Fix CancelAsync Cause Deadlock

Author: zeotuan

src/Renci.SshNet/SshCommand.cs

@@ -26,6 +26,7 @@ public class SshCommand : IDisposable
         private CommandAsyncResult _asyncResult;
         private AsyncCallback _callback;
         private EventWaitHandle _sessionErrorOccuredWaitHandle;
+        private EventWaitHandle _commandCancelledWaitHandle;
         private Exception _exception;
         private StringBuilder _result;
         private StringBuilder _error;
@@ -186,7 +187,7 @@ internal SshCommand(ISession session, string commandText, Encoding encoding)
             _encoding = encoding;
             CommandTimeout = Session.InfiniteTimeSpan;
             _sessionErrorOccuredWaitHandle = new AutoResetEvent(initialState: false);
-
+            _commandCancelledWaitHandle = new AutoResetEvent(initialState: false);
             _session.Disconnected += Session_Disconnected;
             _session.ErrorOccured += Session_ErrorOccured;
         }
@@ -356,13 +357,12 @@ public string EndExecute(IAsyncResult asyncResult)
         /// <summary>
         /// Cancels command execution in asynchronous scenarios.
         /// </summary>
-        public void CancelAsync()
+        /// <param name="forceKill">if true send SIGKILL instead of SIGTERM.</param>
+        public void CancelAsync(bool forceKill = false)
         {
-            if (_channel is not null && _channel.IsOpen && _asyncResult is not null)
-            {
-                // TODO: check with Oleg if we shouldn't dispose the channel and uninitialize it ?
-                _channel.Dispose();
-            }
+            var signal = forceKill ? "KILL" : "TERM";
+            _ = _channel?.SendExitSignalRequest(signal, coreDumped: false, "Command execution has been cancelled.", "en");
+            _ = _commandCancelledWaitHandle.Set();
         }
 
         /// <summary>
@@ -506,6 +506,7 @@ private void WaitOnHandle(WaitHandle waitHandle)
             var waitHandles = new[]
                 {
                     _sessionErrorOccuredWaitHandle,
+                    _commandCancelledWaitHandle,
                     waitHandle
                 };
 
@@ -515,7 +516,8 @@ private void WaitOnHandle(WaitHandle waitHandle)
                 case 0:
                     ExceptionDispatchInfo.Capture(_exception).Throw();
                     break;
-                case 1:
+                case 1: // Command cancelled
+                case 2:
                     // Specified waithandle was signaled
                     break;
                 case WaitHandle.WaitTimeout:
@@ -620,6 +622,9 @@ protected virtual void Dispose(bool disposing)
                     _sessionErrorOccuredWaitHandle = null;
                 }
 
+                _commandCancelledWaitHandle?.Dispose();
+                _commandCancelledWaitHandle = null;
+
                 _isDisposed = true;
             }
         }

test/Renci.SshNet.IntegrationTests/OldIntegrationTests/SshCommandTest.cs

@@ -51,6 +51,30 @@ public void Test_Execute_SingleCommand()
             }
         }
 
+        [TestMethod]
+        [Timeout(5000)]
+        public void Test_CancelAsync_Running_Command()
+        {
+            using var client = new SshClient(SshServerHostName, SshServerPort, User.UserName, User.Password);
+            #region Example SshCommand CancelAsync
+            client.Connect();
+            var testValue = Guid.NewGuid().ToString();
+            var command = $"sleep 10s; echo {testValue}";
+            using var cmd = client.CreateCommand(command);
+            try
+            {
+                var asyncResult = cmd.BeginExecute();
+                cmd.CancelAsync();
+                cmd.EndExecute(asyncResult);
+            }
+            catch (OperationCanceledException)
+            {
+            }
+            client.Disconnect();
+            Assert.AreNotEqual(cmd.Result.Trim(), testValue);
+            #endregion
+        }
+
         [TestMethod]
         public void Test_Execute_OutputStream()
         {
@@ -222,7 +246,7 @@ public void Test_Execute_Command_ExitStatus()
                 client.Connect();
 
                 var cmd = client.RunCommand("exit 128");
-                
+
                 Console.WriteLine(cmd.ExitStatus);
 
                 client.Disconnect();
@@ -443,7 +467,7 @@ public void Test_Execute_Invalid_Command()
         }
 
         [TestMethod]
-        
+
         public void Test_MultipleThread_100_MultipleConnections()
         {
             try