LockConnection Method (IEasyUAClientConnectionControl)

Locks a connection to the specified endpoint descriptor.

When the connection is locked, the component will attempt to open it and keep open, and will not automatically disconnect from the server after the connection is unused for certain time.

Syntax

int LockConnection( 
   UAEndpointDescriptor endpointDescriptor
)

int LockConnection( 
   UAEndpointDescriptor^ endpointDescriptor
)

'Declaration
 
Function LockConnection( _
   ByVal endpointDescriptor As UAEndpointDescriptor _
) As Integer

'Usage
 
Dim instance As IEasyUAClientConnectionControl
Dim endpointDescriptor As UAEndpointDescriptor
Dim value As Integer
 
value = instance.LockConnection(endpointDescriptor)

Parameters

endpointDescriptor

The OPC UA endpoint descriptor of the connection ot be locked.

Because the OpcLabs.EasyOpc.UA.UAEndpointDescriptor has implicit conversions from System.String and System.Uri, in languages that support implicit conversion operators (such as C# or VB.NET), you can simply use a string (representing the endpoint URL, or a so-called OPC UA endpoint descriptor string), or a System.Uri object, in place of this parameter, and the corresponding endpoint descriptor will be constructed automatically. When the implicit conversion operators are not supported (such as with Python.NET), you can use the OpcLabs.EasyOpc.UA.UAEndpointDescriptor.FromString or OpcLabs.EasyOpc.UA.UAEndpointDescriptor.FromUri static method instead.

If you are using OPC Wizard (for server development), an implicit conversion from OpcLabs.EasyOpc.UA.EasyUAServerCore can be used in the same way to simply pass the server object in place of this parameter, which will use its OpcLabs.EasyOpc.UA.EasyUAServerCore.EffectiveServerDescriptor property for the connection.

The value of this parameter cannot be null (Nothing in Visual Basic).

Return Value

Returns a lock handle that can be used to unlock the connection later.

Exceptions

Exception Description

Exception	Description
System.ArgumentNullException	A `null` reference (`Nothing` in Visual Basic) is passed to a method that does not accept it as a valid argument. This is a usage error, i.e. it will never occur (the exception will not be thrown) in a correctly written program. Your code should not catch this exception.

System.ArgumentNullException

A null reference (Nothing in Visual Basic) is passed to a method that does not accept it as a valid argument.

This is a usage error, i.e. it will never occur (the exception will not be thrown) in a correctly written program. Your code should not catch this exception.

Example

// This example shows how to lock and unlock connections to an OPC UA server. The component attempts to keep the locked
// connections open, until unlocked.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
// OPC client and subscriber examples in C# on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-CSharp .
// Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
// a commercial license in order to use Online Forums, and we reply to every post.

using System;
using Microsoft.Extensions.DependencyInjection;
using OpcLabs.EasyOpc.UA;
using OpcLabs.EasyOpc.UA.OperationModel;
using OpcLabs.EasyOpc.UA.Services;

namespace UADocExamples._EasyUAClientConnectionControl
{
    class LockAndUnlockConnection
    {
        public static void Main1()
        {
            UAEndpointDescriptor endpointDescriptor =
                "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer";
            // or "http://opcua.demo-this.com:51211/UA/SampleServer" (currently not supported)
            // or "https://opcua.demo-this.com:51212/UA/SampleServer/"

            // Instantiate the client object and hook events
            using (var client = new EasyUAClient())
            {
                // Obtain the client connection monitoring service.
                IEasyUAClientConnectionMonitoring clientConnectionMonitoring = client.GetService<IEasyUAClientConnectionMonitoring>();
                if (clientConnectionMonitoring is null)
                {
                    Console.WriteLine("The client connection monitoring service is not available.");
                    return;
                }

                // Obtain the client connection control service.
                IEasyUAClientConnectionControl clientConnectionControl = client.GetService<IEasyUAClientConnectionControl>();
                if (clientConnectionControl is null)
                {
                    Console.WriteLine("The client connection control service is not available.");
                    return;
                }

                // Display the server condition changed events.
                clientConnectionMonitoring.ServerConditionChanged += (sender, args) => Console.WriteLine(args);

                int lockHandle = 0;
                bool locked = false;
                try
                {
                    Console.WriteLine("Reading (1)");
                    // The first read will cause a connection to the server.
                    UAAttributeData attributeData1 =
                        client.Read(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10853");
                    Console.WriteLine(attributeData1);

                    Console.WriteLine("Waiting for 10 seconds...");
                    // Since the connection is now not used for some time, and it is not locked, it will be closed.
                    System.Threading.Thread.Sleep(10 * 1000);

                    Console.WriteLine("Locking");
                    // Locking the connection causes it to open, if possible.
                    lockHandle = clientConnectionControl.LockConnection(endpointDescriptor);
                    locked = true;

