no way to cancel receive operation

Solution: add cancellation token to all receive operation (thread safe only, for now)

src/NetMQ.Tests/ClientServer.cs

@@ -1,3 +1,6 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
 using NetMQ;
 using NetMQ.Sockets;
 using Xunit;
@@ -59,5 +62,16 @@ public async void Async()
             var serverMsg = await client.ReceiveStringAsync();
             Assert.Equal("World", serverMsg);
         }
+
+        [Fact]
+        public async void AsyncWithCancellationToken()
+        {
+            using CancellationTokenSource source = new CancellationTokenSource();
+            using var server = new ServerSocket();
+
+            source.CancelAfter(100);
+
+            await Assert.ThrowsAsync<OperationCanceledException>(async () => await server.ReceiveStringAsync(source.Token));
+        }
     }
 }

src/NetMQ/Core/CommandType.cs

@@ -106,6 +106,11 @@ internal enum CommandType
         /// <summary>
         /// Send to reaper to stop the reaper immediatly
         /// </summary>
-        ForceStop
+        ForceStop,
+
+        /// <summary>
+        /// Send a cancellation request to the socket from a cancellation token
+        /// </summary>
+        CancellationRequested
     }
 }

src/NetMQ/Core/SocketBase.cs

@@ -25,6 +25,7 @@ You should have received a copy of the GNU Lesser General Public License
 using System.Diagnostics;
 using System.Linq;
 using System.Net.Sockets;
+using System.Threading;
 using AsyncIO;
 using JetBrains.Annotations;
 using NetMQ.Core.Patterns;
@@ -982,6 +983,7 @@ public bool TrySend(ref Msg msg, TimeSpan timeout, bool more)
         /// </summary>
         /// <param name="msg">the <c>Msg</c> to read the received message into</param>
         /// <param name="timeout">this controls whether the call blocks, and for how long.</param>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is <see cref="CancellationToken.None"/>.</param>
         /// <returns><c>true</c> if successful, <c>false</c> if it timed out</returns>
         /// <remarks>
         /// For <paramref name="timeout"/>, there are three categories of value:
@@ -993,7 +995,7 @@ public bool TrySend(ref Msg msg, TimeSpan timeout, bool more)
         /// </remarks>
         /// <exception cref="FaultException">the Msg must already have been uninitialised</exception>
         /// <exception cref="TerminatingException">The socket must not already be stopped.</exception>
-        public bool TryRecv(ref Msg msg, TimeSpan timeout)
+        public bool TryRecv(ref Msg msg, TimeSpan timeout, CancellationToken cancellationToken = default)
         {
             Lock();
             try
@@ -1056,7 +1058,10 @@ public bool TryRecv(ref Msg msg, TimeSpan timeout)
                 bool block = m_ticks != 0;
                 while (true)
                 {
-                    ProcessCommands(block ? timeoutMillis : 0, false);
+                    if (cancellationToken.IsCancellationRequested)
+                        return false;
+
+                    ProcessCommands(block ? timeoutMillis : 0, false, cancellationToken);
 
                     isMessageAvailable = XRecv(ref msg);
                     if (isMessageAvailable)
@@ -1168,15 +1173,21 @@ internal void StartReaping([NotNull] Poller poller)
         /// </summary>
         /// <param name="timeout">how much time to allow to wait for a command, before returning (in milliseconds)</param>
         /// <param name="throttle">if true - throttle the rate of command-execution by doing only one per call</param>
+        /// <param name="cancellationToken">allows the caller to cancel the process commands operation</param>
         /// <exception cref="TerminatingException">The Ctx context must not already be terminating.</exception>
-        private void ProcessCommands(int timeout, bool throttle)
+        private void ProcessCommands(int timeout, bool throttle, CancellationToken cancellationToken = default)
         {
             bool found;
             Command command;
             if (timeout != 0)
             {
-                // If we are asked to wait, simply ask mailbox to wait.
-                found = m_mailbox.TryRecv(timeout, out command);
+                if (cancellationToken.CanBeCanceled)
+                {
+                    using var registration = cancellationToken.Register(SendCancellationRequested);
+                    found = m_mailbox.TryRecv(timeout, out command);
+                }
+                else
+                    found = m_mailbox.TryRecv(timeout, out command);
             }
             else
             {

src/NetMQ/Core/ZObject.cs

@@ -240,6 +240,14 @@ protected void SendDone()
             m_ctx.SendCommand(Ctx.TermTid, new Command(null, CommandType.Done));
         }
 
+        /// <summary>
+        /// Socket sends a CancellationRequested command to itself when a CancellationToken has been cancelled 
+        /// </summary>
+        protected void SendCancellationRequested()
+        {
+            SendCommand(new Command(this, CommandType.CancellationRequested, null));
+        }
+
         /// <summary>
         /// Send the given Command, on that commands Destination thread.
         /// </summary>
@@ -324,6 +332,10 @@ public void ProcessCommand([NotNull] Command cmd)
                 case CommandType.ForceStop:
                     ProcessForceStop();
                     break;
+
+                case CommandType.CancellationRequested:
+                    ProcessCancellationRequested();
+                    break;
 
                 default:
                     throw new ArgumentException();
@@ -468,6 +480,13 @@ protected virtual void ProcessSeqnum()
             throw new NotSupportedException();
         }
 
