Package org.apache.zookeeper.client

Class StaticHostProvider

  • All Implemented Interfaces:
    HostProvider
    @Public
public final class StaticHostProvider
extends Object
implements HostProvider
    Most simple HostProvider, resolves on every next() call. Please be aware that although this class doesn't do any DNS caching, there're multiple levels of caching already present across the stack like in JVM, OS level, hardware, etc. The best we could do here is to get the most recent address from the underlying system which is considered up-to-date.

    • Constructor Detail

      • StaticHostProvider

        public StaticHostProvider​(Collection<InetSocketAddress> serverAddresses)
        Constructs a SimpleHostSet.
        Parameters:
        serverAddresses - possibly unresolved ZooKeeper server addresses
        Throws:
        IllegalArgumentException - if serverAddresses is empty or resolves to an empty list

      • StaticHostProvider

        public StaticHostProvider​(Collection<InetSocketAddress> serverAddresses,
                          StaticHostProvider.Resolver resolver)
        Constructs a SimpleHostSet. Introduced for testing purposes. getAllByName() is a static method of InetAddress, therefore cannot be easily mocked. By abstraction of Resolver interface we can easily inject a mocked implementation in tests.
        Parameters:
        serverAddresses - possibly unresolved ZooKeeper server addresses
        resolver - custom resolver implementation

      • StaticHostProvider

        public StaticHostProvider​(Collection<InetSocketAddress> serverAddresses,
                          long randomnessSeed)
        Constructs a SimpleHostSet. This constructor is used from StaticHostProviderTest to produce deterministic test results by initializing sourceOfRandomness with the same seed
        Parameters:
        serverAddresses - possibly unresolved ZooKeeper server addresses
        randomnessSeed - a seed used to initialize sourceOfRandomnes
        Throws:
        IllegalArgumentException - if serverAddresses is empty or resolves to an empty list

    • Method Detail

      • updateServerList

        public boolean updateServerList​(Collection<InetSocketAddress> serverAddresses,
                                InetSocketAddress currentHost)
        Update the list of servers. This returns true if changing connections is necessary for load-balancing, false otherwise. Changing connections is necessary if one of the following holds: a) the host to which this client is currently connected is not in serverAddresses. Otherwise (if currentHost is in the new list serverAddresses): b) the number of servers in the cluster is increasing - in this case the load on currentHost should decrease, which means that SOME of the clients connected to it will migrate to the new servers. The decision whether this client migrates or not (i.e., whether true or false is returned) is probabilistic so that the expected number of clients connected to each server is the same. If true is returned, the function sets pOld and pNew that correspond to the probability to migrate to ones of the new servers in serverAddresses or one of the old servers (migrating to one of the old servers is done only if our client's currentHost is not in serverAddresses). See nextHostInReconfigMode for the selection logic. See ZOOKEEPER-1355 for the protocol and its evaluation, and StaticHostProviderTest for the tests that illustrate how load balancing works with this policy.
        Specified by:
        updateServerList in interface HostProvider
        Parameters:
        serverAddresses - new host list
        currentHost - the host to which this client is currently connected
        Returns:
        true if changing connections is necessary for load-balancing, false otherwise

      • next

        public InetSocketAddress next​(long spinDelay)
        Description copied from interface: HostProvider
        The next host to try to connect to. For a spinDelay of 0 there should be no wait.
        Specified by:
        next in interface HostProvider
        Parameters:
        spinDelay - Milliseconds to wait if all hosts have been tried once.

      • onConnected

        public void onConnected()
        Description copied from interface: HostProvider
        Notify the HostProvider of a successful connection. The HostProvider may use this notification to reset it's inner state.
        Specified by:
        onConnected in interface HostProvider