                    Console.WriteLine("Waiting for 10 seconds...");
                    // The connection is locked, it will not be closed now.
                    System.Threading.Thread.Sleep(10 * 1000);

                    Console.WriteLine("Reading (2)");
                    UAAttributeData attributeData2 =
                        client.Read(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10853");
                    Console.WriteLine(attributeData2);

                    Console.WriteLine("Waiting for 10 seconds...");
                    // The connection is still locked, it will not be closed now.
                    System.Threading.Thread.Sleep(10 * 1000);
                }
                catch (UAException uaException)
                {
                    Console.WriteLine("*** Failure: {0}", uaException.GetBaseException().Message);
                }
                finally
                {
                    if (locked)
                    {
                        Console.WriteLine("Unlocking");
                        clientConnectionControl.UnlockConnection(lockHandle);
                    }
                }

                Console.WriteLine("Waiting for 10 seconds...");
                // After some delay, the connection will be closed, because there are no subscriptions to the server and no
                // connection locks.
                System.Threading.Thread.Sleep(10 * 1000);

                Console.WriteLine("Finished.");
            }
        }


        // Example output:
        //
        //Reading (1)
        //"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Connecting; Success; Attempt #1
        //"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Connected; Success
        //-1.034588E+18 {Single} @2021-11-15T15:26:39.169 @@2021-11-15T15:26:39.169; Good
        //Waiting for 10 seconds...
        //"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Disconnecting; Success
        //"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Disconnected(RetrialDelay=Infinite); Success
        //Locking
        //"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Connecting; Success; Attempt #1
        //"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Connected; Success
        //Waiting for 10 seconds...
        //Reading (2)
        //2.288872E+21 {Single} @2021-11-15T15:26:59.836 @@2021-11-15T15:26:59.836; Good
        //Waiting for 10 seconds...
        //Unlocking
        //Waiting for 10 seconds...
        //"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Disconnecting; Success
        //"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Disconnected(RetrialDelay=Infinite); Success
        //Finished.
    }
}

' This example shows how to lock and unlock connections to an OPC UA server. The component attempts to keep the locked
' connections open, until unlocked.
'
' Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
' OPC client and subscriber examples in VB.NET on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-VBNET .
' Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
' a commercial license in order to use Online Forums, and we reply to every post.

Imports Microsoft.Extensions.DependencyInjection
Imports OpcLabs.EasyOpc.UA
Imports OpcLabs.EasyOpc.UA.OperationModel
Imports OpcLabs.EasyOpc.UA.Services

Namespace _EasyUAClientConnectionControl
    Partial Friend Class LockAndUnlockConnection
        Public Shared Sub Main1()
            Dim endpointDescriptor As UAEndpointDescriptor =
                    "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"
            ' or "http://opcua.demo-this.com:51211/UA/SampleServer" (currently not supported)
            ' or "https://opcua.demo-this.com:51212/UA/SampleServer/"

            ' Instantiate the client object and hook events
            Using client = New EasyUAClient()
                ' Obtain the client connection monitoring service.
                Dim clientConnectionMonitoring As IEasyUAClientConnectionMonitoring = client.GetService(Of IEasyUAClientConnectionMonitoring)
                If clientConnectionMonitoring Is Nothing Then
                    Console.WriteLine("The client connection monitoring service is not available.")
                    Exit Sub
                End If

                ' Obtain the client connection control service.
                Dim clientConnectionControl As IEasyUAClientConnectionControl = client.GetService(Of IEasyUAClientConnectionControl)
                If clientConnectionControl Is Nothing Then
                    Console.WriteLine("The client connection control service is not available.")
                    Exit Sub
                End If

                ' Display the server condition changed events.
                AddHandler clientConnectionMonitoring.ServerConditionChanged, Sub(sender, args)
                                                                                  Console.WriteLine(args)
                                                                              End Sub

                Dim lockHandle As Integer = 0
                Dim locked As Boolean = False
                Try
                    Console.WriteLine("Reading (1)")
                    ' The first read will cause a connection to the server.
                    Dim attributeData1 As UAAttributeData =
                        client.Read(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10853")
                    Console.WriteLine(attributeData1)

                    Console.WriteLine("Waiting for 10 seconds...")
                    ' Since the connection is now not used for some time, and it is not locked, it will be closed.
                    System.Threading.Thread.Sleep(10 * 1000)

                    Console.WriteLine("Locking")
                    ' Locking the connection causes it to open, if possible.
                    lockHandle = clientConnectionControl.LockConnection(endpointDescriptor)
                    locked = True

                    Console.WriteLine("Waiting for 10 seconds...")
                    ' The connection is locked, it will not be closed now.
                    System.Threading.Thread.Sleep(10 * 1000)

