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Fix potential deadlock in WebSocket timeout checker #249

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Merged
josesimoes merged 2 commits into from
Sep 24, 2026
Merged

Fix potential deadlock in WebSocket timeout checker #249

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4e7f097
Fix potential deadlock in WebSocket timeout checker
josesimoes Sep 24, 2026
f7c1169
Several fixes with Close()
josesimoes Sep 24, 2026
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78 changes: 41 additions & 37 deletions WebSockets/ReceiveAndControllThread.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@
internal class ReceiveAndControllThread
{
private readonly WebSocket _webSocket;
private int _checkingTimeouts = 0;

public ReceiveAndControllThread(WebSocket webSocket)
{
Expand All @@ -21,8 +22,8 @@

public void WorkerThread() //this thread is always running and thus the best place for controlling ping and other messages
{
var timeoutCheckerTimer = new Timer(CheckTimeouts, Thread.CurrentThread, 5000, 5000);
var timeoutCheckerTimer = new Timer(CheckTimeouts, null, 5000, 5000);


while (!_webSocket.Stopped)
{
Expand Down Expand Up @@ -52,12 +53,12 @@
}
}

_webSocket.ReceiveStream.Close();
timeoutCheckerTimer.Change(Timeout.Infinite, Timeout.Infinite);
timeoutCheckerTimer.Dispose();
_webSocket.ReceiveStream.Close();
}

private void ProcessIncomingMessage()

Check failure on line 61 in WebSockets/ReceiveAndControllThread.cs

View check run for this annotation

SonarQubeCloud / SonarCloud Code Analysis

Refactor this method to reduce its Cognitive Complexity from 28 to the 15 allowed. 


See more on https://sonarcloud.io/project/issues?id=nanoframework_nanoframework.System.Net.WebSockets&issues=AaDTyIWNWGWVc_hLtQJG&open=AaDTyIWNWGWVc_hLtQJG&pullRequest=249
{
var messageFrame = _webSocket.WebSocketReceiver.StartReceivingMessage();

Expand All @@ -80,7 +81,7 @@
{
byte[] buffer = _webSocket.WebSocketReceiver.ReadBuffer(messageFrame.MessageLength, messageFrame.Masks);

_webSocket.LastContactTimeStamp = DateTime.UtcNow;
_webSocket.TouchLastContact();

switch (messageFrame.OpCode)
{
Expand All @@ -95,7 +96,7 @@
case OpCode.PongFrame:
// received a Pong
// checking if content Pong matches Ping is not implemented due to thread safety and memory consumption considerations
_webSocket.Pinging = false;
_webSocket.OnPongReceived();
break;

case OpCode.ConnectionCloseFrame:
Expand All @@ -112,17 +113,19 @@
}

//connection asked to be closed return answer
if (_webSocket.State != WebSocketFrame.WebSocketState.CloseSent)
if (_webSocket.TryMarkCloseReceived())
{
_webSocket.State = WebSocketFrame.WebSocketState.CloseReceived;

_webSocket.RawClose(WebSocketCloseStatus.NormalClosure, buffer, true);
}
//response to connection close we can shut down the socket.
else
{
_webSocket.HardClose();
// our close message can still be queued behind pending messages (simultaneous close)
_webSocket.WaitForCloseMessageSent();
}

// either this is the response to our close, or RawClose lost a race with another close,
// so we can shut down the socket (no-op if already closed)
_webSocket.HardClose();
break;
}
}
Expand All @@ -138,7 +141,7 @@
{
messageFrame.Buffer = _webSocket.WebSocketReceiver.ReadBuffer(messageFrame.MessageLength, messageFrame.Masks);

_webSocket.LastContactTimeStamp = DateTime.UtcNow;
_webSocket.TouchLastContact();

OnNewMessage(messageFrame);
}
Expand All @@ -147,37 +150,41 @@
}


private void CheckTimeouts(object thread)
// Runs on the timer thread, concurrently with the receive thread.
// Shared state is accessed through WebSocket helpers that only hold a lock for field access,
// and nothing here blocks, so a receive thread holding a lock can't stall this check.
private void CheckTimeouts(object state)
{
var receiveThread = (Thread)thread;

#pragma warning disable S3889 // OK to use in .NET nanoFramework context
receiveThread.Suspend();
#pragma warning restore S3889 // Neither "Thread.Resume" nor "Thread.Suspend" should be used
// skip this tick if the previous one is still running
if (Interlocked.CompareExchange(ref _checkingTimeouts, 1, 0) != 0)
{
return;
}

try
{
//Controlling ping and ControllerMessagesTimeout
if (_webSocket.Pinging
&& _webSocket.PingTime.Add(_webSocket.ServerTimeout) < DateTime.UtcNow)
if (_webSocket.Stopped)
{
_webSocket.RawClose(WebSocketCloseStatus.PolicyViolation, Encoding.UTF8.GetBytes("Ping timeout"), true);

Debug.WriteLine($"{_webSocket.RemoteEndPoint} ping timed out");
return;
}

if (_webSocket.State == WebSocketFrame.WebSocketState.CloseSent
&& _webSocket.ClosingTime.Add(_webSocket.ServerTimeout) < DateTime.UtcNow)
//Controlling ping and ControllerMessagesTimeout
switch (_webSocket.EvaluateTimeouts(DateTime.UtcNow))
{
_webSocket.HardClose();
}
case WebSocket.TimeoutAction.PingTimeout:
Debug.WriteLine($"{_webSocket.RemoteEndPoint} ping timed out");

if (_webSocket.KeepAliveInterval != Timeout.InfiniteTimeSpan
&& _webSocket.State != WebSocketFrame.WebSocketState.CloseSent
&& !_webSocket.Pinging
&& _webSocket.LastContactTimeStamp.Add(_webSocket.KeepAliveInterval) < DateTime.UtcNow)
{
_webSocket.SendPing();
// don't wait for the close message to be sent, a following check will close the connection
_webSocket.BeginClose(WebSocketCloseStatus.PolicyViolation, Encoding.UTF8.GetBytes("Ping timeout"));
break;

case WebSocket.TimeoutAction.HardClose:
_webSocket.HardClose();
break;

case WebSocket.TimeoutAction.SendPing:
_webSocket.SendPing();
break;
}
}
catch (Exception ex)
Expand All @@ -186,10 +193,7 @@
}
finally
{
// always resume the receive thread, otherwise it will be left suspended forever
#pragma warning disable S3889 // OK to use in .NET nanoFramework context
receiveThread.Resume();
#pragma warning restore S3889 // Neither "Thread.Resume" nor "Thread.Suspend" should be used
Interlocked.Exchange(ref _checkingTimeouts, 0);
}
}

Expand Down
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