Design of Server Software #

Introduction #

Conceptually, a as server follows a simple algorithm

1. Create and bind a socket to a well-known port
2. Enter an infinite loop
   • Accept the next request from a client
   • Process the request and reply the result to client

Types of servers

Iterative Servers #

Connectionless server #

1. Create and bind a socket to a well-known port
2. Enter an infinite loop
   • Accept the next request from a client
   • Process the request and reply the result to client

The server only procides one single socket. Server can use sendto() and recvfrom() to get the address information of clients.

Connection-oriented #

1. Create and bind a socket to a well-known port
2. Place the socket in passive mode by calling listen()
3. Accept the next connection and obtain a new socket for the connection
4. Enter an infinite loop
   • Accept the next request from a client
   • Process the request and reply the result to client
5. When finishing with a client, close the connection and reutrn to step 3 to accept a new connection

Concurrent Servers #

Concurrency reduces response time for multiple clients under serveral conditions

• Siginificant I/O exists
• Processing time varies dramatically among requests
  • Small processes don't have to wait for big processes to finish
• Computer with multiple processors

Most concurrent server use multiple processes (or threads) tp achieve concurrency

• A single process (called mastser) begins execution initially
• The master process then
  1. Open a socekt at the well-know port
  2. Wait for the next request
  3. Create a slave to handle each request
• Each slave process handles communication with one client. Once the client disconnectm the slave process exits

Connectionless server #

Master algorithm

1. Create and bind the socket to a well-known port
2. Reapeatedly call recvfrom() to receive the next request from a client and create a new slave processs (or thread) to handle that response

Slave algorithm

1. Access to the corresponding socket
2. Form a reply and send it to the client using sendto()
3. Exit when finish

Connection-oriented server #

Master algorithm

1. Create and bind a socket to a well-known port
2. Place the socket in passive mode
3. Repeatedly call accept() to receive the next request and create a new slave process to handle the response

Slave algorithm

1. Begin with a connection passed from the master
2. Interact with client
3. Close the connection and exit

Advanced Issues #

Create a new process #

Use only one thread to achieve concurrency #

Guidelines to select different types of servers #

Deadlock #

Example of Iterative Servers #