coordinator.py 文件源码

def grant(self, lock, unit):
        '''Maybe grant the lock to a unit.

        The decision to grant the lock or not is made for $lock
        by a corresponding method grant_$lock, which you may define
        in a subclass. If no such method is defined, the default_grant
        method is used. See Serial.default_grant() for details.
        '''
        if not hookenv.is_leader():
            return False  # Not the leader, so we cannot grant.

        # Set of units already granted the lock.
        granted = set()
        for u in self.grants:
            if lock in self.grants[u]:
                granted.add(u)
        if unit in granted:
            return True  # Already granted.

        # Ordered list of units waiting for the lock.
        reqs = set()
        for u in self.requests:
            if u in granted:
                continue  # In the granted set. Not wanted in the req list.
            for _lock, ts in self.requests[u].items():
                if _lock == lock:
                    reqs.add((ts, u))
        queue = [t[1] for t in sorted(reqs)]
        if unit not in queue:
            return False  # Unit has not requested the lock.

        # Locate custom logic, or fallback to the default.
        grant_func = getattr(self, 'grant_{}'.format(lock), self.default_grant)

        if grant_func(lock, unit, granted, queue):
            # Grant the lock.
            self.msg('Leader grants {} to {}'.format(lock, unit))
            self.grants.setdefault(unit, {})[lock] = self.requests[unit][lock]
            return True

        return False