Saturday, August 25, 2007

MTU is really a matter

Long time ago, I lower the MTU of my router to solve a networking issue (see my previous blog entry). However, it is not the end of story.
Recently, I have changed my job. My new company provides Citrix Presentation Server for employees to work at home via remote desktop.
Then, at home, I tried to connect to Citrix server and run remote desktop. I can login but the link is very unstable. It disconnected every 10 to 20 seconds.
After some investigation, I found it is the MTU problem again. The problem is fully explained at the following site:
http://www.netheaven.com/pmtu.html
I should change the MTU of my desktop at home to match the router. Finally, it works!

Sunday, July 01, 2007

Boost C++ Libraries

Recently, I checked some job ad. on the web and found some jobs require knowledge about "Boost". I have not heard "Boost" before. After some googling, I visit the web site of Boost. Boost is really a great thing. It is a set of C++ libraries contains many useful programming constructs with good documentation, e.g. smart pointers, regular expression, object pools, state machines.... Lastly, it is open source and free.

Sunday, June 17, 2007

Dig out dead looping thread

It is not easy to write multi-threading applications. One of the common bugs is dead looping of a thread. To kill this kind of bugs, the first step is to find out which thread causes dead looping. However, an application may have dozens of threads. How to dig out the dead looping thread? My trick is to issue the ps -eLf command to list the information of threads in the whole system. The "time" column of the output of ps shows the CPU time have spent by the threads. Most likely, the dead looping thread would be the thread spending most CPU time. Then, drop down the LWP number of the thread. Next, you use gdb to attach the process and to debug the thread.

Sunday, June 10, 2007

Job Interview Questions

Recently, I got some job interviews. The interviewers asked me tones of questions. Most of them were very technical. The most difficult question was an IQ puzzle. Under stress, it is difficult to overclock my brain :<
At home, I found a web site which included the IQ puzzle:
http://www.techinterview.org/index.html

Saturday, May 12, 2007

Undefined symbols in C++

In C++ programming, we sometimes encounter "undefined symbols" problem during compilation or dlopen. The name of undefined symbols looks obfuscated. E.g.:
Unable to dlopen(test.so): test.so: Undefined symbol "_ZN6moduleD2Ev"
You may wonder why the symbol looks so ugly. Actually, this conversion of symbol is called name mangling. C++ supports polymorphism, this means functions can have same name but different types and numbers of parameters. Therefore, compiler cannot just use the function name as the symbol. Instead, both function name and parameter types should be included in symbol naming. Name mangling is the technique to encode a function name and parameter types into one symbol.

To translate the mangled symbols to more meaningful text, we can use the c++flit utility. E.g.
ahlam@oxygen:~$ c++filt _ZN6moduleD2Ev
module::~module()
Now, you know "_ZN6moduleD2Ev" is the destructor of class module.

Friday, May 11, 2007

More than "command not found"

In old days, if I try to run a command which doesn't exist in my Linux box, it just prompts "command not found". Today, Ubuntu gives me a nice response:
ahlam@oxygen:/usr/bin$ cdecl
The program 'cdecl' can be found in the following packages:
* cutils
* cdecl
Try: sudo apt-get install <selected package>
Make sure you have the 'universe' component enabled
bash: cdecl: command not found

It's surprising!

Wednesday, May 09, 2007

Using new Chinese fonts from M$

One of my friends told me that the Chinese fonts in M$ Vista is much more beautiful. So, I try to install the fonts to my Ubuntu box today. The new Chinese fonts called YaHei and JhengHei. If you don't have Vista, you can download from somewhere (:P). The screenshot below shows the result.


For details about how to install the new fonts, you can refer to http://imtx.cn/feed.php?go=entry_332