                    Console.WriteLine("Reading (2)")
                    Dim attributeData2 As UAAttributeData =
                        client.Read(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10853")
                    Console.WriteLine(attributeData2)

                    Console.WriteLine("Waiting for 10 seconds...")
                    ' The connection is still locked, it will not be closed now.
                    System.Threading.Thread.Sleep(10 * 1000)
                Catch uaException As UAException
                    Console.WriteLine("*** Failure: {0}", uaException.GetBaseException().Message)
                Finally
                    If locked Then
                        Console.WriteLine("Unlocking")
                        clientConnectionControl.UnlockConnection(lockHandle)
                    End If
                End Try

                Console.WriteLine("Waiting for 10 seconds...")
                ' After some delay, the connection will be closed, because there are no subscriptions to the server and no
                ' connection locks.
                System.Threading.Thread.Sleep(10 * 1000)

                Console.WriteLine("Finished.")
            End Using
        End Sub

        ' Example output
        '
        'Reading (1)
        '"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Connecting; Success; Attempt #1
        '"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Connected; Success
        '-1.034588E+18 {Single} @2021-11-15T15:26:39.169 @@2021-11-15T15:26:39.169; Good
        'Waiting for 10 seconds...
        '"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Disconnecting; Success
        '"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Disconnected(RetrialDelay=Infinite); Success
        'Locking
        '"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Connecting; Success; Attempt #1
        '"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Connected; Success
        'Waiting for 10 seconds...
        'Reading (2)
        '2.288872E+21 {Single} @2021-11-15T15:26:59.836 @@2021-11-15T15:26:59.836; Good
        'Waiting for 10 seconds...
        'Unlocking
        'Waiting for 10 seconds...
        '"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Disconnecting; Success
        '"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Disconnected(RetrialDelay=Infinite); Success
        'Finished.
    End Class
End Namespace

Rem This example shows how to lock and unlock connections to an OPC UA server. The component attempts to keep the locked
Rem connections open, until unlocked.
Rem
Rem Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
Rem OPC client and subscriber examples in VBScript on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-VBScript .
Rem Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
Rem a commercial license in order to use Online Forums, and we reply to every post.

Option Explicit

Dim endpointDescriptorUrlString: endpointDescriptorUrlString = "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"
Dim EndpointDescriptor: Set EndpointDescriptor = CreateObject("OpcLabs.EasyOpc.UA.UAEndpointDescriptor")
EndpointDescriptor.UrlString = endpointDescriptorUrlString

' Instantiate the client object.
Dim Client: Set Client = CreateObject("OpcLabs.EasyOpc.UA.EasyUAClient")

' Obtain the client connection monitoring service.
Dim ClientConnectionMonitoring: Set ClientConnectionMonitoring = Client.GetServiceByName("OpcLabs.EasyOpc.UA.Services.IEasyUAClientConnectionMonitoring, OpcLabs.EasyOpcUA")
If ClientConnectionMonitoring Is Nothing Then
    WScript.Echo "The client connection monitoring service is not available."
    WScript.Quit
End If

' Obtain the client connection control service.
Dim ClientConnectionControl: Set ClientConnectionControl = Client.GetServiceByName("OpcLabs.EasyOpc.UA.Services.IEasyUAClientConnectionControl, OpcLabs.EasyOpcUA")
If ClientConnectionControl Is Nothing Then
    WScript.Echo "The client connection control service is not available."
    WScript.Quit
End If

' Display the server condition changed events.
WScript.ConnectObject ClientConnectionMonitoring, "ClientConnectionMonitoring_"

WScript.Echo "Reading (1)"
' The first read will cause a connection to the server.
Dim AttributeData1: Set AttributeData1 = Client.Read(endpointDescriptorUrlString, "nsu=http://test.org/UA/Data/ ;i=10853")
WScript.Echo AttributeData1

WScript.Echo "Waiting for 10 seconds..."
' Since the connection is now not used for some time, and it is not locked, it will be closed.
WScript.Sleep 10*1000

WScript.Echo "Locking..."
' Locking the connection causes it to open, if possible.
Dim lockHandle: lockHandle = ClientConnectionControl.LockConnection(EndpointDescriptor)

WScript.Echo "Waiting for 10 seconds..."
' The connection is locked, it will not be closed now.
WScript.Sleep 10*1000

WScript.Echo "Reading (2)"
' The second read, because it closely follows the first one, will reuse the connection that is already open.
Dim AttributeData2: Set AttributeData2 = Client.Read(endpointDescriptorUrlString, "nsu=http://test.org/UA/Data/ ;i=10853")
WScript.Echo AttributeData2

WScript.Echo "Waiting for 10 seconds..."
' The connection is still locked, it will not be closed now.
WScript.Sleep 10*1000

WScript.Echo "Unlocking..."
ClientConnectionControl.UnlockConnection(lockHandle)

WScript.Echo "Waiting for 10 seconds..."
' After some delay, the connection will be closed, because there are no subscriptions to the server and no
' connection locks.
WScript.Sleep 10*1000

WScript.Echo "Finished."



