From efb66187b4d72c2a384e7a50444d9b5a93807102 Mon Sep 17 00:00:00 2001
From: Evgeny Arshinov <earshinov@nvidia.com>
Date: Wed, 27 Mar 2024 18:59:21 +0100
Subject: [PATCH] watch_safely

---
 src/django_watchfiles/__init__.py | 58 +++++++++++++++++++++++++------
 1 file changed, 48 insertions(+), 10 deletions(-)

diff --git a/src/django_watchfiles/__init__.py b/src/django_watchfiles/__init__.py
index 08a1b87..f33ce54 100644
--- a/src/django_watchfiles/__init__.py
+++ b/src/django_watchfiles/__init__.py
@@ -1,15 +1,49 @@
 from __future__ import annotations
 
 import fnmatch
+import logging
 import threading
+import time
 from pathlib import Path
-from typing import Any
 from typing import Callable
 from typing import Generator
+from typing import Iterable
+from typing import Optional
+from typing import Set
+from typing import Tuple
+from typing import TypeVar
 
 import watchfiles
 from django.utils import autoreload
 
+logger = logging.getLogger("django_watchfiles")
+
+
+# Duplicate `FileChange` type from `watchfiles`, which is not exported
+FileChange = Tuple[watchfiles.Change, str]
+
+
+T = TypeVar("T")
+
+
+def watch_safely(f: Callable[[], Iterable[T]], default: T) -> Iterable[T]:
+    """
+    Yield from `f()`, but when it fails, yield `default` once, log the exception and retry,
+    unless there are 2 exceptions within 1 second, in which case the exception is raised.
+    """
+    ts: Optional[float] = None
+    while True:
+        try:
+            yield from f()
+        except Exception as e:
+            current_ts = time.monotonic()
+            if ts is not None and current_ts - ts < 1.0:
+                # Consider 2 exceptions within 1 second critical and exit to avoid endlessly looping
+                raise
+            logger.warn(e, exc_info=True)
+            ts = current_ts
+            yield default
+
 
 class MutableWatcher:
     """
@@ -34,17 +68,21 @@ def set_roots(self, roots: set[Path]) -> None:
     def stop(self) -> None:
         self.stop_event.set()
 
-    def __iter__(self) -> Generator[Any, None, None]:  # TODO: better type
+    def __iter__(self) -> Generator[Set[FileChange], None, None]:
+        no_changes: Set[FileChange] = set()
         while True:
             self.change_event.clear()
-            for changes in watchfiles.watch(
-                *self.roots,
-                watch_filter=self.filter,
-                stop_event=self.stop_event,
-                debounce=False,
-                rust_timeout=100,
-                yield_on_timeout=True,
-                ignore_permission_denied=True,
+            for changes in watch_safely(
+                lambda: watchfiles.watch(
+                    *self.roots,
+                    watch_filter=self.filter,
+                    stop_event=self.stop_event,
+                    debounce=False,
+                    rust_timeout=100,
+                    yield_on_timeout=True,
+                    ignore_permission_denied=True,
+                ),
+                default=no_changes,
             ):
                 if self.change_event.is_set():
                     break