This content originally appeared on DEV Community and was authored by Zacchaeus Bolaji
From red lights to frozen apps, the rules that keep traffic — and your computer — moving smoothly.
Ever been stuck at a red light forever? Your computer has the same issue with its programs!
The Problem: Everyone Wants the Same Thing
Picture this: You’re at a busy intersection. Cars from all four directions want to go through at the same time. If everyone just floors it, you get a massive crash.
Now imagine your computer: Multiple programs all want to use the printer at the same time. If they all try to print simultaneously, you get a mess.
Same problem, different scale.
What is Deadlock?
Deadlock happens when everyone is waiting for everyone else, and nobody can move. It’s like this classic scenario:
Traffic Version:
- North-bound cars are waiting for East-bound cars to clear the intersection
- East-bound cars are waiting for South-bound cars
- South-bound cars are waiting for West-bound cars
- West-bound cars are waiting for North-bound cars
- Result: Nobody moves. Ever.
Computer Version:
- Program A has the printer, wants the scanner
- Program B has the scanner, wants the hard drive
- Program C has the hard drive, wants the printer
- Result: All programs freeze. Forever.
The Four Rules of Deadlock
Computer scientists figured out that deadlock happens when these four things are all true:
- Resources can’t be shared (only one car can be in the intersection center)
- Hold and wait (you keep what you have while waiting for more)
- No takebacks (you can’t force someone to give up what they have)
- Circular waiting (everyone waits for someone else in a circle)
Break any one of these rules, and deadlock becomes impossible!
How Cities Solve Traffic Deadlock
Traffic Lights = Resource Schedulers
Traffic lights are basically schedulers that prevent deadlock by breaking rule #4 (circular waiting). They say “North-South, you go first. East-West, you wait your turn.”
Smart Traffic Systems
Modern cities use crazy smart systems:
- SCOOT (used in 350+ cities): Adjusts light timing in real-time
- SCATS (used in 55,000+ intersections): Detects traffic and adapts instantly
These systems work like advanced computer schedulers, constantly analyzing traffic patterns and preventing gridlock before it happens.
“Don’t Block the Box”
Ever see those yellow grid markings at intersections? That’s deadlock prevention 101. The rule is simple: Don’t enter the intersection unless you can completely exit it. This prevents the circular waiting that causes gridlock.
Fun fact: In NYC, blocking the box gets you a $90 ticket!
.
How Computers Solve Program Deadlock
The Banker’s Algorithm
Computers use something called the Banker’s Algorithm – imagine a banker who only loans money if they’re sure everyone can pay it back. The computer only gives resources to programs if it can guarantee no deadlock will happen.
Resource Ordering
Just like traffic lights give green to one direction at a time, computers can require programs to request resources in a specific order. No cutting in line = no deadlock.
The Ostrich Algorithm
Sometimes the solution is… ignore it! If deadlock is super rare, some systems just restart when it happens. It’s like how most intersections don’t have traffic lights – crashes are rare enough that stop signs work fine.
See It in Action
Want to see this in action? Check out traffic intersections during rush hour, or look up videos of cities like London or Sydney where smart traffic systems prevent gridlock in real-time. It’s basically watching a massive distributed computer system manage thousands of moving resources!
The Cool Connection
Next time you’re at a red light, remember: you’re experiencing the same fundamental computer science problem that happens inside your phone, laptop, and every computer system. The traffic light above you is running the same type of algorithms that prevent your apps from freezing.
Traffic engineers and computer scientists are solving the exact same puzzle – just with different pieces.
Want to learn more? Look up “dining philosophers problem” – it’s another classic example of the same deadlock challenge, but with hungry philosophers and chopsticks!
This content originally appeared on DEV Community and was authored by Zacchaeus Bolaji