Tag Archives: Work

Debugging Assembly loading

Does a referenced assembly get loaded if no types in the assembly are “not used”?The term used is is very subjective. For a developer it would mean that you probably never created an instance or called a method on it. But this does not cover the whole story. You can instead consider what are the reasons for an assembly load occurring. Suzanne’s blog on Assembly loading Failures would give you a good understanding of failures if that is what you are interested in. This post focuses on how to identify what exactly is causing an assembly to load.We in the WCF team are very cautious on introducing assembly dependencies and how how our code paths can cause assembly loads since this impacts the reference set of your process. Images that get loaded during a WCF call can become the cause of slow start up since every assembly is a potential disk look up and larger the number the higher the impact to startup.  As a guidance for quick app startup is that you can eliminate a lot of the unnecessary assemblies from being loaded to speed up application startup if you refactor types properly. Continue reading

How do I find all the ETW sessions on the machine?

logman is your tool for this. Here is how you can query for all the sessions and also how to see values from a particular session.

c:> logman -etsData Collector Set                      Type                          Status-------------------------------------------------------------------------------AITEventLog                             Trace                         RunningAudio                                   Trace                         RunningDiagLog                                 Trace                         RunningEventLog-Application                    Trace                         RunningEventLog-System                         Trace                         RunningNtfsLog                                 Trace                         RunningSQMLogger                               Trace                         RunningUBPM                                    Trace                         RunningWdiContextLog                           Trace                         RunningMpWppTracing                            Trace                         RunningFSysAgentTrace                          Trace                         RunningMSMQ                                    Trace                         RunningMSDTC_TRACE_SESSION                     Trace                         Runningtest_trace                              Trace                         RunningThe command completed successfully.c:> logman test_trace -etsName:                 test_traceStatus:               RunningRoot Path:            C:Segment:              OffSchedules:            OnSegment Max Size:     500 MBName:                 test_tracetest_traceType:                 TraceOutput Location:      C:9_19_44.etlAppend:               OffCircular:             OnOverwrite:            OffBuffer Size:          8Buffers Lost:         0Buffers Written:      1Buffer Flush Timer:   0Clock Type:           PerformanceFile Mode:            FileProvider:Name:                 Microsoft-Windows-Application Server-ApplicationsProvider Guid:        {C651F5F6-1C0D-492E-8AE1-B4EFD7C9D503}Level:                5KeywordsAll:          0x0KeywordsAny:          0xffffffffProperties:           0Filter Type:          0The command completed successfully.

Checkin #199390

Here is something for you performance guys. This was a hard one to crack but. Let me know what you think of this and how you would like to see this evolve. It will be a while before this is actually available.

Media_httpsajaycomwpw_kcneb

Thanks to Wenlong for driving this all the way and for being our custodian for WCF/WF performance.

Linq over Excel

I was writing a tool and needed to quickly query an excel sheet. I’m not diving into linq but you get general idea of how to query/sort over the datatable and once you have an enumerable object you can pretty easily run a linq query over it.

public static DataTable GetData(string filename){    string fullPath = Path.GetFullPath(filename);    String conn = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source={0};Extended Properties="Excel 12.0 Xml;HDR=YES"";    OleDbConnection cn = new OleDbConnection(string.Format(conn, fullPath));    OleDbCommand cmd = new OleDbCommand(@"SELECT * FROM [Sheet1$]", cn);    OleDbDataAdapter da = new OleDbDataAdapter(cmd);    cn.Open();    DataTable dt = new DataTable();    da.Fill(dt);    return dt;}static IEnumerable<T> GetData<T>(DataTable dt) where T : new(){    PropertyInfo[] properties = typeof(T).GetProperties();    foreach (DataRow item in dt.Rows)    {        T o = default(T);        foreach (var property in properties)        {            if (dt.Columns.Contains(property.Name))            {                if (o == null)                {                    o = new T();                }                property.SetValue(o, item[property.Name], null);            }        }        if (o == null)            continue;        yield return o;    }}

Here is an intersting project – http://code.google.com/p/linqtoexcel/

If you want to use an excel project you could do something like this.

How to synchronize multiple threads?

