Silviu-Marius Ardelean's blog

a software engineer's web log

Happy Birthday, Romania!

Today it’s the Nation Day of my country!

La Mulţi Ani, România!
Happy Birthday, Romania!
Joyeux Anniversaire, Roumanie!
Alles Gute zum Geburtstag, Rumänien!

Because my country is not well-known in reality I dedicated a special page about the real Romania here!

In case you don’t know:




Fun IT – 2011 Collection

Here it is a collection of funny topics that I met this year in my daily activities. In case I will get new info, the topic will be updated!
Nobody is perfect and especially the software! 🙂 But it’s nice to immortalize funny things.

Chatting with a virus
Few weeks ago I was chatting with a virus. A friend of mine just got a Yahoo Messenger virus and unsealed it to me. 🙂

After that I emailed to my friend and his computer is safe now.

Mission Impossible in Eclipse

This year I was involved in a Java project using Eclipse IDE. Once day I tried to export few files in a .jar and I got impossible situation to close the export dialog: all the buttons where disabled and when I tried to close the window using Alt+F4 or X button I got next message error.


The only solution to escape this message box was to kill the Eclipse process. Fortunately, the issue didn’t reproduce second time.

Idle 41 years

This summer, my Pidgin chat application shown over 41 years of Idle status for one of my high school colleagues. He is 30 years old. The issue was fixed when he turned back to his computer.

An original way to say “Happy Birthday, Austria”

26 October is the National Day of Austria. On this occasion, Google Translate wished Happy Birthday Austria in an original way.

The translation from Deutsche to Romanian of “Happy Birthday Austria! See you soon!” is “Happy Birthday USA! See you soon!“. Today, 14.11.2011, the issue still exists. So Enjoy!

Pidgin relapses
Today, 15.12.2011, according to Pidgin 2.7.11 one of my office colleagues was out of office over 41 years.

Out of Memory – Yahoo mail
Few days ago I was visiting few private insurances companies. One of the most friendly company’s employee staid close to me with her laptop. In the moment she tried to send me a PDF file by email using a Yahoo email I was delighted with an amazing message error:

The using browser was IE 8 in Windows 7. It’s amazing how she got out of memory at line 1. I don’t thing Yahoo writes all the code in one line (even if the don’t use CR + LN). 🙂

Simple Pictures Unifier 1.1 application is up!

At the beginning of this year, I have launched an application that helps you to organize the pictures of your important moments. The application helps you especially if you have photos from different sources (different cameras of friends) and you want to have a fluent images story.

From the moment I have launched the first release until now I made up to 12GB pictures (3200+ pictures of 10 MB) and honestly I never found time in order to organize the pictures. Always I said that I will complete my application and finally I found time to implement export by date time folders and so on.

Simple Pictures Unifier 1.1 allows merging and exporting pictures in one folder or in date time folders. The application comes with a better user-friendly experience and few internal improvements.
The Start Export button launched a new wizard dialog that allows the selection of the preferred export method.

Export Wizard dialog

If the user chooses the default export to date time folders the Export wizard window shows a list with detected time folders.

Selecting Finish button the pictures merging is realized and the files are copied to the destination folders. If the user wants to abort the export process it can just press Stop button or close the application with now damages.

Feel free to add comments, suggestions or bugs reports. Any constructive feedback is sincerely appreciated.

Adventures with _chkstk

Called by the compiler when you have more than one page of local variables in your function.
_chkstk Routine is a helper routine for the C compiler. For x86 compilers, _chkstk Routine is called when the local variables exceed 4K bytes; for x64 compilers it is 8K.

That’s all that you get from _chkstk()’s msdn web page. Nothing more…

Overview
A process starts with a fixed stack space. The top of a stack is pointed to by the ESP register (Extended Stack Pointer) and this is a decrementing pointer. Every function calls results in a stack created for the function inside this Process Stack. Every thread function has its own stack. The stack is a downward growing array. When a function starts, the default stack reservation size is 1 MB.
This is contrasting with the heap’s size whether theoretically increases to a limit of 4 GB on 32bits OS. See more information here.

