Enhance job store functionality with file locking and improved JSON handling

- Introduced file locking mechanisms in the JobStore class to ensure safe concurrent access to job metadata.
- Updated the read and write methods for JSON files to handle locking, preventing data corruption during simultaneous operations.
- Modified the read_meta method to provide a default value if the metadata file does not exist.
- Refactored the write_json method to create temporary files for safer writes, replacing the original file only after successful serialization.
- Updated the try.sh script to change the input image and include commented-out examples for additional inputs.

job_store.py

@@ -1,5 +1,7 @@
 import json
 import shutil
+import fcntl
+from contextlib import contextmanager
 from datetime import datetime, timedelta, timezone
 from pathlib import Path
 from typing import Any
@@ -42,7 +44,7 @@ class JobStore:
         return self.job_dir(job_id).is_dir()
 
     def read_meta(self, job_id: str) -> dict[str, Any] | None:
-        return self.read_json(self.job_dir(job_id) / "meta.json")
+        return self.read_json(self.job_dir(job_id) / "meta.json", default={})
 
     def read_request(self, job_id: str) -> dict[str, Any] | None:
         return self.read_json(self.job_dir(job_id) / "request.json")
@@ -52,11 +54,12 @@ class JobStore:
 
     def update_status(self, job_dir: Path, status: str, **extra: Any) -> None:
         meta_path = job_dir / "meta.json"
-        meta = self.read_json(meta_path, default={})
-        meta.update(extra)
-        meta["status"] = status
-        meta["updated_at"] = utc_now().isoformat()
-        self.write_json(meta_path, meta)
+        with self._locked_file(meta_path, exclusive=True):
+            meta = self._read_json_unlocked(meta_path, default={})
+            meta.update(extra)
+            meta["status"] = status
+            meta["updated_at"] = utc_now().isoformat()
+            self._write_json_unlocked(meta_path, meta)
 
     def record_failure(
         self,
@@ -101,11 +104,45 @@ class JobStore:
                 shutil.rmtree(child, ignore_errors=True)
 
     @staticmethod
-    def write_json(path: Path, payload: dict[str, Any]) -> None:
-        path.write_text(json.dumps(payload, indent=2, sort_keys=True), encoding="utf-8")
+    @contextmanager
+    def _locked_file(path: Path, *, exclusive: bool):
+        lock_path = path.with_name(f"{path.name}.lock")
+        lock_path.parent.mkdir(parents=True, exist_ok=True)
+        with lock_path.open("a+", encoding="utf-8") as lock_file:
+            fcntl.flock(
+                lock_file.fileno(),
+                fcntl.LOCK_EX if exclusive else fcntl.LOCK_SH,
+            )
+            try:
+                yield
+            finally:
+                fcntl.flock(lock_file.fileno(), fcntl.LOCK_UN)
+
+    @classmethod
+    def write_json(cls, path: Path, payload: dict[str, Any]) -> None:
+        path.parent.mkdir(parents=True, exist_ok=True)
+        with cls._locked_file(path, exclusive=True):
+            cls._write_json_unlocked(path, payload)
+
+    @classmethod
+    def read_json(cls, path: Path, default: Any = None) -> Any:
+        if not path.exists():
+            return default
+        with cls._locked_file(path, exclusive=False):
+            try:
+                return cls._read_json_unlocked(path, default=default)
+            except json.JSONDecodeError:
+                return default
+
+    @staticmethod
+    def _write_json_unlocked(path: Path, payload: dict[str, Any]) -> None:
+        serialized = json.dumps(payload, indent=2, sort_keys=True)
+        temp_path = path.with_name(f"{path.name}.{uuid4().hex}.tmp")
+        temp_path.write_text(serialized, encoding="utf-8")
+        temp_path.replace(path)
 
     @staticmethod
-    def read_json(path: Path, default: Any = None) -> Any:
+    def _read_json_unlocked(path: Path, default: Any = None) -> Any:
         if not path.exists():
             return default
         return json.loads(path.read_text(encoding="utf-8"))

try.sh

@@ -1,5 +1,9 @@
 node eggs/test4/main.js \
-  eggs/inputs/0/tank.png \
+  eggs/inputs/0/armor.png \
+#   eggs/inputs/0/elephant.png \
+#   eggs/inputs/0/goofy.png \
+#   eggs/inputs/0/pika.png \
+#   eggs/inputs/0/tank.png \
   # <generate>
 
 # node eggs/test4/main.js \