Implementing Semaphores, locks and condition variables

Question

I wanted to know how to go about implementing semaphores, locks and condition variables in C/C++. I am learning OS concepts but want to get around implementing the concepts in C.

Any tutorials?

Answer 1

Semaphore at the very simplest is just a counter you can add and subtract from with a single atomic operation. Wikipedia has an easy to understand explanation that pretty much covers your question about them:

http://en.wikipedia.org/wiki/Semaphore_(programming)

Answer 2

You can catch up with alot of IPC( Inter Process Communication) Books, that can explain the ins and outs of what you need. There is one classic book. Unix Network Programming Inter Process Communication by Richard Stevens. you will get all you need. :)

Answer 3

For basic understanding, you can refer book Operating System Concepts, by Avi Silberschatz, Peter Baer Galvin, Greg Gagne and is really good.

You can also visit Dave Marshall's site for some support. Refer Semaphore section there.

Answer 4

At the ground level, if you want to implement that sort of thing, you're going to need to use assembly language. C and C++ simply don't expose the sort of features necessary to write concurrent code --- except by using libraries, which use assembler in their implementation.

Answer 5

A good starting point for learning OS concepts is probably Andrew Tanenbaum's "Modern Operating Systems". He also has another book on his own OS (Minix), which is called "Operating Systems: Design and Implementation" which goes more into detail about coding. You should be able to find those books in your local library.

Related topics you might want to look up to get the grip on how and why to use semaphores: race conditions, synchronization, multithreading, consumer-producer-problem.

Answer 6

Semaphores, locks, condition variables etc. are operating system concepts and must typically be implemented in terms of features of the operating system kernel. It is therefore not generally possible to study them in isolation - you need to consider the kernel code too. Probably the best way of doing this is to take a look at the Linux Kernel, with the help of a book such as Understandiong The Linux Kernel.

Answer 7

The minix stuff is pretty good. A simpler example is the MicroC/OS stuff. It comes with a textbook that goes into good detail, all the source is there. It has the basic elements there and the code is small enough that you can understand it in a relatively short period of time.

http://www.micrium.com/products/rtos/kernel/rtos.html

http://en.wikipedia.org/wiki/MicroC/OS-II

Another thing you can do, is make a faked out OS in an application on linux. I did this by setting up the basic tick with an itimer, then swapping threads around with the function call swapcontext (man 2 swapcontext) which will save the regs on the stack. That gets the ugly stuff out of the way and you are left to implement the semaphores/mutexes/timers and all that. It was quite fun.

Despite what some of the posts say, assembler is not required. A knowledge of it will always help. It never hurts to understand how the internals/complilers/etc work when you are writing even high level applications.

Answer 8

Funny, Stevens Book is one of the classic texts for describing the use of synchronisation primitives and their uses. He certainly seems to think they can be used to control inter process communication. I tend to agree with him. Networking, no, IPC yes. most certainly yes.