Global variables are bad

<This post is about C++ (C# folks are saved from this pain)>

One of our devs taking care of NETCF on Nokia S60 reported that after the latest code reached their branch things are working very slow. It was observed that Garbage Collector is getting kicked in way more than it should. Investigation showed something interesting.

I added a global var gcConfig which had a fairly complex constructor and that among other things sets the various member variables like the GC trigger threshold to default value (1mb). All of these works fine on Windows variants.

However, TCPL states “It is generally best to minimize the use of global variables and in particular to limit the use of global variables requiring complicated initialization.”. This is especially true for dlls. We tend to ignore good advice sometimes :)

For Symbian OS (S60) on device complex ctors of global objects are not run (without any warning). The members are all set to 0 (default member initialization). So in the gcConfig GC-trigger was being set to 0 instead of 1mb. The allocation byte count is compared against this value to figure out when it’s time to start a GC. Since it was 0 the collection condition is being met for every allocation and hence for every allocation request GC was being fired!!!

Actually considering that even after that the app was actually running shows that we have pretty good perf ;)

A good alternative of using global vars is as follows

MyClass& useMC()
{
    static MyClass mc; // static ensures objects are not created on each call
    return mc;
}

MyClass& mc = useMC();

Do note that this has some multi-threading issue. See http://blogs.msdn.com/oldnewthing/archive/2004/03/08/85901.aspx.

Installing S60 development tools on Windows 7

My first attempt to install Carbide on Win 7 failed. So I thought I’d document the exact steps I followed the second time to make that work

Install Pre-requisites

1. Perl
   1. I used ActivePerl 5.6.1.638
   2. To ensure UAC didn’t cause any issues I first launched an elevated command prompt by going to All Programs –> Accessories, right click on Command Prompt and choose Run as administrator
   3. In that I ran the command msiexec /i ActivePerl-5.6.1.638-MSWin32-x86.msi
   4. I choose the path c:\perl\bin
   5. I ran path command from another newly launched command prompt to ensure that c:\perl\bin is present in it (so Path environment variable is updated)
2. Java
   1. I downloaded jre-6u7-windows-i586-p.exe
   2. Right clicked on it and used Run as administrator to install it

Installing the S60 Tools

1. S60 SDK
   1. Downloaded S60_5th_Edition_SDK_v0_9_en.zip
   2. Unzipped to a folder
   3. Right clicked on setup.exe and used Run as administrator to install it
   4. Used c:\S60\devices\ as the install path. So my final installation is in C:\S60\devices\S60_5th_Edition_SDK_v0.9
2. Carbide
   1. Downloaded Carbide V2.0
   2. Right clicked on it and used Run as administrator to install it
   3. Used C:\Apps\ as the install path
3. PC Suite
   1. Downloaded Nokia_PC_Suite_7_1_18_0_eng_us_web.exe
   2. Right click on the exe and choose Troubleshoot compatibility
   3. In the wizard that opens click next
   4. Ensure the following is checked on the next page of that wizard
      
   5. Hit Next and in the next page choose Window Vista
   6. Go on hitting next and finally the installer will launch

At this point you are done and should be able to launch Carbide, Emulator and PC Suite.