ITCE320 - Ch6: Server Architecture and Multithreading

Study Notes

Single-Thread Programs

A single-thread program is a script with statements and expressions executed in sequence
Easier to design and used in programs that handle single connection/session at a time
Vulnerable to denial-of-service attacks
Connect and keep the connection on, keeping the server blocked at recv() expression
Resend some data before the blockage timeout (if it is configured)

Behavior with Multiple Connections

When a client tries to connect to a single-threaded server that is in session with another client
The OS starts a three-way TCP handshake with the second client to set up a connection
The connection will be kept at OS’s listen queue until the ongoing conversation is concluded
Once the server code has looped back to its next call to accept(), the second client’s connection will be available to the server
Start exchanging requests and responses over that socket

Single-Threaded Server and CPU Utilization

Poor resources utilization
recv() causes blockage, and no other expressions are executed during blockage time
Until receive data from the client
Timeout

Single-Thread Server Example

Create a socket and bind it to the loopback address and port 22221
Listen for incoming connections
Accept a connection and receive client name
Start a chat loop to send and receive messages
Close the connection when the client sends "quit"

Multi-process and Multi-Thread Programs

Multiple lightweight flow of executions running at the same time
Multi-threading: technique that allows an execution of several tasks of one process at the same time
Single core: execution of different codes are all queued, no parallel processing for both single and multi-threaded scripts
Multiple cores: parallel executions at the same time

Multi-process vs Multi-threaded

Multi-process Programming: each process runs as a standalone program, allocated code and data memory for every process
Multi-threaded: multiple threads running in a single process, sharing code and data memory
Use join() method to block until a thread terminates

Returning Threads

The Main Thread: return the main Thread object
The Current Thread: return the current Thread object
Returning list of threads: use threading.enumerate() to get a list of active threads

Example: Wait for all Active Non-Main Threads

Get a list of active threads using threading.enumerate()
Iterate through the list and join each thread

Multithreaded Server

Create multiple threads to handle multiple client connections
Each thread handles a separate client connection
Use threading and socket libraries to create a multithreaded server

Background

The Internet is used to share services
Entities to provide services need to be available, approachable, reliable, and scalable
Connected by program entities to ask for services

Server

A server provides a service that is needed by one or more clients
Can be a single server or a server farm (mirrored/cloud)
Example: Apache web server responds to requests from Firefox as the web client

Reaching Services

Requests are generated by clients
Clients can be at the same host as the server or at a remote machine
Reaching the server mechanisms:
- Common servers use well-known common port numbers
- Not common servers need a mechanism to verify the server port number to the client

Description

This quiz covers the basics of single-thread programs, including their characteristics, advantages, and limitations. It also touches on the vulnerability of single-threaded programs to denial-of-service attacks.