opening only one single instance of the application and adding the possibility to send messages to it

Qt/SingleApplication.py

@@ -0,0 +1,90 @@
+#!/usr/bin/env python2
+
+# from http://stackoverflow.com/questions/8786136/pyqt-how-to-detect-and-close-ui-if-its-already-running
+
+from PyQt4 import QtGui, QtCore, QtNetwork
+
+class SingleApplication(QtGui.QApplication):
+    def __init__(self, argv, key):
+        QtGui.QApplication.__init__(self, argv)
+        self._memory = QtCore.QSharedMemory(self)
+        self._memory.setKey(key)
+        if self._memory.attach():
+            self._running = True
+        else:
+            self._running = False
+            if not self._memory.create(1):
+                raise RuntimeError(
+                    self._memory.errorString().toLocal8Bit().data())
+
+    def isRunning(self):
+        return self._running
+
+class SingleApplicationWithMessaging(SingleApplication):
+    def __init__(self, argv, key):
+        SingleApplication.__init__(self, argv, key)
+        self._key = key
+        self._timeout = 1000
+        self._server = QtNetwork.QLocalServer(self)
+        if not self.isRunning():
+            self._server.newConnection.connect(self.handleMessage)
+            self._server.listen(self._key)
+
+    def handleMessage(self):
+        socket = self._server.nextPendingConnection()
+        if socket.waitForReadyRead(self._timeout):
+            self.emit(QtCore.SIGNAL('messageAvailable'),
+                      QtCore.QString.fromUtf8(socket.readAll().data()))
+            socket.disconnectFromServer()
+        else:
+            QtCore.qDebug(socket.errorString().toLatin1())
+
+    def sendMessage(self, message):
+        if self.isRunning():
+            socket = QtNetwork.QLocalSocket(self)
+            socket.connectToServer(self._key, QtCore.QIODevice.WriteOnly)
+            if not socket.waitForConnected(self._timeout):
+                print(socket.errorString().toLocal8Bit().data())
+                return False
+            socket.write(unicode(message).encode('utf-8'))
+            if not socket.waitForBytesWritten(self._timeout):
+                print(socket.errorString().toLocal8Bit().data())
+                return False
+            socket.disconnectFromServer()
+            return True
+        return False
+
+class Window(QtGui.QWidget):
+    def __init__(self):
+        QtGui.QWidget.__init__(self)
+        self.edit = QtGui.QLineEdit(self)
+        self.edit.setMinimumWidth(300)
+        layout = QtGui.QVBoxLayout(self)
+        layout.addWidget(self.edit)
+
+    def handleMessage(self, message):
+        self.edit.setText(message)
+
+if __name__ == '__main__':
+
+    import sys
+
+    key = 'FOO_BAR'
+
+    if len(sys.argv) > 1:
+        app = SingleApplicationWithMessaging(sys.argv, key)
+        if app.isRunning():
+            app.sendMessage(sys.argv[1])
+            sys.exit(1)
+    else:
+        app = SingleApplication(sys.argv, key)
+        if app.isRunning():
+            print('app is already running')
+            sys.exit(1)
+
+    window = Window()
+    app.connect(app, QtCore.SIGNAL('messageAvailable'),
+                window.handleMessage)
+    window.show()
+
+    sys.exit(app.exec_())