 | CGI Programming with Perl |  |
FastCGI is a web server extension that allows you to convert CGI programs into persistent, long-lived server-like applications. The web server spawns a FastCGI process for each specified CGI application at startup, and these processes respond to requests, until they are explicitly terminated. If you expect a certain application to be used more than others, you can also ask FastCGI to spawn multiple processes to handle concurrent requests.
There are several advantages to this approach. A typical Perl CGI application has startup overhead for each request that includes the process of spawning a process and interpreting the code. And, if the code has a lengthy initialization process, that simply adds to the overhead. A typical FastCGI application does not suffer from any of these problems. There is no extra spawning for each request, and all the initialization is done at startup. Since these applications are long-lived, they allow you to store data between requests, which is also an advantage.
Example 17-1 shows what a typical CGI script looks like.
#!/usr/bin/perl -wT
use strict;
use vars qw( $count );
use FCGI;
local $count = 0;
while ( FCGI::accept >= 0 ) {
$count++;
print "Content-type: text/plain\n\n";
print "You are request number $count. Have a good day!\n";
}Other than a few extra details, this is not much different than a regular CGI program. Since this is initialized only once, the value of $count (a global variable) will be zero at startup and will be persistent for all subsequent requests. If the web server receives a request for this FastCGI application, it passes it on and the FCGI::accept accepts the request and returns a response, which executes the body of the while loop. In this case, you will notice that the value of $count will be incremented for each request.
If your CGI script uses CGI.pm, you can use CGI.pm's FastCGI interface, CGI::Fast, instead. CGI::Fast is included in the standard CGI.pm distribution. Example 17-2 shows how Example 17-1 looks with CGI::Fast.
#!/usr/bin/perl -wT
use strict;
use vars qw( $count );
use CGI::Fast;
local $count = 0;
while ( my $q = new CGI::Fast ) {
$count++;
print $q->header( "text/plain" ),
"You are request number $count. Have a good day!\n";
}This works the same way. Everything before the creation of a CGI::Fast object is only executed once. Then the script waits until it receives a request, which creates a new CGI::Fast object and runs the body of the while loop.
Now that you've seen how FastCGI works, let's see how to install it. FastCGI works with a wide variety of web servers, but we'll walk through the setup for Apache.
Early versions of FastCGI required a modified version of Perl to work its magic. Fortunately, this is no longer the case. However, FastCGI does require a change to your web server. The FastCGI distribution includes modules for your web server as well as the Perl module, FCGI (which is also available on CPAN). You can obtain it from http://www.fastcgi.com/, the home of the FastCGI open source project. Note this is separate from http://www.fastcgi.org/, which offers commercial solutions built upon FastCGI. In this case the .org and .com web sites are the reverse of what you might expect.
Here are the instructions for installing FastCGI with Apache. If you're using a version of Apache greater than 1.3, you can simply run Apache's configure in the following manner:
configure --add-module=/usr/local/src/apache-fastcgi/src/mod_fastcgi.c
Then, you need to determine where you will place your FastCGI applications. We let Apache know the location by adding the following directives in httpd.conf (Location goes in access.conf, and Alias in srm.conf if used):
<Location /fcgi> SetHandler fastcgi-script </Location> Alias /fcgi/ /usr/local/apache/fcgi/
For each FastCGI application that you want to start, you need to make an entry like the following:
AppClass /usr/local/apache/fcgi/fast_count.cgi
Now, when you start your Apache server, you should see a fcgi_count process in your system's process table. And you can access it by simply pointing your browser at:
http://localhost/fcgi/fast_count.cgi
Go ahead and convert one of your applications to FastCGI. You'll see a major speed improvement. Before you do that, however, a few things to note. You should fix all memory leaks within your FastCGI programs, or else it could drastically effect your system resources. So, make sure to begin your scripts this way:
#!/usr/bin/perl -wT use strict;
to check for warnings and to restrict variable scope.
Also, you should think about collapsing the functionality from your various CGI applications. Since CGI applications incur significant overhead for each request, it is a common practice to split the functionality into several little applications to reduce the overhead. But, with FastCGI, that is no longer a concern.
FastCGI offers other functionality as well, including the ability for the local web server to run FastCGI programs on remote machines. It's beyond the scope of this chapter to go into detail about that topic, but you can find more information in the FastCGI documentation.
The technology we are about to look at offers high speed improvements over conventional CGI applications, much like FastCGI, but does so in an entirely different manner.
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| 17. Efficiency and Optimization |  | 17.3. mod_perl |
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