Every caller writes a whole JSON document, and a plain open/write can
leave a torn or empty file when the process dies or another writer
overlaps, which readfile then returns as {}. Writes now go through the
temp file and replace unless atomic=False or the mode is append. A read
waits out an open that Windows refuses while a replace of the same name
is in flight, and an empty file is reported when the read is not
silent, since a zero-byte config.json otherwise resets settings without
a trace.
The fasteners lock is inter-process only. On Linux fcntl record locks
belong to the process, so two threads writing the same file were never
serialized and could tear it; on Windows they were, until the lock
switched itself off. Every writer of these files runs inside one
multi-threaded process, so that is the case that matters.
readfile(lock=True) and writefile now take a re-entrant lock per
normalized path, held from the snapshot through the replace so writes
to one path land in call order. Other processes are covered by the
atomic replace. A .lock file left next to a JSON file by the old lock
is removed the first time that path is used.
writefile(atomic=True) renamed the temp file while it was still open,
which Windows refuses, so every atomic save failed there and left a temp
file behind. The temp file is now created with mkstemp, closed before
os.replace and removed when the save fails; the replace retries briefly
when another handle holds the target, which Windows reports as a
permission error.
Both helpers removed the .lock file after releasing it. That removal
raced other holders on both platforms, and any failure switched locking
off for the whole process without a log line. The lock file now stays in
place; a failed release or a lock timeout is logged instead.
writefile deep-copied and validated the live object in Python, so a
concurrent insert into a shared dict raised "dictionary changed size
during iteration" and dropped the save. dict.copy and list.copy run
under the GIL, so the deep copy and the per-key validation now walk that
snapshot; nested containers remain the caller's responsibility.
test/test-json-helpers.py covers all three on Linux and Windows.
CalamitousFelicitousness
Vladimir Mandic
awsr