Grokking Petri-Nets

TLDR: Petri nets introduce the concept of a token, which can be in more than one state at the same time. As opposed to a state diagram where you can be in only one state at the same time.

1. The Basic Stuff

Here's what we're working with:

⭕ Places (circles) - like variables that can hold multiple tokens
▢ Transitions (rectangles) - like functions that do stuff
→ Arrows - show how stuff moves around

2. Why They're Cool

Remember how in state diagrams you can only be in one state at a time? Well, Petri nets let you be in multiple states at once.

3. Printer Example

Two processes fighting over one printer. In a state diagram, this would be messy. In a Petri net, it's piece of cake!

3.1 State Diagram Version (The Messy Way)

stateDiagram-v2 [*] --> Idle Idle --> P1Using: Process1 starts Idle --> P2Using: Process2 starts P1Using --> P1Done: Process1 finishes P2Using --> P2Done: Process2 finishes P1Done --> Idle: Release printer P2Done --> Idle: Release printer P1Using --> P1P2Waiting: Process2 requests P2Using --> P2P1Waiting: Process1 requests P1P2Waiting --> P2Using: Process1 finishes P2P1Waiting --> P1Using: Process2 finishes

In a state diagram, we need separate states for:

Idle (nobody using printer)
Process1 using printer
Process2 using printer
Process1 using, Process2 waiting
Process2 using, Process1 waiting

3.2 Petri Net Version (The Elegant Way)

4. When To Use Them

Use Petri nets when you need to show:

Multiple things happening at once (like multithreading)
Resources being shared (like memory or printers)
Things that need to wait for other things (like process synchronization)

And that's basically it! Petri nets are just state diagrams that grew up and learned how to multitask.