🧠 High-Level View
| Concept | Process | Thread |
|---|---|---|
| 💡 Definition | Independent program in execution | Lightweight unit of execution within a process |
| 🧠 Memory Space | Has its own memory | Shares memory with other threads of the same process |
| 🔁 Communication | Slow (uses IPC, pipes, sockets) | Fast (direct access to shared memory) |
| ⚡ Overhead | High | Low |
| 💥 Isolation | Strong – one process can’t corrupt another | Weak – one thread can crash all others |
| 🧩 Creation Cost | Expensive (new PCB, new memory) | Cheap (just a stack + registers) |
| 🧰 Use Case | Run independent apps | Run parallel tasks inside the same app |
| 📊 Scheduling | Handled by OS | Handled by OS or user-level libraries |
🔍 Analogy
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A process is like a house.
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A thread is a person inside the house.
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Everyone shares the same kitchen (memory).
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If one person burns the kitchen, everyone suffers.
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🧩 What Threads Share Within a Process
| Shared Among Threads | Unique per Thread |
|---|---|
| Code section | Stack |
| Data & heap | Program Counter |
| Open files | CPU registers |
| Address space | Thread ID (TID) |
🧪 Real Example: Web Browser
| Component | Process or Thread? |
|---|---|
| Chrome tabs | Separate processes (isolation, security) |
| Rendering, JS engine, networking | Separate threads inside each tab process |
⚔️ Process vs Thread – Comparison Table
| Feature | Process | Thread |
|---|---|---|
| 💽 Memory | Separate | Shared |
| 🚀 Speed | Slower | Faster |
| ⚙️ Switching | Costly (context switch) | Lightweight |
| 🔒 Security | Isolated | Shared — less secure |
| 🧪 Use Case | Run different apps | Parallel tasks in one app |
| 📦 Crash Impact | One process crash ≠ others | One thread crash → whole process can fail |
⚠️ Threading Risks
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Race conditions: Two threads modify the same variable
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Deadlocks: Thread A waits for Thread B, and vice versa
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Harder to debug: Non-deterministic behavior
🧠 Interview-Ready One-Liner:
A process is an independent program with its own memory space, while a thread is a lightweight execution unit within a process that shares memory and resources with other threads, allowing faster communication but requiring careful synchronization.
✅ When to Use What?
| Scenario | Use |
|---|---|
| Isolated apps (browser tab crash shouldn’t affect others) | Processes |
| Concurrent tasks (UI + network + DB) | Threads |
| Performance-intensive app (game engine, web server) | Multi-threading |
| Microservice architecture | Multiple processes (one per service) |