Archive

Posts Tagged ‘ACT’

Talk – A software of quality journey

July 29th, 2009 Bali No comments

讲稿@
http://libaocun.com/wp-content/uploads/2009/07/Journey.ppt

Code @
http://balionweb.googlecode.com/svn/trunk/SoftwareQualityControl/

Categories: Chinese - 中文 Tags: ,

Memory Leaks Demo & Detection in .NET Application

July 29th, 2009 Bali No comments

Memory leaks are always headache of developers. Do .NET developers no longer bother to worry about memory leaks because of garbage collection? Yes and NO. GC periodically find objects that cannot be accessed in the future and then reclaim the resources used by the objects. GC achieves this by maintaining a list of references to live objects. When this mechanism is broken, memory leak happens.

There are many reasons to leak memory. In addition to calling unmanaged code from managed code, another one of general cases is about event handler. If you do this:

Foo.FooEvent += new EventHandler(MemoryLeaksHere.Method);

When you complete using MemoryLeaksHere, but you are still using Foo, then MemoryLeaksHere will still remain alive as well. MemoryLeaksHere object will leak memory as a result of failing to GC.

Let us take a look at one simple example first.

using System;

namespace MemoryLeakSample

{

class Foo

{

public static Foo myFoo;

public event EventHandler FooEvent;

public Foo()

{

myFoo = this;

}

public void FooMethod()

{

MemoryLeaksHere memLeak = new MemoryLeaksHere();

memLeak.TryQuit();

}

public void FireEvent()

{

FooEvent(null, null);

}

static void Main(string[] args)

{

Foo foo = new Foo();

for (int i = 0; i < 5; ++i)

{

foo.FooMethod();

}

GC.Collect();

GC.WaitForPendingFinalizers();

GC.Collect();

Console.WriteLine(“Check memory leak here.”);

}

}

/// <summary>

/// This object will cause memory leak

/// </summary>

public class MemoryLeaksHere

{

public MemoryLeaksHere()

{

Foo.myFoo.FooEvent += new EventHandler(OnMyFooEventFired);

Console.WriteLine(“\nObject-{0}: Construct. Subscribe.”, this.GetHashCode());

}

~MemoryLeaksHere()

{

Console.WriteLine(“Object-{0}: Deconstruct.”, this.GetHashCode());

}

public void TryQuit()

{

Console.Write(“Object-{0}: leak me?”, this.GetHashCode());

string input = Console.ReadLine();

if (string.Equals(input, “no”))

{

Foo.myFoo.FooEvent -= new EventHandler(OnMyFooEventFired);

Console.WriteLine(“Object-{0}: Unsubscribe.”, this.GetHashCode());

}

else

{

Console.WriteLine(“Object-{0}: Not Unsubscribe”, this.GetHashCode());

}

}

private void OnMyFooEventFired(object sender, EventArgs e)

{

// Do something

}

}

}

In MemoryLeaksHere object’s constructor, Foo starts to hold a reference to MemoryLeaksHere by registering event handler. In MemoryLeaksHere.TryQuit(), if we don’t unregister, memory leak will happen.

To be more intuitive, you can copy/paste sample code to VS2008, and then enable unmanged code debugging by following:

Project->Properties->Debug->Enable Unmanaged Code debugging

Now set a breakpoint at “Check memory leak here”, and start build/debug. When being asked leak me or not, you can choose either yes or no. For example:

Here, looks like we leak two of them. Finally app will hit the breakpoint and stop. At this point, we can go to VS immedate window to load sos.dll, and then check how many objects in the heap:

!load sos.dll

extension C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\sos.dll loaded

!dumpheap -type MemoryLeaksHere

PDB symbol for mscorwks.dll not loaded

Address MT Size

0132e7d0 00983104 12

0132eba0 00983104 12

total 2 objects

Statistics:

MT Count TotalSize Class Name

00983104 2 24 MemoryLeakSample.MemoryLeaksHere

Total 2 objects

So now we know there are two object instances are not recycled. Why are they not GC-ed? Because someone has a reference to them. Choose one of them, and use gcroot command.

!gcroot 0132e7d0

Note: Roots found on stacks may be false positives. Run “!help gcroot” for

more info.

Error during command: Warning. Extension is using a callback which Visual Studio does not implement.

Scan Thread 7592 OSTHread 1da8

ESP:12f434:Root:01312d48(MemoryLeakSample.Foo)->

0132f704(System.EventHandler)->

0132f6ec(System.Object[])->

0132e7dc(System.EventHandler)->

0132e7d0(MemoryLeakSample.MemoryLeaksHere)

Scan Thread 4704 OSTHread 1260

Now we can see that MemoryLeakSample.Foo is still referencing MemoryLeakSample.MemoryLeaksHere via event handler. If it is not 5 iterations, image what would happen if every incoming request results in a slice of memory leak… Soon or later, you online service will be down.

