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Programming Interfaces Guide     Oracle Solaris 11 Information Library
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Document Information


1.  Memory and CPU Management

2.  Remote Shared Memory API for Oracle Solaris Clusters

3.  Session Description Protocol API

4.  Process Scheduler

5.  Locality Group APIs

6.  Input/Output Interfaces

7.  Interprocess Communication

Pipes Between Processes

Named Pipes

Sockets Overview

POSIX Interprocess Communication

POSIX Messages

POSIX Semaphores

POSIX Shared Memory

System V IPC

Permissions for Messages, Semaphores, and Shared Memory

IPC Interfaces, Key Arguments, and Creation Flags

System V Messages

Initializing a Message Queue

Controlling Message Queues

Sending and Receiving Messages

System V Semaphores

Initializing a Semaphore Set

Controlling Semaphores

Semaphore Operations

System V Shared Memory

Accessing a Shared Memory Segment

Controlling a Shared Memory Segment

Attaching and Detaching a Shared Memory Segment

8.  Socket Interfaces

9.  Programming With XTI and TLI

10.  Packet Filtering Hooks

11.  Transport Selection and Name-to-Address Mapping

12.  Real-time Programming and Administration

13.  The Oracle Solaris ABI and ABI Tools

A.  UNIX Domain Sockets


Pipes Between Processes

A pipe between two processes is a pair of files that is created in a parent process. The pipe connects the resulting processes when the parent process forks. A pipe has no existence in any file name space, so it is said to be anonymous. A pipe usually connects only two processes, although any number of child processes can be connected to each other and their related parent by a single pipe.

A pipe is created in the process that becomes the parent by a call to pipe(2). The call returns two file descriptors in the array passed to it. After forking, both processes read from p[0] and write to p[1]. The processes actually read from and write to a circular buffer that is managed for them.

Because calling fork(2) duplicates the per-process open file table, each process has two readers and two writers. Closing the extra readers and writers enables the proper functioning of the pipe. For example, no end-of-file indication would ever be returned if the other end of a reader is left open for writing by the same process. The following code shows pipe creation, a fork, and clearing the duplicate pipe ends.

#include <stdio.h>
#include <unistd.h>
        int p[2];
        if (pipe(p) == -1) exit(1);
        switch( fork() )
                case 0:                   /* in child */
                        close( p[0] );
                        dup2( p[1], 1);
                        close P[1] );
                        exec( ... );
                default:                  /* in parent */
                        close( p[1] );
                        dup2( P[0], 0 );
                        close( p[0] );

The following table shows the results of reads from a pipe and writes to a pipe, under certain conditions.

Table 7-1 Read/Write Results in a Pipe

Empty pipe, writer attached
Read blocked
Full pipe, reader attached
Write blocked
Empty pipe, no writer attached
EOF returned
No reader

Blocking can be prevented by calling fcntl(2) on the descriptor to set FNDELAY. This causes an error return (-1) from the I/O call with errno set to EWOULDBLOCK.