Queue¶
A queue is a basic data structure that, like a stack, organizes elements in a linear fashion. A key feature of a queue is the FIFO (First In, First Out) principle, which means that the first element added to the queue is the first element to be removed from it. This behavior is analogous to an actual queue, for example in a store - the first person to join the queue is the first person to leave the queue.
The basic operations performed on a queue are:
- Enqueue (add to queue): adds an item to the end of the queue.
- Dequeue (remove from queue): removes an element from the beginning of the queue.
Additional operations that may be available in some queue implementations are:
- Front/Peek: returns the first element of the queue without deleting it.
- IsEmpty: checks if the queue is empty.
- Size: returns the number of elements in the queue.
Applications¶
Queues are widely used in computer science, including:
- Data synchronization: queues are often used to synchronize data between processes. For example, they can be used to securely transfer requests from a producer thread to a consumer thread.
- Data buffering: queues can serve as buffers for data transferred between two CPU units or between a peripheral and the CPU.
- CPU scheduling: operating systems often use queues to manage processes that are waiting to access resources such as CPU, memory, disk, etc.
- Graph algorithms: queues are used in graph search algorithms such as breadth-first search (BFS).
By knowing the basics of queues, we can understand many key aspects of data management in computing, both in operating systems and in more complex algorithms.
Implementation¶
Queues can be implemented using various data structures, including arrays and linked lists. The choice of data structure to implement a queue depends on specific requirements, such as efficiency of operations, memory consumption and ease of implementation.
Below you will find examples of queue implementations in selected programming languages.