Remember to sync (or what the heck is that RAW C: partition on my Windows on mac?)

Our current computers use MBR to store the table of primary partitions. MBR for convention allows only 4 primary partitions and then uses Logical Partitions inside Extended Boot Records for the successive. Instead Apple computers use the new Extensible Firmware Interface with the GUID Partition Table to describe disk partitions permitting any number of primary partitions to be allocated.

MacOSX uses the GPT partition table while Windows expects to find the MBR one (Actually Windows for Itanium can boot from GPT, but that is not what you are usually installing on your desktop). Fortunately the EFI keeps a “fake” MBR table for backward compatibility and that is why we can install Windows on our MacIntel. But what happens when we change our GPT partitions from OSX/Linux which supports GPT? It happens that our MBR becames out of sync with the GPT.

Recently I had to install a triple boot with OSX+Win+Linux on my MacBookPro. This required 5 partitions (1 for EFI, 1 for OSX, 1 for Linux, 1 for Windows, 1 Linux Swap). After creating them from OSX I synchronized the MBR to GPT with refit tools to have the first four partition available also on MBR (this way I lost only the SWAP partition)  then I installed Windows XP. Everything went well but after booting, Windows ended up installing on D: and there was a C: partition resulting of RAW type. I just thought that obviously this was because there was the un-formatted Linux partition before the Windows one and restarted to install Linux.

Then I formatted my linux partition as EXT3 and installed Gentoo over it. Everything was fine until I had to restart windows to install the Service Pack 3 for XP. My wonderful RAW C: partition was still there… and I wasn’t able to install the service pack because SP3 installer wasn’t able to install on anything else then C: even if my Windows installation resulted on D: and C: didn’t result as a valid partition (off course… It’s my Linux partition!)

Windows should have known that it isn’t a valid partition for him and should hide it, that didn’t happen… Why? After thinking a bit I remembered that the Partition Type is also a field inside the MBR. When we format a partition the system specifies also the partition type inside the MBR to tell everyone that partition has been reserved by some OS. Having initialized my EXT3 partition from Linux had as a result that only the GPT was updated and the MBR still thought that my third partition was un-formatted.

After losing about an hour fighting with the Service Pack installer I just realized that I had to resynchronize the two tables… After doing that the RAW C: partition disappeared from Windows and my service pack installed correctly.

New Lesson: Ok, Microsoft could make a better installer and stop preventing their OS to install from something different from what they call “C:” but sometimes you have to think more before enraging with your OS 😀

PyHP improvements

New features in PyHP this week on the SVN version

  • it is now possible to set sessions timeout with PyHPSessionTimeout config variable
  • The Result object from the Database Layer is now iterable and will work as performing multiple .fetch() calls
  • pyhp.status is now exposed to return a status code different from HTTP_OK (200)
  • pyhp.content_type is now exposed to permit serving images and files different from text/html

Also some performance tests has been performed on mod_pyhp in production mode and the results are here available:

Time taken for tests:   1.419409 seconds
Complete requests:      500
Failed requests:        0
Write errors:           0
Non-2xx responses:      500 (hello_world.pyhp returns 500 on last pyhp)
Total transferred:      1558000 bytes
HTML transferred:       1344000 bytes
Requests per second:    352.26 [#/sec] (mean)
Time per request:       2.839 [ms] (mean)
Time per request:       2.839 [ms] (mean, across all concurrent requests)
Transfer rate:          1071.57 [Kbytes/sec] received

The results reveal to be quite good compared to other popular web development tools like WEBrick, mod_python and mod_php. Still they have a bunch of space for improvement to reach the “standard” ~600req/sec that more mature solutions obtain. Probably .pyhp files caching might be implemented to increase a lot performances.

I will provide a complete comparations to the other major web tools as soon as I have some time to set up a concrete test suite.

The misunderstood one

I’m a usual follower of C++ related blogs and newsgroups and still I’m impressed how much this language is misunderstood after 10 years of a precise standard. I’m actually starting to ponder if we are ready for C++0x while a lot of people yet misunderstand C++98 and C++03.

I often end up discussing with my colleagues about the fact that they prefer a less powerful, but more reliable and less obscure language like C. I know that C++ isn’t one of the easiest languages to master correctly and I also know that it has some problems about compilers often changing their behaviour and with slow templates compilation time. All things that C++0x is trying to make easier or faster with extern templates, move constructors, delegate constructors and type determination.

C++0x will be a quite complex and advanced language, which will give the programmer a lot of control over the compiler, but still after 10 years of existence of the standard C++ and formal STL libraries you can find posts like this which confuse good design practices and theories with runtime optimizations.

Having the stack container with the pop method returning void is exception neutrality not a runtime optimization. Strong exceptions safety means that the operation has either completed successfully or thrown an exception, leaving the program state exactly as it was before the operation started.

What would happen if we have a T pop() method returning the head after removing it? We might have the copy-constructor of T fail throwing an exception and find that after removing our head we also lost it forever. Having it just remove the item means that our code might only have success removing our item or fail to remove our item leaving the state exactly as it was before.

This is one of the first issues raised years ago, an issue discussed in depth since the article of Tom Cargil in 1994. An issues explained by Meyers and Sutter in their books and available in a lot of community blogs like the boost one. And still this isn’t clear even to long time C++ developers.

C++ is a multipurpose language, having all that freedom of movement requires more deep knowledge of the language itself. Shouldn’t we change how C++ is taught and more strictly enforce some practices before moving to a new standard? As a sporadic C++ teacher I often end up with this question…