🍴 2 Philosophers (Minimal Table)

Dining Philosophers Problem simulated with virtual time
🎬 GenServerVirtualTime Actor Simulation
This diagram shows the interactions between philosophers and forks over virtual time. All synchronous fork requests, grants, and releases are captured.

The Problem

2 philosophers sit at a round table with 2 forks between them. Each philosopher alternates between thinking and eating. To eat, a philosopher needs both adjacent forks.

Challenge: How to prevent deadlock when all philosophers simultaneously grab their left fork? This would create a circular wait condition.

Solution: Asymmetric fork acquisition strategy - odd-numbered philosophers grab their right fork first, even-numbered philosophers grab their left fork first. This breaks the symmetry and prevents circular deadlock.

→ Solid Arrow
Synchronous call (request/release fork)
Activation Box
Fork is processing a request
Timestamps
Virtual time progression
Self-loops
Philosopher internal state changes
sequenceDiagram philosopher_1->>philosopher_1: {:start_hungry, :fork_0, :fork_1} Note over philosopher_1,philosopher_1: t=150ms philosopher_0->>philosopher_0: {:start_hungry, :fork_0, :fork_1} Note over philosopher_0,philosopher_0: t=150ms philosopher_0->>philosopher_0: {:mumble, "I'm hungry!"} Note over philosopher_0,philosopher_0: t=150ms philosopher_1->>philosopher_1: {:mumble, "I'm hungry!"} Note over philosopher_1,philosopher_1: t=150ms philosopher_0->>fork_0: {:request_fork, :philosopher_0} Note over philosopher_0,fork_0: t=150ms philosopher_1->>fork_0: {:request_fork, :philosopher_1} Note over philosopher_1,fork_0: t=150ms fork_0->>philosopher_1: {:fork_granted, :fork_0} Note over fork_0,philosopher_1: t=150ms fork_0->>philosopher_0: {:fork_denied, :fork_0} Note over fork_0,philosopher_0: t=150ms philosopher_1->>fork_1: {:request_fork, :philosopher_1} Note over philosopher_1,fork_1: t=150ms fork_1->>philosopher_1: {:fork_granted, :fork_1} Note over fork_1,philosopher_1: t=150ms philosopher_1->>philosopher_1: {:mumble, "I'm full!"} Note over philosopher_1,philosopher_1: t=225ms philosopher_1->>fork_0: {:release_fork, :philosopher_1} Note over philosopher_1,fork_0: t=225ms philosopher_1->>fork_1: {:release_fork, :philosopher_1} Note over philosopher_1,fork_1: t=225ms philosopher_0->>philosopher_0: {:start_hungry, :fork_0, :fork_1} Note over philosopher_0,philosopher_0: t=300ms philosopher_1->>philosopher_1: {:start_hungry, :fork_0, :fork_1} Note over philosopher_1,philosopher_1: t=300ms philosopher_1->>fork_0: {:request_fork, :philosopher_1} Note over philosopher_1,fork_0: t=300ms philosopher_0->>fork_0: {:request_fork, :philosopher_0} Note over philosopher_0,fork_0: t=300ms fork_0->>philosopher_0: {:fork_granted, :fork_0} Note over fork_0,philosopher_0: t=300ms fork_0->>philosopher_1: {:fork_denied, :fork_0} Note over fork_0,philosopher_1: t=300ms philosopher_0->>fork_1: {:request_fork, :philosopher_0} Note over philosopher_0,fork_1: t=300ms fork_1->>philosopher_0: {:fork_granted, :fork_1} Note over fork_1,philosopher_0: t=300ms philosopher_0->>philosopher_0: {:mumble, "I'm full!"