To implement a new Procedure type, extend this class and override remoteCallBuild() and + * complete(). The dispatch and callback will be handled for you here, internally. * - * If sending the operation to remote RS failed, dispatcher will call remoteCallFailed() to - * handle this, which actually call remoteOperationDone with the exception. - * If the targetServer crashed but this procedure has no response, than dispatcher will call - * remoteOperationFailed() to handle this, which also calls remoteOperationDone with the exception. - * If the operation is successful, then remoteOperationCompleted will be called and actually calls - * the remoteOperationDone without exception. + *
The Procedure works as follows. It uses {@link RSProcedureDispatcher}, the same system + * used dispatching Region OPEN and CLOSE RPCs, to pass a Callable to a RegionServer. Examples + * include {@link org.apache.hadoop.hbase.regionserver.SplitWALCallable} and + * {@link org.apache.hadoop.hbase.replication.regionserver.RefreshPeerCallable}. Rather than + * assign/unassign, the Master calls #executeProcedures against the remote RegionServer wrapping + * a Callable in a {@link ExecuteProceduresRequest}. Upon successful dispatch, + * the Procedure then suspends itself on the Master-side and relinqushes its executor worker. + * On receipt, the RegionServer submits the Callable to its executor service. When the Callable + * completes, it adds itself to a queue on the RegionServer side for processing by a background + * thread, the {@link RemoteProcedureResultReporter}. It picks up the completed Callable from the + * queue and RPCs the master at #reportProcedureDone with the procedure id and whether success or + * failure. The master calls complete() setting success or failure state and then reschedules the + * suspended Procedure so it can finish. + * + *
Here are some details on operation: + *
If adding the operation to the dispatcher fails, addOperationToNode will throw + * FailedRemoteDispatchException, and this Procedure will return 'null'. The Procedure Executor + * will then mark this procedure as 'complete' (though we failed to dispatch our task). In this + * case, the upper layer of this procedure must have a way to check if this Procedure really + * succeeded or not and have appropriate handling. + * + *
If sending the operation to remote RS failed, dispatcher will call remoteCallFailed() to + * handle this which calls remoteOperationDone with the exception. If the targetServer crashed but + * this procedure has no response, than dispatcher will call remoteOperationFailed() which also + * calls remoteOperationDone with the exception. If the operation is successful, then + * remoteOperationCompleted will be called and actually calls the remoteOperationDone without + * exception. * * In remoteOperationDone, we'll check if the procedure is already get wake up by others. Then * developer could implement complete() based on their own purpose.