From a545749b0e6c56cab853c5c8df3c199b9707994f Mon Sep 17 00:00:00 2001
From: Kumar Aditya <kumaraditya@python.org>
Date: Sat, 15 Feb 2025 15:01:53 +0530
Subject: gh-130145: fix `loop.run_forever` when loop is already running
 (#130146)

---
 Lib/asyncio/base_events.py                               |  2 +-
 Lib/test/test_asyncio/test_events.py                     | 16 ++++++++++++++++
 .../2025-02-15-07-50-37.gh-issue-130145.I0CkV0.rst       |  1 +
 3 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2025-02-15-07-50-37.gh-issue-130145.I0CkV0.rst

diff --git a/Lib/asyncio/base_events.py b/Lib/asyncio/base_events.py
index ed85242..546361f 100644
--- a/Lib/asyncio/base_events.py
+++ b/Lib/asyncio/base_events.py
@@ -671,8 +671,8 @@ class BaseEventLoop(events.AbstractEventLoop):
 
     def run_forever(self):
         """Run until stop() is called."""
+        self._run_forever_setup()
         try:
-            self._run_forever_setup()
             while True:
                 self._run_once()
                 if self._stopping:
diff --git a/Lib/test/test_asyncio/test_events.py b/Lib/test/test_asyncio/test_events.py
index 3838993..3506960 100644
--- a/Lib/test/test_asyncio/test_events.py
+++ b/Lib/test/test_asyncio/test_events.py
@@ -3004,6 +3004,22 @@ class GetEventLoopTestsMixin:
                 self.loop.run_until_complete(main()),
                 'hello')
 
+    def test_get_running_loop_already_running(self):
+        async def main():
+            running_loop = asyncio.get_running_loop()
+            loop = asyncio.new_event_loop()
+            try:
+                loop.run_forever()
+            except RuntimeError:
+                pass
+            else:
+                self.fail("RuntimeError not raised")
+
+            self.assertIs(asyncio.get_running_loop(), running_loop)
+
+        self.loop.run_until_complete(main())
+
+
     def test_get_event_loop_returns_running_loop(self):
         class TestError(Exception):
             pass
diff --git a/Misc/NEWS.d/next/Library/2025-02-15-07-50-37.gh-issue-130145.I0CkV0.rst b/Misc/NEWS.d/next/Library/2025-02-15-07-50-37.gh-issue-130145.I0CkV0.rst
new file mode 100644
index 0000000..9c8c469
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-02-15-07-50-37.gh-issue-130145.I0CkV0.rst
@@ -0,0 +1 @@
+Fix :meth:`!asyncio.AbstractEventloop.run_forever` when another loop is already running.
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