relaxed stream id supplement (#814)

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2015-2018 the original author or authors.
+ * Copyright 2015-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,14 +16,11 @@
 package io.rsocket.core;
 
 import io.netty.util.collection.IntObjectMap;
-import java.util.concurrent.atomic.AtomicLongFieldUpdater;
 
 final class StreamIdSupplier {
   private static final int MASK = 0x7FFFFFFF;
 
-  private static final AtomicLongFieldUpdater<StreamIdSupplier> STREAM_ID =
-      AtomicLongFieldUpdater.newUpdater(StreamIdSupplier.class, "streamId");
-  private volatile long streamId;
+  private long streamId;
 
   // Visible for testing
   StreamIdSupplier(int streamId) {
@@ -38,10 +35,18 @@ static StreamIdSupplier serverSupplier() {
     return new StreamIdSupplier(0);
   }
 
+  /**
+   * This methods provides new stream id and ensures there is no intersections with already running
+   * streams. This methods is not thread-safe.
+   *
+   * @param streamIds currently running streams store
+   * @return next stream id
+   */
   int nextStreamId(IntObjectMap<?> streamIds) {
     int streamId;
     do {
-      streamId = (int) STREAM_ID.addAndGet(this, 2) & MASK;
+      this.streamId += 2;
+      streamId = (int) (this.streamId & MASK);
     } while (streamId == 0 || streamIds.containsKey(streamId));
     return streamId;
   }