1 files changed, 99 insertions, 0 deletions
diff --git a/simple/simple-http/src/main/java/org/simpleframework/http/socket/service/OutputBarrier.java b/simple/simple-http/src/main/java/org/simpleframework/http/socket/service/OutputBarrier.java
new file mode 100644
index 0000000..3da2635
--- /dev/null
+++ b/simple/simple-http/src/main/java/org/simpleframework/http/socket/service/OutputBarrier.java
@@ -0,0 +1,99 @@
+/*
+ * OutputBarrier.java February 2014
+ *
+ * Copyright (C) 2014, Niall Gallagher <niallg@users.sf.net>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or 
+ * implied. See the License for the specific language governing 
+ * permissions and limitations under the License.
+ */
+
+package org.simpleframework.http.socket.service;
+
+import static java.util.concurrent.TimeUnit.MILLISECONDS;
+
+import java.io.IOException;
+import java.util.concurrent.locks.ReentrantLock;
+
+import org.simpleframework.http.Request;
+import org.simpleframework.transport.Channel;
+import org.simpleframework.transport.ByteWriter;
+
+/**
+ * The <code>OutputBarrier</code> is used to ensure that control
+ * frames and data frames do not get sent at the same time. Sending
+ * both at the same time could lead to the status checking thread 
+ * being blocked and this could eventually exhaust the thread pool.
+ * 
+ * @author Niall Gallagher
+ */
+class OutputBarrier {   
+   
+   /**
+    * This is used to check if there is an operation in progress.
+    */
+   private final ReentrantLock lock;
+   
+   /**
+    * This is the underlying sender used to send the frames.
+    */
+   private final ByteWriter writer;    
+   
+   /**
+    * This is the TCP channel the frames are delivered over.
+    */
+   private final Channel channel;
+   
+   /**
+    * This is the length of time to wait before failing to lock.
+    */
+   private final long duration;      
+   
+   /**
+    * Constructor for the <code>OutputBarrier</code> object. This
+    * is used to ensure that if there is currently a blocking write
+    * in place that the <code>SessionChecker</code> will not end up
+    * being blocked if it attempts to send a control frame.
+    * 
+    * @param request this is the request to get the TCP channel from
+    * @param duration this is the length of time to wait for the lock
+    */
+   public OutputBarrier(Request request, long duration) {
+      this.lock = new ReentrantLock();      
+      this.channel = request.getChannel();
+      this.writer = channel.getWriter();
+      this.duration = duration;
+   }
+   
+   /**
+    * This method is used to send all frames. It is important that 
+    * a lock is used to protect this so that if there is an attempt
+    * to send out a control frame while the connection is blocked
+    * there is an exception thrown.
+    * 
+    * @param frame this is the frame to send over the TCP channel
+    */
+   public void send(byte[] frame) throws IOException {
+      try {        
+         if(!lock.tryLock(duration, MILLISECONDS)) {
+            throw new IOException("Transport lock could not be acquired");
+         }
+         try {
+            writer.write(frame);
+            writer.flush();  // less throughput, better latency          
+         } finally {
+            lock.unlock();                           
+         }
+      } catch(Exception e) {
+         throw new IOException("Error writing to transport", e);
+      }       
+   }
+}