What is queue?
A queue is a way of organizing items so that the first one added is the first one taken out, just like a line of people waiting for a ticket. This “first‑in, first‑out” (FIFO) rule means you always serve items in the order they arrived.
Let's break it down
- Front: the end of the line where items are removed (served).
- Rear: the end where new items are added (join the line).
- Enqueue: the action of adding an item to the rear.
- Dequeue: the action of removing an item from the front. Think of a queue as a simple list with two pointers: one pointing to the front, one to the rear. When you enqueue, you move the rear pointer; when you dequeue, you move the front pointer.
Why does it matter?
Queues give computers a predictable way to handle tasks that must happen in order. Because the order is guaranteed, you avoid chaos and can safely share resources, process requests, or manage data without losing or mixing items.
Where is it used?
- Print jobs waiting for a printer.
- Customer service call centers handling incoming calls.
- Operating systems scheduling processes or threads.
- Network routers buffering packets before sending them onward.
- Web servers managing incoming HTTP requests.
- Any situation where tasks arrive over time and need to be processed sequentially.
Good things about it
- Simple to understand and implement.
- Guarantees fair, ordered processing (FIFO).
- Works well for buffering and smoothing bursts of activity.
- Low overhead: only need to track two ends of the structure.
- Naturally fits many real‑world scenarios, making debugging easier.
Not-so-good things
- Access is limited to the front and rear; you can’t quickly get an item from the middle.
- If not managed properly, a queue can grow indefinitely and consume too much memory (overflow).
- Fixed‑size queues can become full, causing new items to be rejected or lost.
- In multi‑threaded environments, you need extra synchronization to avoid race conditions, which adds complexity.