Archive for the 'C++' Category

MuthTV sluggish when buttons pressed on remote?

Recently I built myself a media center of old HP/Compaq computer and MythBuntu. It all worked as a top and I spent weeks learning about great features it has.

This week I was hoping to put some finishing touches on it. The last missing piece arrived – so-called “Vista Rock Remote”.

7.jpg

According to MythBunty HOWTO, this MCE-compatible remote should work out of box, despite some reviews saying it would only work with Vista. Don’t know if it works with Vista though, but it worked in MythBunty just fine. I only had to enable it in Mythbuntu control center. And restart MythTV frontend, of course.

Funnily enough, I noticed the big problem straight away. Every time I put recorded TV show on and tried to use volume up/down buttons on remote, the picture was getting sluggish and jumpy for noticeable time. Actually, it felt so weird I even thought that I might be only one who had that problem. I was not right – there were plenty of similar reports on Internet. And there was a workaround proposed also.

The root cause of the problem is that MythTV pokes X screensaver every time button on remote is pressed. It does not have to do so when you use keyboard, but must do it when you use remote as screensaver has no idea about it. MythTV kicks the screensaver by invoking “gnome-screensaver-command” with parameter –poke, and there are reports it does it twice every time you press the button. It isn’t itself a problem, the problem is that when this command is called often (and it exactly what happens when you try to put volume up or down) XOrg CPU usage jumps to 100%, which causes that unwanted “special effect” in your video.

This bug, however, has already been reported (here and here)  and the fix will probably be included in next MythTV release. For now, the only workaround was to disable screensaver and create a symbolic link to /bin/true with name gnome-screensaver-command somwehre in one of PATH’s directories that comes in front of where the original program resides. Say, if your PATH looks like

/usr/sbin;/usr/bin;/usr/local/bin

and gnome-screensaver-command is in /usr/local/bin, you can stop it from being called by creating link to /bin/true in either/usr/sbin or /usr/bin:

ln -s /bin/true /usr/bin/gnome-screensaver-command

But it would only work if you decide to disable the screensaver. You can try not to, but once display goes to sleep, you won’t be able to wake it up by using remote. So I decided to invent something more sophisticated.

Of course, I could  download sources, fix the bug and build MythTV myself, but I decided to leave it to mythbuntu team. Instead, I written small program that simply does not allow screensaver to be poked more often than once in a minute, which fixed the problem.

The good news: you can download it from this site: Mythtv screensaver proxy

The bad news: you must build it yourself. So, installing build-essentials first would be a good idea.

Download cpp file above somewhere in your home directory and then follow simple steps described in file header:

/*
 * Usage:
 *      1. execute "which gnome-screensaver-comand"
 *      If output is different from what you find below in
 *      DEF_PROGRAM, modify this macro accordingly.
 *
 *      2. build the program:
 *      g++ myth-screensaver-proxy.cpp -o gnome-screensaver-command
 *
 *      3. Find what directory original gnome-screensaver-command is in
 *              (/usr/bin/ by default).
 *
 *      4. Look at your PATH settings (printenv | grep PATH).
 *
 *      5. copy binary buld on step 2 to any of the directories that
 *      come in PATH before original gnome-screensaver-command directory.
 *
 */

Useful C++ template magic. Hiding nasty global static’s

In C++, often there is a need to provide and support single instance of certain class, accessible on demand from anywhere in the program. That is encyclopedic example given in many books promoting singleton pattern. For instance, if your program has a log file, it is strongly recommended that you make a class that encapsulates all logging and make it singleton. This approach, without any doubts, is much much better than making global static instance of the logger and then referring to it from whatever you need as it reduces number of cross-dependencies, an issue that stays among the most bad techniques making code less maintainable.

This is easy to understand – while there is nothing wrong in static variable, even in global static variable, we must ensure that it is initialized before it is used first, which is especially important if the object has to be created dynamically. And this is the problem Singleton pattern solves.

Take the example

// SomeSourceFile.h
#include "CoffeePlantation.h"
static CoffeePlantation g_Plantation;

// SomeSourceFile.cpp
#include "SomeSourceFile.h"
// Initialize the instance
g_Plantation = CoffeePlantation();

Note: coffee plantation…

Unmanaged C++ client for WCF service.

Recently I have been evaluating different options and solutions for creating distributed network applications. Of course, this definition is too broad and there might be hundreds of answers and they all would be useful in different circumstances but I paid special attention to WCF.

As Microsoft released a Visual Studio 2008, I can hardly see any reasons why someone who is up to developing a distributed network application might choose anything different. New Studio even has a project template for WCF services, what makes network servers and clients development as easy as can be… But, of course, that would only work if no other platform except Windows is considered. Which is not uncommon.

So, what options are there if we need to build a client for existing WCF service that would work where .NET framework is not installed (because it is not available for that platform)? There is one way offered by Microsoft (using sproxy.exe) and some could use it. Other way involves writing “moniker” in .NET and then use it via COM. They both would work on windows platform only, moreover, I couldn’t make sproxy.exe to work with WCF service at all, so I had to look for the third option, which was gSOAP. And this worked.
Continue reading ‘Unmanaged C++ client for WCF service.’

About design patterns

Well.. it seems to me that they will soon ask about anti-patterns than proper patterns at job interviews. At least there are some books available.  Can’t even imagine what comes after that.. :)

Hit the wall

Need to find as much information about pattern recognition as possible.

Does anybody know good books or sites? “Bayesian theory” and “fuzzy logic” sound good, but question is how to apply theory in practice?




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