https://github.com/python/cpython/commit/ac3694b008e4f9d5d5ea6ff8584078f92f6906ab
commit: ac3694b008e4f9d5d5ea6ff8584078f92f6906ab
branch: main
author: Ivan Marton <[email protected]>
committer: serhiy-storchaka <[email protected]>
date: 2026-06-04T13:50:33Z
summary:
gh-84649: Make TimedRotatingFileHandler use CTIME instead of MTIME (GH-24660)
The TimedRotatingFileHandler previously only used st_mtime attribute of the
log file to detect whether it has to be rotate yet or not. In cases when the
file is changed within the rotatation period the st_mtime is also updated
to the current time and the rotation never happens.
It's more appropriate to check the file creation time (st_ctime) instead.
Whenever available, the more appropriate st_birthtime will be in use. (This
feature is available on FreeBSD, MacOS and Windows at the moment.) If
the st_mtime would be newer than st_ctime (e.g.: because the inode
related to the file has been changed without any file content
modification), then the earliest attribute will be used.
files:
A Misc/NEWS.d/next/Library/2021-02-26-13-17-57.bpo-40469.yJHeQg.rst
M Lib/logging/handlers.py
M Lib/test/support/__init__.py
M Lib/test/test_logging.py
M Misc/ACKS
diff --git a/Lib/logging/handlers.py b/Lib/logging/handlers.py
index 575f2babbc47853..73782f53041008c 100644
--- a/Lib/logging/handlers.py
+++ b/Lib/logging/handlers.py
@@ -282,7 +282,16 @@ def __init__(self, filename, when='h', interval=1,
backupCount=0,
# path object (see Issue #27493), but self.baseFilename will be a
string
filename = self.baseFilename
if os.path.exists(filename):
- t = int(os.stat(filename).st_mtime)
+ # Use the minimum of file creation and modification time as
+ # the base of the rollover calculation
+ stat_result = os.stat(filename)
+ # Use st_birthtime whenever it is available or use st_ctime
+ # instead otherwise
+ try:
+ creation_time = stat_result.st_birthtime
+ except AttributeError:
+ creation_time = stat_result.st_ctime
+ t = int(min(creation_time, stat_result.st_mtime))
else:
t = int(time.time())
self.rolloverAt = self.computeRollover(t)
diff --git a/Lib/test/support/__init__.py b/Lib/test/support/__init__.py
index cd85ef60a80f4bf..84f735c1537efa7 100644
--- a/Lib/test/support/__init__.py
+++ b/Lib/test/support/__init__.py
@@ -40,6 +40,7 @@
"has_fork_support", "requires_fork",
"has_subprocess_support", "requires_subprocess",
"has_socket_support", "requires_working_socket",
+ "has_st_birthtime",
"has_remote_subprocess_debugging", "requires_remote_subprocess_debugging",
"anticipate_failure", "load_package_tests", "detect_api_mismatch",
"check__all__", "skip_if_buggy_ucrt_strfptime",
@@ -620,6 +621,10 @@ def skip_wasi_stack_overflow():
or is_android
)
+# At the moment, st_birthtime attribute is only supported on Windows,
+# MacOS and FreeBSD.
+has_st_birthtime = sys.platform.startswith(("win", "freebsd", "darwin"))
+
def requires_fork():
return unittest.skipUnless(has_fork_support, "requires working os.fork()")
diff --git a/Lib/test/test_logging.py b/Lib/test/test_logging.py
index 08678119200d427..31c052bfb56cd7a 100644
--- a/Lib/test/test_logging.py
+++ b/Lib/test/test_logging.py
@@ -6615,6 +6615,56 @@ def test_rollover(self):
print(tf.read())
self.assertTrue(found, msg=msg)
+ @unittest.skipUnless(support.has_st_birthtime,
+ "st_birthtime not available or supported by Python on this OS")
+ def test_rollover_based_on_st_birthtime_only(self):
+ def add_record(message: str) -> None:
+ fh = logging.handlers.TimedRotatingFileHandler(
+ self.fn, when='S', interval=4, encoding="utf-8",
backupCount=1)
+ fmt = logging.Formatter('%(asctime)s %(message)s')
+ fh.setFormatter(fmt)
+ record = logging.makeLogRecord({'msg': message})
+ fh.emit(record)
+ fh.close()
+
+ add_record('testing - initial')
+ self.assertLogFile(self.fn)
+ # Sleep a little over the half of rollover time - and this value
+ # must be over 2 seconds, since this is the mtime resolution on
+ # FAT32 filesystems.
+ time.sleep(2.1)
+ add_record('testing - update before rollover to renew the st_mtime')
+ time.sleep(2.1) # a little over the half of rollover time
+ add_record('testing - new record supposedly in the new file after
rollover')
+
+ # At this point, the log file should be rotated if the rotation
+ # is based on creation time but should be not if it's based on
+ # creation time.
+ found = False
+ now = datetime.datetime.now()
+ GO_BACK = 5 # seconds
+ for secs in range(GO_BACK):
+ prev = now - datetime.timedelta(seconds=secs)
+ fn = self.fn + prev.strftime(".%Y-%m-%d_%H-%M-%S")
+ found = os.path.exists(fn)
+ if found:
+ self.rmfiles.append(fn)
+ break
+ msg = 'No rotated files found, went back %d seconds' % GO_BACK
+ if not found:
+ # print additional diagnostics
+ dn, fn = os.path.split(self.fn)
+ files = [f for f in os.listdir(dn) if f.startswith(fn)]
+ print('Test time: %s' % now.strftime("%Y-%m-%d %H-%M-%S"),
file=sys.stderr)
+ print('The only matching files are: %s' % files, file=sys.stderr)
+ for f in files:
+ print('Contents of %s:' % f)
+ path = os.path.join(dn, f)
+ print(os.stat(path))
+ with open(path, 'r') as tf:
+ print(tf.read())
+ self.assertTrue(found, msg=msg)
+
def test_rollover_at_midnight(self, weekly=False):
os_helper.unlink(self.fn)
now = datetime.datetime.now()
diff --git a/Misc/ACKS b/Misc/ACKS
index 14f0db7549534be..71466e0804ae3c1 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1226,6 +1226,7 @@ Owen Martin
Sidney San Martín
Westley Martínez
Sébastien Martini
+Iván Márton
Roger Masse
Nick Mathewson
Simon Mathieu
diff --git a/Misc/NEWS.d/next/Library/2021-02-26-13-17-57.bpo-40469.yJHeQg.rst
b/Misc/NEWS.d/next/Library/2021-02-26-13-17-57.bpo-40469.yJHeQg.rst
new file mode 100644
index 000000000000000..eab474dfd2ea82a
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-02-26-13-17-57.bpo-40469.yJHeQg.rst
@@ -0,0 +1,6 @@
+A bug has been fixed that made the ``TimedRotatingFileHandler`` use the
+MTIME attribute of the configured log file to to detect whether it has to be
+rotated yet or not. In cases when the file was changed within the rotation
+period the value of the MTIME was also updated to the current time and as a
+result the rotation never happened. The file creation time (CTIME) is used
+instead that makes the rotation file modification independent.
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