Provides Prioritised delivering of Zero Streams Frames

build.gradle

@@ -88,8 +88,11 @@ subprojects {
     repositories {
         mavenCentral()
 
-        if (version.endsWith('BUILD-SNAPSHOT') || project.hasProperty('platformVersion')) {
+        if (version.endsWith('SNAPSHOT') || project.hasProperty('platformVersion')) {
             maven { url 'http://repo.spring.io/libs-snapshot' }
+            maven {
+                url 'https://oss.jfrog.org/artifactory/oss-snapshot-local'
+            }
         }
     }
 

rsocket-core/src/main/java/io/rsocket/RSocketRequester.java

@@ -124,7 +124,7 @@ class RSocketRequester implements RSocket {
           new ClientKeepAliveSupport(allocator, keepAliveTickPeriod, keepAliveAckTimeout);
       this.keepAliveFramesAcceptor =
           keepAliveHandler.start(
-              keepAliveSupport, sendProcessor::onNext, this::tryTerminateOnKeepAlive);
+              keepAliveSupport, sendProcessor::onNextPrioritized, this::tryTerminateOnKeepAlive);
     } else {
       keepAliveFramesAcceptor = null;
     }
@@ -411,7 +411,7 @@ private Mono<Void> handleMetadataPush(Payload payload) {
               MetadataPushFrameFlyweight.encode(allocator, payload.sliceMetadata().retain());
           payload.release();
 
-          sendProcessor.onNext(metadataPushFrame);
+          sendProcessor.onNextPrioritized(metadataPushFrame);
         });
   }
 

rsocket-core/src/main/java/io/rsocket/RSocketResponder.java

@@ -85,7 +85,7 @@ class RSocketResponder implements ResponderRSocket {
         .subscribe(null, this::handleSendProcessorError);
 
     Disposable receiveDisposable = connection.receive().subscribe(this::handleFrame, errorConsumer);
-    Disposable sendLeaseDisposable = leaseHandler.send(sendProcessor::onNext);
+    Disposable sendLeaseDisposable = leaseHandler.send(sendProcessor::onNextPrioritized);
 
     this.connection
         .onClose()

rsocket-core/src/main/java/io/rsocket/internal/UnboundedProcessor.java

@@ -56,6 +56,7 @@ public final class UnboundedProcessor<T> extends FluxProcessor<T, T>
       AtomicLongFieldUpdater.newUpdater(UnboundedProcessor.class, "requested");
 
   final Queue<T> queue;
+  final Queue<T> priorityQueue;
   volatile boolean done;
   Throwable error;
   volatile CoreSubscriber<? super T> actual;
@@ -67,11 +68,12 @@ public final class UnboundedProcessor<T> extends FluxProcessor<T, T>
 
   public UnboundedProcessor() {
     this.queue = new MpscUnboundedArrayQueue<>(Queues.SMALL_BUFFER_SIZE);
+    this.priorityQueue = new MpscUnboundedArrayQueue<>(Queues.SMALL_BUFFER_SIZE);
   }
 
   @Override
   public int getBufferSize() {
-    return Queues.capacity(this.queue);
+    return Integer.MAX_VALUE;
   }
 
   @Override
@@ -84,6 +86,7 @@ void drainRegular(Subscriber<? super T> a) {
     int missed = 1;
 
     final Queue<T> q = queue;
+    final Queue<T> pq = priorityQueue;
 
     for (; ; ) {
 
@@ -93,10 +96,18 @@ void drainRegular(Subscriber<? super T> a) {
       while (r != e) {
         boolean d = done;
 
-        T t = q.poll();
-        boolean empty = t == null;
+        T t;
+        boolean empty;
+
+        if (!pq.isEmpty()) {
+          t = pq.poll();
+          empty = false;
+        } else {
+          t = q.poll();
+          empty = t == null;
+        }
 
-        if (checkTerminated(d, empty, a, q)) {
+        if (checkTerminated(d, empty, a)) {
           return;
         }
 
@@ -110,7 +121,7 @@ void drainRegular(Subscriber<? super T> a) {
       }
 
       if (r == e) {
-        if (checkTerminated(done, q.isEmpty(), a, q)) {
+        if (checkTerminated(done, q.isEmpty() && pq.isEmpty(), a)) {
           return;
         }
       }
@@ -129,12 +140,10 @@ void drainRegular(Subscriber<? super T> a) {
   void drainFused(Subscriber<? super T> a) {
     int missed = 1;
 
-    final Queue<T> q = queue;
-
     for (; ; ) {
 
       if (cancelled) {
-        q.clear();
+        clear();
         actual = null;
         return;
       }
@@ -188,14 +197,9 @@ public void drain() {
     }
   }
 
