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Top Forums Programming IPC between processes, pipes, etc Post 302425222 by Corona688 on Thursday 27th of May 2010 11:00:20 AM
Old 05-27-2010
If you have to connect existing processes with pipes, you'll need to use named pipes, which can be created with the mkfifo() call and opened with the open() syscall, and duplicated over the required FD's with the dup2() syscall.

What's generally done so as to use anonymous pipes, is the parent process creates the necessary pipes with the pipe() syscall, does its own redirections with dup2(), forks, then the child does its own redirections. Any unnecessary duplicates of the pipe descriptors should be closed as soon as possible so your processes don't end up waiting on them.
 

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PIPE(2) 							System Calls Manual							   PIPE(2)

NAME
pipe - create an interprocess channel SYNOPSIS
pipe(fildes) int fildes[2]; DESCRIPTION
The pipe system call creates an I/O mechanism called a pipe. The file descriptors returned can be used in read and write operations. When the pipe is written using the descriptor fildes[1] up to 4096 bytes of data are buffered before the writing process is suspended. A read using the descriptor fildes[0] will pick up the data. Writes with a count of 4096 bytes or less are atomic; no other process can inter- sperse data. It is assumed that after the pipe has been set up, two (or more) cooperating processes (created by subsequent fork calls) will pass data through the pipe with read and write calls. The Shell has a syntax to set up a linear array of processes connected by pipes. Read calls on an empty pipe (no buffered data) with only one end (all write file descriptors closed) returns an end-of-file. SEE ALSO
sh(1), read(2), write(2), fork(2) DIAGNOSTICS
The function value zero is returned if the pipe was created; -1 if too many files are already open. A signal is generated if a write on a pipe with only one end is attempted. BUGS
Should more than 4096 bytes be necessary in any pipe among a loop of processes, deadlock will occur. ASSEMBLER
(pipe = 42.) sys pipe (read file descriptor in r0) (write file descriptor in r1) PIPE(2)
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