I'm reading a book on ASP.NET MVC, and it states:
"NVelocity is a port of the Java Apache Velocity template engine, and NHaml is a port of the Ruby on Rails Haml engine".
What does the word 'port' mean in this instance?
From the Porting (Software Engineering) entry on Wikipedia:
In software engineering, porting is the process of adapting software so that an executable program [or library] can be created for a computing environment that is different from the one for which it was originally designed (e.g. [different language, ] different CPU, operating system, or third party library) ..
.. the term "port" is derived from the Latin portare, meaning "to carry". When code is not compatible with a particular operating system [or language] or architecture, the code must be "carried" [or "ported"] to the new system.
Thus, "a port" is the result of "porting", and there are many different kinds of "ports".
In some cases a port might be "only in spirit" that heavily borrows from the ideas of the original implementation but otherwise shares no code; libraries often further diverge to take advantage of the target language features.
On the other hand, application ports - especially those that are designed to be portable between different "UNIX" environments - might share everything but the build process.
Related
What is the main difference between configurations and environment variables in a software?
For configurations in a conf-file, like address, port, and file path, they may be regarded as environment variables as well. But for configurations like dfs.namenode.audit.log.debug.cmdlist(A comma-separated list of NameNode commands that are written to the HDFS namenode audit log only if the audit log level is debug.) in HDFS, should not be environment variables. In my opinion, both of configurations and environment variables are setting parameters for the software running environment. Therefore, configurations can be regarded as generalized environment variables. But there do exist some counterexamples. I want to know what's wrong with this idea and the difference between configurations and environment variables.
Parameters for an application might be specified not just via configuration files or environment variables, but in other ways too, such as command-line arguments, the Windows Registry, or a database table.
I don't think it is useful to think of any one approach to be a generalisation of another approach. Instead, the different approaches are competing technologies. By Analogy, CDs competed against audio tapes and vinyl discs rather than being a generalisation of them.
It can be possible to integrate several competing technologies. For example, a music system might integrate a tape deck, turntable, CD player, radio and an AUX-in port (to connect to, say, an MP3 player) so you can enjoy music from any of several competing technologies. If you want to see an example of integrating several competing configuration technologies, I suggest you read Sections 2.5 and 3.5 of the Config4* Getting Started Guide to see how the Config4* configuration-file parser (developed by me) integrates with environment variables and command-line options.
Time and again I am faced with the issue of having multiple environments that must be configured individually for an application that would run in all of them (e.g. QA, regional production env's, dev, staging, etc.) and I am wondering what would be the best way to organize different configurations?
Would it be in the database? Different configuration files per environment? Or maybe the same file with different sections/xml tags? How would these be then deployed? Embedded within the app? Or put manually in after installation to be modified in-place?
This question is not technology-specific - I've worked with .net and Java, web-apps and desktop apps and this issue comes up time and again. I'm looking to learn different approaches to maybe adapt a hybrid to address this.
EDIT: There's one caveat that I must point out - when configuration is part of the deployed solution, it is generally installed under root user on the host. In large organizations developers usually don't have a root access to production hosts so any changes to the configuration require a new build and deployment. Needless to say this isn't the nicest approach - especially at organizations that have a very strict release process involving multiple teams and approval levels... (sigh I know!)
Borrowed from Jez Humble and David Farley's book "Continuous Delivery (page 41)", you can:
Your build scripts can pull configuration in and incorporate it into your binaries at build time.
Your packaging software can inject configuration at packaging time, such as when creating assemblies, ears, or gems.
Your deployment scripts or installers can fetch the necessary information or ask the user for it and pass it to your application at
deployment time as part of the installation process.
Your application itself can fetch configuration at startup time or run time.
It is considered bad practice by them to inject configuration files in build and compile times, because you should be able to deploy the same binary file to every environments.
My experience was that you could bake all configuration files for every environments (except sensitive information) to your deployment file (war, jar, zip, etc). And you design your application to take in an extra parameter when starts, to pickup the right sets of configuration files (from your extracted deployment file, or from local/remote file system if they are sensitive, or from a database) during application's startup time.
The question is difficult to answer because it's somewhat vague. There is no technology-agnostic approach to configuration as far as I know. Exactly how configuration is set up will depend on the language/technology in question.
I'm not familiar with .net but with java a popular approach is to have a maven build set up with different profiles. Each profile is specific to an environment. You can then define different properties files that have environment-specific values, an example from the above link is:
environment.properties - This is the default configuration and will be packaged in the artifact by default.
environment.test.properties - This is the variant for the test environment.
environment.prod.properties - This is basically the same as the test variant and will be used in the production environment.
You can then build your project as follows:
mvn -Pprod package
I have good news and bad news.
The good news is that Config4* (of which I am the maintainer) neatly addresses this issue with its support for adaptive configuration. Basically, this is the ability for a configuration file to adapt itself to the environment (including hostname, username, environment variables, and command-line options) in which it is running. Read Chapter 2 of the "Getting Started" manual for details. Don't worry: it is a short chapter.
The bad news is that, currently, Config4* implementations exist only for C++ and Java, so your .Net applications are out of luck. And even with C++ and Java applications, it won't make pragmatic sense to retrofit Config4* into an existing application. Because of this, I'd advise trying to use Config4* only in new applications.
Despite the bad news, I think it is worth your while to read the above-mentioned chapter of the Config4* documentation, because doing so may provide you with ideas that you can adapt to fit your needs.
