Package org.apache.hadoop.hbase.executor

Class EventHandler

java.lang.Object
org.apache.hadoop.hbase.executor.EventHandler
All Implemented Interfaces:
Comparable<EventHandler>, Runnable
Direct Known Subclasses:
AssignRegionHandler, CloseRegionHandler, CompactedHFilesDischargeHandler, OpenRegionHandler, ParallelSeekHandler, RegionReplicaFlushHandler, RSProcedureHandler, TakeSnapshotHandler, UnassignRegionHandler, WALSplitterHandler
@Private public abstract class EventHandler extends Object implements Runnable, Comparable<EventHandler>
Abstract base class for all HBase event handlers. Subclasses should implement the process() and prepare() methods. Subclasses should also do all necessary checks up in their prepare() if possible -- check table exists, is disabled, etc. -- so they fail fast rather than later when process is running. Do it this way because process be invoked directly but event handlers are also run in an executor context -- i.e. asynchronously -- and in this case, exceptions thrown at process time will not be seen by the invoker, not till we implement a call-back mechanism so the client can pick them up later.

Event handlers have an EventType. EventType is a list of ALL handler event types. We need to keep a full list in one place -- and as enums is a good shorthand for an implemenations -- because event handlers can be passed to executors when they are to be run asynchronously. The hbase executor, see ExecutorService, has a switch for passing event type to executor.

See Also:

  • Field Details

  • Constructor Details

  • Method Details

    • prepare

      public EventHandler prepare() throws Exception
      Event handlers should do all the necessary checks in this method (rather than in the constructor, or in process()) so that the caller, which is mostly executed in the ipc context can fail fast. Process is executed async from the client ipc, so this method gives a quick chance to do some basic checks. Should be called after constructing the EventHandler, and before process().
      Returns:
      the instance of this class
      Throws:
      Exception - when something goes wrong

    • run

      public void run()
      Specified by:
      run in interface Runnable

    • process

      public abstract void process() throws IOException
      This method is the main processing loop to be implemented by the various subclasses.
      Throws:
      IOException

    • getEventType

      public EventType getEventType()
      Return the event type
      Returns:
      The event type.

    • getPriority

      public int getPriority()
      Get the priority level for this handler instance. This uses natural ordering so lower numbers are higher priority.

      Lowest priority is Integer.MAX_VALUE. Highest priority is 0.

      Subclasses should override this method to allow prioritizing handlers.

      Handlers with the same priority are handled in FIFO order.

      Returns:
      Integer.MAX_VALUE by default, override to set higher priorities

    • getSeqid

      public long getSeqid()
      Returns This events' sequence id.

    • compareTo

      public int compareTo(EventHandler o)
      Default prioritized runnable comparator which implements a FIFO ordering.

      Subclasses should not override this. Instead, if they want to implement priority beyond FIFO, they should override getPriority().

      Specified by:
      compareTo in interface Comparable<EventHandler>

    • toString

      public String toString()
      Overrides:
      toString in class Object

    • getInformativeName

      public String getInformativeName()
      Event implementations should override thie class to provide an informative name about what event they are handling. For example, event-specific information such as which region or server is being processed should be included if possible.

    • handleException

      protected void handleException(Throwable t)
      Event exception handler, may be overridden
      Parameters:
      t - Throwable object