Every thread under Windows gets its own block of contiguous memory, and while function calls are made, the stack pointer is increasing and decreasing. In contrast, a different thread within the same process might get a different block of contiguous memory – its own stack. When a context switch occurs, the current thread’s ESP (along with the IP and other registers) are saved in the thread’s context structure, and restored when the thread is activated the next time.
To specify a different default stack reservation size for all threads and fibers, use the STACKSIZE statement in the module definition (.def) file. To change the initially committed stack space, use the dwStackSize parameter of the CreateThread, CreateRemoteThread, or CreateFiber function.
Most stack problems occur in overflows of existing stacks, as their sizes are fixed and they cannot be expanded.

_chkstk() increases the stack when needed by committing some of the pages previously reserved for the stack. If there is no more physical memory available for committed pages, _chkstk fails. When you enter a function (VC++ with the stack checking enabled), it will call the _chkstk located in CHKSTK.ASM. This function does a stack page probing and causes the necessary pages of memory to be allocated using the guard page scheme, if possible. In this function, it is stated that when it encounters _XCPT_GUARD_PAGE_VIOLATION, the OS will attempt to allocate another guarded page and if it encounters _XCPT_UNABLE_TO_GROW_STACK then it’s a stack overflow error. When _XCPT_UNABLE_TO_GROW_STACK is encountered, the stack is not yet set up properly, that is why, that it will not call the catch because calling it will use invalid stack variables which will again cause another exception.

Case – Too many or too big variables on stack
As I said on top, the function stack size is 1 MB. If you miss that and you’re trying to define and use internally an array like this:

When you’ll compile with VC++ compiler in debug mode you will have a big surprise: the application is crashing on _chkstk() in the moment the _chkstk() tries to create new memory page on stack and fails.
The output window shows next message:
First-chance exception at 0x004116e7 in testApp.exe: 0xC00000FD: Stack overflow.
Unhandled exception at 0x004116e7 in testApp.exe: 0xC00000FD: Stack overflow.

This happens because the 1MB limit is overloaded even on a win32 OS: 4000*200*4 = 3.2MB (approx.).
Same story if you define many local variables and their stack usage overloads the 1MB limit. Off-course the thread stack size can be changed but think once again if it is really needed to do that.
If you really need this big array then the best solution to avoid this crash is using the heap.

Case – Recursive functions
If you have an infinite recursion then you will gate same stack overflow error and the application crashes in _chkstk.asm. Recursive function is not the subject of this article so I don’t go in deep… Here it is a good example of what happens with recursive functions.
The solution is to avoid using recursive functions as much as possible and try to implement an iterative function.

Case – A stack corruption
I have started looking over _chkstk() function in the moment when I got few bugs with crashes with some similarly details. I had to analyze some .dump files and solve few bugs that contained a call stack with _chkstk() on top.
Most of the .dump files call stack contained a second similarly thing: the call of a thread function (so called ThreadFoo()) that was running in a threads pool.
In that moment I started to research why _chkstk() fails and my first track was to debug the stack overflows. I followed a MSDN debugging tutorial and unfortunately I didn’t find something strange. I checked if the local stack variables are not so big in order to fill the ThreadFoo() function’s stack and it did not.
Then a new study of ThreadFoo() function has followed in order to detect the internal functions calls that can fail in some circumstances. I stopped to some trace function calls and I studied deeply. Those trace functions where defined in an external debug class and each time when a new trace file was added it used an internal buffer (TCHAR szBuff[2048] = _T(“”);).
The writing of this buffer was done using: swprintf(). As we know this function is unsafe and is not recommended to use. As long as the content of these trace lines was dynamically build (in some cases those line may contain even dynamically build SQL queries that failed) then the length of these trace lines could be higher than 2048 bytes and then guess what: a stack corruption appears! UPS! The stack pointer will be corrupted (the classic stack overflow case).

So I have implemented and used the next macros:

Now, if we’re using the safe macro we will have no issues.

A safety alternative way to that buffer was the heap using but the heap access is not fast as the stack access so I preferred this approach (in a business application every milliseconds matters for the log system).
After that fixed I met no other stack corruptions in ThreadFoo() and other code areas.

