Named Pipe Example Using Raspberry Pi

Multi-tasking Operating Systems can run several processes at a time creating and effect of parallel processing with the help of the high speed processor. There are different kinds of Inter Process Communication (IPC) system and the Named Pipe is one of the simplest of them. The Named Pipe is actually a temporary file having a particular name and stored at a particular directory whose name and location are known to the processes which needs to communicate with each other. The Named Pipe is also called First In First Out (FIFO).

This project basically requires two programs which are meant to send data in between them, and a named pipe which will be created by anyone of them. The entire system can be represented with the help of the following diagram:

The function mkfifo() creates a temporary file at the required directory with the required access permissions set on it. The prototype of the function is declared as the following;

The first argument is the required pathname of the directory where the named pipe needs to be created. The second argument is the user permission that needs to be set on the file. Using the value 0777 as the second argument allows permission to all users of the system to read from and write into that named pipe. For using this function in the C code, two header files <sys/types.h> and <sys/stat.h> should be included.

The open () function opens a particular file at a specified path with the required flags set and it returns a file descriptor corresponding to that file to the process which called the open function. Using that file descriptor the process can access the file.

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#define OUR_INPUT_FIFO_NAME “/tmp/my_fifo”

unsigned char rx_buffer [ 256 ];
int rx_length;
int our_input_fifo_filestream = -1;int result;

int main (){printf ( “Making FIFO…\n” );
result = mkfifo ( OUR_INPUT_FIFO_NAME, 0777 );
our_input_fifo_filestream = open ( OUR_INPUT_FIFO_NAME, ( O_RDONLY | O_NONBLOCK ) );

while ( 1 )
{rx_length = read ( our_input_fifo_filestream, ( void* ) rx_buffer, 255 ); //Filestream, buffer to store in, number of bytes to read (max)
if ( rx_length > 0 )
{rx_buffer [ rx_length ] = ‘\0’;
printf ( “FIFO %i bytes read : %s\n”, rx_length, rx_buffer );}else;}}