pipe.2

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)pipe.2	8.1	9/11/90
.TH pipe 2
.SH Name
pipe \- create an interprocess channel
.SH Syntax
include <limits.h> /*Definition of PIPE_MAX*/
.nf
pipe(\fIfildes\fP)
int \fIfildes[2]\fP;
.fi
.SH Arguments
.TP 10
.I fildes
Passing an address as an array of two integers into the
.PN pipe
system call.
.SH Description
.NXR "pipe system call"
.NXR "pipe" "creating"
The
.PN pipe
system call
creates an I/O mechanism called a pipe.
The file descriptors returned can
be used in
.PN read
and
.PN write
operations.  Their integer values will be the two lowest available at the time
of the
.PN pipe
function call.  The O_NONBLOCK and FD_CLOEXEC flags
will be clear on both file descriptors.
.PP
When the pipe is written using the descriptor
.IR fildes [1],
up to PIPE_MAX bytes of data are buffered
before the writing process is suspended.
A read using the descriptor
.IR fildes [0]
picks up the data.
.PP
It is assumed that after the pipe has been set up, two (or more)
cooperating processes (created by subsequent
.PN fork
calls) pass data through the pipe with
.PN read
and
.PN write
calls.
.PP
The shell has a syntax to set up a linear array of processes
connected by pipes.
.PP
For further information on how 
.PN read
and
.PN write
calls behave with pipes, see the
.MS read 2
and
.MS write 2
reference pages.
.PP
A signal is generated
if a write on a pipe with only one end is attempted.
.SH Restrictions
Should more than 4096 bytes be necessary in any
pipe among a loop of processes, deadlock may occur.
.PP
The underlying implementation of pipes is no longer
socket based, but rather implemented through the
file system.  Any application that needs socket
functionality from pipes should use the 
.PN socketpair 
system call.
.SH Return Values
The function value zero is returned if the
pipe was created; \-1 if an error occurred.
.SH Diagnostics
The 
.PN pipe
call fails if:
.TP 15
[EMFILE]
Too many descriptors are active.
.TP 15
[ENFILE]
The system file table is full.
.TP 15
[EFAULT]
The
.I fildes
buffer is in an invalid area of the process's address space.
.SH Environment
Differs from the System V definition in that ENFILE
is not a possible error condition.
.SH See Also
sh(1), fork(2), read(2), socketpair(2), write(2)