Even if the top of the call stack was _chkstk() this was not the function that failed. The error appeared because of that stack corruption and _chkstk() has just detected.

Conclusion
If your code produces a stack overflow, then you have to rethink your design in right away:

  • If you see _chkstk() on the top of call stack, check if you have no stack corruptions – stack overflow.
  • Don’t try to manipulate the stack by yourself. The default 1MB stack size is basically enough
  • Allocate dynamically if you’re using big arrays
  • If you have recursive functions producing a stack overflow, re-write them using loops (a tip: it is a proven fact that any recursive functions can be programmed non-recursive)

References
Set stack size
Thread Stack Size
_chkstk Routine
Stack (data structure)
Debugging a Stack Overflow – tutorial
Visual C++ apps crashing in _chkstk() under load
Optimization Note (C++) 1: push, pop, call _chkstk
What is Recursion?

pre vs. post increment operator – benchmark

Compiler: Visual C++ 2010
Operating System: Windows 7 32bits
Tested machine CPU: Intel core i3
Download: preVSpost (demo project) (1081 downloads)

A recent Visual C++ team’s comment on twitter.com reminded me a hot topic that exists in C++ programming world: there is a long discussion of using pre versus post increment operators, specially, for iterators. Even me I was witness to a discussion like this. The discussion started from a FAQ written by me on www.codexpert.ro.

The reason of preferring pre increment operators is simple. For each post-increment operator a temporary object is needed.
Visual C++ STL implementation looks similarly with next code:

But for pre-increment operator implementation this temporary object is not needed anymore.

In the discussion that I mentioned above, somebody came with a dummy application and tried to prove that things have changed because of new compilers optimizations (the code exists in the attached file, too). This sample is too simple and far away to the real code. Normally the real code has more code line codes that eat CPU time even if you’re compiling with /O2 settings (is obviously).
Base on that VC++ team’s tweet related to viva64.com’s research I decided to create my own benchmark base on single and multicore architectures. For those that don’t know Viva64 is a company specialized on Static Code Analysis.
Starting from their project I extended the tested for other STL containers: std::vector, std::list, std::map, and std::unordered_map (VC++ 2010 hash table implementation).
For parallel core tests I used Microsoft’s new technology called Parallel Pattern Library.

1. How the tests were made
1.1. Code stuff
In order to get execution time I used same timer as Viva64 team (with few changes). Each container instance was populated with 100000 elements of same random data. An effective computing function was repeated 10 times. Into this function some template functions are called for 300 times. The single core computing function contains loops like this:

For the parallel core computing the first simple for loop has changed in:

Where cnt is an instance of combinable class and the sum of partial computed elements is obtained by calling combine() method:

As you can see, the parallel_for function uses one of the new C++ standard features: a lambda function. This lambda function and the combinable class implements the so called parallel aggregation pattern and helps you to avoid the multithreaded common share resource issues. The code is executed on independent tasks. The reason that this approach is fast is that there is very little need for synchronization operations. Calculating the per-task local results uses no shared variables, and therefore requires no locks. The combine operation is a separate sequential step and also does not require locks.

1.2. Effective results
The tests were running on a Intel core i3 machine (4 cores) running Windows 7 on 32bits OS. I tested debug and release mode for single and multi cores computation. The test application was build in VC++ 2010 one of the first C++11 compliant.
The OX axis represents the execution repeated times, and the OY axis means time in seconds.

1.2.1. Single core computation
Debug

Release

1.2.2. Multi cores computation
As you know, multi core programming is the future. For C++ programmers Microsoft propose a very interesting library called Parallel Pattern Library.
The overall goal is to decompose the problem into independent tasks that do not share data, while providing a sufficient number of tasks to occupy the number of cores available.

This is how it looks my task manager when the demo application runs in parallel mode.

