TCPServerConnectionFactoryImpl template class
 	/// can be used to automatically instantiate a
@@ -45,23 +51,55 @@ class Net_API TCPServerConnectionFactory
 public:
 	using Ptr = Poco::SharedPtr<TCPServerConnectionFactory>;
 
+	TCPServerConnectionFactory(const TCPServerConnectionFactory&) = delete;
+	TCPServerConnectionFactory& operator = (const TCPServerConnectionFactory&) = delete;
+	TCPServerConnectionFactory(TCPServerConnectionFactory&&) = delete;
+	TCPServerConnectionFactory& operator = (TCPServerConnectionFactory&&) = delete;
+
 	virtual ~TCPServerConnectionFactory();
 		/// Destroys the TCPServerConnectionFactory.
 
 	virtual TCPServerConnection* createConnection(const StreamSocket& socket) = 0;
 		/// Creates an instance of a subclass of TCPServerConnection,
 		/// using the given StreamSocket.
+		/// This function is allowed to return nullptr, in which case an accepted
+		/// socket will be destroyed by the TCPServerDispatcher.
+
+	void stop();
+		/// Stops the factory.
+		/// Normally, this function is called by TCPServerDispatcher
+		/// to indicate that the server is shutting down; the expected
+		/// implementation behavior after this call is to return nullptr
+		/// on all subsequent connection creation attempts.
+
+	bool isStopped() const;
+		/// Returns true if the factory was stopped, false otherwise.
 
 protected:
 	TCPServerConnectionFactory();
 		/// Creates the TCPServerConnectionFactory.
 
 private:
-	TCPServerConnectionFactory(const TCPServerConnectionFactory&);
-	TCPServerConnectionFactory& operator = (const TCPServerConnectionFactory&);
+	std::atomic<bool> _stopped;
 };
 
 
+//
+// inlines
+//
+
+inline void TCPServerConnectionFactory::stop()
+{
+	_stopped = true;
+}
+
+
+inline bool TCPServerConnectionFactory::isStopped() const
+{
+	return _stopped;
+}
+
+
 template <class S>
 class TCPServerConnectionFactoryImpl: public TCPServerConnectionFactory
 	/// This template provides a basic implementation of
@@ -78,7 +116,10 @@ public:
 
 	TCPServerConnection* createConnection(const StreamSocket& socket)
 	{
-		return new S(socket);
+		if (!isStopped())
+			return new S(socket);
+
+		return nullptr;
 	}
 };