I have looked online at making a multi-threaded server in perl, but i cannot find any good ones that clearly explain how to create one. I have created a server and client in perl but i do not seem to be able to make it multi-threaded. Can someone help me?
Assuming you are using the Net::Server CPAN module (rather than rolling your own), you could make use of Net::Server::Coro to build a multi-threded server. Note that Net::Server can handle (pre)forking (i.e. multi-processes) servers and these may be easer to use.
I think POE might be what you're looking for.
See the POE Cookbook for examples.
Related
Im required to use wget for its ability to work like a crawler to develop one for my project. But all around in google searches im seeing people recommend to use LWP instead of Wget. Can you guys enlighten me on why this is so?
If you're writing Perl and need to make an HTTP request, you should generally use LWP. It's silly to shell out to do something that is easily supported within the Perl process.
If you want to do something more complex, like recursive web crawling, you may want to look at the WWW::Mechanize or Mojolicious modules available from CPAN. But at that point it might be reasonable to shell out to take advantage of an external tool that already has recursive web-crawling capability.
If you're writing a shell script rather than a Perl program, then you have no choice but to use an external tool. The choice among wget, curl, and the LWP scripts (lwp-request, GET, etc) really comes down to what's easiest for your use case. They all have have approximately the same features, but some things are easier in one tool than the others. Use what's readily available for your system; there's usually more than one option, in which case you should give them all a try - read the doc, try a few use cases, see which one you like.
I have least knowledge on network domain.Please bare with my question if it is basic
I would like to know how to communicate between two applications using TCP/ip protocol in
windows XP say for example
Using Perl and TK I am building a GUI with entry widget and i have an other external application which is installed in the system say APPLICATION.exe
Now i need to establish the connection using TCP between my perl program and external application APPLICATION.exe
for testing purpose what ever I type in the GUI Entry this external application has to receive (hope it receives as bytes)and external application will send some data and i need to process that data in my perl program..
I am totally unaware whether this is simple task or complicated.
If there are any modules existing in perl for similar programming please suggest me.
I highly appreciate if anyone can provide me the answer with an example.
Thanks to all
It is simple if you have done network programming before. If not, it is intermediately difficult because you need to get a grip on the underlying concepts and terminology first - read a book about the topic if necessary.
I recommend to use IO::Socket::IP. If you have Perl 5.14 or later, you can also use IO::Socket::INET that is distributed with Perl. See https://stackoverflow.com/a/8582550/46395 for a code example and links to further documentation.
I recently joined a Perl project and I need to start being productive with the codebase fairly quickly. However, I'm finding that I'm getting stuck because I don't know where I need to change or how all the parts of the code fit together.
What are your tips and tools for becoming familiar with a Perl codebase that you have no experience with?
(Note: I realize that there's already a similar question. I'm wondering if there's any Perl-specific strategies.)
First, if the previous maintainers were doing their job well, you should have an extensive test suite and perldoc documentation for each module and script in the codebase. If so, read through the perldoc, and read through the tests. The perldoc should give you an overview of what things do, and the test suite will give you examples of the code being used in context.
Depending on the author, the internal comments may be useful in understanding the intention of the code, so looking through the actual source my provide insights into algorithms, bugs, and intended use as well.
If you don't have any of these, proceed as you would for any badly-maintained codebase: start small, writing programs that try to use the code, and use Test::More and the like to start turning these into a test suite.
In the first case, you may find it to be very simple, in the second, very hard. Peter Scott's Perl Medic can be very useful in assisting you in turning such a codebase into something usable and useful if you're stuck with the second case, and Mike Thomsen's recommendation of Effective Perl Programming is also a good one.
I work on Melody which is written primarily in Perl. It's a rather large code base, and I've found the process of learning the Melody code base is identical to any Java system I've worked on.
It really comes down to just working with it, googling when you see behavior you've never seen before and experimentation.
This book is a great reference for picking up Perl in a serious way. It's not very dense and it will teach you a lot about proper Perl development.
Besides the "similar question", http://perldoc.perl.org/ and an empty test.pl file is a good starting point!
I would like to see a real answer here. The only thing I have is more questions (you don't have to provide answers here, just ask yourself):
Goal
What is the goal of the project, what it is supposed to do?
Who knows the workflow?
Environment
Can you set up the project in a clean test environment?
Does it use a versioning system?
Where are the entry points (i.e. executable files)?
Does it rely on external programs?
Does it require additional system tweaks (i.e. cron scripts)?
Perl code
Is your project using strict and warnings everywhere?
Which CPAN modules are used?
Are there any frameworks used (Moose, Catalyst, probably some ORM, ...)?
Are there any perldocs in the project's modules?
Are there any tests (notably t/*.t)?
I usually start with working on some simple bug report or a simple feature I want to add. While working on code I write comments for code and commit them. Writing tests also helps.
I have been trying to decide if my web project is a candidate for implementation using PSGI, but I don't really see what good it would do for my application at this stage.
