From f53f6657b6aff0411b5346931033a5a3a92752a6 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Tue, 18 Aug 2026 13:41:09 +0300
Subject: [PATCH] gh-155997: Fix list_all() if an interpreter is destroyed
 during the call

Creating the Interpreter objects can start a garbage collection which
finalizes an object owning the last reference to a listed interpreter.
Skip interpreters which no longer exist instead of failing.
---
 Lib/concurrent/interpreters/__init__.py           | 10 ++++++++--
 Lib/test/test_interpreters/test_api.py            | 15 +++++++++++++++
 ...2026-08-18-13-41-00.gh-issue-155997.CjbD1F.rst |  3 +++
 3 files changed, 26 insertions(+), 2 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2026-08-18-13-41-00.gh-issue-155997.CjbD1F.rst

diff --git a/Lib/concurrent/interpreters/__init__.py b/Lib/concurrent/interpreters/__init__.py
index ea4147ee9a25da..335a744b727d10 100644
--- a/Lib/concurrent/interpreters/__init__.py
+++ b/Lib/concurrent/interpreters/__init__.py
@@ -68,8 +68,14 @@ def create():
 
 def list_all():
     """Return all existing interpreters."""
-    return [Interpreter(id, _whence=whence)
-            for id, whence in _interpreters.list_all(require_ready=True)]
+    interps = []
+    for id, whence in _interpreters.list_all(require_ready=True):
+        try:
+            interps.append(Interpreter(id, _whence=whence))
+        except InterpreterNotFoundError:
+            # It was destroyed after it was listed.
+            pass
+    return interps
 
 
 def get_current():
diff --git a/Lib/test/test_interpreters/test_api.py b/Lib/test/test_interpreters/test_api.py
index 13d23af5aceb47..aac3cdd717668c 100644
--- a/Lib/test/test_interpreters/test_api.py
+++ b/Lib/test/test_interpreters/test_api.py
@@ -289,6 +289,21 @@ def test_idempotent(self):
         for interp1, interp2 in zip(actual, expected):
             self.assertIs(interp1, interp2)
 
+    def test_destroyed_by_gc(self):
+        # gh-155997: the interpreter is destroyed while list_all() runs.
+        interp = interpreters.create()
+        interpid = interp.id
+        cycle = []
+        cycle.append(cycle)
+        cycle.append(interp)
+        # The cycle holds the only reference, so only the collector frees it.
+        with support.disable_gc():
+            del interp, cycle
+
+        with support.gc_threshold(1):
+            ids = [i.id for i in interpreters.list_all()]
+        self.assertNotIn(interpid, ids)
+
     def test_created_with_capi(self):
         mainid, *_ = _interpreters.get_main()
         interpid1 = _interpreters.create()
diff --git a/Misc/NEWS.d/next/Library/2026-08-18-13-41-00.gh-issue-155997.CjbD1F.rst b/Misc/NEWS.d/next/Library/2026-08-18-13-41-00.gh-issue-155997.CjbD1F.rst
new file mode 100644
index 00000000000000..2727ba34aad8ff
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-08-18-13-41-00.gh-issue-155997.CjbD1F.rst
@@ -0,0 +1,3 @@
+Fix :func:`concurrent.interpreters.list_all`.  It failed if an interpreter
+was destroyed during the call, in particular by a garbage collection which
+finalized the object owning the last reference to it.