Package org.apache.hadoop.crypto.key.kms

Class ValueQueue<E>

java.lang.Object
org.apache.hadoop.crypto.key.kms.ValueQueue<E>
@Private public class ValueQueue<E> extends Object
A Utility class that maintains a Queue of entries for a given key. It tries to ensure that there is are always at-least numValues entries available for the client to consume for a particular key. It also uses an underlying Cache to evict queues for keys that have not been accessed for a configurable period of time. Implementing classes are required to implement the QueueRefiller interface that exposes a method to refill the queue, when empty

  • Constructor Details

    • ValueQueue

      public ValueQueue(int numValues, float lowWatermark, long expiry, int numFillerThreads, ValueQueue.SyncGenerationPolicy policy, ValueQueue.QueueRefiller<E> refiller)
      Constructor takes the following tunable configuration parameters
      Parameters:
      numValues - The number of values cached in the Queue for a particular key.
      lowWatermark - The ratio of (number of current entries/numValues) below which the fillQueueForKey() funciton will be invoked to fill the Queue.
      expiry - Expiry time after which the Key and associated Queue are evicted from the cache.
      numFillerThreads - Number of threads to use for the filler thread
      policy - The SyncGenerationPolicy to use when client calls "getAtMost"
      refiller - implementation of the QueueRefiller

    • ValueQueue

      public ValueQueue(int numValues, float lowWaterMark, long expiry, int numFillerThreads, ValueQueue.QueueRefiller<E> fetcher)

  • Method Details

    • initializeQueuesForKeys

      public void initializeQueuesForKeys(String... keyNames) throws IOException
      Initializes the Value Queues for the provided keys by calling the fill Method with "numInitValues" values
      Parameters:
      keyNames - Array of key Names
      Throws:
      IOException - if initialization fails for any provided keys

    • getNext

      public E getNext(String keyName) throws IOException, ExecutionException
      This removes the value currently at the head of the Queue for the provided key. Will immediately fire the Queue filler function if key does not exist. If Queue exists but all values are drained, It will ask the generator function to add 1 value to Queue and then drain it.
      Parameters:
      keyName - String key name
      Returns:
      E the next value in the Queue
      Throws:
      IOException - raised on errors performing I/O.
      ExecutionException - executionException.

    • drain

      public void drain(String keyName)
      Drains the Queue for the provided key.
      Parameters:
      keyName - the key to drain the Queue for

    • getSize

      @VisibleForTesting public int getSize(String keyName)
      Get size of the Queue for keyName. This is only used in unit tests.
      Parameters:
      keyName - the key name
      Returns:
      int queue size. Zero means the queue is empty or the key does not exist.

    • getAtMost

      public List<E> getAtMost(String keyName, int num) throws IOException, ExecutionException
      This removes the "num" values currently at the head of the Queue for the provided key. Will immediately fire the Queue filler function if key does not exist How many values are actually returned is governed by the SyncGenerationPolicy specified by the user.
      Parameters:
      keyName - String key name
      num - Minimum number of values to return.
      Returns:
      List<E> values returned
      Throws:
      IOException - raised on errors performing I/O.
      ExecutionException - execution exception.

    • shutdown

      public void shutdown()
      Cleanly shutdown