try adding a test

Author: oconnor663

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.9", "3.10", "3.11", "3.12", "3.13", "3.14"]
+        python-version: ["3.9", "3.10", "3.11", "3.12", "3.13", "3.13t", "3.14", "3.14t"]
         os: [ubuntu-latest, windows-latest, macOS-latest]
 
     steps:

test_duct.py

@@ -1005,3 +1005,47 @@ def test_zombies_reaped():
         while ps_observes_pid(pid):
             tries += 1
             assert tries < 100, f"child #{i} (PID {pid}) never went away?"
+
+
+def test_pipe_inheritance():
+    """Spawn 300 child processes: 100 writers, 100 readers, and 100 waiters.
+    The goal is to see whether any of the waiters inherits a write end of one
+    of the pipes. If so, it will deadlock a reader and deadlock this test."""
+    waiters = []
+    threads = []
+
+    def reader_writer_fn():
+        # Open a pipe for the child to read from. This can deadlock if a waiter
+        # inherits this pipe and keeps it open.
+        reader_fd, writer_fd = os.pipe()
+        reader = os.fdopen(reader_fd, "rb")
+        writer = os.fdopen(writer_fd, "wb")
+        writer_child = echo_cmd("foo").stdout_file(writer).start()
+        writer.close()
+        output = cat_cmd().stdin_file(reader).read()
+        reader.close()
+        writer_child.wait()
+        assert output == "foo"
+
+    def waiter_fn():
+        # Spawn a child that won't exit until we kill it. This is intended to
+        # keep pipes open if they're inherited unintentionally. Without
+        # something like this, we'd need an inheritance *cycle* between
+        # readers, which might be unlikely.
+        waiters.append(sleep_cmd(365 * 24 * 60 * 60).unchecked().start())
+
+    for _ in range(100):
+        thread1 = threading.Thread(target=reader_writer_fn)
+        thread1.start()
+        threads.append(thread1)
+
+        thread2 = threading.Thread(target=waiter_fn)
+        thread2.start()
+        threads.append(thread2)
+
+    for thread in threads:
+        thread.join()
+
+    for waiter in waiters:
+        waiter.kill()
+        waiter.wait()