sched: add held cross-process ownership with real-process tests (T11)

tests/scheduling/test_ownership.py

@@ -0,0 +1,98 @@
+"""Exclusive ownership with real competing processes (T11)."""
+
+from __future__ import annotations
+
+import subprocess
+import sys
+import time
+from pathlib import Path
+
+import pytest
+
+from wf_scheduling.ownership import (
+    SchedulerOwnership,
+    SecondOwnerError,
+)
+
+
+def test_second_owner_rejected_while_held(tmp_path: Path) -> None:
+    first = SchedulerOwnership(tmp_path, owner="proc-A").acquire()
+    try:
+        with pytest.raises(SecondOwnerError):
+            SchedulerOwnership(tmp_path, owner="proc-B").acquire()
+    finally:
+        first.release()
+    # After release, a new owner acquires.
+    second = SchedulerOwnership(tmp_path, owner="proc-B").acquire()
+    second.release()
+
+
+def test_competing_process_cannot_acquire_while_held(tmp_path: Path) -> None:
+    holder = SchedulerOwnership(tmp_path, owner="parent").acquire()
+    try:
+        script_path = tmp_path / "compete.py"
+        script_path.write_text(
+            "import sys\n"
+            "sys.path.insert(0, '.')\n"
+            "from pathlib import Path\n"
+            "from wf_scheduling.ownership import SchedulerOwnership, SecondOwnerError\n"
+            f"root = Path({str(tmp_path)!r})\n"
+            "try:\n"
+            "    SchedulerOwnership(root, owner='child').acquire()\n"
+            "except SecondOwnerError:\n"
+            "    print('second-owner-rejected')\n"
+            "    raise SystemExit(0)\n"
+            "print('unexpectedly-acquired')\n"
+            "raise SystemExit(1)\n",
+            encoding="utf-8",
+        )
+        proc = subprocess.run(
+            [sys.executable, str(script_path)],
+            capture_output=True,
+            text=True,
+            timeout=30,
+        )
+        assert proc.returncode == 0, proc.stderr
+        assert "second-owner-rejected" in proc.stdout
+    finally:
+        holder.release()
+
+
+def test_lock_released_on_process_death(tmp_path: Path) -> None:
+    script_path = tmp_path / "hold.py"
+    script_path.write_text(
+        "import sys, time\n"
+        "sys.path.insert(0, '.')\n"
+        "from pathlib import Path\n"
+        "from wf_scheduling.ownership import SchedulerOwnership\n"
+        f"root = Path({str(tmp_path)!r})\n"
+        "own = SchedulerOwnership(root, owner='dying').acquire()\n"
+        "print('acquired', flush=True)\n"
+        "time.sleep(30)\n",
+        encoding="utf-8",
+    )
+    proc = subprocess.Popen(
+        [sys.executable, str(script_path)],
+        stdout=subprocess.PIPE,
+        text=True,
+    )
+    try:
+        assert proc.stdout is not None
+        line = proc.stdout.readline()
+        assert "acquired" in line
+        # Competing acquisition fails while the child lives.
+        with pytest.raises(SecondOwnerError):
+            SchedulerOwnership(tmp_path, owner="parent").acquire()
+    finally:
+        proc.kill()
+        proc.wait(timeout=30)
+    # After process death the OS releases the held lock; allow a beat.
+    acquired = None
+    for _ in range(50):
+        try:
+            acquired = SchedulerOwnership(tmp_path, owner="parent").acquire()
+            break
+        except SecondOwnerError:
+            time.sleep(0.1)
+    assert acquired is not None
+    acquired.release()