In certain load tests you want to make sure a bunch of threads reach a particular state before they proceed with the rest of the work. You cannot make sure that all threads execute a point simultaneously since the CPU scheduling would determine this. However you can move these threads to Ready. A ready-thread is a thread can be scheduled for execution on a particular core – http://msdn.microsoft.com/en-us/library/dd627187%28VS.85%29.aspx

WaitForMultipleObjects helps synchronize multiple user mode threads.

“The WaitForMultipleObjects function determines whether the wait criteria have been met. If the criteria have not been met, the calling thread enters the wait state until the conditions of the wait criteria have been met or the time-out interval elapses.”

Here is a small example of how to start multiple threads and then let them proceed after all of them have reached a particular point in execution.

using System;using System.Threading;using System.IO;namespace TestThreading{    class Program    {        const int ThreadCount = 10;        static ManualResetEvent[] events = new ManualResetEvent[ThreadCount];        static ThreadStart onStart = new ThreadStart(Start);        static int locked = -1;        static void Main(string[] args)        {            Thread[] threads = new Thread[ThreadCount];            for (int i = 0; i < ThreadCount; i++)            {                threads[i] = new Thread(onStart);                events[i] = new ManualResetEvent(false);            }            for (int i = 0; i < ThreadCount; i++)            {                threads[i].Start();            }            Console.ReadLine();        }        private static void Start()        {            int threadCount = Interlocked.Increment(ref locked);            Console.WriteLine("Thread {0} started & waiting", threadCount);            Thread.Sleep(3000); //Simulate some work befor setting.            events[threadCount].Set();            ManualResetEvent.WaitAll(events);            Console.WriteLine("Thread {0} proceeded", threadCount);        }    }}

How to collect stacks during context switches?

With xperf being more and more adopted and with rich stackwalking capabilities, its only natural to use it for finding out bottlenecks and cause for switch out.
Findout the ready thread information and what causes the threads to switch out and the associated stack that woke up when a thread switches back in is one way to determine what was the offending stack that causes other threads to switch out. This helps us identify potential hot locks or just really expensive locks or issues due to false data sharing.

You can run the following command to capture stack traces with ready thread information.

xperf –on base+cswitch+dispatcher –stackwalk cswitch+readythread

How to throttle callbacks or completions?

WCF enables throttling execution of operations but not their completions. This becomes and issue when a large number of outstanding operations complete almost simultaneously causing the callback on the client to be overwhelmed with completions.  Generally we don’t expect the client to issue of infinite number of pending operations but if you do end up with very high CPU usage and all suspect all your operations are stuck in the callback method which takes a lock then you need to throttle the callbacks yourself.You could try Setting the minThreads but this affects the whole app domain. The issue is due to the large number of callbacks that come in concurrently. The sample attached throttles the callbacks to have only one thread execute completions while there are 20 threads starting the operations and all completing almost simultaneously. The idea is to wrap the AsyncResult  of your operation and complete only the required number of results in parallel and this would throttle the service operation Ends automatically.Sample Source: AsyncEndThrottling

ServiceHosts & executing Operations from a crash/hang dump

Incase you are not sure of how to debug managed code with with a crash/hang dump, then you most likely need to read this first. Once you have SOS and mscordacwks(.net 3.5 and up)  loaded you first dump the heap to find out if you have any services hosts at all.

  1. We quickly find the method table entry for the ServiceHost type. We can get this from !dumpheap command as shown below. The following command helps to filter out just the types we are interested in.

    !dumpheap –stat –type System.Servicemodel.ServiceHost

    Media_httpsajaycomwpw_epnjz
  2. The next step is to dump all the ServiceHost using the method table entry shown above. The foreach command in the debugger helps us to loop through all objects that below to the type.

    .foreach(x {!dumpheap -short -mt 000007fef39ba7f0}) {!do x}
    Media_httpsajaycomwpw_flyio
  3. Our next step would be to find out how many calls are pending on the service. For this we can examine the ServiceThrottle on calls Field the service host. You can either use the instance value of the service throttle or offset. The following shows the call throttle and the count value in the flow throttle object would show how many services are being executed. The FlowThrottle is the object that holds the counters for the calls for the service.
    Media_httpsajaycomwpw_xcije

    In this case there is nothing executing so this dump was probably collected when there was no load. This is a quick way to identify if your service was actually executing any operations when collecting a process dump.