From b44d115295fd1e9d9cdcf684e85d6c47c4a3f579 Mon Sep 17 00:00:00 2001
From: Marcel Nadzam <mnadzam@redhat.com>
Date: Wed, 27 May 2026 13:02:53 +0200
Subject: [PATCH] test(threading_utils): add coverage for thread safety
 decorator

Add dedicated test file for with_thread_lock() in threading_utils.py
with tests for mutual exclusion, independent locks, and reentrance.

Closes #1170

Signed-off-by: Marcel Nadzam <mnadzam@redhat.com>

Co-authored-by: Cursor
---
 tests/test_threading_utils.py | 91 +++++++++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)
 create mode 100644 tests/test_threading_utils.py

diff --git a/tests/test_threading_utils.py b/tests/test_threading_utils.py
new file mode 100644
index 00000000..a92ac7a2
--- /dev/null
+++ b/tests/test_threading_utils.py
@@ -0,0 +1,91 @@
+import threading
+import time
+
+import pytest
+
+from fromager.threading_utils import with_thread_lock
+
+
+def test_decorated_function_returns_value() -> None:
+    @with_thread_lock()
+    def add(a: int, b: int) -> int:
+        return a + b
+
+    assert add(2, 3) == 5
+    assert add(a=10, b=20) == 30
+
+
+def test_mutual_exclusion() -> None:
+    events: list[str] = []
+    ready = threading.Barrier(2)
+
+    @with_thread_lock()
+    def slow() -> None:
+        events.append("enter")
+        time.sleep(0.05)
+        events.append("exit")
+
+    def worker() -> None:
+        ready.wait()  # ensure both threads race for the lock
+        slow()
+
+    t1 = threading.Thread(target=worker)
+    t2 = threading.Thread(target=worker)
+    t1.start()
+    t2.start()
+    t1.join()
+    t2.join()
+
+    assert events == ["enter", "exit", "enter", "exit"]
+
+
+def test_independent_locks_do_not_block_each_other() -> None:
+    barrier = threading.Barrier(2)
+
+    @with_thread_lock()
+    def func_a() -> None:
+        barrier.wait(timeout=2)
+
+    @with_thread_lock()
+    def func_b() -> None:
+        barrier.wait(timeout=2)
+
+    t1 = threading.Thread(target=func_a)
+    t2 = threading.Thread(target=func_b)
+    t1.start()
+    t2.start()
+    t1.join(timeout=3)
+    t2.join(timeout=3)
+
+    assert not t1.is_alive()
+    assert not t2.is_alive()
+
+
+def test_lock_released_after_exception() -> None:
+    call_count = 0
+
+    @with_thread_lock()
+    def throws_on_first_call() -> str:
+        nonlocal call_count
+        call_count += 1
+        if call_count == 1:
+            raise ValueError("first call exception")
+        return "ok"
+
+    with pytest.raises(ValueError, match="first call exception"):
+        throws_on_first_call()
+
+    assert throws_on_first_call() == "ok"
+
+
+def test_nested_call_to_different_decorated_function() -> None:
+    @with_thread_lock()
+    def inner() -> str:
+        return "ok"
+
+    @with_thread_lock()
+    def outer() -> str:
+        result: str = inner()
+        return result
+
+    assert outer() == "ok"