• Guido Trotter's avatar
    Fix issue when acquiring empty lock sets · 6683bba2
    Guido Trotter authored
    By design if an empty list of locks is acquired from a set, no locks are
    acquired, and thus release() cannot be called on the set. On the other
    hand if None is passed instead of the list, the whole set is acquired,
    and must later be released. When acquiring whole empty sets, a release
    must happen too, because the set-lock is acquired.
    
    Since we used to overwrite the required locks (needed_locks) with the
    acquired ones, we weren't able to distinguish the two cases (empty list
    of locks required, and all locks required, but an empty list returned
    because the set is empty). Valid solutions include:
      (1) forbidding the acquire of empty lists of locks
      (2) skipping the acquire/release on empty lists of locks
      (3) separating the to-acquire and the acquired list
    
    This patch implements the third approach, and thus LUs will find
    acquired locks in the acquired_locks dict, rather than in needed_locks.
    The LUs which used this feature before have been updated. This makes it
    easier because it doesn't force LUs to do more checks on corner cases,
    which are easily forgettable (1) and allows more flexibility if we want
    LUs to release (part-of) the locks (which is still a possibly scary
    operation, but anyway). This easily combines with (2) should we choose
    to implement it.
    
    Reviewed-by: imsnah
    6683bba2
mcpu.py 12.6 KB