Ye Olde Mirror Effect!

I use a Mac normally. I have to go back to Windows from time to time. After Mac OS X Lion reverse-scrolling, switching between Mac and Windows became a pain. I started to use AutoHotKey on my Windows machines to simulate the reverse-scrolling from Lion. All was well. Until I remoted from one of my Windows machines into another Windows machine which also had AutoHotKey installed with reverse-scroll script enabled. Guess what, it went back to the original scroll direction. I couldn't figure out for a while what was happening, until I suddenly realized what had happened. I couldn't stop laughing at myself for a long time :)

(Of course the solution was to suspend AHK on the target machine when I was remoted in)

Windbg + SOS Cheat Sheet

This is a useful link for people who use windbg/cdb for debugging Managed code.

Cheat Sheet

Visual Studio debugging might not always be helpful or it might not always be available.
Sometimes when you want to take a quick look at what's wrong, saying c:\debuggers\cdb -pn helps a lot.

Reporting issues with Windows Azure

For those of you out there who have tried Windows Azure and face problems, here is how you are supposed to report issues at the Windows Azure forum:

http://social.msdn.microsoft.com/Forums/en-US/windowsazure/threads/

Steps you need to follow:

1. Sign into Windows Azure portal.
2. Go to your Hosted Service Project which is causing issues.
3. Wait for the project info to load.
4. Copy the private deployment id.
5. Write a brief description of what you did, what you are seeing and add your private deployment id.

Here is a screen shot of my service showing the private deployment id.

ThreadStaticAttribute

Reminder to self:

ThreadStaticAttribute only works with static fields!

Here is why:

public class TestingTLS
{
    [ThreadStatic]
    public static int value = 0;
    [ThreadStatic]
    public int value2 = 0;   
}

public class MyClass
{
    public static void TLSTest()
    {
        TestingTLS tls = new TestingTLS();
        Dictionary<int, Thread> threads = new Dictionary<int, Thread>();
        Semaphore sem = new Semaphore(100, 100);
        long count = 0;
        for ( int i = 0 ; i < 100 ; i ++ )
        {
            Thread t = new Thread(state => {
                int tid = Thread.CurrentThread.ManagedThreadId;
                TestingTLS.value = tid; 
                Thread.Sleep(0);
                if ( tid != TestingTLS.value )
                {
                    Console.Error.WriteLine( "Value 1: {0} read {1}", tid, TestingTLS.value );
                    Interlocked.Increment(ref count);
                }
                tls.value2 = tid;
                Thread.Sleep(0);
                if ( tid != tls.value2 )
                {
                    Console.Error.WriteLine( "Value 2: {0} read {1}", tid, tls.value2);
                    Interlocked.Increment(ref count);

                }
                threads.Remove(tid);
                if ( threads.Count == 0 )
                    sem.Release();
            });
            threads.Add(t.ManagedThreadId, t);
            sem.WaitOne();
            t.Start();   
        }
        Console.WriteLine("Waiting for all threads to finish...");
        sem.WaitOne();
        Console.WriteLine("Total races: " + count);
    }
}

You will see races for value2 but not for value.

Update: The code snippet was updated, since the previous example had a race where the Total Race count would reach before all threads have finished reporting the wrong number of total races in cases where there were large number of races.

First Azure Service is live!

This is my first Azure service that I wrote a couple of weeks ago. It only uses the front end roles and no storage. I will add other applications to this portal, which will use other services offered by Azure.

XmlTextReader fiasco

I hit a snag a few days ago while doing some Xml parsing in one of my applications.

I am using XDocument for Xml parsing(XLinq is beautiful (K)).

