[New-bugs-announce] [issue35391] threading.RLock exception handling while waiting

[Omer Bartal]

New submission from Omer Bartal <omerb at prospera.ag>:

(tested on python 2.7)

Created a threading.Condition(threading.RLock())
A piece of code acquires the lock using a with block and waits (for a notify)
While wait() is running a KeyboardInterrupt is raised
An exception is raised while exiting the lock's with block:
  File "/usr/lib/python2.7/threading.py", line 289, in __exit__
    return self.__lock.__exit__(*args)
  File "/usr/lib/python2.7/threading.py", line 216, in __exit__
    self.release()
  File "/usr/lib/python2.7/threading.py", line 204, in release
    raise RuntimeError("cannot release un-acquired lock")

example code running on the main thread:
def waiting(lock): # (the lock was created using Condition(RLock()))
  with lock:
    lock.wait(timeout=xxx) # while waiting a keyboard interrupt is raised

The issue is caused because threading.RLock doesn't handle the exception correctly:
    def _acquire_restore(self, count_owner):
        count, owner = count_owner
        self.__block.acquire()
        self.__count = count
        self.__owner = owner
        if __debug__:
            self._note("%s._acquire_restore()", self)

The exception is raised after the acquire() returns and the count and owner are not restored.

The problem was solved using the following fix (added try, finally):
    def _acquire_restore(self, count_owner):
        count, owner = count_owner
        try:
            self.__block.acquire()
        finally:
            self.__count = count
            self.__owner = owner
            if __debug__:
                self._note("%s._acquire_restore()", self)


Looking at the code, this issue exists in python 3.8 as well.

----------
components: Library (Lib)
messages: 330972
nosy: Omer Bartal
priority: normal
severity: normal
status: open
title: threading.RLock exception handling while waiting
type: crash
versions: Python 2.7, Python 3.4, Python 3.5, Python 3.6, Python 3.7, Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35391>
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