FR: Revising the Threading Model and Async APIs

There are several issues in the Admin SDK with respect to how it creates and uses threads:

1. Most public APIs are asynchronous, and returns Task instances. This tends to make implementing simple use cases unnecessarily complex (e.g. creating a custom token and sending back as a servlet response).
2. Main thread pool is initialized statically, and not configurable.
3. ThreadFactory is initialized statically, and not configurable.
4. Tasks API is visible to user code. A user can kick off arbitrary background tasks using this API, which will get executed on the main thread pool of the SDK, un-regulated.

In order to address these limitations, we can consider the following changes:

• Expose synchronous/blocking variants of public APIs where it makes sense (most notably at FirebaseAuth).

BlockingFirebaseAuth auth = FirebaseAuth.getBlockingInstance();
String customToken = auth.createCustomToken("user1");

• Make the thread pool and thread factory configurable via app options.
• Hide or decommission the Tasks API. We can consider using the ApiFutures from Google Cloud Commons (this is similar to Guava’s ListenableFutures) as a replacement.

FirebaseAuth auth = FirebaseAuth.getInstance();
ApiFuture<String> customTokenFuture = auth.createCustomToken("user1");

// The following should not be supported 
// Tasks.call(new Callable(){...}); 

[samodadela]

Well… in the end I came up with this:

    SettableApiFuture<String> future = SettableApiFuture.create();
    final Query mDatabase = getDatabaseReference( firebaseProjectDatabase ).child( valueName );

    mDatabase.addListenerForSingleValueEvent( new ValueEventListener() {
        @Override
        public void onDataChange( DataSnapshot snapshot ) {
            String value = "got it";
            future.set( value );
        }

        @Override
        public void onCancelled( DatabaseError error ) {
            future.set( null );
        }
    } );

    String value = null;
    try {
        value = future.get( 10, TimeUnit.SECONDS );
    } catch( InterruptedException e ) {
        log.error( "getValue interrupted: {}", e );
    } catch( ExecutionException e ) {
        log.error( "getValue did not execute: {}", e );
    } catch( TimeoutException e ) {
        log.error( "getValue timed-out: {}", e );
    }

[pontello]

@samodadela , ApiFuture extends java.util.concurrent.Future.

This article should be enough to learn how to use it.

If you still need extra help, try another articles from here.