Doing XDocument.Load(urlString) or XmlTextReader() would make my application choke with an Xml parsing error (invalid character). Using StreamReader to wrap the actual stream (WebResponse.GetResponseStream) and passing it to XDocument works like a charm. I wrote a sample app to figure out the issue and it turns out that XmlTextReader is the culprit. Maybe it fails to correctly recognize UTF-8 markers, or maybe it's stricter than other Readers, it didn't work for me. So beware. :)

Code Snippet (fails):
WebRequest req = WebRequest.Create("");
WebResponse res = req.GetResponse();
XmlTextReader reader = new XmlTextReader(res.GetResponseStream());
XDocument xdoc = XDocument.Load(reader, LoadOptions.SetLineInfo); //LoadOptions.SetLineInfo helps with debugging.

Code Snippet (works):
WebRequest req = WebRequest.Create("");
WebResponse res = req.GetResponse();
StreamReader reader = new StreamReader(res.GetResponseStream());
XDocument xdoc = XDocument.Load(reader, LoadOptions.SetLineInfo); //LoadOptions.SetLineInfo helps with debugging.


Happy XLinq-ing.

A Custom SpinLock based CriticalSection Implementation

Just something I implemented for fun :)

#include "stdafx.h"
#include <intrin.h>
#include <process.h>
#include <vector>
#include <utility>
#include <algorithm>
#include <iostream>
#pragma intrinsic (_InterlockedCompareExchange, _InterlockedExchange)
namespace DotFermion
{
    class CCriticalSection
    {
        enum { LOCK_IS_FREE = 0, LOCK_IS_TAKEN = 1 };
    private:
        long lock;
        long ownerThreadId;
        long acquireCount;
    public:
        CCriticalSection():
          lock(LOCK_IS_FREE),ownerThreadId(-1),acquireCount(0){}
          ~CCriticalSection()
          {
              Release();
          }
          //Non-recursive Acquire. Once its called, all threads, even the one owning the lock block on this lock.
          //Even a subsequent AcquireRecursive call after this one blocks.
          void Acquire()
          {
              while (_InterlockedExchange(&lock, LOCK_IS_TAKEN) == LOCK_IS_TAKEN);
          }
          //Recursive Acquire. It doesn't block if called multiple times from the same thread.
          void AcquireRecursive(long threadId)
          {
              if(ownerThreadId != -1 && threadId == ownerThreadId)
              {
                  _InterlockedIncrement(&acquireCount);
                  return;
              }
              Acquire ();
              _InterlockedExchange(&ownerThreadId, threadId );
              _InterlockedIncrement(&acquireCount);
          }

          void Release()
          {
              if(acquireCount > 1)
              {
                  _InterlockedDecrement(&acquireCount);
                  return;
              }
              _InterlockedExchange(&acquireCount, 0);
              _InterlockedExchange(&ownerThreadId, -1);
              _InterlockedExchange(&lock, LOCK_IS_FREE);
          }
    };

}

#define LIST_POS = 4;
#define INDEX_POS = 8;

typedef void (*LPFNTHREADPROC) (void*);
typedef std::vector<uintptr_t> THREADLIST;
typedef THREADLIST* PTHREADLIST;
typedef struct _args_t
{
    DotFermion::CCriticalSection* pCs;
    PTHREADLIST pThreadList;
    int index;
} args_t;

THREADLIST g_ThreadList;
int g_ThreadCount = 0;
int g_SharedCounter = 0;

void ThreadProc(void* argList)
{
    args_t* args = (args_t*)argList;
    args->pCs->AcquireRecursive((long)args->pThreadList->at(args->index));
    g_SharedCounter++;
    args->pCs->AcquireRecursive((long)args->pThreadList->at(args->index));
    g_SharedCounter++;
    args->pCs->Release();
    args->pThreadList->at(args->index) = -1L;
    g_ThreadCount--;
    args->pCs->Release();
    delete args;
}

int StartThreads ( int n, PTHREADLIST pThreadList, DotFermion::CCriticalSection* cs )
{
    pThreadList->resize(n);
    for ( int i = 0 ; i < n ; i ++ )
    {
        args_t* args = new args_t;
        if ( args == NULL ) continue;
        args->pCs = cs;
        args->pThreadList = pThreadList;
        args->index = i;
        uintptr_t threadId = _beginthread(ThreadProc, 0, (void*)args);
        if ( threadId != -1L )
        {
            cs->Acquire();
            pThreadList->at(i) = threadId;
            g_ThreadCount ++;
            cs->Release();
        }
    }
    return g_ThreadCount;
}


