Serialize TinyDB access across independently spawned processes

tests/test_database_regressions.py

@@ -0,0 +1,56 @@
+import multiprocessing as mp
+import time
+from pathlib import Path
+from typing import Any
+from unittest.mock import patch
+
+from tinydb.table import Table
+
+from great_ai import ParallelTinyDbDriver, Trace
+
+
+def write_traces(path: str, index: int, barrier: Any) -> None:
+    ParallelTinyDbDriver.path_to_db = Path(path)
+    read_table = Table._read_table
+
+    def slow_read(self: Table) -> Any:
+        data = read_table(self)
+        time.sleep(0.02)
+        return data
+
+    barrier.wait(timeout=10)
+    with patch.object(Table, "_read_table", slow_read):
+        for i in range(3):
+            ParallelTinyDbDriver().save(
+                Trace(
+                    trace_id=f"{index}-{i}",
+                    created="2026-01-01",
+                    original_execution_time_ms=0,
+                    models=[],
+                    tags=[],
+                    logged_values={},
+                )
+            )
+
+
+def test_spawned_writers_share_database_lock(tmp_path: Path) -> None:
+    ctx = mp.get_context("spawn")
+    path = tmp_path / "traces.json"
+    barrier = ctx.Barrier(2)
+    processes = [
+        ctx.Process(target=write_traces, args=(str(path), i, barrier)) for i in range(2)
+    ]
+    try:
+        for process in processes:
+            process.start()
+        for process in processes:
+            process.join(timeout=15)
+            assert process.exitcode == 0
+    finally:
+        for process in processes:
+            if process.is_alive():
+                process.kill()
+                process.join()
+            process.close()
+    with patch.object(ParallelTinyDbDriver, "path_to_db", path):
+        assert len(ParallelTinyDbDriver().query()[0]) == 6