public virtual Task CreateSubscriptionCoreAsync(Uri subscriptionUri, Expression subscription, object state, CancellationToken token)
{
if (subscriptionUri == null)
{
throw new ArgumentNullException(nameof(subscriptionUri));
}
if (subscription == null)
{
throw new ArgumentNullException(nameof(subscription));
}
var rewritten = _rewriter(subscription);
// NB: The functionality to insert the hook needs to be revisited in order to have an effect on subscriptions created via subscription
// factories. However, its applicability will be limited when factories for things like "composite subscriptions" are used. While
// only observable.Subscribe(observer) subscriptions can be "hooked" using a Finally operator, it's unclear how the same technique
// could be applied to e.g. composite subscriptions. The better option is likely to add a mechanism that can detect the transition
// of a subscription to a disposed state trigger from within the engine. However, that will lack information about the cause of
// termination, e.g. due to an OnError or OnCompleted message (in fact, in a general notion of subscriptions there's no requirement
// to have an observer given that the ISubscription algebra is one that operates on "traversable resources" in the most general
// sense imaginable).
//
// One temporary workaround could be for the QC to intercept subscription factory definition operations and scan for a single
// top-level occurrence of rx://observable/subscribe, and attach the hook the the observable portion. Other non-hookable expressions
// could be rejected for the time being. The mechanism to put in this hook could simply rewrite rx://observable/subscribe to some
// other subscription factory which expands into (o, v) => rx://observable/subscribe(o.CleanupHook(), v).
//
// See Reaqtor.Remoting.QueryCoordinator\QueryCoordinatorServiceProvider.cs for an implementation of the latter.
var subscribeExpressionWithCompletedHook = rewritten.GetExpressionWithSubscriptionCleanupHook(throwWhenNotAttached: false);
var subscribeExpressionSync = ExpressionRewriteHelpers.RewriteAsyncToSync(subscribeExpressionWithCompletedHook);
return(_queryEngine.ServiceProvider.CreateSubscriptionAsync(subscriptionUri, subscribeExpressionSync, state, token));
}
public virtual Task CreateStreamCoreAsync(Uri streamUri, Expression stream, object state, CancellationToken token)
{
if (streamUri == null)
{
throw new ArgumentNullException(nameof(streamUri));
}
if (stream == null)
{
throw new ArgumentNullException(nameof(stream));
}
var syncStream = ExpressionRewriteHelpers.RewriteAsyncToSync(stream);
return(_queryEngine.ServiceProvider.CreateStreamAsync(streamUri, syncStream, state, token));
}
