🧠 What is a Thread?
A Thread is the smallest unit of execution within a process.
It represents a single flow of control that runs in the context of a process and shares the same memory, files, and resources as other threads in the same process.
🧵 One process = one or more threads
📦 Key Characteristics of a Thread
| Property | Description |
|---|---|
| 🧠 Shares memory | All threads in a process share the same address space |
| 📁 Shares resources | Share open files, heap, data segment |
| 🧵 Owns stack | Each thread has its own stack and registers |
| 🔀 Lightweight | Creating/switching threads is cheaper than processes |
| 💥 Crash impact | One thread crashing can affect the entire process |
| ⛓️ Tight coupling | Threads are tightly bound — easy communication, but less isolation |
🔁 How Threads Work in a Process
[ Process ]
├── Thread 1 (Main)
├── Thread 2 (Worker)
└── Thread 3 (I/O)
All threads:
-
Access same code, data, heap
-
But each has its own stack + instruction pointer
⚙️ Thread vs Process (Quick Comparison)
| Feature | Thread | Process |
|---|---|---|
| 💾 Memory | Shared between threads | Separate between processes |
| 🔁 Context switch | Very fast (lightweight) | Slower (full state switch) |
| 🧠 Communication | Easy (shared memory) | Harder (IPC required) |
| 🧵 Crash Impact | Can crash the whole process | Usually isolated |
🧰 Use Cases of Threads
| Use Case | How Threads Help |
|---|---|
| 🧮 CPU parallelism | Run tasks on multiple cores |
| 🖥️ UI responsiveness | Background tasks (e.g., animations, downloads) |
| 🌐 Server apps | Handle multiple client connections |
| 🚀 Asynchronous ops | Do I/O or wait tasks without blocking main thread |
📚 Real-World Example
In a browser:
-
One thread handles UI rendering
-
Another handles JavaScript execution
-
Another does network requests
In a web server:
- Each client request may be handled by a separate thread
🧠 Interview-Ready Definition:
A Thread is a lightweight unit of execution within a process. Multiple threads in the same process share memory and resources but operate independently with their own stack and execution flow. Threads enable efficient multitasking and parallelism, but require careful synchronization to avoid race conditions.
⚠️ Common Pitfalls
| Problem | Description |
|---|---|
| ❗ Race Conditions | Multiple threads modifying shared data unsafely |
| ❄️ Deadlocks | Threads waiting on each other forever |
| ⛓️ Starvation | Low-priority threads never getting CPU time |
| 🔥 Shared Failure | One buggy thread can crash the whole process |