2. Remote Shared Memory API for Solaris Clusters
3. Session Description Protocol API
POSIX Interprocess Communication
Permissions for Messages, Semaphores, and Shared Memory
IPC Interfaces, Key Arguments, and Creation Flags
Sending and Receiving Messages
Accessing a Shared Memory Segment
Controlling a Shared Memory Segment
Attaching and Detaching a Shared Memory Segment
9. Programming With XTI and TLI
11. Transport Selection and Name-to-Address Mapping
12. Real-time Programming and Administration
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( ... ); exit(1); default: /* in parent */ close( p[1] ); dup2( P[0], 0 ); close( p[0] ); break; } ...
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
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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.