Serialize operations

serialize.py

def serialize(func):
    """
    Decorator to make operations which modify state in the cluster happen one
    at a time
    """
    def wrap(self, *a, **kw):
        return self._do_operation(func, self, *a, **kw)
    return wrap


class HybridClusterAPI(jsonrpc.JSONRPC):
    """
    The web cluster's API.
    """

    def __init__(self):
        self._operations = []
        self._current_operation = None

    def _update_operations(self, _result=None):
        """
        Called when the current operation completes.  Runs the next operation
        if there is one, chaining the completion of that operation onto a
        recursive call back to this function to check the next operation, etc.
        """
        if self._operations:
            d, f, a, kw = self._operations.pop(0)
            self._current_operation = defer.maybeDeferred(f, *a, **kw)
            (self._current_operation
                .addBoth(self._update_operations)
                .chainDeferred(d))
        else:   
            self._current_operation = None
        return _result
        
    def _do_operation(self, func, *a, **kw):
        """
        Add an operation to the queue and run the queue if it's not running
        already.
        """
        d = defer.Deferred()
        self._operations.append((d, func, a, kw))
        if self._current_operation is None:
            self._update_operations() 
        return d
        
    @serialize
    def jsonrpc_deleteSite(self, site):
        # ...
        pass

    @serialize
    @defer.inlineCallbacks
    def jsonrpc_installWordpress(self, domain, database):
        # ...
        yield someDeferred