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 intersperse 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.  A signal is generated if a write on a pipe with only one end is attempted. 

DIAGNOSTICS

The pipe call will fail if:

[EFAULT] The fildes buffer is in an invalid area of the process’s allocated address space. 

[EMFILE] Too many file descriptors are active. 

[ENFILE] No more system file descriptors are available. 

[ENFILE] Insufficient system space to contain i-node. 

[ENOSPC] No more i-nodes are available on the device. 

RESTRICTIONS

Should more than 4096 bytes be necessary in any pipe among a loop of processes, deadlock will occur. 

SEE ALSO

sh(1), read(2), write(2), fork(2)

ASSEMBLER

(pipe = 42.) 
sys pipe
(read file descriptor in r0)
(write file descriptor in r1)