CODEWITHSUNDEEP
coperating-systemxv6
BarryMerkohkener
BarryMerkohkener

Reputation: 1

How do I use pipes in xv6 to communicate between unrelated processes?

I understand how IPC works and how when you make a pipe before fork() the child/children can inherit the pipe for communication. However, I cant wrap my head around how I would do this for two unrelated processes? (i.e processes that are not the parent or children of each other?).

Im asking because Im trying to get one of my .c files to communicate with another .c file via pipes, but I dont know how that works explicitly in xv6. Any help/ideas would be greatly appreciated!!

Upvotes: 0

Views: 1264

Answers (3)

AlpacaMax
AlpacaMax

Reputation: 479

What pipe does is to connect the standard output of one program to the standard input of another program.

Consider the cat and wc program in xv6. cat displays the content of a file or files. Let's say we have a text file test.txt with Hello World in it. cat can display its content like this:

$ cat test.txt
Hello World

wc calculates the number of lines, words, and characters in a file, files, OR stdin. So it can be used either like this(read from a file):

$ wc test.txt
1 2 12 test.txt

or this(read from stdin):

$ wc
Hello World
<Press Ctrl-D>
1 2 12

We can use pipe to connect these two commands:

$ cat test.txt | wc
1 2 12

So here cat reads the file and prints its content into stdout, but it doesn't get displayed onto the screen. Instead it gets feeded into the stdin of wc and wc counts the lines, words, and characters in it. Notice that this communication is unidirectional. It only goes from left to right, no backwards.

You can refer to the source code of these two commands to write your program. Basically all you have to do is to make sure the previous command outputs into stdout and the subsequent command reads from stdin.

Upvotes: 0

Devon Caron
Devon Caron

Reputation: 29

Pipes are not able to communicate between 2 processes unless those two processes share a common ancestor, regardless of the Linux distro you use. If you are trying to allow 2 unrelated files to communicate, one of the exec() commands must be used in the child or parent process; this page may have what you're looking for.

Upvotes: 0

codyne
codyne

Reputation: 552

There are several ways to accomplish this, for something simple, try checking out popen(). One program can spawn an unrelated one and then can then read and write to each other.

https://man7.org/linux/man-pages/man3/popen.3.html

For other solutions you should look into FIFO files or even sockets as a means of IPC.

Upvotes: 0

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