Use Twisted for VLC communication (#353)

* Port VLCPlayer from asyncore/asynchat to Twisted

Rationale: asyncore/asynchat are deprecated since Python 3.6 and
are going to be removed from the standard library from Python 3.10.
It is unclear if these libraries will be picked up by maintainers
and independently published on PyPI. At the moment, we are working
on replacing them, in this commit with Twisted LineReceiver.

Known issues: does not work with GUI. There is a conflict with
qt5reactor -> "QSocketNotifier: Can only be used with threads
started with QThread".

* Fix QSocketNotifier issue with qt5reactor

Sending the call to transport.write wrapped in a
self.reactor.callFromThread instead of directly does the trick.
Include also fixes to allow correct quit of VLC and Syncplay when
either one is closed.

Known issues: there is a noticeable lag (~ 1 second) between the
start of Syncplay MainWindow and the start of VLC.

* Re-add try/except to VLC

* Bring back missing try

Co-authored-by: Alberto Sottile <alby128@gmail.com>

syncplay/players/vlc.py

@@ -32,13 +32,13 @@ class VLCProtocol(LineReceiver):
             if not self.factory.requestedVLCVersion:
                 self.factory.requestedVLCVersion = True
                 self.sendLine("get-vlc-version")
-            # try:
-            lineToSend = line.encode('utf-8') + self.delimiter
-            self.transport.write(lineToSend)
-            if self.factory._playerController._client and self.factory._playerController._client.ui:
-                self.factory._playerController._client.ui.showDebugMessage("player >> {}".format(line))
-            # except:
-                # pass
+            try:
+                lineToSend = line.encode('utf-8') + self.delimiter
+                self.transport.write(lineToSend)
+                if self.factory._playerController._client and self.factory._playerController._client.ui:
+                    self.factory._playerController._client.ui.showDebugMessage("player >> {}".format(line))
+            except:
+                pass
 
     def connectionMade(self):
         self.factory.connected = True
@@ -82,10 +82,10 @@ class VLCClientFactory(ClientFactory):
         self._playerController._vlcclosed.set()
         if not self.connected and not self.timeVLCLaunched:
             # For circumstances where Syncplay is not connected to VLC and is not reconnecting
-            #try:
-            self._process.terminate()
-            #except:  # When VLC is already closed
-            #    pass
+            try:
+                self._process.terminate()
+            except:  # When VLC is already closed
+                pass
 
 
 class VlcPlayer(BasePlayer):
@@ -139,12 +139,14 @@ class VlcPlayer(BasePlayer):
             return
 
     def initWhenConnected(self):
-        self._client.ui.showErrorMessage(getMessage("vlc-initial-warning"))
-        if not self._vlcready.wait(constants.VLC_OPEN_MAX_WAIT_TIME):
-            self._vlcready.set()
-            self._client.ui.showErrorMessage(getMessage("vlc-failed-connection"), True)
-            self.reactor.callFromThread(self._client.stop, True,)
-        self.reactor.callFromThread(self._client.initPlayer, self,)
+        try:
+            if not self._vlcready.wait(constants.VLC_OPEN_MAX_WAIT_TIME):
+                self._vlcready.set()
+                self._client.ui.showErrorMessage(getMessage("vlc-failed-connection"), True)
+                self.reactor.callFromThread(self._client.stop, True,)
+            self.reactor.callFromThread(self._client.initPlayer, self,)
+        except:
+            pass
 
     def _fileUpdateClearEvents(self):
         self._durationAsk.clear()
@@ -514,4 +516,4 @@ class VlcPlayer(BasePlayer):
             out.close()
 
         def sendLine(self, line):
-            self.reactor.callFromThread(self._factory.protocol.sendLine, line)
+            self.reactor.callFromThread(self._factory.protocol.sendLine, line)