See also:

http://www.codeproject.com/KB/dotnet/Memory_Leak_Detection.aspx

http://blogs.msdn.com/jgoldb/archive/2008/02/04/finding-memory-leaks-in-wpf-based-applications.aspx

http://blogs.msdn.com/calvin_hsia/archive/2008/04/11/8381838.aspx

http://www.automatedqa.com/techpapers/net_allocation_profiler.asp

http://blogs.msdn.com/greg_schechter/archive/2004/05/27/143605.aspx

Categories: English - 英文, Uncategorized Tags: ,

Designing Your Own Recent Posts Widget for MSDN Blog

July 29th, 2009 Bali 1 comment

In my MSDN blog, I need “Recent Posts”, but I don’t need archive side bar. After having played with template for a while, still no luck. Hmmm, looks like I have to DIY it. Fortunately in News sidebar, you can fill in raw html including JavaScript. Then next question is where we can retrieve post tiles. The immediate idea is from current DOM document. Through experiments, I found this is impossible because the DOM is not fully loaded yet when the script is executed. Later, I figured it out that all posts title can be gotten from RSS. For my blog, the address is http://blogs.msdn.com/bali_msft/rss.xml. One thing worth noticing is the fact that RSS in MSDN blog is not up to date – Your post will not instantly appear in the RSS. After I get all posts in RSS format, things became much easier. And then I go ahead to add more interesting things:

  • Posts background use two colors in turn
  • Show a new tag for posts less than 3 days old
  • Show latest 8 posts only
  • Show posts’ age

So, the final thing will look like this:

If you find it is useful, feel free to paste below code to you blog’s news section. Note to customize “Configurable params” to your own needs and leave other code intact. It works well at least in my IE 8 and Firefox 3.0.6.

<div id=”RecentPosts”></div>

<Script>

// Configurable params

var recentPostNumber = 8;

var rssUrl = “http://blogs.msdn.com/bali_msft/rss.xml”;

var title = “My Recent Posts”;

var newPostAgeInHour = 72;

// Cacluate age of one post. It is all about getting time span in Javascript

// return formate: x min; x hour y min, x day y min, x days, x yeas (ago)

// Refer to: http://www.w3schools.com/jsref/jsref_obj_date.asp

function calculateAge(postDate)

{

var ret = “fresh!”;

CurrentDate = new Date();

TimeSpan = new Date(CurrentDate – postDate);

var mySpanArray = new Array();

mySpanArray[0] = TimeSpan.getUTCFullYear()-1970;
mySpanArray[1] = TimeSpan.getUTCMonth();
mySpanArray[2] = TimeSpan.getUTCDate()-1;
mySpanArray[3] = TimeSpan.getUTCHours();
mySpanArray[4] = TimeSpan.getUTCMinutes();

var TimeSpanTagArray_1 = new Array(“years”, “months”, “days”, “hours”, “minutes”);

var TimeSpanTagArray_2 = new Array(“year”, “month”, “day”, “hour”, “minute”);

// Starting from non-zero element and pick two significant values

for(i = 0; i < mySpanArray.length; i++) {

if(mySpanArray[i] != 0) {

var correctTag = (mySpanArray[i] == 1)?(TimeSpanTagArray_2[i]):(TimeSpanTagArray_1[i]);

ret = mySpanArray[i] + ” “ + correctTag;

if(i+1 < mySpanArray.length && mySpanArray[i+1] != 0) {

correctTag = (mySpanArray[i+1] == 1)?(TimeSpanTagArray_2[i+1]):(TimeSpanTagArray_1[i+1]);

ret = ret + “, “ + mySpanArray[i+1] + ” “ + correctTag;

}

break;

}

}

return ret;

}

// Display the recent posts

// Refer to:

// http://www.w3schools.com/DOM/dom_node.asp

// http://www.w3schools.com/DOM/dom_methods.asp

function displayPosts (xmldoc)

{

var newTag = “<SPAN style=\”COLOR: red\”>(New!)</SPAN>”;

var posts = xmldoc.getElementsByTagName(“item”);

var displayText = “<h3>” + title + “</h3><UL>”;

if (posts.length < recentPostNumber) {

recentPostNumber = posts.length;

}

for(var i = 0; i < recentPostNumber; i++)

{

PostTitle = posts[i].firstChild.firstChild.nodeValue;

PostLink = posts[i].firstChild.nextSibling.firstChild.nodeValue;

PostDateStr = posts[i].firstChild.nextSibling.nextSibling.firstChild.nodeValue;

PostDate = new Date(PostDateStr);

CurrentDate = new Date();

// Calculate age

var _PostAge = calculateAge(PostDate);

var PostAge = “<SPAN style=\”font-size: 80%; color: black\”> (“ +_PostAge + ” ago)</SPAN>”;

