🧠 What is Concurrency?
Concurrency refers to the ability of a system to manage and make progress on multiple tasks at the same time — but not necessarily by executing them simultaneously.
👉 In simpler terms:
Concurrency is about dealing with many things at once, while not necessarily doing them all at once.
A concurrent system can switch between tasks so quickly that it appears that the tasks are running at the same time — even on a single-core CPU.
💡 Real-Life Analogy
Imagine a single barber in a shop (single-core CPU). He has multiple customers (tasks) waiting. He:
- Starts cutting hair for Customer A,
- Pauses midway to take a phone call (Customer B),
- Goes back to A, then to B again, and so on.
This is concurrency: interleaving work on multiple tasks.
Concurrency vs Parallelism
| Aspect | Concurrency | Parallelism |
|---|---|---|
| Meaning | Managing multiple tasks at once | Executing multiple tasks simultaneously |
| CPU Requirement | Possible on single-core CPU | Requires multi-core/multi-processor |
| Focus | Structure and responsiveness | Speed and efficiency |
| Analogy | A single chef cooking many dishes by switching between them | Multiple chefs each cooking a dish |
Concurrency is a software concept; parallelism is a hardware capability.
🔐 Challenges in Concurrency
Concurrency introduces non-determinism, making it difficult to debug and test. Common issues include:
| Problem | Description |
|---|---|
| Race Conditions | Two threads access shared data at the same time, causing inconsistent results. |
| Deadlocks | Two or more threads are waiting on each other’s resources — forever. |
| Starvation | A low-priority task never gets CPU time due to high-priority tasks. |
| Priority Inversion | A low-priority task holds a resource needed by a high-priority one. |
🔒 Synchronization Tools
To prevent race conditions and ensure correctness, we use:
| Tool | Purpose |
|---|---|
| Mutex | Mutual exclusion — only one thread can access a section of code. |
| Semaphore | Counting lock that controls access to resources. |
| Monitors | High-level abstraction combining mutex and condition variables. |
| Atomic Variables | Operations that complete without interruption. |