pipe(2)

pipe -- create an interprocess channel

Synopsis

   #include <unistd.h>
   
   int pipe(int fildes[2]);

Description

pipe creates an I/O mechanism called a pipe and returns two file descriptors, fildes[0] and fildes[1]. The files associated with fildes[0] and fildes[1] are streams and are both opened for reading and writing. The O_NDELAY and O_NONBLOCK flags are cleared.

A read from fildes[0] accesses the data written to fildes[1] on a first-in-first-out (FIFO) basis and a read from fildes[1] accesses the data written to fildes[0] also on a FIFO basis.

The FD_CLOEXEC flag will be clear on both file descriptors.

If pipe succeeds, it marks for update the st_atime, st_ctime, and st_mtime fields of the pipe.

Return values

On success, pipe returns 0. On failure, pipe returns -1 and sets errno to identify the error.

Errors

In the following conditions, pipe fails and sets errno to:

EMFILE: The maximum number of file descriptors are currently open.
ENFILE: A file table entry could not be allocated.

References

fcntl(2), getmsg(2), poll(2), putmsg(2), read(2), sh(1), stat(2), streamio(7), write(2)

Notices

Since a pipe is bi-directional, there are two separate flows of data. Therefore, the size (st_size) returned by a call to fstat with argument fildes[0] or fildes[1] is the number of bytes available for reading from fildes[0] or fildes[1] respectively. Previously, the size (st_size) returned by a call to fstat with argument fildes[1] (the write-end) was the number of bytes available for reading from fildes[0] (the read-end). See stat(2).

Considerations for threads programming

Open file descriptors are a process resource and available to any sibling thread; if used concurrently, actions by one thread can interfere with those of a sibling. For example, data read from a pipe (destructive) by one thread is not available to siblings.