What is the difference between a process and a thread?

Processes and threads are fundamental to how operating systems manage tasks, but they differ in resource usage, isolation, and communication. Here’s a concise breakdown:

Key Differences

Aspect	Process	Thread
Definition	Independent program with its own memory/resources	Subunit of a process; shares the process’s memory
Memory/Resources	Has its own virtual memory space, file handles, etc.	Shares memory/resources with other threads in the same process
Creation	Heavyweight (slower, more resource-intensive)	Lightweight (faster, less overhead)
Isolation	Failures in one process don’t affect others	A crashing thread can crash the entire process
Communication	Uses IPC (pipes, sockets, files)	Directly shares data via shared memory
Context Switching	Slower (requires OS kernel intervention)	Faster (handled within the process)

Real-World Analogy

• Process: A self-contained office building with its own staff, supplies, and security.
• Thread: A department within that building sharing resources (e.g., printers, break rooms).

Examples

1. Web Browser:

• Processes: Each tab runs as a separate process (prevents one tab crash from killing the entire browser).
• Threads: A single tab uses threads for rendering, JavaScript execution, and network requests.

1. Video Game:

• Process: The game itself.
• Threads: Separate threads for physics, AI, and rendering.

When to Use Which

Use Processes When…	Use Threads When…
Tasks need strict isolation (security/stability)	Tasks require shared data (e.g., real-time updates)
Leveraging multi-core CPUs for parallelism	Minimizing overhead for quick tasks
Running independent programs (e.g., separate apps)	Building responsive UIs (e.g., background tasks)

Technical Deep Dive

• Memory Sharing:
  Threads share the heap (global data) but have their own stack (local variables).
  Processes have entirely separate memory spaces.
• Synchronization:
  Threads use mutexes/semaphores to avoid race conditions.
  Processes use IPC mechanisms like message queues.
• Overhead:
  Creating a process duplicates memory (fork()), while threads reuse the parent’s memory.

Code Example (C++)

// Process example (simplified)
pid_t pid = fork(); // Creates a new process
if (pid == 0) {
  // Child process code
}

// Thread example (C++11)
#include <thread>
void task() { /* ... */ }
std::thread t1(task); // Creates a thread
t1.join();

Summary

• Processes = Isolation + Stability (at the cost of overhead).
• Threads = Speed + Shared Data (but riskier for crashes).
• Modern apps (e.g., browsers, servers) often use both for performance and safety.