Threads and processes? [closed]

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In computer science, a thread of execution is the smallest unit of processing that can be scheduled by an operating system. This is very abstract!

1. What would be real world/tangible/physical interpretation of threads?

2. 开发者_高级运维How could I tell if an application (by looking at its code) is a single threaded or multi threaded?

3. Are there any benefits in making an application multi threaded? In which cases could one do that?

4. Is there anything like multi process application too?

5. Is technology a limiting factor to decide if it could be made multi threaded os is it just the design choice? e.g. is it possible to make multi threaded applications in flex?

If anyone can could give me an example or an analogy to explain these things, it would be very helpful.

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• What would be real world/tangible/physical interpretation of threads?

  Think about a thread as an independent unit of execution that can be executed concurrently (at the same time) on a given CPU(s). A good analogy would be multiple cars driving around independently on the same road. Here a "car" is a thread, and a road is that CPU. So the function of all these cars is somewhat the same: "drive people around", but the kicker is that people should not stand in line to wait for a single car => they can drive at the same time in different cars (threads). Technically, however, depending on number of CPU cores, and overall hardware / OS architecture there will be some context switching, where CPU would make it seem it happens simultaneously, but in reality it switches from one thread to another.

• How could I tell if an application (by looking at its code) is a single threaded or multi threaded?

  This depends on several things, a language the code is written in, your understanding of the language, what code is trying to accomplish, etc.. Usually you can tell, but I do not believe this will solve anything. If you already have access to the code, it's a lot simpler to just ask the developer, or, in case it is an open source product, read documentation, post on user forums to figure it out.

• Are there any benefits in making an application multi threaded? In which cases could one do that?

  Yes, think about the car example above. The benefit = at the same time and decoupled execution of things. For example, you need to calculate how many starts are in a known universe. You can either have a single process go over all the stars and count them, or you can "spawn" multiple threads, and give each thread a galaxy to solve: "thread 1 counts all the stars in Milky Way, thread 2 counts all the starts in Andromeda, etc.."

• Is there anything like multi process application too?

  That is a matter of terminology, but the cleanest answer would be yes. For example, in Erlang, VM is capable of starting many very lightweight processes very fast, where each process does its own thing. On Unix servers if you do "ps -aux / ps -ef", for example, you'd see multiple "processes" executin, where each process may in fact have many threads doing its job.

• Is technology a limiting factor to decide if it could be made multi threaded os is it just the design choice? e.g. is it possible to make multi threaded applications in flex?

  2 threaded application is already multithreaded. You most likely already have 2 or more cores on your laptop / PC, so technology would pretty always encourage you to utilize those cores, rather than limit you. Having said that, the problem and requirements should drive the decision. Not the technology or tools. But if you do decide write a multithreaded application, make sure you understand all the gotchas and solutions to them. The best language I used so far to solve concurrency is Erlang, since concurrency is just built in to it. However, other languages like Scala, Java, C#, and mostly functional languages, where shared state is not a problem would also be a good choice.