PerformanceCounterCategory.InstanceExists Method (String, String)

Determines whether a specified category on the local computer contains the specified performance object instance.

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

public static bool InstanceExists(
	string instanceName,
	string categoryName
)

Parameters

instanceName
Type: System.String

The performance object instance to search for.

categoryName
Type: System.String

The performance counter category to search.

Return Value

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

ExceptionCondition
ArgumentNullException

The instanceName parameter is null.

-or-

The categoryName parameter is null.

ArgumentException

The categoryName parameter is an empty string ("").

Win32Exception

A call to an underlying system API failed.

UnauthorizedAccessException

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

It is not possible to determine whether a performance object instance exists on a computer without specifying a specific category to look in.

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 uses the static overloads of InstanceExists to determine whether the given PerformanceCounter instance exists in the PerformanceCounterCategory. The overload is selected based on whether a computer name is specified. 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;
    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
    {
        // Check whether the specified instance exists. 
        // Use the static forms of the InstanceExists method. 
        if (machineName.Length==0)
        {
            objectExists = PerformanceCounterCategory.InstanceExists(instanceName, categoryName);
        }
        else
        {
            objectExists = PerformanceCounterCategory.InstanceExists(instanceName, categoryName, machineName);
        }

    }
    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, categoryName, machineName);
}

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

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