After closing demo, reuse port if its specified (#3959)

* Reuse port when its specified after closing demo

* Add to changelog

---------

Co-authored-by: Abubakar Abid <abubakar@huggingface.co>

CHANGELOG.md

@@ -17,6 +17,7 @@ No changes to highlight.
 - Fixes type in client `Status` enum by [@10zinten](https://github.com/10zinten) in [PR 3931](https://github.com/gradio-app/gradio/pull/3931)
 - Fix `gr.ChatBot` to handle image url [tye-singwa](https://github.com/tye-signwa) in [PR 3953](https://github.com/gradio-app/gradio/pull/3953)
 - Move Google Tag Manager related initialization code to analytics-enabled block by [@akx](https://github.com/akx) in [PR 3956](https://github.com/gradio-app/gradio/pull/3956)
+- Fix bug where port was not reused if the demo was closed and then re-launched by [@freddyaboulton](https://github.com/freddyaboulton) in [PR 3896](https://github.com/gradio-app/gradio/pull/3959)
 
 ## Documentation Changes:
 

gradio/networking.py

@@ -116,6 +116,7 @@ def start_server(
     else:
         try:
             s = socket.socket()
+            s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
             s.bind((LOCALHOST_NAME, server_port))
             s.close()
         except OSError:

test/test_blocks.py

@@ -263,6 +263,16 @@ class TestBlocksMethods:
                     completed = True
             assert msg["output"]["data"][0] == "Victor"
 
+    def test_socket_reuse(self):
+
+        try:
+            io = gr.Interface(lambda x: x, gr.Textbox(), gr.Textbox())
+            io.launch(server_port=9441, prevent_thread_lock=True)
+            io.close()
+            io.launch(server_port=9441, prevent_thread_lock=True)
+        finally:
+            io.close()
+
     def test_function_types_documented_in_config(self):
         def continuous_fn():
             return 42