Sub ClientConnectionMonitoring_ServerConditionChanged(Sender, e)
    WScript.Echo e
End Sub


' Example output:
'
'Reading (1)
'"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Connecting; Success; Attempt #1
'"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Connected; Success
'-1.034588E+18 {Single} @2021-11-15T15:26:39.169 @@2021-11-15T15:26:39.169; Good
'Waiting for 10 seconds...
'"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Disconnecting; Success
'"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Disconnected(RetrialDelay=Infinite); Success
'Locking
'"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Connecting; Success; Attempt #1
'"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Connected; Success
'Waiting for 10 seconds...
'Reading (2)
'2.288872E+21 {Single} @2021-11-15T15:26:59.836 @@2021-11-15T15:26:59.836; Good
'Waiting for 10 seconds...
'Unlocking
'Waiting for 10 seconds...
'"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Disconnecting; Success
'"opc.tcp://opcua.demo-this.com:51210/UA/SampleServer" Disconnected(RetrialDelay=Infinite); Success
'Finished.

# This example shows how to lock and unlock connections to an OPC UA server. The component attempts to keep the locked
# connections open, until unlocked.
#
# Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
# OPC client and subscriber examples in Python on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-Python .
# Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
# a commercial license in order to use Online Forums, and we reply to every post.
# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import time
import opclabs_quickopc

# Import .NET namespaces.
from Microsoft.Extensions.DependencyInjection import *
from OpcLabs.EasyOpc.UA import *
from OpcLabs.EasyOpc.UA.OperationModel import *
from OpcLabs.EasyOpc.UA.Services import *


endpointDescriptor = UAEndpointDescriptor('opc.tcp://opcua.demo-this.com:51210/UA/SampleServer')
# or 'http://opcua.demo-this.com:51211/UA/SampleServer' (currently not supported)
# or 'https://opcua.demo-this.com:51212/UA/SampleServer/'

# Instantiate the client object and hook events.
client = None
try:
    client = EasyUAClient()

    # Obtain the client connection monitoring service.
    clientConnectionMonitoring = ServiceProviderServiceExtensions.GetService[IEasyUAClientConnectionMonitoring](client)
    if clientConnectionMonitoring is None:
        print('The client connection monitoring service is not available.')
        exit()

    # Obtain the client connection control service.
    clientConnectionControl = ServiceProviderServiceExtensions.GetService[IEasyUAClientConnectionControl](client)
    if clientConnectionControl is None:
        print('The client connection control service is not available.')
        exit()

    # Display the server condition changed events.
    clientConnectionMonitoring.ServerConditionChanged += lambda sender, args: print(args)

    lockHandle = 0
    locked = False
    try:
        print('Reading (1)')
        # The first read will cause a connection to the server.
        attributeData1 = IEasyUAClientExtension.Read(client,
                                                     endpointDescriptor,
                                                     UANodeDescriptor('nsu=http://test.org/UA/Data/ ;i=10853'))
        print(attributeData1)

        print('Waiting for 10 seconds...')
        # Since the connection is now not used for some time, and it is not locked, it will be closed.
        time.sleep(10)

        print('Locking')
        # Locking the connection causes it to open, if possible.
        lockHandle = clientConnectionControl.LockConnection(endpointDescriptor)
        locked = True

        print('Waiting for 10 seconds...')
        # The connection is locked, it will not be closed now.
        time.sleep(10)

        print('Reading (2)')
        attributeData2 = IEasyUAClientExtension.Read(client,
                                                     endpointDescriptor,
                                                     UANodeDescriptor('nsu=http://test.org/UA/Data/ ;i=10853'))
        print(attributeData2)

        print('Waiting for 10 seconds...')
        # The connection is still locked, it will not be closed now.
        time.sleep(10)

    except UAException as uaException:
        print('*** Failure: ' + uaException.GetBaseException().Message)

    finally:
        if locked:
            print('Unlocking')
            clientConnectionControl.UnlockConnection(lockHandle)

    print('Waiting for 10 seconds...')
    # After some delay, the connection will be closed, because there are no subscriptions to the server and no
    # connection locks.
    time.sleep(10)

    print('Finished.')

finally:
    client and client.Dispose()

Requirements

Target Platforms: .NET Framework: Windows 10 (selected versions), Windows 11 (selected versions), Windows Server 2016, Windows Server 2022; .NET: Linux, macOS, Microsoft Windows

Reference

IEasyUAClientConnectionControl Interface
IEasyUAClientConnectionControl Members

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