Restore mutual exclusion of sendChannelRequest() and gotResponse() in AbstractChannel (but rather than make methods synchronized do it on the queue, which itself doesn't need to be thread-safe). Regression due to 1a2351c5ee. Fixes #35.

src/main/java/net/schmizz/sshj/connection/channel/AbstractChannel.java

@@ -53,8 +53,8 @@ import org.slf4j.LoggerFactory;
 
 import java.io.InputStream;
 import java.io.OutputStream;
+import java.util.LinkedList;
 import java.util.Queue;
-import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.locks.ReentrantLock;
 
@@ -76,7 +76,7 @@ public abstract class AbstractChannel
     /** Remote recipient ID */
     private int recipient;
 
-    private final Queue<Event<ConnectionException>> chanReqResponseEvents = new ConcurrentLinkedQueue<Event<ConnectionException>>();
+    private final Queue<Event<ConnectionException>> chanReqResponseEvents = new LinkedList<Event<ConnectionException>>();
 
     /* The lock used by to create the open & close events */
     private final ReentrantLock lock = new ReentrantLock();
@@ -368,6 +368,7 @@ public abstract class AbstractChannel
                                                             Buffer.PlainBuffer reqSpecific)
             throws TransportException {
         log.info("Sending channel request for `{}`", reqType);
+        synchronized (chanReqResponseEvents) {
             trans.write(
                     newBuffer(Message.CHANNEL_REQUEST)
                             .putString(reqType)
@@ -383,9 +384,11 @@ public abstract class AbstractChannel
             }
             return responseEvent;
         }
+    }
 
     private void gotResponse(boolean success)
             throws ConnectionException {
+        synchronized (chanReqResponseEvents) {
             final Event<ConnectionException> responseEvent = chanReqResponseEvents.poll();
             if (responseEvent != null) {
                 if (success)
@@ -396,6 +399,7 @@ public abstract class AbstractChannel
                 throw new ConnectionException(DisconnectReason.PROTOCOL_ERROR,
                         "Received response to channel request when none was requested");
         }
+    }
 
     private synchronized void gotEOF()
             throws TransportException {