I'm looking for a development platform (language and set of libraries) that will allow me to develop a personal project. (In case anyone is curious, I'm looking at making a music library manager, similar to iTunes, that can work on multiple platforms and sync with Android devices).
I want the language to have the following characteristics:
Essential
The program must run flawlessly, with no (or very little) code changes on Mac, Linux, and Windows. That means, notably, that I need to have a cross-platform GUI framework, a consistent API for accessing files and directories, and a consistent interface for talking to USB storage devices
Important
A language that is easy to use, powerful, and expressive. Big standard libraries with a lot of built-in functionality. (I'd probably use C#/.NET but the portability isn't great)
Nice to have
Good tool support (on Linux if possible, but I'll do my development on Windows if needs be)
Not Java. (I have used it and just don't like it - I'm not interested in getting into a language war here).
Please help me choose a language!
Python
Cross platform GUI: more than one option, I'd use WxPython, but Qt bindings are also available (comparison between wxWidgets and Qt).
File System API: this gets into the os package, but there are also convenience methods for just dealing with I/O.
USB I/O: I confess to not having any knowledge here, but suspect if you're talking storage that Python will be able to read and write using its IO package.
Libraries, Ease of Use, etc..: there's a lot built in, but also a huge number of add-ons (called "packages"). Some of the most notable are SciPy and NumPy, used for scientific and numerical analysis.
Tooling: there are a number of IDEs out there, I use PyDev (but it's Eclipse based so you probably won't like it if you don't like Java).
Finally, Python is supported on Android via its scripting environment.
For cross platform GUI, you can explore QT. The back-end can be on c.
Have you explored anything so far?
Qt quick ?
Simple question, I want to know is Java free (especially for web development). Later on if I've build a large website, will the servers, databases cost me much like in .net for example?
Cheers.
Java is free. Check licences of frameworks you're using, but you shouldn't worry about that since most of them are free.
Servers (physical) will, of course, cost you.
There are free application servers like Glassfish and JBoss.
There are free databases like mySQL and PostgreSQL.
So, you can get away with everything being free except hardware and, possibly, hosting of your web app.
Yes and no - depending on how big your site gets, you may be required to invest more money into better servers/databases.
It's not really something that can just be answered, without looking into the future.
Update, as of 2021
Be sure to read the document prepared by pillars of the Java community, Java is Still Free. This document provides a short overview as well as a longer section with all the gory details.
Understand that Java is a set of specifications, not a product.
Java Language and Virtual Machine Specifications
JEPs and JSRs
Many vendors provide binaries or installers for an implementation of Java. Nowadays, all of those implementations are based largely or entirely on the OpenJDK project. Participants including Oracle, IBM, SAP, Apple, Azul Systems, and more have banded together to pool their best technologies for implementing Java as open-source free-of-cost.
The OpenJDK project provides only source-code. Various vendors build that source code to provide binaries or installers for you and me to conveniently put Java on our computers. Some of their distributions of Java are available free-of-cost, and some are commercial with paid support. Some are general-purpose JVMs, and some are special-purpose. Some are a basic JDK and some have bundled extras.
Here is a diagram I made to help you in choosing a vendor for a Java implementation.
And some considerations to think about when choosing a vendor.
I am currently working on a design for a collection of subsystems, and I would like to be able to offer the API's exposed by a given subsystem for use by other subsystems.
In the past, I have used SWIG to expose C api's to a variety of other languages. This has worked well for me, but ultimately the API is defined in C. So basically one side of the API is language agnostic, and the other isn't.
What I would really like is to have something similar to SWIG that could generate the interface between 2 arbitrary languages based on some description of the API.
I don't want to use web services.
For example, I would like to call a 'function' from java, and implement the 'function' in Python. I'd like to be able to generate the language interop using a code generator.
Is there anything that exists which can do this today? At least for simple 'function' calls - ignoring the more complex cases like callbacks and situations where you need to maintain references outside of the 'function' call itself.
I found this after following gooli's link to Protocol Buffers .
This looks so compelling I'm going to propose it as an answer to my own question.
http://incubator.apache.org/thrift/
Thrift is a software framework for scalable cross-language services development. It combines a software stack with a code generation engine to build services that work efficiently and seamlessly between C++, Java, Python, PHP, Ruby, Erlang, Perl, Haskell, C#, Cocoa, Smalltalk, and OCaml.
From the whitepaper:
...we were presented with the challenge of building a transparent,
high-performance bridge across many
programming languages. We found that
most available solutions were either
too limited, did not offer sufficient
datatype freedom, or suffered from
subpar performance
Also from the whitepaper:
A. Similar Systems The following are software systems similar to Thrift.
Each is (very!) briefly described:
SOAP. XML-based. Designed for web services via HTTP, excessive XML
parsing overhead.
CORBA. Relatively comprehensive, debatably overdesigned and
heavyweight. Comparably cumbersome
software installation.
COM. Embraced mainly in Windows client softare. Not an entirely open
solution.
Pillar. Lightweight and high-performance, but missing
versioning and abstraction.
Protocol Buffers. Closed-source, owned by Google. Described in Sawzall
paper.
The last part about Protocol Buffer's is out-of-date - its been open sourced
COM (and to a lesser extent Firefox's XPCOM) might be what you are looking for. In COM, you define the API using a language called IDL which can then be compiled into different languages. When using the same language the calls usually degenerate into efficient function calls.
However, COM is a very complex and dying piece of technology that I would never use for a new project.