+        /// <summary>
+        /// Handler for cancellation requested
+        /// </summary>
+        protected virtual void ProcessCancellationRequested()
+        {
+        }
+
         #endregion
     }
 }

src/NetMQ/ReceiveThreadSafeSocketExtensions.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Text;
+using System.Threading;
 using System.Threading.Tasks;
 using JetBrains.Annotations;
 
@@ -18,19 +19,26 @@ public static class ReceiveThreadSafeSocketExtensions
         /// Receive a bytes from <paramref name="socket"/>, blocking until one arrives.
         /// </summary>
         /// <param name="socket">The socket to receive from.</param>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is <see cref="CancellationToken.None"/>.</param>
         /// <returns>The content of the received message.</returns>
+        /// <exception cref="System.OperationCanceledException">The token has had cancellation requested.</exception>
         [NotNull]
-        public static byte[] ReceiveBytes([NotNull] this IThreadSafeInSocket socket)
+        public static byte[] ReceiveBytes([NotNull] this IThreadSafeInSocket socket,
+            CancellationToken cancellationToken = default)
         {
             var msg = new Msg();
             msg.InitEmpty();
 
-            socket.Receive(ref msg);
-
-            var data = msg.CloneData();
-
-            msg.Close();
-            return data;
+            try
+            {
+                socket.Receive(ref msg, cancellationToken);
+                var data = msg.CloneData();
+                return data;
+            }
+            finally
+            {
+                msg.Close();
+            }
         }
 
         #endregion
@@ -60,14 +68,16 @@ public static bool TryReceiveBytes([NotNull] this IThreadSafeInSocket socket, ou
         /// <param name="socket">The socket to receive from.</param>
         /// <param name="timeout">The maximum period of time to wait for a message to become available.</param>
         /// <param name="bytes">The content of the received message, or <c>null</c> if no message was available.</param>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is <see cref="CancellationToken.None"/>.</param>
         /// <returns><c>true</c> if a message was available, otherwise <c>false</c>.</returns>
+        /// <remarks>The method would return false if cancellation has had requested.</remarks>
         public static bool TryReceiveBytes([NotNull] this IThreadSafeInSocket socket, TimeSpan timeout,
-            out byte[] bytes)
+            out byte[] bytes, CancellationToken cancellationToken = default)
         {
             var msg = new Msg();
             msg.InitEmpty();
 
-            if (!socket.TryReceive(ref msg, timeout))
+            if (!socket.TryReceive(ref msg, timeout, cancellationToken))
             {
                 msg.Close();
                 bytes = null;
@@ -88,15 +98,20 @@ public static bool TryReceiveBytes([NotNull] this IThreadSafeInSocket socket, Ti
         /// Receive a bytes from <paramref name="socket"/> asynchronously.
         /// </summary>
         /// <param name="socket">The socket to receive from.</param>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is <see cref="CancellationToken.None"/>.</param>
         /// <returns>The content of the received message.</returns>
-        public static ValueTask<byte[]> ReceiveBytesAsync([NotNull] this IThreadSafeInSocket socket)
+        /// <exception cref="System.OperationCanceledException">The token has had cancellation requested.</exception>
+        public static ValueTask<byte[]> ReceiveBytesAsync([NotNull] this IThreadSafeInSocket socket,
+            CancellationToken cancellationToken = default)
         {
             if (TryReceiveBytes(socket, out var bytes))
                 return new ValueTask<byte[]>(bytes);
 
             // TODO: this is a hack, eventually we need kind of IO ThreadPool for thread-safe socket to wait on asynchronously
             // and probably implement IValueTaskSource
-            return new ValueTask<byte[]>(Task.Factory.StartNew(socket.ReceiveBytes, TaskCreationOptions.LongRunning));
+            // TODO: should we avoid lambda here as it cause heap allocation for the environment?
+            return new ValueTask<byte[]>(Task.Factory.StartNew(() => socket.ReceiveBytes(cancellationToken),
+                cancellationToken, TaskCreationOptions.LongRunning, TaskScheduler.Default));
         }
 
         #endregion
@@ -111,27 +126,32 @@ public static ValueTask<byte[]> ReceiveBytesAsync([NotNull] this IThreadSafeInSo
         /// Receive a string from <paramref name="socket"/>, blocking until one arrives, and decode using <see cref="SendReceiveConstants.DefaultEncoding"/>.
         /// </summary>
         /// <param name="socket">The socket to receive from.</param>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is <see cref="CancellationToken.None"/>.</param>
         /// <returns>The content of the received message.</returns>
-        public static string ReceiveString([NotNull] this IThreadSafeInSocket socket)
+        /// <exception cref="System.OperationCanceledException">The token has had cancellation requested.</exception>
+        public static string ReceiveString([NotNull] this IThreadSafeInSocket socket,
+            CancellationToken cancellationToken = default)
         {
-            return socket.ReceiveString(SendReceiveConstants.DefaultEncoding);
+            return socket.ReceiveString(SendReceiveConstants.DefaultEncoding, cancellationToken);
         }
 