Isn’t it nice comparing to a single core use? 🙂

Debug

Release

1.2.3. Speedup
Speedup is an efficiency performance metric for a parallel algorithm comparing to a serial algorithm.

Debug

Release

Conclusions:
The biggest differences appear in the debugging area where the pre-increment is “the champion”.
With primitive types (like int and pointers), the opposite might be true, because of the pipe-lining that a CPU does. With post-increment, due to optimizations in release there is no copy to be returned for these simple types.
According to these results I have to agree with Viva64 team. Even if the results are so close in release version I keep my opinion that using pre increment operator is preferred instead of post increment operators. We all know how long it takes the debug period and how important is every second that we win in long debugging days.
If you still have doubts in using pre-increment operator or you need a flexible way of switching this operators in your code you can easily implement some macros like these:

#define VECTOR_ITERATOR(type, var_iter) std::vector::iterator var_iter;
#define VECTOR_FOR(vect, var_iter) for (var_iter = vect.begin(); var_iter != vect.end(); ++var_iter)

Numeric type conversion to std::string and vice versa

In our real applications we have to convert from strings to integer or to real variables and vice versa (double/float/int variable to std::string).
We can realize these conversions using C style CRT function or we can try C++ approach via STL.
Unfortunately, current C standard libraries do not offer a complete support for any type of conversion. For instance, if we try to put an integer into a C++ string object (std::(w)string) using a well known function itoa() then we get next error:

// error C2664: ‘itoa’ : cannot convert parameter 2 from ‘std::string’ to ‘char *’

A C style approach in order to avoid this error means using an intermediary buffer:

Same story if we try to convert a std::string to an int:

// error C2664: ‘atoi’ : cannot convert parameter 1 from ‘std::string’ to ‘const char *’

In this case we can use c_str() in order to return a constant pointer to char.

An elegant way to get rid of such problems is to build two conversion function that use templates and C++ streams.
Base on this idea, I created a Sting2Numeric class that contains two static methods: Type2String() and String2Type().

where BadConvertion is a std::runtime_error‘s derived class.

Because of ANSI and UNICODE project’s compatibility I defined few macros:

Because of this compatibility I strongly recommend using a xstring alias instead of std::wstring or std::string.
When you want to convert an int, float, double, or other numerical type to a xstring in a C++ style you can use the Type2String() function. Vice versa, if you want to convert a xstring to these types you can use String2Type().

In order to avoid possible thrown exception I recommend to you using a try catch block whenever you’re using these functions. I prefer using xstring for string/wstring variables definition, too.
Here is a sample of using this class:

The String2Numeric class can be extended. For instance, if the conversion throw an error then you can add detailed information in the exception message.

Download String2Numeric (1002 downloads) class.

Flexible changes for product version properties – Visual C++ binaries

Manually editing of binary files version in the resource editor of Visual Studio IDE is not a viable solution. If we have dozens of projects in our solution, then for each kit building we should need manual resources file edit. Otherwise, we can use a special tool that does this thing for us.
Unfortunately this approach is not the most flexible and could fail.

For our flexible binaries properties changes and in order to avoid manual edit for each rebuild we can create and include a header file (version.h) that contains some constants of product version and file version of our project (.rc files).

We have to include only these constants into this file (version.h):

Then, for each .rc file wherever we have FileVersion and ProductVersion we have to use this constants.
When we will build a new kit, we have to change only these constants and then to start the kit building process. Everything is fine until we add new controls in our projects resource files. Then, because of Visual Studio IDE automation we can get an unlikely surprise: the FileVersion and the ProductVersion properties could be reset to 1.0.0.0.

In order to avoid this issue and edit the version only in a single place I propose the following workaround:

  • Create a version.h header file that have to contain these constants only (as on top). I should recommend to create it into the root solution in order of being easy included in all the projects.
  • Include this file in the project you need to use.
  • Use a text editor (ex. notepad.exe) and include next code section at the end of .rc2 resource file of your project (res\your_project.rc2) – this section contains the include version.h file section, too.
  • Edit “040904e4” block code with same data as if we should edit in a resources editor and use the version.h‘s file defined constants. As you can see in my example, for the FileVersion and ProductVersion properties I use my version.h constants. These properties will not be edited anymore.
  • Delete “// Version” section from default resource file your_project.rc (including comments – recommended).
  • Insert next lines into your_project.rc file after “3 TEXTINCLUDE BEGIN” and before “#define _AFX_NO_SPLITTER_RESOURCES\r\n“:
  • That code block looks like this:

    Don’t forget to edit .rc2 file name with the right file name of your project.

