Index: fail2ban/fail2ban/server/jailthread.py
===================================================================
--- fail2ban.orig/fail2ban/server/jailthread.py
+++ fail2ban/fail2ban/server/jailthread.py
@@ -120,3 +120,6 @@ class JailThread(Thread):
 ## python 2.x replace binding of private __bootstrap method:
 if sys.version_info < (3,): # pragma: 3.x no cover
 	JailThread._Thread__bootstrap = JailThread._JailThread__bootstrap
+## python 3.9, restore isAlive method:
+elif not hasattr(JailThread, 'isAlive'): # pragma: 2.x no cover
+	 JailThread.isAlive = JailThread.is_alive
Index: fail2ban/fail2ban/tests/sockettestcase.py
===================================================================
--- fail2ban.orig/fail2ban/tests/sockettestcase.py
+++ fail2ban/fail2ban/tests/sockettestcase.py
@@ -83,11 +83,11 @@ class Socket(LogCaptureTestCase):
 		serverThread.start()
 		self.assertTrue(Utils.wait_for(self.server.isActive, unittest.F2B.maxWaitTime(10)))
 		return serverThread
-	
+
 	def _stopServerThread(self):
 		serverThread = self.serverThread
 		# wait for end of thread :
-		Utils.wait_for(lambda: not serverThread.isAlive() 
+		Utils.wait_for(lambda: not serverThread.is_alive()
 			or serverThread.join(Utils.DEFAULT_SLEEP_TIME), unittest.F2B.maxWaitTime(10))
 		self.serverThread = None
 
@@ -98,7 +98,7 @@ class Socket(LogCaptureTestCase):
 		self.server.close()
 		# wait for end of thread :
 		self._stopServerThread()
-		self.assertFalse(serverThread.isAlive())
+		self.assertFalse(serverThread.is_alive())
 		# clean :
 		self.server.stop()
 		self.assertFalse(self.server.isActive())
@@ -139,7 +139,7 @@ class Socket(LogCaptureTestCase):
 		self.server.stop()
 		# wait for end of thread :
 		self._stopServerThread()
-		self.assertFalse(serverThread.isAlive())
+		self.assertFalse(serverThread.is_alive())
 		self.assertFalse(self.server.isActive())
 		self.assertFalse(os.path.exists(self.sock_name))
 
@@ -149,7 +149,7 @@ class Socket(LogCaptureTestCase):
 		client = Utils.wait_for(self._serverSocket, 2)
 		# unexpected stop during message body:
 		testMessage = ["A", "test", "message", [protocol.CSPROTO.END]]
-		
+
 		org_handler = RequestHandler.found_terminator
 		try:
 			RequestHandler.found_terminator = lambda self: self.close()
@@ -180,7 +180,7 @@ class Socket(LogCaptureTestCase):
 		self.server.stop()
 		# wait for end of thread :
 		self._stopServerThread()
-		self.assertFalse(serverThread.isAlive())
+		self.assertFalse(serverThread.is_alive())
 
 	def testLoopErrors(self):
 		# replace poll handler to produce error in loop-cycle:
@@ -216,7 +216,7 @@ class Socket(LogCaptureTestCase):
 		self.server.stop()
 		# wait for end of thread :
 		self._stopServerThread()
-		self.assertFalse(serverThread.isAlive())
+		self.assertFalse(serverThread.is_alive())
 		self.assertFalse(self.server.isActive())
 		self.assertFalse(os.path.exists(self.sock_name))