Use signal.alarm for timeouts if it's available

docs/source/conf.py

@@ -489,24 +489,31 @@ def setup(app):
         import binascii
         paramiko.client.hexlify = lambda x: binascii.hexlify(x).decode()
         paramiko.util.safe_string = lambda x: '' # function result never *actually used*
-    class EndlessLoop(BaseException): pass
-    def sigabrt_handler(signum, frame):
-        raise EndlessLoop()
-    # thread.interrupt_main received the signum parameter in Python 3.10
-    if sys.version_info >= (3, 10):
-        signal.signal(signal.SIGABRT, sigabrt_handler)
-    def alrm_handler():
-        try:
-            import thread
-        except ImportError:
-            import _thread as thread
-        # pre Python 3.10 this raises a KeyboardInterrupt in the main thread.
-        # it might not show a traceback in that case, but it will stop the endless loop.
-        thread.interrupt_main(signal.SIGABRT)
-        timer = threading.Timer(interval=180, function=alrm_handler) # three minutes
+    class EndlessLoop(Exception): pass
+    if hasattr(signal, 'alarm'):
+        def alrm_handler(sig, frame):
+            signal.alarm(180) # three minutes
+            raise EndlessLoop()
+        signal.signal(signal.SIGALRM, alrm_handler)
+        signal.alarm(600) # ten minutes
+    else:
+        def sigabrt_handler(signum, frame):
+            raise EndlessLoop()
+        # thread.interrupt_main received the signum parameter in Python 3.10
+        if sys.version_info >= (3, 10):
+            signal.signal(signal.SIGABRT, sigabrt_handler)
+        def alrm_handler():
+            try:
+                import thread
+            except ImportError:
+                import _thread as thread
+            # pre Python 3.10 this raises a KeyboardInterrupt in the main thread.
+            # it might not show a traceback in that case, but it will stop the endless loop.
+            thread.interrupt_main(signal.SIGABRT)
+            timer = threading.Timer(interval=180, function=alrm_handler) # three minutes
+            timer.daemon = True
+            timer.start()
+        import threading
+        timer = threading.Timer(interval=600, function=alrm_handler) # ten minutes
         timer.daemon = True
         timer.start()
-    import threading
-    timer = threading.Timer(interval=600, function=alrm_handler) # ten minutes
-    timer.daemon = True
-    timer.start()