Lecture Notes: Introduction to Multi-threading in Python

What is Multi-threading?

• Used to perform multiple tasks concurrently (multitasking).
• Good for IO-bound tasks (e.g., reading files, fetching data from an API).

Example Analogy

• Similar to multitasking in daily life: studying, listening to music, and eating at the same time.

Using Multi-threading in Python

Importing the Module

• import threading

Creating Threads

• Use the threading.Thread constructor.
• Pass in a target function.

Example: Performing Chores

1. Functions to Define Chores:

   • Walk the dog: Prints "You finish walking the dog" after sleeping for 8 seconds.
   • Take out trash: Prints "You take out the trash" after sleeping for 2 seconds.
   • Get mail: Prints "You get the mail" after sleeping for 4 seconds.

2. Calling Functions Sequentially:

   • Calls functions one by one on the main thread:
     • Walk the dog -> Take out trash -> Get mail.
   • Takes 14 seconds total (8+2+4).

Implementing Multi-threading

1. Creating Thread Objects for Each Chore:

   • chore1 = threading.Thread(target=walk_dog)
   • chore2 = threading.Thread(target=take_out_trash)
   • chore3 = threading.Thread(target=get_mail)

2. Starting Threads:

   • chore1.start(), chore2.start(), chore3.start()

3. Output Order:

   • Chores finish in the order of completion time due to concurrent execution:
     • Take out trash -> Get mail -> Walk the dog.
   • Total time reduced to 8 seconds (time of the longest task).

Ensuring Completion of All Threads

• Use join method to wait for all threads to complete before printing final message.
  • Example: chore1.join() chore2.join() chore3.join() print("All chores are complete")

Passing Arguments to Threads

• Use args keyword in Thread constructor.
• Example with single argument: threading.Thread(target=walk_dog, args=("Scooby",))
• Example with multiple arguments: threading.Thread(target=walk_dog, args=("Scooby", "Doo"))

Summary

• Multi-threading allows concurrent task execution.
• Beneficial for IO-bound tasks.
• Use threading.Thread with target and args (if needed).
• Use start to begin threads and join to ensure completion.