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Closed 10 years ago.
Define everything to do when something happens,
I really appreciate that,
but never have tried that yet.
my Q is :
How to design a state machine based system?
Have you looked at the State Pattern? Also here. Apache Commons SCXML might also be useful to you.
'State-event' driven architecture is used in quite a few application domains. In fact, there is a tool called smc (State Machine Compiler) that takes a specification for a state machine (much like lex and yacc take scanner and parser definitions) and generates code in C or other languages to implement it.
The basis of a state machine, in my experience, is the switch statement.
Each case within that represents a state of your machine.
The switch statement needs to be called on a regular basis, this can be within a coded loop, or within an event handler. It really depends on what your state machine is doing, how you want your software to run or react.
You update the state variable from within a case statement in order to change state.
Tons and tons of the little buggers.
I suggest that you look up the theoretical basis of finite state machines first and understand for what kind of tasks they are suitable for.
http://en.wikipedia.org/wiki/Finite state machine is a good place to start.
Related
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Closed 9 years ago.
Multitasking seems to be a disaster at times when big projects crashes due to shared mutation of I would say shared resources are accessed by multiple threads. It becomes very difficult to debug and trace the origin of bug and what is causing it. It made me ask, are there any design patterns, which can be used while designing multithreaded programs?
I would really appreciate your views and comments on this and if someone can present good design practices which can be followed to make our program thread safe, it will be a great help.
#WYSIWYG link seems to have a wealth of useful patterns but i can give you some guidelines to follow. The main source of problems with Multi-Threaded programs is Update Operations or Concurrent Modification and some of the less occurring problems are Starvation, Deadlocks , etc which are more deadly if i may say, so to avoid these situations you can:
Make use of the Immutable Object pattern, if an object can't be modified after creation then you can't have uncoordinated updates and as we know the creation operation itself is guaranteed to be atomic by the JVM in your case.
Command Query Segregation Principle: that is separate code that modifies the object from code that reads them because reading can happen concurrently but modification can't.
Take huge benefit of the language and library features you are using such as concurrent lists and threading structures because they are well designed and have good performance.
There is a book (although an old one) but with very good designs for
such systems, it is called Concurrent Programming in Java.
Design patterns are used to solve a specific problem. If you want to avoid deadlocks and increase debugging, there are some dos and donts
User thread-safe library. .Net java, C++ have their own thread safe libraries. Use them. Don't try to create your own data structures.
If you are using .Net, try Task instead of threads. They are more logical and safe.
You might wanna look at list of some Concurrency related patterns
http://www.cs.wustl.edu/~schmidt/patterns-ace.html
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Closed 10 years ago.
I want to compare two collections of entity framework pocos based on union and intersection. I'm trying to find out if out of the box it would be better to process these sets using f# instead of linq?
You don't need to run a profiler -- F# 3.0 supports LINQ, so you should be able to put together a small benchmarking project which uses both LINQ and the standard F# Set<'T> and measures the time to complete whatever operations you need (use System.Diagnostics.Stopwatch for this).
Here's the thing -- the answer to this question is highly dependent on your exact needs, so you need to do a bit of testing to see which is faster for your use case. For example, if you create a little benchmark app and find that LINQ (in C# or F# 3.0) is faster by 10ms, do you just go with LINQ because it's faster? Maybe, or maybe not -- it depends on whether that 10ms savings is important for your application; in most cases, it probably isn't, so you should go with whatever solution is easiest to integrate with the rest of your code.
Personally, I'd go with F# 3.0 and LINQ here, because it allows for a very succinct definition, and it may also be faster if EF can offload some or all of the computation to the database server.
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Closed 11 years ago.
What is the best turnkey (ready to use, industrial-strength) relation detection library?
I have been playing around with NLTK and the results I get are not very satisfactory.
http://nltk.googlecode.com/svn/trunk/doc/book/ch07.html
http://nltk.googlecode.com/svn/trunk/doc/howto/relextract.html
Ideally, I would like a library that can take sentences like:
"Sarah killed a wolf that was eating a child"
and turn it into a data structure that means something like:
killed(Sarah, wolf) AND eating(wolf,child)
I know that this is the subject of a large body of research and that it is not an easy task. That said, is anyone aware of a reasonably robust ready-to-use library for detecting relations?
Update: Extractiv is no longer available.
Extractiv's On-Demand REST service:
http://rest.extractiv.com/extractiv/?url=https://stackoverflow.com/questions/4732686/best-turnkey-relation-detection-library&output_format=html_viewer will process this page, extract and display the two semantic triples you desire in the bottom left corner under "GENERIC". (It throws away some of the text from the page in the html viewer, but this text is not thrown away if you utilize json or rdf output).
This is assuming you're open to a commercial, industrial strength solution, though limited free usage is allowed. It's a web service but open source libraries can be used to access it or could be purchased from Language Computer Corporation.
These relations can be read fairly easily out of the output of dependency notations. For instance, put into the Stanford Parser online, you can see both of the two subject-verb-object triples in your example in the typed dependencies collapsed representation as:
nsubj(killed-2, Sarah-1)
dobj(killed-2, wolf-4)
nsubj(eating-7, wolf-4)
dobj(eating-7, child-9)
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Closed 10 years ago.
Does anyone have a standard project that they use when learning a new language. Kinda like a specification document of a project that includes all aspects of programming. Does anyone use some sort of beginning type project when learning a new language? I guess it also depends on the type of language and what's it's capable of.
Contributing something to an open source project seems to work for me. In addition to getting exposed to some coding habits in the language , you get to work on something useful.
Going through the first few problems of Project Euler is a very good way to get a handle on topics like I/O, recursion, iteration, and basic data structures. I'd highly recommend it.
A friend of mine had a coworker who coded a minesweeper every time when he wanted to learn a new language with GUI.
I like making simple websites for learning.
Pro: you can put it online and show it to people.
Con: the language has to be suitable for web development.
Writing a simple ray tracer:
math functions (pow, sqrt, your own intersection routines)
recursion (because it is a whitted style recursive one)
iteration (for all pixels)
how to write custom types (rays, possibly vectors)
pixel wise graphics
have something to play with compiler's (optimization-) flags
optional:
simple GUI
file reading writing
I've also done so with metatrace.
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Closed 10 years ago.
Please, gurus, give me a detailed explanation of, in the Object-Oriented programming world, what is lightweight object? And in other computer science fields, what does lightweight means then? Is lightweight a design pattern? Is lightweight good, is bad?
There are many meanings for lightweight, but normally it means the object which has less amount of data or which process less amount of data. Sometimes a thread is called as a lightweight process as it does a less things than a process do. Its processing is also fast than the process. A lightweight object is one which has less amount members and which are of basic types (int, float) as member variables. A light function is the one which does very less things compared to others. Normally these are inline functions. (in C context).
There is no such patterns as lightweight pattern. But Normally the systems should be consists of lightweight objects so that the maintaining those objects could be easy.
The advantages are simple debugging, maintenance and easy understanding of code. The disadvantage could be lots of objects.
There is no lightweight pattern as such but the term is fairly used in the industry.
Lightweight X tend to be used in the case where we have a somewhat well known structure X. Lightweight X is then a version of X using fewer resources in some way or the other - or is subtly different from X in some way.
The term, as is the case for most computer science, is not well-defined and is loosely used.