From a2a3236248e453d1a403a3a800803ebd1a99fcc8 Mon Sep 17 00:00:00 2001
From: thePR0M3TH3AN <53631862+PR0M3TH3AN@users.noreply.github.com>
Date: Sun, 29 Jun 2025 22:58:43 -0400
Subject: [PATCH] Add shared file lock and concurrency test

---
 src/tests/test_file_locking.py | 42 ++++++++++++++++++++++++++++++++++
 src/utils/__init__.py          |  3 ++-
 src/utils/file_lock.py         | 22 ++++++++++++++++++
 3 files changed, 66 insertions(+), 1 deletion(-)
 create mode 100644 src/tests/test_file_locking.py

diff --git a/src/tests/test_file_locking.py b/src/tests/test_file_locking.py
new file mode 100644
index 0000000..1fc0e18
--- /dev/null
+++ b/src/tests/test_file_locking.py
@@ -0,0 +1,42 @@
+import threading
+from pathlib import Path
+
+from utils.file_lock import exclusive_lock, shared_lock
+
+
+def _writer(path: Path, content: str, exceptions: list[str]) -> None:
+    try:
+        with exclusive_lock(path):
+            path.write_text(content)
+    except Exception as e:  # pragma: no cover - just capture
+        exceptions.append(repr(e))
+
+
+def _reader(path: Path, results: list[str], exceptions: list[str]) -> None:
+    try:
+        with shared_lock(path):
+            results.append(path.read_text())
+    except Exception as e:  # pragma: no cover
+        exceptions.append(repr(e))
+
+
+def test_concurrent_shared_and_exclusive_lock(tmp_path: Path) -> None:
+    file_path = tmp_path / "data.txt"
+    file_path.write_text("init")
+
+    exceptions: list[str] = []
+    reads: list[str] = []
+    for i in range(5):
+        writer = threading.Thread(
+            target=_writer, args=(file_path, f"value{i}", exceptions)
+        )
+        reader = threading.Thread(target=_reader, args=(file_path, reads, exceptions))
+
+        writer.start()
+        reader.start()
+        writer.join()
+        reader.join()
+
+    assert not exceptions
+    assert file_path.read_text() == "value4"
+    assert len(reads) == 5
diff --git a/src/utils/__init__.py b/src/utils/__init__.py
index 3329ebf..e12cbff 100644
--- a/src/utils/__init__.py
+++ b/src/utils/__init__.py
@@ -4,7 +4,7 @@ import logging
 import traceback
 
 try:
-    from .file_lock import exclusive_lock
+    from .file_lock import exclusive_lock, shared_lock
     from .key_derivation import derive_key_from_password, derive_key_from_parent_seed
     from .checksum import calculate_checksum, verify_checksum
     from .password_prompt import prompt_for_password
@@ -20,5 +20,6 @@ __all__ = [
     "calculate_checksum",
     "verify_checksum",
     "exclusive_lock",
+    "shared_lock",
     "prompt_for_password",
 ]
diff --git a/src/utils/file_lock.py b/src/utils/file_lock.py
index 9c71b62..4d674f2 100644
--- a/src/utils/file_lock.py
+++ b/src/utils/file_lock.py
@@ -22,3 +22,25 @@ def exclusive_lock(
     lock = portalocker.Lock(str(path), mode="a+b", timeout=timeout)
     with lock as fh:
         yield fh
+
+
+@contextmanager
+def shared_lock(
+    path: Path, timeout: Optional[float] = None
+) -> Generator[None, None, None]:
+    """Context manager that locks *path* with a shared lock.
+
+    The function opens the file in binary read/write mode and obtains a
+    shared lock using ``portalocker``. If ``timeout`` is provided, acquiring
+    the lock will wait for at most that many seconds before raising
+    ``portalocker.exceptions.LockException``.
+    """
+    path = Path(path)
+    path.parent.mkdir(parents=True, exist_ok=True)
+    path.touch(exist_ok=True)
+    lock = portalocker.Lock(
+        str(path), mode="r+b", timeout=timeout, flags=portalocker.LockFlags.SHARED
+    )
+    with lock as fh:
+        fh.seek(0)
+        yield fh