} Note over philosopher_0,philosopher_0: t=375ms philosopher_0->>fork_0: {:release_fork, :philosopher_0} Note over philosopher_0,fork_0: t=375ms philosopher_0->>fork_1: {:release_fork, :philosopher_0} Note over philosopher_0,fork_1: t=375ms philosopher_1->>philosopher_1: {:start_hungry, :fork_0, :fork_1} Note over philosopher_1,philosopher_1: t=450ms philosopher_0->>philosopher_0: {:start_hungry, :fork_0, :fork_1} Note over philosopher_0,philosopher_0: t=450ms philosopher_0->>fork_0: {:request_fork, :philosopher_0} Note over philosopher_0,fork_0: t=450ms philosopher_1->>fork_0: {:request_fork, :philosopher_1} Note over philosopher_1,fork_0: t=450ms fork_0->>philosopher_1: {:fork_granted, :fork_0} Note over fork_0,philosopher_1: t=450ms fork_0->>philosopher_0: {:fork_denied, :fork_0} Note over fork_0,philosopher_0: t=450ms philosopher_1->>fork_1: {:request_fork, :philosopher_1} Note over philosopher_1,fork_1: t=450ms fork_1->>philosopher_1: {:fork_granted, :fork_1} Note over fork_1,philosopher_1: t=450ms philosopher_1->>philosopher_1: {:mumble, "I'm full!"} Note over philosopher_1,philosopher_1: t=525ms philosopher_1->>fork_0: {:release_fork, :philosopher_1} Note over philosopher_1,fork_0: t=525ms philosopher_1->>fork_1: {:release_fork, :philosopher_1} Note over philosopher_1,fork_1: t=525ms philosopher_0->>philosopher_0: {:start_hungry, :fork_0, :fork_1} Note over philosopher_0,philosopher_0: t=600ms philosopher_1->>philosopher_1: {:start_hungry, :fork_0, :fork_1} Note over philosopher_1,philosopher_1: t=600ms philosopher_1->>fork_0: {:request_fork, :philosopher_1} Note over philosopher_1,fork_0: t=600ms philosopher_0->>fork_0: {:request_fork, :philosopher_0} Note over philosopher_0,fork_0: t=600ms fork_0->>philosopher_0: {:fork_granted, :fork_0} Note over fork_0,philosopher_0: t=600ms fork_0->>philosopher_1: {:fork_denied, :fork_0} Note over fork_0,philosopher_1: t=600ms philosopher_0->>fork_1: {:request_fork, :philosopher_0} Note over philosopher_0,fork_1: t=600ms fork_1->>philosopher_0: {:fork_granted, :fork_1} Note over fork_1,philosopher_0: t=600ms philosopher_0->>philosopher_0: {:mumble, "I'm full!"} Note over philosopher_0,philosopher_0: t=675ms philosopher_0->>fork_0: {:release_fork, :philosopher_0} Note over philosopher_0,fork_0: t=675ms philosopher_0->>fork_1: {:release_fork, :philosopher_0} Note over philosopher_0,fork_1: t=675ms philosopher_1->>philosopher_1: {:start_hungry, :fork_0, :fork_1} Note over philosopher_1,philosopher_1: t=750ms philosopher_0->>philosopher_0: {:start_hungry, :fork_0, :fork_1} Note over philosopher_0,philosopher_0: t=750ms philosopher_0->>fork_0: {:request_fork, :philosopher_0} Note over philosopher_0,fork_0: t=750ms philosopher_1->>fork_0: {:request_fork, :philosopher_1} Note over philosopher_1,fork_0: t=750ms fork_0->>philosopher_1: {:fork_granted, :fork_0} Note over fork_0,philosopher_1: t=750ms fork_0->>philosopher_0: {:fork_denied, :fork_0} Note over fork_0,philosopher_0: t=750ms philosopher_1->>fork_1: {:request_fork, :philosopher_1} Note over philosopher_1,fork_1: t=750ms fork_1->>philosopher_1: {:fork_granted, :fork_1} Note over fork_1,philosopher_1: t=750ms

Simulation Source Code

simulation =
DiningPhilosophers.create_simulation(
num_philosophers: 2,
think_time: 150,
eat_time: 75,
trace: true
)
|> ActorSimulation.run(duration: 800)

What the Diagram Shows

🔗 Source & Links

📚 GitHub Repository 🧪 Test Source 📖 Documentation 📦 Hex Package