Package com.microsoft.azure.eventprocessorhost

Class InMemoryLeaseManager

  • All Implemented Interfaces:
    ILeaseManager
    public class InMemoryLeaseManager
extends Object
implements ILeaseManager
    An ILeaseManager implementation based on an in-memory store. THIS CLASS IS PROVIDED AS A CONVENIENCE FOR TESTING ONLY. All data stored via this class is in memory only and not persisted in any way. In addition, it is only visible within the same process: multiple instances of EventProcessorHost in the same process will share the same in-memory store and leases created by one will be visible to the others, but that is not true across processes. With an ordinary store, there is a clear and distinct line between the values that are persisted and the values that are live in memory. With an in-memory store, that line gets blurry. If we accidentally hand out a reference to the in-store object, then the calling code is operating on the "persisted" values without going through the manager and behavior will be very different. Hence, the implementation takes pains to distinguish between references to "live" and "persisted" checkpoints. To use this class, create a new instance and pass it to the EventProcessorHost constructor that takes ILeaseManager as an argument. After the EventProcessorHost instance is constructed, be sure to call initialize() on this object before starting processing with EventProcessorHost.registerEventProcessor() or EventProcessorHost.registerEventProcessorFactory().

    • Constructor Detail

      • InMemoryLeaseManager

        public InMemoryLeaseManager()

    • Method Detail

      • initialize

        public void initialize​(com.microsoft.azure.eventprocessorhost.HostContext hostContext)

      • setLatency

        public void setLatency​(long milliseconds)

      • getLeaseDurationInMilliseconds

        public int getLeaseDurationInMilliseconds()
        Description copied from interface: ILeaseManager
        The lease duration is mostly internal to the lease manager implementation but may be needed by other parts of the event processor host.
        Specified by:
        getLeaseDurationInMilliseconds in interface ILeaseManager
        Returns:
        Duration of a lease before it expires unless renewed, specified in milliseconds.

      • leaseStoreExists

        public CompletableFuture<Boolean> leaseStoreExists()
        Description copied from interface: ILeaseManager
        Does the lease store exist?

        The returned CompletableFuture completes with true if the checkpoint store exists or false if it does not. It completes exceptionally on error.

        Specified by:
        leaseStoreExists in interface ILeaseManager
        Returns:
        CompletableFuture -> true if it exists, false if not

      • getLease

        public CompletableFuture<CompleteLease> getLease​(String partitionId)
        Description copied from interface: ILeaseManager
        Returns the lease info for the given partition..
        Specified by:
        getLease in interface ILeaseManager
        Parameters:
        partitionId - Get the lease info for this partition.
        Returns:
        CompletableFuture -> Lease, completes exceptionally on error.

      • getAllLeases

        public CompletableFuture<List<BaseLease>> getAllLeases()
        Description copied from interface: ILeaseManager
        Returns lightweight BaseLease for all leases, which includes name of owning host and whether lease is expired. An implementation is free to return CompleteLease or its own class derived from CompleteLease, but it is important that getAllLeases run as fast as possible. If it is faster to obtain only the information required for a BaseLease, we heavily recommend doing that.
        Specified by:
        getAllLeases in interface ILeaseManager
        Returns:
        CompletableFuture -> list of BaseLease, completes exceptionally on error.

      • createAllLeasesIfNotExists

        public CompletableFuture<Void> createAllLeasesIfNotExists​(List<String> partitionIds)
        Description copied from interface: ILeaseManager
        Create in the store a lease for each of the given partitions, if it does not exist. Do nothing for any lease which exists in the store already.
        Specified by:
        createAllLeasesIfNotExists in interface ILeaseManager
        Parameters:
        partitionIds - ids of partitions to create lease info for
        Returns:
        CompletableFuture -> null on success, completes exceptionally on error

      • deleteLease

        public CompletableFuture<Void> deleteLease​(CompleteLease lease)
        Description copied from interface: ILeaseManager
        Delete the lease info for a partition from the store. If there is no stored lease for the given partition, that is treated as success.
        Specified by:
        deleteLease in interface ILeaseManager
        Parameters:
        lease - the currently existing lease info for the partition
        Returns:
        CompletableFuture -> null on success, completes exceptionally on error.

      • acquireLease

        public CompletableFuture<Boolean> acquireLease​(CompleteLease lease)
        Description copied from interface: ILeaseManager
        Acquire the lease on the desired partition for this EventProcessorHost.

        Note that it is legal to acquire a lease that is currently owned by another host, which is called "stealing". Lease-stealing is how partitions are redistributed when additional hosts are started.

        The existing Azure Storage implementation can experience races between two host instances attempting to acquire or steal the lease at the same time. To avoid situations where two host instances both believe that they own the lease, acquisition can fail non-exceptionally by returning false and should do so when there is any doubt -- the worst that can happen is that no host instance owns the lease for a short time. This is qualitatively different from, for example, the underlying store throwing an access exception, which is an error and should complete exceptionally.

        Specified by:
        acquireLease in interface ILeaseManager
        Parameters:
        lease - Lease info for the desired partition
        Returns:
        CompletableFuture -> true if the lease was acquired, false if not, completes exceptionally on error.

      • notifyOnSteal

        public void notifyOnSteal​(String expectedOwner,
                          String partitionId,
                          Callable<?> notifier)

      • renewLease

        public CompletableFuture<Boolean> renewLease​(CompleteLease lease)
        Description copied from interface: ILeaseManager
        Renew a lease currently held by this host instance.

        If the lease has been taken by another host instance (either stolen or after expiration) or explicitly released, renewLease must return false. With the Azure Storage-based implementation, it IS possible to renew an expired lease that has not been taken by another host, so your implementation can allow that or not, whichever is convenient. If it does not, renewLease should return false.

        Specified by:
        renewLease in interface ILeaseManager
        Parameters:
        lease - Lease to be renewed
        Returns:
        true if the lease was renewed, false as described above, completes exceptionally on error.

      • releaseLease

        public CompletableFuture<Void> releaseLease​(CompleteLease lease)
        Description copied from interface: ILeaseManager
        Give up a lease currently held by this host.

        If the lease has expired or been taken by another host, releasing it is unnecessary but will succeed since the intent has been fulfilled.

        Specified by:
        releaseLease in interface ILeaseManager
        Parameters:
        lease - Lease to be given up
        Returns:
        CompletableFuture -> null on success, completes exceptionally on error.

      • updateLease

        public CompletableFuture<Boolean> updateLease​(CompleteLease lease)
        Description copied from interface: ILeaseManager
        Update the store with the information in the provided lease.

        It is necessary to currently hold a lease in order to update it. If the lease has been stolen, or expired, or released, it cannot be updated. Lease manager implementations should renew the lease before performing the update to avoid lease expiration during the process.

        Specified by:
        updateLease in interface ILeaseManager
        Parameters:
        lease - New lease info to be stored
        Returns:
        true if the update was successful, false if lease was lost and could not be updated, completes exceptionally on error.