Code after suspended function call not executed in Kotlin coroutine

Question

I'm using Kotlin coroutines to manage a TLS socket connection. In my minimal version of sendMessageToServerTest, I call connectTest() when the socket is not connected, then log the result. However, although connectTest() logs "connectTest: OK" and returns successfully, the log immediately following the call in sendMessageToServerTest never appears. Here’s the minimal code:

    Log.d(TAG, "sendMessageToServer: START")
    if (TcpSocketSSL.socketState.get() != TcpSocketSSL.SocketState.CONNECTED) {
        Log.d(TAG, "sendMessageToServer: connect")
        val res = TcpSocketSSL.connectTest()
        Log.d(TAG, "sendMessageToServer: connect 2 $res")
    }
    Log.d(TAG, "sendMessageToServer: XXX  $message")
}

and function connectTest

    suspend fun connectTest(): Result<Unit> = withContext(Dispatchers.IO) {
        Log.d(TAG, "connectTest: START")
        mutexConnect.withLock {
            if (socketState.get() == SocketState.DISCONNECTED) {
                try {
                    socketState.set(SocketState.CONNECTING)
                    _socketStateFlow.emit(SocketState.CONNECTING)
                    selectorManager.close()
                    selectorManager = SelectorManager(Dispatchers.IO)
                    val tcpSocket = withTimeout(SOCKET_TIMEOUT) {
                        aSocket(selectorManager).tcp().connect(hostname = DNS, port = PORT)
                    }
                    socket = tcpSocket.tls(coroutineContext)
                    receiveChannel = socket?.openReadChannel()
                    sendChannel = socket?.openWriteChannel(autoFlush = true)
                    socketState.set(SocketState.CONNECTED)
                    _socketStateFlow.emit(SocketState.CONNECTED)
                    Log.d(TAG, "connectTest: OK")
                    return@withLock Result.success(Unit)
                } catch (e: Exception) {
                    disconnect(who = "connect", cancelSocketJob = false)
                    return@withLock Result.failure(exception = e)
                }
            } else {
                return@withLock if (socketState.get() == SocketState.CONNECTED) {
                    Result.success(Unit)
                } else {
                    Result.failure(Exception("Unexpected Socket State. Socket state is ${socketState.get()}"))
                }
            }
        }
    }
}

Logcat
2025-03-03 08:57:14.660 18642-18682 TcpSocketManager D sendMessageToServer: START
2025-03-03 08:57:14.660 18642-18682 TcpSocketManager D sendMessageToServer: connect
2025-03-03 08:57:14.661 18642-18682 TcpSocketSSL D connectTest: START
2025-03-03 08:57:14.941 18642-18696 TcpSocketSSL D connectTest: OK
But log Log.d(TAG, "sendMessageToServer: connect 2 $res") never shows. Why? UPDATE: if I use TCP connection without TLS, it works okay

socket = withTimeout(SOCKET_TIMEOUT) {
   aSocket(selectorManager).tcp().connect(hostname = DNS, port = PORT)
}

It seems Ktor TLS handshake is problem in this case. Why?

Please edit your question to provide a minimal reproducible example that we can execute. — tyg
– tyg, Commented Mar 3 at 10:02

Brian Yencho · Accepted Answer · 2025-03-10 20:00:37Z

0

Try changing this:

_socketStateFlow.emit(SocketState.CONNECTED)

to this:

_socketStateFlow.tryEmit(SocketState.CONNECTED)

The emit function suspends while tryEmit does not and this can sometimes cause you to infinitely suspend if you are not careful.

answered Mar 10 at 20:00

Brian Yencho

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