// Show a new tag for posts happening last days defined by ‘newPostAgeInHour’

var myNewTag = “”;

if((CurrentDate.getTime() – PostDate.getTime())/1000/60 < newPostAgeInHour * 60) {

myNewTag = newTag;

}

// Get background color

var BKColor = (i%2 == 0)?(“#B8CCE4″):(“#DBE5F1″);

displayText = displayText + “<LI style=\”background-color:” + BKColor + “\”><A href=\”" + PostLink + “\”>” + myNewTag + PostTitle + PostAge + “</A></LI>”

}

displayText = displayText + “</UL>”;

var target = document.getElementById(“RecentPosts”);

target.innerHTML=displayText;

}

// Call back

function complete(){

if (req.readyState == 4) {

if (req.status == 200) {

displayPosts (req.responseXML);

}

}

}

// Initial async call

function getPosts()

{

if (window.XMLHttpRequest) {

req = new XMLHttpRequest();

}else if (window.ActiveXObject) {

req = new ActiveXObject(“Microsoft.XMLHTTP”);

}

if(req){

req.open(“GET”, rssUrl, true);

req.onreadystatechange = complete;

req.send(null);

}

}

// Entry point

getPosts();

</Script>

Categories: English - 英文, Uncategorized Tags: , , ,

Searching For a Number in Shifted Sorted Array within O(log(n)) time

July 29th, 2009 Bali No comments

Run into the algorithm problem long time ago. Now post my answer here. A sorted array, say: {1,2,3,4,5,6,7,8,9,10,11,12}, do right rotate through carry unknown times, and then it might become: {6,7,8,9,10,11,12,1,2,3,4,5}. Now we need get the index of a given number, say 4, from the array within O(log(n)) time. Apparently a 8-year-old can get it done with O(n) time.

We can think of it this way: take the middle element of array, if target is found, fine; if not, and then array become two parts, one is sorted array, the other is shifted sorted array. As illustrated as below diagram:

If the target falls into the sorted array half, we can simple do a binary search; otherwise, repeat this operation in the other half in recursive way. You can see this is divide-and-conquer algorithm. Obviously this is O(log(n)).

Code

//

// A typical binary search implementation

//

int _BinarySearch(unsigned int ShiftedArray[], unsigned int start, unsigned int end, unsigned int target)

{

// Not found

if( start == end && ShiftedArray[start] != target) {

return -1;

}

unsigned int middle = start + (end – start)/2;

if(target == ShiftedArray[middle])

{

return middle;

} else if (target > ShiftedArray[middle]) {

return _BinarySearch(ShiftedArray, middle + 1, end, target);

} else {

return _BinarySearch(ShiftedArray, start, middle – 1, target);

}

}

//

// Select a given number from shifted array.

// ShiftedArray is something like = {6,7,8,9,10,11,12,1,2,3,4,5}

// If found, return index of the number; if not, reutrn -1

// Require log(N)

//

int SearchShiftedArray(unsigned int ShiftedArray[], unsigned int start, unsigned int end, unsigned int target)

{

// Start meets end

if( start == end && ShiftedArray[start] != target) {

return -1;

}

unsigned int middle = start + (end – start)/2;

if(target == ShiftedArray[middle])

{

return middle;

} else if(ShiftedArray[middle] < ShiftedArray[start]) { // Right half is sorted linearly

if((target > ShiftedArray[middle]) && (target <= ShiftedArray[end])) {

return _BinarySearch(ShiftedArray, middle + 1, end, target);

} else {

return SearchShiftedArray(ShiftedArray, start, middle-1, target);

}

} else { // Left half is sorted linearly

if((target >= ShiftedArray[start]) && (target < ShiftedArray[middle])) {

return _BinarySearch(ShiftedArray, start, middle – 1, target);

} else {

return SearchShiftedArray(ShiftedArray, middle + 1, end, target);

}

}

}

Test cases

Positive: {6,7,8,9,10,11,12,1,2,3,4,5}, target = 3, target = 8

Negative: {6,7,8,9,10,11,12,1,2,3,4,5}, target = 0, target = 13

Boundary: {6,7,8,9,10,11,12,1,2,3,4,5}, target = 6, target = 5

Exceptional: {…max}, target = max

One more interesting thing is the statement that “only about 10 percent of the professional programmers implemented binary search correctly.” Do you know why? Check this.

Categories: English - 英文, Uncategorized Tags: , ,

Building Objects from XML of eBay API with LINQ

July 29th, 2009 Bali No comments

In this post, I’d like to illustrate the power of LINQ with code sample. I query the web service published by eBay. Refer to this article about eBay API concepts.

EbayItem.cs

EbayItem.cs

Program.cs

Programs

Done! in-memory objects are built. You can also follow ScottGu’s blog to wire up this code with Silverlight UI.

Categories: Uncategorized Tags: , ,