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In a program, I can design lock to threads,lock to object or files.
Are there difference between these locks?
If yes,
how many kinds of lock are there which can be used to design?
Are there some tutorials to design locks in object-oriented programming?
As someone dss538 said, the "answer" really depends on the context of the question.
What exactly is it that you need to protect access to?
An piece of data or single object, items in a container of some sort, a piece of code, a system resource like a shared file?
Another really meaningful question is how frequently are you going to be accessing this "thing" and what are you going to do with it?
Different locking techniques tend to have different overheads and while a critical section or mutex may be perfectly fine for something that is rarely accesseed and rarely updated, if you're rarely updating it and frequently accessing it you might want to look at a reader writer lock. Another follow up question here is "should I be using spin-locks" here, and again the answer is it depends? What else is going on in the system and are you going to trade one kind of bottleneck (a coarse grained lock) for another?
A final question I like to ask is what are the alternatives to "locking" something, i.e. if I can "safely" take a copy of my protected thing and work with that copy "safely" (ideally without modifying it), it's certainly a lot easier than worrying about every place I might modify said "thing."
I apologize for the vague answer but a more specific question would help here.
I would encourage you to read up on concurrency prinicples and understand the traditional "Dining Philosopers" "Sleeping Barber" and perhaps even "Santa Clause" problems to understand more context of how these things work.
A lot of the content on Wikipedia is good, particularly 'Concurrency Control' is a useful starting reference point if you don't have a good OS / Concurrency book on your shelf.
The answer depends on the context of your question.
Are you obtaining locks from some API? Check the API documentation.
In general, though, I would say no. A lock is a lock. The fact that you are using it to protect a file or an object does not matter to the API. How you use it is up to you. You certainly could abstract away and have FileLocks and ObjectLocks if you wish, but that is up to you.
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I've started to study concepts like Cohesion and principles like Single Responsibility Principle. I am very confused about the difference between them.
The web has a lot of information, but I find it very difficult to filter out the correct comparison.
What is the relationship between Cohesion and Single Responsibility?
Is it possible for a class to have only one responsibility but low cohesion?
Cohesion can be seen a software quality metric, while SRP is more of a subjective software quality principle. As the Pragmatic Programmers describe it, cohesive code happens when things that belong together and depend on one another stay together.
For instance, if a class's instance variables or properties are all used by its methods and its methods alone, but the methods also do not use any external data or methods from other objects, that class is said to be highly cohesive. However, if that class happens to be reading and writing from a file, that class can be seen as not adhering to the Single Responsibility Principle, as reading and writing can be viewed as two very distinct tasks. Regardless, you can also see the class's main task as "do IO operations with the file system", so SRP is somewhat open to interpretation depending on the context it's applied.
This concepts are described in a concise manner in Wikipedia here and here.
One responsability is still an abstract concept. If the responsability is to build a report, it is one task, but still a task with several steps and data parts. So there is some space for low cohesion to happen in the class. Just making a calculation, if simple, is much more "atomic" and high cohesion.
If you see SRP as having a single reason to change the class, I think that helps too.
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Why do we use OOPs concepts?
What are the advantages/disadvantages of OOP?
Where do we use OOP?
How do we tell if a program can be written in OOP paradigm? How is it organized?
Note : I'm not related to technical field... So please consider this in your answers.
In short: to reduce the cognitive load required to write, maintain and understand the software.
Software systems are inherently complex, so developers need some tools to break things down to the modules and individual components that could be analyzed and understood without enormous efforts — and OOP is just that kind of tool.
Thats quite a big question. And I try to give you a feeling why we do develop principals like oop ,soa,....
Most of the principal target to make software less complex. Imagine a file with 1.000.000 functions. it would become difficult to find the you want to change. Especially if there are not veryx wqell name like "Update" so you could have a thousand "update" methods.
Often things are less complex if you don't see the complete information pool so you can focus and things you may need. Thats also why there ideas like the information hiding principle .
Another thing is that when you have standards you have to think about. For example in Real life you know that you can sit on a chair (thats a standard) you don't ahve to think about it. Thats why standards make like easier. Some aspects of OOP establish standards (e.g. use of classes) therefore there is little less complexity.
Having class which are grouping the functions may be the first step towards oop. Now when you search a function you would most propably know what you want to udpat "a custoemr" so you know this function may be in the customer class and you have to only look over these methods.
And most of the time thats what principals are made for. making software more read and understandable
OOP is much much more and not the only paradigm .But there is so much more and OOP has so much principals and interprations. It would be too much to explaind and discuss it here. I would also recommend you to have a look at the CleanCoders Movement which provide this in a more general way.