I don't really understand all the fuss. To me PSGI seems like a framework that provides a common interface between different Apache modules which lets you move your application between them. e.g Easily move your application from running on mod_perl to fastcgi, and provide the application support for running on both options.
Is that right, or have I missed something?
As I and the team I am a part of not only develop the application, but also pretty much do maintenance and setup of servers I don't see the value for us of being able to run on fastcgi, cgi, and mod_perl, we do just fine with just mod_perl.
Have I misunderstood the PSGI functionality, or is it just not suitable for my project?
Forget the Apache bit. It's a way of writing your application so that the choice of webserver becomes less relevant. At $work we switched to Plack/PSGI after finding our app running with very high CPU load after upgrading to Apache2 - benchmarking various Apache configs and NYTProf'ing were unable to determine the reason, and using PSGI and the Starman webserver worked out much better for us.
Now everything is handled in one place by our PSGI app (URL re-writes, static content, expiry headers, etc) rather than Apache configuration, so it's a) Perl, and b) easily tested via our standard /t/ scripts. Also our tests are now testing exactly what a user sees, rather than just the basic app itself.
It may well not be relevant to you if you're happy with Apache and mod_perl, and I'm sure others will be able to give much better answers, but for us not having to deal with anything Apache-related again is such a relief in itself. The ease of testing, and the ability to just stick in a Data::Dumper and see what's going on rather than wrestling with ModRewrite and friends, is a great boon.
Borrowing from a recent blog post by chromatic, Why PSGI/Plack Matters (Testing), here's what it is:
It's a good idea borrowed from Python's WSGI and Ruby's Rack but made Perlish; it's a simple formalizing of a pattern of web application development, where the entry point into the application is a function reference and the exit point is a tuple of header information and a response body.
That's it. That's as simple as it can be, and that simplicity deceives a lot of people who want to learn it.
An important benefit is, ibid.,
Given a Plack application, you don't have to deploy to a web server—even locally—to test your application as if it were deployed … Plack and TWMP (and Plack::Test) use the well-defined Plack pattern to make something which was previously difficult into something amazingly easy. They're not the first and they won't be the last, but they do demonstrate the value of Plack.
Started wrote an answer and after 50 lines I deleted it. Simply because it is impossible tell (in short) why is PSGI extremely cool. I'm new in PSGI too, but zilion things now are much easier as before in my apache/mod_perl era.
I can give you next advices:
read the Plack advent calendar - all days, step-by-step. You must understand the basic philosophy, what is good on onions and so on... :)
search CPAN for "Plack::Middleware::" - and read the first few lines in each. Here are MANY. (Really should be somewhere some short overview for each one, unfortunately don't know any faster way. Simply it is good to know, what middlewares are already developed. (For example, you sure will need the Plack::Middleware::Session, or Plack::Middleware::Static and so on...)
read about Plack::Builder (already done, when you done with the advent calendar) :)
try write some apps with it and will find than Plack is like the first sex - now you didn't understand that you could live without it.
ps:
If was here something like "Perl Oscar", will sure nominating MyiagavaSan. :)
looking into connecting to a secure ftp site (using perl), and downloading all the .log files, saving in new directories named after the day I downloaded the files. I want to do this without modules, as a learning experience, but before I start I wanted to know if you guys thought it was doing, or is way too much for a relatively new programmer and I should just learn the modules?
If it's production work, no, use the modules. Your implementation will be buggy, missing features and unknown to the next person maintaining that code.
Otherwise, yes. It's good to learn the principles of a network protocol. I do have a reservation about FTP as it is a bit baroque, insecure, inefficient and on its way out. scp, HTTP or rsync would be more useful to put your energy into.
I'd start with reading the RFC and putting together your own FTP module using just network sockets. Document and test it as if you were going to release to CPAN as a full learning exercise in making a network module. Run it against some various FTP server implementations as they often interpret the spec differently (or not at all). Don't be afraid to cheat and look at what the existing modules do. Who knows, you might write something better than what's already there.
Learning the principals, just like we did at school for long multiplication and division, means we know how things work when we use a short hand.
However, when new to the world,just like when you learn to speak, you did "A is for Apple" etc, you didnt get explained about the finesse of grammar and all that, you learnt to express yourself enough to be understood.
Programming is a little like the same. While in an ideal world you can easily argue a prewritten generic library is often way less efficient than a specifically targeted set of routines. If the wheel you are using was already invented, it seems a lot of work to make a new one.
So, use the wheels and cogs afailable, once you really have the hang of it, NOW look at inventing your own more efficient ones.
Ad cpan modules:
Modules are an great learning source. Here is zilion modules and you can really learn much studying some of them.
And when/while you mastering your perl, you will start writing you own modules. When your program will use modules anyway (yours one), you can ask - why don't use modules already developed and debugged?
So, learn perl basics, study some modules (for example Net::SFTP) and if you still want write your own solution - it is up to you. :)
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