event/MultiSocketMonitor: add method Reset()

src/event/MultiSocketMonitor.cxx

@@ -31,9 +31,15 @@ MultiSocketMonitor::MultiSocketMonitor(EventLoop &_loop)
 	:IdleMonitor(_loop), TimeoutMonitor(_loop) {
 }
 
-MultiSocketMonitor::~MultiSocketMonitor()
+void
+MultiSocketMonitor::Reset()
 {
-	// TODO
+	assert(GetEventLoop().IsInsideOrNull());
+
+	fds.clear();
+	IdleMonitor::Cancel();
+	TimeoutMonitor::Cancel();
+	ready = refresh = false;
 }
 
 void

src/event/MultiSocketMonitor.hxx

@@ -119,11 +119,26 @@ public:
 	static constexpr unsigned HANGUP = SocketMonitor::HANGUP;
 
 	MultiSocketMonitor(EventLoop &_loop);
-	~MultiSocketMonitor();
 
 	using IdleMonitor::GetEventLoop;
 
-public:
+	/**
+	 * Clear the socket list and disable all #EventLoop
+	 * registrations.  Run this in the #EventLoop thread before
+	 * destroying this object.
+	 *
+	 * Later, this object can be reused and reactivated by calling
+	 * InvalidateSockets().
+	 *
+	 * Note that this class doesn't have a destructor which calls
+	 * this method, because this would be racy and thus pointless:
+	 * at the time ~MultiSocketMonitor() is called, our virtual
+	 * methods have been morphed to be pure again, and in the
+	 * meantime the #EventLoop thread could invoke those pure
+	 * methods.
+	 */
+	void Reset();
+
 	/**
 	 * Invalidate the socket list.  A call to PrepareSockets() is
 	 * scheduled which will then update the list.

src/input/plugins/AlsaInputPlugin.cxx

@@ -98,12 +98,8 @@ public:
 	}
 
 	~AlsaInputStream() {
-		/* ClearSocketList must be called from within the
-		   IOThread; if we don't do it manually here, the
-		   ~MultiSocketMonitor() will do it in the current
-		   thread */
 		BlockingCall(MultiSocketMonitor::GetEventLoop(), [this](){
-				ClearSocketList();
+				MultiSocketMonitor::Reset();
 			});
 
 		snd_pcm_close(capture_handle);