         /// <summary>
         /// Receive a string from <paramref name="socket"/>, blocking until one arrives, and decode using <paramref name="encoding"/>.
         /// </summary>
         /// <param name="socket">The socket to receive from.</param>
         /// <param name="encoding">The encoding used to convert the data to a string.</param>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is <see cref="CancellationToken.None"/>.</param>
         /// <returns>The content of the received message.</returns>
-        public static string ReceiveString([NotNull] this IThreadSafeInSocket socket, [NotNull] Encoding encoding)
+        /// <exception cref="System.OperationCanceledException">The token has had cancellation requested.</exception>
+        public static string ReceiveString([NotNull] this IThreadSafeInSocket socket, [NotNull] Encoding encoding,
+            CancellationToken cancellationToken = default)
         {
             var msg = new Msg();
             msg.InitEmpty();
 
-            socket.Receive(ref msg);
-
             try
             {
+                socket.Receive(ref msg, cancellationToken);
                 return msg.Size > 0
                     ? msg.GetString(encoding)
                     : string.Empty;
@@ -182,11 +202,14 @@ public static bool TryReceiveString([NotNull] this IThreadSafeInSocket socket, [
         /// </summary>
         /// <param name="socket">The socket to receive from.</param>
         /// <param name="timeout">The maximum period of time to wait for a message to become available.</param>
-        /// <param name="str">The content of the received message, or <c>null</c> if no message was available.</param>
+        /// <param name="str">The conent of the received message, or <c>null</c> if no message was available.</param>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is <see cref="CancellationToken.None"/>.</param>
         /// <returns><c>true</c> if a message was available, otherwise <c>false</c>.</returns>
-        public static bool TryReceiveString([NotNull] this IThreadSafeInSocket socket, TimeSpan timeout, out string str)
+        /// <remarks>The method would return false if cancellation has had requested.</remarks>
+        public static bool TryReceiveString([NotNull] this IThreadSafeInSocket socket, TimeSpan timeout, out string str,
+            CancellationToken cancellationToken = default)
         {
-            return socket.TryReceiveString(timeout, SendReceiveConstants.DefaultEncoding, out str);
+            return socket.TryReceiveString(timeout, SendReceiveConstants.DefaultEncoding, out str, cancellationToken);
         }
 
         /// <summary>
@@ -197,14 +220,16 @@ public static bool TryReceiveString([NotNull] this IThreadSafeInSocket socket, T
         /// <param name="timeout">The maximum period of time to wait for a message to become available.</param>
         /// <param name="encoding">The encoding used to convert the data to a string.</param>
         /// <param name="str">The content of the received message, or <c>null</c> if no message was available.</param>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is <see cref="CancellationToken.None"/>.</param>
         /// <returns><c>true</c> if a message was available, otherwise <c>false</c>.</returns>
+        /// <remarks>The method would return false if cancellation has had requested.</remarks>
         public static bool TryReceiveString([NotNull] this IThreadSafeInSocket socket, TimeSpan timeout,
-            [NotNull] Encoding encoding, out string str)
+            [NotNull] Encoding encoding, out string str, CancellationToken cancellationToken = default)
         {
             var msg = new Msg();
             msg.InitEmpty();
 
-            if (socket.TryReceive(ref msg, timeout))
+            if (socket.TryReceive(ref msg, timeout, cancellationToken))
             {
                 try
                 {
@@ -215,7 +240,7 @@ public static bool TryReceiveString([NotNull] this IThreadSafeInSocket socket, T
                 }
                 finally
                 {
-                    msg.Close();    
+                    msg.Close();
                 }
             }
 
@@ -232,15 +257,19 @@ public static bool TryReceiveString([NotNull] this IThreadSafeInSocket socket, T
         /// Receive a string from <paramref name="socket"/> asynchronously.
         /// </summary>
         /// <param name="socket">The socket to receive from.</param>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is <see cref="CancellationToken.None"/>.</param>
         /// <returns>The content of the received message.</returns>
-        public static ValueTask<string> ReceiveStringAsync([NotNull] this IThreadSafeInSocket socket)
+        /// <exception cref="System.OperationCanceledException">The token has had cancellation requested.</exception>
+        public static ValueTask<string> ReceiveStringAsync([NotNull] this IThreadSafeInSocket socket,
+            CancellationToken cancellationToken = default)
         {
             if (TryReceiveString(socket, out var msg))
                 return new ValueTask<string>(msg);
 
             // TODO: this is a hack, eventually we need kind of IO ThreadPool for thread-safe socket to wait on asynchronously
             // and probably implement IValueTaskSource
-            return new ValueTask<string>(Task.Factory.StartNew(socket.ReceiveString, TaskCreationOptions.LongRunning));
+            return new ValueTask<string>(Task.Factory.StartNew(() => socket.ReceiveString(cancellationToken),
+                cancellationToken, TaskCreationOptions.LongRunning, TaskScheduler.Default));
         }
 
         #endregion