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Annotation of ExtFile/TM.pyc, revision 1.1

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        !             5: TMRegistry and ProxyTM
        !             6: 
        !             7: Use case
        !             8: --------
        !             9: 
        !            10: Persistent objects (ExtFiles) need to participate in ZODB transactions.
        !            11: ExtFiles perform all operations using temporary files which are saved on
        !            12: commit or deleted on abort.
        !            13: 
        !            14: Constraints
        !            15: -----------
        !            16: 
        !            17: - TransactionManagers (TM) must not be persistent themselves, i.e. must
        !            18:   not have a _p_jar attribute.
        !            19: 
        !            20: - We have to make sure the ExtFile's _abort is called *before* the ZODB
        !            21:   destroys the attributes of the persistent object.
        !            22: 
        !            23: Solution
        !            24: --------
        !            25: 
        !            26: - ProxyTM is a subclass of TM.TM that keeps a (hard) reference to the
        !            27:   (wrapped) persistent object it manages. Calls to _begin, _finish, and
        !            28:   _abort are forwarded to the target object.
        !            29: 
        !            30: - TMRegistry is a module-level container for ProxyTMs. It creates and
        !            31:   holds ProxyTMs keyed by (target_id, thread_id).
        !            32: 
        !            33: - ExtFiles implement _finish and _abort and register with the machinery
        !            34:   by calling TM.register(self).
        !            35: 
        !            36: - On commit (or abort) the ProxyTM notifies its target object and removes
        !            37:   itself from the registry.
        !            38: 
        !            39: Hacks
        !            40: -----
        !            41: 
        !            42: - We manipulate the transaction's _resources attribute directly. This is
        !            43:   to guarantee the ProxyTM is processed before other resources. There may
        !            44:   be a way to achieve this using official APIs only, but I can't seem to
        !            45:   find one.
        !            46: 
        !            47: (&sTM(&saq_base(&s    get_ident(&stransactiont
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