WMI call takes too much time when system Starts/Re

问题:

I want to get the path of the Windows Service,

var managementObjectSearcher = new ManagementObjectSearcher("Select * from Win32_Service where serviceName = MyService");

this code is written of the constructor of some other service...

everything works fine when system is UP and running but if i restart the system put the StopWatch class for this call and it shows that it shows that the service takes 35-45 seconds to start because of this call..

Any suggestions to improve the performance on system restart...

回答1:

The Windows32_Services class doesn't exist, so assuming which you are using the Win32_Service WMI class you can improve the performance only returning the properties which you want to use, in this case the PathName, so change your WQL sentence to

SELECT PathName FROM Win32_Service Where Name='MyService'

UPDATE

The observation made for @Bacon is quite correct, since you know the name of thes service to retrieve, you can build the object path of the Win32_Service which look like

Win32_Service.Name="ServiceName"

And then using the ManagementObject class you can retrieve the instance to the service in a fastest way.

回答2:

Since you're retrieving the service by Name, which a key property of the Win32_Service class, try retrieving the instance directly instead of searching for it:

string GetMyServicePath()
{
    string path = "Win32_Service.Name=\"MyService\"";

    using (ManagementObject service = new ManagementObject(path))
        return (string) service.GetPropertyValue("PathName");
}

Here's a quick benchmark I threw together to compare direct retrieval vs. searching:

private const int LoopIterations = 1000;

private const string ServiceClass = "Win32_Service";
private const string ServiceName = "MyService";
private const string ServiceProperty = "PathName";

private static readonly string ServicePath = string.Format("{0}.Name=\"{1}\"", ServiceClass, ServiceName);
private static readonly string ServiceQuery = string.Format(
    "SELECT {0} FROM {1} Where Name=\"{2}\"",
    ServiceProperty, ServiceClass, ServiceName
);
private static ManagementObjectSearcher ServiceSearcher = new ManagementObjectSearcher(ServiceQuery);

static void Main(string[] args)
{
    var watch = new Stopwatch();

    watch.Start();
    for (int i = 0; i < LoopIterations; i++)
    {
        var servicePath = GetServicePathByKey();
    }
    watch.Stop();
    Console.WriteLine(
        "{0:N0} iterations of GetServicePathByKey() took {1:N0} milliseconds",
        LoopIterations, watch.ElapsedMilliseconds
    );

    watch.Restart();
    for (int i = 0; i < LoopIterations; i++)
    {
        var servicePath = GetServicePathFromExistingSearcher();
    }
    watch.Stop();
    Console.WriteLine(
        "{0:N0} iterations of GetServicePathFromExistingSearcher() took {1:N0} milliseconds",
        LoopIterations, watch.ElapsedMilliseconds
    );

    watch.Restart();
    for (int i = 0; i < LoopIterations; i++)
    {
        var servicePath = GetServicePathFromNewSearcher();
    }
    watch.Stop();
    Console.WriteLine(
        "{0:N0} iterations of GetServicePathFromNewSearcher() took {1:N0} milliseconds",
        LoopIterations, watch.ElapsedMilliseconds
    );
}

static string GetServicePathByKey()
{
    using (var service = new ManagementObject(ServicePath))
        return (string) service.GetPropertyValue(ServiceProperty);
}

static string GetServicePathFromExistingSearcher()
{
    using (var results = ServiceSearcher.Get())
    using (var enumerator = results.GetEnumerator())
    {
        if (!enumerator.MoveNext())
            throw new Exception();

        return (string) enumerator.Current.GetPropertyValue(ServiceProperty);
    }
}

static string GetServicePathFromNewSearcher()
{
    using (var searcher = new ManagementObjectSearcher(ServiceQuery))
    using (var results = searcher.Get())
    using (var enumerator = results.GetEnumerator())
    {
        if (!enumerator.MoveNext())
            throw new Exception();

        return (string) enumerator.Current.GetPropertyValue(ServiceProperty);
    }
}

Enumerating the searcher results directly is about as fast as I could make it, marginally faster than using a foreach block and twice as fast as using LINQ. On my 64-bit Windows 7 Professional system with the ServiceName constant set to Power I got these results:

1,000 iterations of GetServicePathByKey() took 8,263 milliseconds
1,000 iterations of GetServicePathFromExistingSearcher() took 64,265 milliseconds
1,000 iterations of GetServicePathFromNewSearcher() took 64,875 milliseconds

回答3:

If it is the "latency" of WMI that is bothering you, you don't have to use WMI to get a service's path, ie. executable name. You can also P/invoke QueryServiceConfig.

http://www.pinvoke.net/default.aspx/advapi32/queryserviceconfig.html