  • In your_project.rc file the section “// Generated from the TEXTINCLUDE 3 resource.” have to contain only next declaration:
  • The rest of the section’s lines have to be deleted.

  • We save both resources files: your_project.rc and your_project.rc2.
  • Rebuild the project and check the new generated binary properties. In the FileVersion we will have the major version (in my case 4.0.0.0) and in ProductVersion we have the current build version (4.3.2.198).
  • Observations
    Once you apply these steps, the product version properties will not possible from the Visual Studio IDE resource editor, anymore (only as edit text file or an external text editor). If we didn’t define something special in our project’s String Table we will see only IDS_ABOUTBOX.

    Demo application - AutoProductVersion (1184 downloads)

    Simple Pictures Unifier – first version

    Have you just returned from vacation and you have a lot of pictures? You just downloaded your taken pictures and you got your friends pictures, too? Then, probably, the pictures are scattered, with a random order in your computer.
    Would you like seeing pictures from all sources in order of events happening?
    If so, try to sort your photos using Simple Pictures Unifier tool! 🙂

    Simple Pictures Unifier application

    Please, feel free to add comments, suggestions or bugs reports to this application.
    Any constructive feedback is sincerely appreciated. Thanks you!

    File size fast detection

    Many times in our job, we need to work with files and need to know file properties.
    One of the most important properties is file size. Of course, there are a lot of API that allows finding this property, but most of them needs additional file operations: open file, find file size and close file.

    A direct and fast way in order to detect the file size without these operations means the CRT run-time library’s function _tstat64() and stuff.

    In the header file or on .cpp file please add next macros definitions:

    Then, write next function:

    If you’re using WinAPI there is an even faster way in order to get file size.

    Finally, call these functions wherever you need.

    Hungry boy – Google Chrome 5

    My currently default bowser is Google Chrome. I use it more then 90% of my browsing time. I like it because it’s launching so fast, is a secure broswer, respects major W3C standards and has an interesting application architecture. Each tab is an independent process and if appears some troubles in one process, you can stop that process only, without loosing other Chrome’s tabs (processes) data.

    Unfortunately, two weeks ago, watching few slides presentations over slideshare.net I was shocked by a Windows message on my laptop (Windows 7 Ultimate x64 OS): “Your computer is low on memory. Save your files and close these programs: Google Chrome.
    What the hack?!

    Windows special MessageBox

    I closed that window and I investigated Task Manager in order to detect witch process was using my memory.
    I was socked again when I saw that one Chrome process was using even 701 MB!

    huge used memory

    Briliant!

    Memory graph

    The main Google Chrome process had 13 tabs: 8 tabs contained slideshare.net presentations, one with twitter.com and the rest normal web pages.

    Release space on a Windows partition – SpaceMonger

    Few time ago I observed that my laptop’s first partition (48 GB size) free space reduced to 4 GB.
    There are a lot of file managers application (Windows Explorer, Total Commander, Far Manager, etc). All of them provide folder and file lists, but have not intuitive display of most important detail: the size.
    Of course, there are some known paths that store not useful data (see bottom folders list) and with each file manager you can delete major not useful data. But, you can miss some old huge file (some forgotten video files, etc).

    Fortunately there is a tool witch display folders and files size graphically called SpaceMonger. I used it and now my laptop free space is approximately 20 GB. 🙂 At the end of this process I applied the same story on my old workstation, too.
    Using this visual tool is easy to observer big files, folders and is easy to clean Windows temporary files, Windows updates install files, easy to observe hibernate and virtual memory files (if you have enough RAM memory you can disable this feature), etc.
    Unfortunately SpaceMonger project development was stopped. Fortunately the free version 1.4 runs fine on Windows 7, even if it was written for Windows 9x OSs.
    On my workstation (Windows XP SP3 station with 1792 MB RAM) I observed some troubles when I selected a huge folder in order to delete. SpaceMonger application crushed few times. I recommend individual file delete actions.