CleanCoders Webcasts
Does ORganization matter
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I'm currently developing the front end of a new CMS for a digital streaming company, the main problem the project has is keeping track of the technical language that has sprung up around it.
It currently involves around 60 staff in four countries, aside from a wiki (which has thus far failed to be kept up-to-date), anyone have any good tools or tips for building and maintaining a glossary for a project like this?
aside from a wiki (which has thus far failed to be kept up-to-date)
This comment makes me pretty nervous about suggesting other solutions. Wiki's can come with their own problems, but keeping it up to date is not a problem inherent in the platform. It's a cultural or organizational problem. A wiki provides a very easy way to track and update data. If, today, you cannot keep it up to date, ask yourself how you will solve this problem if you change the tool?
Changing to another platform could solve things like: The wiki isn't scalable for that amount of data; we want to make controlled edits; we need to release in multiple languages; we need to release in other formats.
For the updating problem, try something simple to start, like assigning a dedicated team member to glossary maintenance. They don't have to be the only contributor, but if you have someone who is dedicated to paying some attention to this area you will have a much better chance of keeping things up to date.
In an untended garden, it's not the fault of the soil that you have no flowers.
DITA has a glossary specialization. You can maintain a central company glossary in it. In individual company documents, you create a mini glossary topic then use a content reference to pull any terms you need into your document.
It does sound more like a version control issue though.
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I am a student, with decent knowledge of SQL, but have had very little to do with triggers in the past. I've looked at a few sites for guidance, but comprehensive explanation on all commonly used statements seems fairly sparse.
Is there a 'definitive' site for this kind of thing? Perhaps like a w3chools for advanced SQL?
Once you know a little SQL, try to check out Joe Celko's books. Advanced SQL Programming has a short section on triggers. Since you're a student, you can probably get a copy at the library. If you think you're going to be doing deeper SQL dev work, you'll be glad to score your own personal copy of the book. You can get the relational DB engine to do a significant amount of work in a small amount of code - thinking that way will make you a much more efficient programmer. Most book stores (my local Borders always has a couple copies) will have a copy on the shelf, so browse before you buy.
Also, check out the online manuals for the database you're using as itsmatt suggests.
I've always thought that the SQL Server Books Online (installed with SQL Server) were a good source of info.
This sounds a bit like an "old shoe or glass bottle" question.
Triggers are one of those things that you should really stay away from unless you really really know what you're doing and have a very good reason for doing what you're doing. So naturally, one of the prerequisites to ever using a trigger is that you should have a thorough understanding of how they work and their implications. Thus, you can see how the idea of an "Intro to Triggers" text may sound like a very dangerous thing to some people.
So my advice, cruel as it may sound, is this: If you're the sort of person who needs an intro text on this particular topic, then you might be better served in the long run by simply avoiding Triggers for the time being.
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Perhaps if I make the my documentation better I could spend less time supporting developers and more time developing myself:
I develop a critical platform used by 10 other developers and 50 end users. The developers are of mixed ability ranging from domain-experts to relative beginners. Since I'm one of the people who know how the core platform works support requests from other developers usually go via me.
Our documentation is the usual sort of descriptive stuff any mature project will have: We have a large wiki containing details of all the usual operating procedures plus extensive API documentation.
Unfortunately it does not cater well for "how do I fix " type questions:
Would it be possible to make some interactive fault diagnostic documentation that puts users through a standardized fault-finding routine. The documentation would ask users a series of questions, and depending on the user's input would tell them what to do... it would be a very simple expert system, or possibly a documentation state-machine.
The idea would be to help newbies think more methodically about diagnosing faults in this complex system.
My question:
Are there any free tools intended to implement this kind of user-experience? I'd rather not hand-roll this. There must be some kind of framework for interactive help & documentation.
Has anybody implemented this kind of system before?
If you just wanted to have a flowchart/stat-machine thing where the user moves from the start point to a set of possible solutions by answering questions, then you could probably implement this as a set of wiki pages, where the possible responses to questions on one page are links to other pages.
This solution relies on being able to represent the answers to questions as links, which isn't going to work if the information is more form-like. For example, suppose one question is "What brand of graphics card do you have?" where the answer is one of 300 possible options. In this case it's going to be tiresome to create the links :)
If the developers are asking too many questions then I would suggest making them research the question themselves and come up with an answer, then double-check with you instead of encouraging them to ask you every time. It's much easier to ask somebody else than to find the answer yourself, but they're never going to learn if they don't look for themselves.
If the users are asking a lot of questions then you may need some user interface improvements. Try putting hints in the application itself at the top or bottom of the screen maybe.
For both groups of users a wiki can help.
a FAQ in your wiki
if an error happens too often, try preventing it or output a more useful error message (like "if this happens, the likely cause is that...)