Programming

Yes. For example say you call a bunch of functions or sub-routines in a c-program, they would appear on the call stack in the following order (where function2() is the most recent function to be called, function1() was called before function2() etc... )

Code:

 function2()
 
 function1()

  main()

Please let me know if that helps in anyway

You are absolutely correct.
A main is also a thread; they way it has a calling sequence to a function, the way a posix thread calls to functions look like.

Ramen: Can't we call epoll()/kqueue() in the threads; why to call in the main thread (in the hi-performing server apps -as you have said) even in the asynchronous nonblocking calls?? I know kqueue() a bit but still not much can we discuss this in the rest of the thread?

thanks Praveen

Praveen: As you yourself noted the utilization of whatever event servicing mechanism you use is going to execute in a thread. Soo I don't think that your question is ingenuous.

My point was that if you service a client with a separate thread you will run out of resources pretty quickly given a sufficiently complex interaction and number of clients.
With asynchronous service and a single thread you do not incur the memory overhead of separate threads and stack space for each.

Frankly Ramen, I never got a chance to use epoll()/kqueue(). I've only been able to use select()/poll() for such event notification machanism, at least in the commercial projects, we've worked on. I also wanted the discussion to be carried further on event notification machanisms so that we get benefited along with many others in the forum and kqueue()/epoll() are good candidates to be discussed. Pl don't take otherwise.

Still may we discuss them further on which Unix/Unix Like platforms support it apart from Linux/BSD (which I've only worked so far)?

Praveen:
Your use of select and poll in commercial (I'm reading as designedly portable software to various unixes) is understandable. epoll and kqueue are, after all, linux/*bsd specific.

Still pselect/select and poll are perfectly good event interfaces after all.
epoll seems to have a superior interface to select/poll with the notable absence of signal processing ala pselect.

I haven't worked with kqueue but am familiar with the interface from reading 'The Design and Implementation of The FreeBSD Operating System'.
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