    If you decide to follow this tutorial for your station is your responsibility. I am not responsible for any damage of your operating system or if you’re loosing your personal data. Do it only if you know what you do. You need a user with administrator rights.
    You can download and unzip last freeware SpaceMonger application, 1.4.0 version from:
    SpaceMonger v1.4.0 -> Free Software tab -> SpaceMonger v1.4.0 -> Download it! button.

    Start running SpaceMonger application. Press Open button, select partition driver and wait partition scanning process. Your scanning results should look like this:

    You can see how much free space you have, and all big files and folders. With this tool you can find forgotten huge files, too.
    On each Windows partition there are two huge files that can be deleted in some circumstances: hiberfil.sys and pagefile.sys.

    Disable hibernate feature – hiberfil.sys
    Normally this file is located at C:\hiberfil.sys and file size can vary from 250MB to over 2GB. Trying to delete it it’s not a good idea if you don’t understand what means this file.
    This file is used by Windows hibernate. This feature is used instead of shutting down when we need a faster Windows start. Windows takes a snapshot of current operation Windows state, copy everything on this file and turns off most of your hardware. To wake up from hibernation you normally move the mouse or hit the spacebar on the keyboard.
    If you are using Windows 7 or Windows Vista, you can easy disable hibernate feature in command prompt window typing powercfg -h off on and press Enter.
    If you are sure that you don’t need this feature you can disable it in Windows XP following next steps:
    – Go to Control Panel (Start -> Control Panel) and select Power Options feature.
    – Click the Hibernate tab, uncheck the ‘Enable hibernate support‘ check box, and then click Apply.
    – You need to restart your computer and hiberfil.sys should be automatically deleted.
    Later, if you need hibernation feature, you need to go back to Hibernate tab from Power Options and check Enable hibernate support.

    Disable virtual memory – pagefile.sys
    This file is used by Windows virtual memory extension. Virtual memory is allowing your computer’s operating system pretend that you have more RAM than you actually do and run the Windows application smoother.
    Usually this file size is 1.5 times than your actual physical memory size and might consume a huge disk space of your computer hard drive space.
    Be carefully if you want to delete disable virtual memory feature. You need to have enough RAM memory.
    In order disable virtual memory follow next steps:
    – Go to Control Panel and run System.
    – Click on Advanced tab and click the Settings button on Performance.
    – Click Advanced button and Virtual Memory window appears. Select “No paging file” item and click the Set button if you want to remove pagefile.sys.
    – In order to apply these changes you need to restart Windows.

    Delete individual files
    Using SpaceMonger application you can easy delete temporary file, updates installer files and other huge files. But, BE CARFEFULL WHAT YOU DELETE. Don’t delete Windows files, Program Files files, or other important files.
    This application provides zoom in/zoom out features in order to have a complete overview of what you intend to delete.
    Some paths that could be deleted are:

  • \Windows\Temp
  • \Documents and Settings\user_name\Local Settings\Temp
  • \Documents and Settings\user_name\Application Data\Microsoft\Office\Recent
  • \Documents and Settings\user_name\Local Settings\Temporary Internet Files
  • \WINNT\TEMP
  • If you are using Windows Vista or Windows 7 and you are tempted to remove \Windows\Winsxs, forget this idea. The Winsxs folder, stores multiple copies of dll’s in order to let multiple applications run in Windows without any compatibility problem. These are actually, different versions of the same files which are being stored; as different programs may require different versions. Winsxs is Win 7 and Vista’s native assembly cache. Libraries which are being by multiple applications are stored there. So, don’t delete WinSxS folder!

    Because many application creates own temporary files, I should recommend to you the running of another nice freeware tool, CCleaner. It’s easy to clean all other temporary data and registry, too.
    You can use SpaceMonger tool on other non-system partition, too.

    Console2 application fail

    The tests for my job tasks sometimes involves the execution of command line applications. One year ago I used for a while Console2 application because of nice features (transparency, easy copy+paste, etc).

    I stopped using this application when I saw how it behave when I searched an application with a little bit complex command sintax.

    Console2 fail

    So, I returned to cmd.exe. 🙂