Re: [Qexo-general] XQuery as CGI scripts

[Per Bothner]

Jun Yu wrote:

> Hello everybody,
> I have a few questions about "Installing XQuery as CGI scripts".
>
> 1. In the description "Installing Kawa programs as CGI scripts", there are
> such steps:
> (1)kawa --servlet --xquery -C hello.xql
> (2)cp hello*.class /var/www/cgi-bin/
> (3)find the cgi-servlet program that Kawa builds and installs.
> (4)Copy this program into the same CGI directory:
>      cp /usr/local/bin/cgi-servlet /var/www/cgi-bin/
> (5)Run the Kawa program: http://localhost/cgi-bin/hello
>
> my question is:
> (1)The step(1) will get a group of class files like hello*.class , not
> only a single hello.class ?

Yes - because occasionally the Kawa compiler will create more than
just hello.class, but may also create some extra helper classes.

> (2)Normally Java class files have to be executed through Java interpreter.
> Why do not need it? 

It does - cgi-server program invokes a Java VM.  See the source code
in bin/cgi-servlet.c.

> The cgi-servlet program is Kawa's supplied
> CGI-to-servlet bridge ? Does it function as Java interpreter?

It invokes a JVM.

> (3)Usually, executing a CGI program, we should use
> "http://localhost/cgi-bin/hello.class";, but step(5) use
> "http://localhost/cgi-bin/hello"; ?

Step (4) is a typo.  It should be:

cp /usr/local/bin/cgi-servlet /var/www/cgi-bin/hello

(You can instead create a link, if you have multiple scripts.)
So 'hello' is the CGI executable.  The Web server runs the
hello program, which is really just the cgi-servet program,
but which get the name it was invoked under and uses that
as the name of the servlet class.

> 2. Comparing "Running XQuery as CGI scripts" with "Running XQuery as
> servlet".
> It says, the former "may take a few seconds to get the reply, mainly
> because of the start-up time of the Java VM. That is why servlets are 
> preferred."
> I have some thought, but I am not sure if it is right. The following is my
> description:
> ----
> A CGI program parse a client request through environment variables. Some
> of these variables may change for each HTTP request. The web server starts a new
> system process for each request. Thus the server must give the Java VM a new set
> of environment variables for each client request. Both the Java VM and the
> CGI program end this request and restart for next request.
>
> The Java Servlets technology process each request with either doGet() or
> doPost() method. Both of them read a client request from the object
> "HttpServletRequest", and respond the client with the object
> "HttpServletResponse". It avoids using environment variables.
>
> That is why running XQuery programs as CGI takes more time than as
> Servlets.
> ---

Yes, that is correct.  Running a servlet only requires starting up the
Java VM once, on the first request.  If your web server is Tomcat,
you already have a JVM running, of course.
--
        --Per Bothner
address@hidden   http://per.bothner.com/