zyd

Hi. I want to work with threads in linux using fork(), but i don't know how to share variables between diferent threads (or instances) of the same program. How do i need to declare my variables for them to work in that way?.
Thanks in advance.

Dameon

Fork creates a new process, not a new thread.

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zyd

ok, i misused terms, but that's what i meant, it is possible for a child process to inherit or to use the same variables than his parent process?, something like a global value for all process of the same program.

zyd

ok. i guess i also hurried in thinking the solution to my problem. what i need is the clone system call. According to what i read, with fork you can only share the text segment of the process. Does anybody know a way to share data too with fork?

Dameon

Perhaps you should reconsider your design. A threaded application shares a single address space, the result being that any change made by one thread is apparent to all the other threads because it was made to the same physical address. In the case of fork(), memory and file descriptors are copied. The address of the variables doesn't change from the program's perspective, but the physical address maps to somewhere else. If you want several points of execution that affect each other, use threads. If you want to allow two copies of the app to go two seperate and independent ways, use fork (hence the name).

If you seriously need to communicate between processes, this is fairly thorough as far as the major ways of doing things on *nix.
http://www.tldp.org/LDP/lpg/node1.html

Threading is often a good solution, but watch out for deadlocks and sychronization.
http://www.cs.nmsu.edu/~jcook/Tools/pthreads/pthreads.html
http://www.yolinux.com/TUTORIALS/Lin...ixThreads.html

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zyd

thanks for the advice. the thing is that that is precisaly what i want. i want to show all the problems that can arise with threads and the diferent ways to solve them, i made a little scheduler that creates threads using interruptions (though it was for M$-DO$). But what i want to emphasize are the problems and the methods to solve them, more than the way of creating threads, so my natural choice is a *nix system since it has system calls to efficiently create threads