Parallel processes execution using fork()

Thodoris21 · 05-15-2012, 02:06 PM

Hi.I have to do an exercise and i want your help.I want to create dynamicaly a number of processes using fork.The processes will be created must run in parallel and execute a common code using semaphores.Any idea?

Thank you.

sundialsvcs · 05-15-2012, 03:14 PM

Sure... I can help you a little with your homework!

When you use fork(), a process literally "splits itself in two." One of them perceives that the function-call returned true while the other one perceives that it returned false.

So, the first part of your assignment is to figure out how to correctly split-off n copies of yourself.

The second part of your assignment is to figure out how to cause the various split-off copies to be able to accomplish a task cooperatively, i.e. without smashing into each other because they are all trying to access the same shared data-structures (and what not...) at the same time. Here is where the idea of "semaphores" comes into play. A semaphore is like those "take a number" gadgets that you find at popular meat-counters in popular grocery stores: everybody "takes a number" so that everybody gets served, "fairly, but one-at-a-time." The mechanism allows each process to "take a number, wait patiently in line, then proceed when their 'turn' arrives."

At this point, I turn you over to the vast amount of material that is at your beck-and-call in this instantaneous worldwide research library called "the Internet." Or, as the case may be, to your instructor.

(And let me be clear on this: I have been an instructor myself. If you are confused, you're not the only one. Go to your instructor and talk to him or her. This will serve, in part, as extremely valuable feedback and guidance to him or her. Don't feel embarrassed or reticent: this process is called learning, and it's a two-way street. Do your part to expedite the process.)

Thodoris21 · 05-15-2012, 03:35 PM

Thank you very much for your reply.I have made efforts to learn from my instructor but he doesn't want to help.So, i am trying to learn and do the exercise on my own.

The subject of the exercise is:
Write a program in C to produce source code without comments.Specifically,the program must read a *.c file which include c language code.After this,will be created a number of processes using fork.(it does not need to refer to the way will give the number of processes).The processes should execute parallel.Each process should remove the c language comments from the file but for specific number of characters.(it does not need to refer to the way will give the number of characters which process should edit).When all processes finished,the original(main process) process should produce the final c file without comments!

I tried to do the exercise without processes and semaphores and it's work perfect in serial mode.
In parallel?

Thank you.

Nominal Animal · 05-15-2012, 04:36 PM

The exercise seems not only silly, but something that is really not suited for neither distributed processing (multiple processes) nor parallel processing (multiple threads).

In modern C (C99), there are two types of comments:

Code:

// This comment runs only to the end of the line

/* This kind of comments
 * may easily span
 * a number of lines. */

Furthermore,

Code:

const char example[] = "This /* has nothing // to do with comments.";

In other words, you cannot remove comments without parsing the entire file from start to finish. Sure, you can do something half-assed that will not work for even the trivial example above, but why teach half-assisms? The world is already full of half-arsers, we don't need more of them!

I think your instructor is lazy, stupid, or most likely, both. Get a better instructor.