Asynchronous Database Access: Difference between revisions

ThereMarauroa should behas a DatabaseOperationQueueDBCommandQueue, which is singleton and has a background thread to execute enqueued DatabaseOperationsDBCommands. DatabaseOperationDBCommand is an interface that specifies an execute()-method, that handlesprocessed the database operationrequest by invoking the DAO-classes. It is called from the background thread of DatabaseOperationQueueDBCommandQueue.

The following example for a simple write operation assumes that GameEvent implements/extends DatabaseOperationDBCommand:

DatabaseOperationQueueDBCommandQueue.get().enqueue(

UUID uuid = DatabaseOperationQueueDBCommandQueue.get().enqueueAndNotifyenqueueAndAwaitResult(

The DatabaseOperationQueueDBCommandQueue will process the GetCharacterList at some future time in the background thread. It will then put the GetCharacterList which now contains the results from the database in a second queue ("waiting to be fetched by program"). Here comes the tricky part: We need a way to notify the program in the thread that requested the operation about the results. The easiest way is to remember the requesting thread by Thread.getCurrentThread() and provide a List<DatabaseOperationDBCommand>

getResults() method, which fetches all results of OperationsCommands enqueueenqueued by the current thread.

We havehad to decide here whether we wantwanted an ''interrupt'' or ''polling'' based approach: An interrupt based approach would then distribute the results to various program parts of the current thread using an interface DatabaseOperationResultReceiverDBCommandResultReceiver<T extends DatabaseOperationDBCommand>, which is implemented by those classes who requested the data. AWe chose a a polling based

approach. would result inHere, the program parts to look for specific results. So theThe program part that sends the character list back to the client would callcalls:

List<GetCharacterList> DatabaseOperationQueueDBCommandQueue.get().getResults(this).