Fix CreateMonitorSocket causing NetMQContext dispose hang. Closes zer…

…omq#223.

src/NetMQ.Tests/MonitorPollTests.cs

@@ -125,5 +125,16 @@ public void MonitorDisposeProperlyWhenDisposedAfterMonitoredTcpSocket()
             }
             // NOTE If this test fails, it will hang because context.Dispose will block
         }
+
+        [Test]
+        public void CreateMonitorSocket_ShouldntHangContextDispose_GitHubIssue223()
+        {
+            var context = NetMQContext.Create();
+
+            using (context.CreateMonitorSocket("inproc://monitor1234"))
+            {}
+
+            Assert.True(Task.Factory.StartNew(() => context.Dispose()).Wait(1000));
+        }
     }
 }

src/NetMQ/Monitoring/NetMQMonitor.cs

@@ -41,15 +41,19 @@ public NetMQMonitor([NotNull] NetMQContext context, [NotNull] NetMQSocket monito
         /// </remarks>
         /// <param name="socket">The socket to monitor.</param>
         /// <param name="endpoint">a string denoting the endpoint which will be the monitoring address</param>
-        public NetMQMonitor([NotNull] NetMQSocket socket, [NotNull] string endpoint)
+        /// <param name="ownsSocket">
+        /// A flag indicating whether ownership of <paramref name="socket"/> is transferred to the monitor.
+        /// If <c>true</c>, disposing the monitor will also dispose <paramref name="socket"/>.
+        /// </param>
+        public NetMQMonitor([NotNull] NetMQSocket socket, [NotNull] string endpoint, bool ownsSocket = false)
         {
             Endpoint = endpoint;
             Timeout = TimeSpan.FromSeconds(0.5);
             m_monitoringSocket = socket;
 
             m_monitoringSocket.ReceiveReady += Handle;
 
-            m_ownsMonitoringSocket = false;
+            m_ownsMonitoringSocket = ownsSocket;
         }
 
         /// <summary>

src/NetMQ/NetMQContext.cs

@@ -261,7 +261,7 @@ public NetMQMonitor CreateMonitorSocket([NotNull] string endpoint)
                 throw new ArgumentException("Unable to monitor to an empty endpoint.", "endpoint");
             }
 
-            return new NetMQMonitor(CreatePairSocket(), endpoint);
+            return new NetMQMonitor(CreatePairSocket(), endpoint, ownsSocket: true);
         }
 
         #endregion