Re: [PATCH 0/2] gitweb: Add support for running gitweb as FastCGI script

On Thu, 13 May 2010, Peter Vereshagin wrote:

`perldoc -f exit` says 'The exit() function ...', while `perldoc -f last` says 'The "last" command is like the "break" statement in C ...'.

Sidenote: The 'Monkey patch' article on Wikipedia says that the
technique of adding method dirctly to class instead of subclassing was
originally called "guerilla patching", then it mutated into "gorilla
patching", and finally into "monkey patching".

Perl hacker should know the difference between command such as "last" and "next", and functions such as exit() and die(). Just like C programmer should know the difference between "break" statement and exit() function.

Not true. The 'last LABEL;' command is very useful to exit nested loops. If used right it makes code much simpler (allowing to avoid extra flag variable and/or complicating loop conditional). If I remember correctly in O.-J. Dahl, Edsger W. Dijkstra, C. A. R. Hoare "Structured Programming" the programming language described includes "break <n>" statement, with similar purpose as "last LABEL" in Perl.

Note also that Dijkstra wrote in seminal article "Go To Statement Considered Harmful" that the problem with abused 'goto' is that it compilcates and muddles control flow of program. But there are legitimate uses of 'goto' that make the program simpler to understand, and not harder,... among those is handling exceptions.

Yes, it is a problem mainly in developemtn, where changes to the file included via "do <file>" might introduce parsing errors.

The problem is that "do <file>;" is similar to "eval `cat <file>`;" (except that it's more efficient and concise), it that it silences parsing errors. From `perldoc -f do`:

  If "do" cannot read the file, it returns undef and sets $! to the error.
  If "do" can read the file but cannot compile it, it returns undef and sets
  an error message in $@.   If the file is successfully compiled, "do"
  returns the value of the last expression evaluated.

Wrong!
 

First, both "use Module;" and "require Module;" (and "require '<file>';") do automatic error checking and raise an exception if there is problem.

Second, "use Module <LIST>;" is equivalent to

  BEGIN { require Module; import Module <LIST>; }

and therefore it doesn't make sense to use it for conditional inclusion.

Therefore, to load Perl module / file, if you can 'die' you can simply use

  require "<file>";

If you don't want to die, but want to know if loading and parsing file succeeded or not, you should use the following syntax:

  if (eval { require "<file>"; 1 }) {
    ...
  } else {
    ...
  }

If you want to use 'do "<file>";' (it is preferred in some circumstances), you really should check for error conditins:

  unless (my $return = do "<file>") {
    if ($@) {
       # couldn't parse <file>
    } elsif (!defined $return) {
       # couldn't do <file> (e.g. couldn't find <file>)
    }
    ...
  }

[...]

Gitorious is in Ruby, therefore is not a CGI.pm application, as it is not even in Perl.

By using Plack::App::CGIBin you can load CGI scripts from a directory and convert them into a <persistent> PSGI application. You can use Plack::App::WrapCGI to convert single CGI script into PSGI application. You can use Plack::Buuilder's domain specific language to join (map) together a bunch of PSGI applications (in different paths) in a single app (via Plack::App::URLMap).

You can then run PSGI application (for example the PSGI app which loads CGI apps via Plack::App::CGIBin) on any supported web server, which includes FCGI (FastCGI).