-  boolean checkTerminated(boolean d, boolean empty, Subscriber<? super T> a, Queue<T> q) {
+  boolean checkTerminated(boolean d, boolean empty, Subscriber<? super T> a) {
     if (cancelled) {
-      while (!q.isEmpty()) {
-        T t = q.poll();
-        if (t != null) {
-          release(t);
-        }
-      }
+      clear();
       actual = null;
       return true;
     }
@@ -237,6 +241,23 @@ public Context currentContext() {
     return actual != null ? actual.currentContext() : Context.empty();
   }
 
+  public void onNextPrioritized(T t) {
+    if (done || cancelled) {
+      Operators.onNextDropped(t, currentContext());
+      release(t);
+      return;
+    }
+
+    if (!priorityQueue.offer(t)) {
+      Throwable ex =
+          Operators.onOperatorError(null, Exceptions.failWithOverflow(), t, currentContext());
+      onError(Operators.onOperatorError(null, ex, t, currentContext()));
+      release(t);
+      return;
+    }
+    drain();
+  }
+
   @Override
   public void onNext(T t) {
     if (done || cancelled) {
@@ -319,25 +340,24 @@ public void cancel() {
     }
   }
 
-  @Override
-  public T peek() {
-    return queue.peek();
-  }
-
   @Override
   @Nullable
   public T poll() {
+    Queue<T> pq = this.priorityQueue;
+    if (!pq.isEmpty()) {
+      return pq.poll();
+    }
     return queue.poll();
   }
 
   @Override
   public int size() {
-    return queue.size();
+    return priorityQueue.size() + queue.size();
   }
 
   @Override
   public boolean isEmpty() {
-    return queue.isEmpty();
+    return priorityQueue.isEmpty() && queue.isEmpty();
   }
 
   @Override
@@ -348,6 +368,12 @@ public void clear() {
         release(t);
       }
     }
+    while (!priorityQueue.isEmpty()) {
+      T t = priorityQueue.poll();
+      if (t != null) {
+        release(t);
+      }
+    }
   }
 
   @Override

rsocket-core/src/main/java/io/rsocket/internal/UnicastMonoEmpty.java

@@ -9,10 +9,8 @@
 import reactor.util.annotation.Nullable;
 
 /**
- * Represents an empty publisher which only calls onSubscribe and onComplete.
- *
- * <p>This Publisher is effectively stateless and only a single instance exists. Use the {@link
- * #instance()} method to obtain a properly type-parametrized view of it.
+ * Represents an empty publisher which only calls onSubscribe and onComplete and allows only a
+ * single subscriber.
  *
  * @see <a href="https://github.com/reactor/reactive-streams-commons">Reactive-Streams-Commons</a>
  */

rsocket-core/src/test/java/io/rsocket/internal/UnboundedProcessorTest.java

@@ -17,6 +17,7 @@
 package io.rsocket.internal;
 
 import io.rsocket.Payload;
+import io.rsocket.util.ByteBufPayload;
 import io.rsocket.util.EmptyPayload;
 import java.util.concurrent.CountDownLatch;
 import org.junit.Assert;
@@ -82,6 +83,36 @@ public void testOnNextAfterSubscribe_1000() throws Exception {
     testOnNextAfterSubscribeN(1000);
   }
 
+  @Test
+  public void testPrioritizedSending() {
+    UnboundedProcessor<Payload> processor = new UnboundedProcessor<>();
+
+    for (int i = 0; i < 1000; i++) {
+      processor.onNext(EmptyPayload.INSTANCE);
+    }
+
+    processor.onNextPrioritized(ByteBufPayload.create("test"));
+
+    Payload closestPayload = processor.next().block();
+
+    Assert.assertEquals(closestPayload.getDataUtf8(), "test");
+  }
+
+  @Test
+  public void testPrioritizedFused() {
+    UnboundedProcessor<Payload> processor = new UnboundedProcessor<>();
+
+    for (int i = 0; i < 1000; i++) {
+      processor.onNext(EmptyPayload.INSTANCE);
+    }
+
+    processor.onNextPrioritized(ByteBufPayload.create("test"));
+
+    Payload closestPayload = processor.poll();
+
+    Assert.assertEquals(closestPayload.getDataUtf8(), "test");
+  }
+
   public void testOnNextAfterSubscribeN(int n) throws Exception {
     CountDownLatch latch = new CountDownLatch(n);
     UnboundedProcessor<Payload> processor = new UnboundedProcessor<>();