Scope: To setup the communication link between two or more processes so as to transfer data to and fro in between the processes.

Description: We have many IPC techniques in Linux like PIPE, FIFO, Shared Memory, Message Queue. We will start this article from our first topic i.e. PIPE.

PIPE is a stream or we can say a path from where we transfer the data from one process to another. For creating a pipe we us system call “PIPE()”. This call will create a stream between two processes and will return two file descriptors. The two file descriptors returned are connected in a special way. Any data written to file_descriptor[1] can be read back from file_descriptor[0]. The data is processed in a first in, first out basis, usually abbreviated to FIFO. This means that if you write the bytes 1, 2, 3 to file_descriptor[1], reading from file_descriptor[0] will produce 1, 2, 3. This is different from a stack, which operates on a last in, first out basis, usually abbreviated to LIFO. As this stream is unnamed, hence it is visible to only those processes in which one process act as parent and another process act as a child. Now the question arises – What is a child process & Parent process.

We have a system call as “fork()”, this call will create process from main process. The created process is called as child and the main process will be named as parent. After creation of child process, we will send the file descriptors to that child process by calling a call “exec()”. This “exec()” call will create a new process and will replace it with the process from which this was called. Child process generated by the fork() call uses same process context but PCB is different. This replace process created by exec() call will have everything different i.e PCB & process context are different. Now this new process and the parent process both are having the file descriptors and with the help of these descriptors these two processes will share data with each other. Important topics here we have are “Orphan Process” & “Zombies”.

Orphan Process - After a call to fork(), generally its the child process that get time slice to execute. Now say of parent process terminates for some reason before child process, we will have a orphan process as it parent process have died. As every child process have some parent this must be made child of some process, in this condition Dispatcher i.e. Process with PID 1 is automatically made its parent.

Zombies – If for some reason a process is dead but haven’t been removed from the process table it is called as Zombie process. Now this can happen in situation when a child process has terminated and parent process gas gone in some kind of infinite loop which don’t allow child process to exit.

 In the next article we will briefly discuss about other IPC techniques – FIFO, Shared memory and Message queue.

Scope: This project is used to setup communication between server and client. With the help of this we can send and receive data from one client to another or between server and client.

Description: We have done this project in phases -

Phase – I: One server One client

At the server end we have created one socket which will help to communicate with the client. After creating the socket using command “socket()”, we named it using command “bind()”. Naming the socket will give the easy access to the client as this socket will be visible to the client.

If we are performing this communication within the system/computer, then we will use AF_UNIX to name the socket.(Here we can give any alpha or alphanumeric name). Other wise, if we are establishing between two networks the we use AF_INET. In this we have to mention the port number and IP address of the server). We have used TCP/IP protocol for our project.

Note: we will never give name to the socket of client, we always give name to the socket of server which is visible to all the client.

Simultaneously, at the client end we have created a socket through which it will communicate with the server. After that client sent a request to the server to get connected using command “connect()”. At the server end, server will listen the request sent from the client using command “listen()” and it will create a queue. (Note: If in the mean time another client wants to connect with the server, the 2^nd client request will go to the queue.) After getting the request from the client , server will accept the request using command “accept()”and this command will return a file descriptor (a stream) through which client will send and receive data to and from the server respectively.

At end of data transfer client will close the socket and simultaneously server will delete the stream connected to the particular client.

Phase – II: One server several clients

The procedure for this second phase is almost same as phase I. In the same way as mentioned above, we will create many clients which will send requests to the server to communicate simultaneously. Server will create a queue to manage the request .

Phase – III: One server several clients using threads

In this phase we have many clients who wants to communicate with the server. Every client will send request to the server, and at the server end queue is created (as explained above). One by one server will except the request and will assign the work to different functions. Here instead of calling different functions we have used concept of threads. Server will create threads on every receipt of request from the client end.

With the help of these threads the process time of the server is reduced as it is distributing its workload within threads.

Functionality:

1. This basic project will help to reduce the process timing of client. If client wants to process some data, it will send the raw data to the server and server will send back the processed output to the client.

2. Planning for phase IV. In this phase we will establish the link between different clients through one server. In this project clients will communicate with themselves or we can say these clients will share data with each other.

Still waiting for the suggesions on below question –
“write a program to printa cycle of cosine, sine wave”….

Kindly advice what to do in this??

Kindly help me to understand the below question –
“write a program to printa cycle of cosine, sine wave”….

This is all about what I have done till date in character driver coding.

Thanks
Rahul Attreja