void Join (int* threadCount)
{
    while ( *threadCount );
}

int _tmain(int argc, _TCHAR* argv[])
{
    DotFermion::CCriticalSection cs;
    StartThreads(100, &g_ThreadList, &cs);
    Join(&g_ThreadCount);
    std::cout << g_SharedCounter << std::endl;
    return 0;
}

My own GetWsdl tool

I finally figured it out. It was there right in front of my eyes. I stumbled upon it so many times, but I always missed it.

I have been doing web service development for quite some time now. These services are part of pretty complex systems that require a long time to deploy. Imagine, every time there was a build number change and I wanted to modify one of the services. I wrote the code, built it, deployed the services (this step was the longest and most painful), got the wsdl, generated the proxy and updated and built again. The reason it required full redeployment on build number changes is that the assemblies are bound by strong names. It was one heck of a time consuming job. All this work, just to update the proxy; WSDL generation required a live service. :)

Though I still have to do this to verify that the code that I wrote actually works, proxy generation is not that much of a hassle, especially when I am writing code that I know works already and there is minimal need to try it out.

This time has been drastically reduced. Thanks to System.Web.Services.Description.
ServiceDescriptionReflector.

 

The GetWsdl tool is here. I will publish it soon. Stay tuned.

-UG

Update

I haven’t updated my blog for ages. This is a just a refresh post :)

This is neat

http://scrapzilla.blogspot.com/2007/11/remember-remember_7668.html

A picture (and a good line) is worth a million words.

Update: There was a picture of masks (the ones worn by revolutionaries in Vendetta)  stored inside a fire extinguisher container with a hammer by its side saying, “In case of revolution, break glass”. Below the picture, it says: “And the hammer hangs on”.

Update 2: Here is the original picture :)

Gra(n)d Finale

This is my first exam as a grad student.

The Grand Finale

The finals start from Sunday November 11, 2007. The first quarter has ended. Phew J

Fear

Train yourself to let go… of everything you fear to lose.

The fear of loss is the path to the dark side.

You're a towel!!

You're a beaner towel.

Trying Windows Live Writer (Beta)

This is an awesome product.

The Microsoft Trilogy

Microsoft ? Me ? No! it cant be like that !! That was the first question I asked for atleast one week when I got up !! It all happened in a snap and I never knew. It all started with a phone interview and the next thing I knew was a congratulations email from Microsoft telling me that I was hired.

It all started like this:

One of my friends sent me an email about Microsoft coming to Dubai to hire Pakistanis. I did not send my CV at first. But then a friend of mine sent his CV, and he got a phone interview. I sent my CV somewhere near the end of January, and got a phone interview in a couple of days. That was unbelievable. It was a lady named Priya, who emailed me and then took my phone interview. That interview was one heck of an experience for me. I thought I had a terrible interview and I never saw myself clearing that one. I got all the technical questions right, but I failed the IQ question. And as I had heard, the IQ question was the decider, which was wrong. In a week I got an email inviting me to Dubai for in-person interviews. This was the beginning of a very long and painful process....

To be continued...

http://www.sellsbrothers.com/

This is the home of king of COM, Chris Sells. Also has some stuff related to MS interviews.

http://www.joelonsoftware.com

Home of the founder of FogCreek software and the former Program Manager of the Excel team, Joel Spolsky.

Also see the archive for some interesting articles by Joel.

http://blogs.msdn.com/oldnewthing/

The blog maintained by Raymond Chen, the Windows guru. It has some very interesting articles on Windows history.

I'm a SOFTIE now !!

I am SDE ( Software Design Engineer ) with the OneCare team now.
Oh, I cant believe it yet.