PerformanceCounterCategory.InstanceExists Method (String)

Determines whether the specified performance object instance exists in the category that is identified by this PerformanceCounterCategory object's CategoryName property.

Namespace:  System.Diagnostics
Assembly:  System (in System.dll)

public bool InstanceExists(
	string instanceName
)

Parameters

instanceName
Type: System.String
The performance object instance in this performance counter category to search for.

Return Value

Type: System.Boolean
true if the category contains the specified performance object instance; otherwise, false.

ExceptionCondition
InvalidOperationException

The CategoryName property is null. The property might not have been set.

ArgumentNullException

The instanceName parameter is null.

Win32Exception

A call to an underlying system API failed.

UnauthorizedAccessException

Code that is executing without administrative privileges attempted to read a performance counter.

This overload of InstanceExists is not static. It requires you to create a PerformanceCounterCategory object and to set the CategoryName property.

NoteNote

To read performance counters in Windows Vista and later, Windows XP Professional x64 Edition, or Windows Server 2003, you must either be a member of the Performance Monitor Users group or have administrative privileges.

To avoid having to elevate your privileges to access performance counters in Windows Vista and later, add yourself to the Performance Monitor Users group.

In Windows Vista and later, User Account Control (UAC) determines the privileges of a user. If you are a member of the Built-in Administrators group, you are assigned two run-time access tokens: a standard user access token and an administrator access token. By default, you are in the standard user role. To execute the code that accesses performance counters, you must first elevate your privileges from standard user to administrator. You can do this when you start an application by right-clicking the application icon and indicating that you want to run as an administrator.

The following code example determines whether a PerformanceCounter instance exists within a PerformanceCounterCategory. It first creates a PerformanceCounterCategory object, using the appropriate constructor based on whether a computer name was specified. It then uses InstanceExists(String) to determine whether the specified instance exists, then informs the user. If no instance name is specified, the example uses the default single-instance name.


public static void Main(string[] args)
{
    string categoryName = "";
    string instanceName = "";
    string machineName = "";
    bool objectExists = false;
    PerformanceCounterCategory pcc;
    const string SINGLE_INSTANCE_NAME = "systemdiagnosticsperfcounterlibsingleinstance";

    // Copy the supplied arguments into the local variables.
    try
    {
        categoryName = args[0];
        instanceName = args[1];
        machineName = (args[2]=="."? "": args[2]);
    }
    catch(Exception ex)
    {
        // Ignore the exception from non-supplied arguments.
    }

    // Use the given instance name or use the default single-instance name.
    if (instanceName.Length==0)
    {
        instanceName = SINGLE_INSTANCE_NAME;
    }

    try
    {
        if (machineName.Length==0)
        {
            pcc = new PerformanceCounterCategory(categoryName);
        }
        else
        {
            pcc = new PerformanceCounterCategory(categoryName, machineName);
        }

        // Check whether the instance exists.
        // Use the per-instance overload of InstanceExists.
        objectExists = pcc.InstanceExists(instanceName);

    }
    catch(Exception ex)
    {
        Console.WriteLine("Unable to check for the existence of " +
            "instance \"{0}\" in category \"{1}\" on " + 
            (machineName.Length>0? "computer \"{2}\":": "this computer:") + 
            "\n" + ex.Message, instanceName, categoryName, machineName);
        return;
    }

    // Tell the user whether the instance exists.
    Console.WriteLine("Instance \"{0}\" " + (objectExists? "exists": "does not exist") + 
        " in category \"{1}\" on " + (machineName.Length>0? "computer \"{2}\".": "this computer."), 
        instanceName, pcc.CategoryName, pcc.MachineName);
}


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
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