[3.12] gh-126775: make linecache.checkcache threadsafe and GC re-entrency safe (GH-126776) (#127779)

gh-126775: make linecache.checkcache threadsafe and GC re-entrency safe (GH-126776)

(cherry picked from commit 2233c303e4)

Co-authored-by: Thomas Grainger <tagrain@gmail.com>
Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Bartosz Sławecki <bartoszpiotrslawecki@gmail.com>

Lib/linecache.py

@@ -54,14 +54,17 @@ def checkcache(filename=None):
     (This is not checked upon each call!)"""
 
     if filename is None:
-        filenames = list(cache.keys())
-    elif filename in cache:
-        filenames = [filename]
+        # get keys atomically
+        filenames = cache.copy().keys()
     else:
-        return
+        filenames = [filename]
 
     for filename in filenames:
-        entry = cache[filename]
+        try:
+            entry = cache[filename]
+        except KeyError:
+            continue
+
         if len(entry) == 1:
             # lazy cache entry, leave it lazy.
             continue

Misc/NEWS.d/next/Library/2024-11-13-10-44-25.gh-issue-126775.a3ubjh.rst

@@ -0,0 +1 @@
+Make :func:`linecache.checkcache` thread safe and GC re-entrancy safe.