Applications of Queue: 15 Real-World Uses, Explained in Plain English

Queues are a crucial data structure in the field of programming and computer science to comprehend and be aware of. Queues are a relatively simple structure with a wide range of uses, from technological to more practical. At first, queues may seem entirely speculative. However, there are multiple instances in real life where we can observe the queue structure in action. This article will explore the applications of the queue data structure.

What Is the Queue Data Structure, and How Does It Work?

Much like a real-life queue, a queue data structure is a collection of items. Except, in this case, these are data elements and not humans. These elements are ordered within a list, with a front end and a rear end just like a real queue. Data queues work by a first-in, first-out principle. This means that, whenever we add an element, this will be the first element to be removed when we remove an element. We mostly used queues where items don’t need to be processed instantly.

What Are the Queue Operations?

There are two major queue operations, Enqueue and Dequeue. Enqueue is used to add an element to the back of the queue. In contrast, dequeue is used to remove an element from the front of the queue. This maintains the first-in, first-out principle because we process the data in the order we added it to the queue. We do this to ensure that no data gets ignored and to maintain an ordered list.

While those are the two primary operations, there are some other commonly used queue operations, namely IsFull, IsEmpty and Peek. IsFull and IsEmpty are used to check if the queue is full or empty, respectively. Peek, on the other hand, is used to retrieve the data value at the front of the queue. Peek does this without removing it as Dequeue would.

How Are Queue Operations Used?

Next, we’re covering how to use each of these operations in practice to give you a better understanding. Initially, we set the queue with two pointers. These are called “front” and “rear”, and track the first and last elements in the queue, respectively. We initialize the values for both to -1. This is because we could potentially be using 0 as an integer value in the queue. This declaration helps to avoid confusion and helps us know if we have an empty queue or not.

Enqueue

To use enqueue, we have to first check if the queue is full. If it is, then we can’t use enqueue. If the queue isn’t full, we increment the value of “rear” by 1. This shows that there will be 1 more element in the queue. Finally, we add the element to the end of the queue, to the position that the rear pointer is pointing to.

Dequeue

Dequeue works similarly to enqueue. But first, we check if the queue is empty, since if it is empty, we can’t remove anything. After this, we return the value that “front” points to, so we know which element to remove. We then increased the front index by 1, to show that we have removed an element. Finally, when removing the last element, we reset the values of front and rear to -1. This shows that the queue is empty again.

Real-World Applications of Queue Data Structure

There are many real-world uses of the queue data structure, but we will cover the most common ones here.

Computer Science

In computer science and programming, we often use queues for a range of tasks. Applications of the queue data structure include the following:

• Scheduling tasks: Queues are used to prioritize tasks so that they are completed as they’re ordered. By using queues, we can make sure tasks are completed predictably and optimally.
• Breadth-first search: This is a type of algorithm that’s used to search through graphs and trees. It relies on a queue structure to order a series of nodes, which are processed in the desired order.
• Web servers: These use queues to manage requests that are coming in, to make sure they handle the most important requests first.
• Network protocols: Protocols like TCP manage the packets of data being transmitted by using queues. This maintains the correct order and helps to control the rate at which data is being received.
• Operating systems: These must handle a vast amount of resources and processes, usually at the same time. Therefore, queues are used to manage which resources are allocated and what processes are executed, so that everything runs smoothly. Queues are also used to handle interrupts, where something has disrupted normal processing. This allows prioritization of the interrupts, as well as controlling the rate at which interrupts are handled, especially if they’re frequent.
• Data transfer: Where transfer is asynchronous, i.e. where data is not being synchronized, queues are used to manage data flow. The sender adds the data to the queue, and the receiver may process it at a different rate. This allows both to operate independently.

Business

In business, queues are extremely common. They’re usually found in these situations:

• Customer service: Businesses have countless customer requests and interactions to deal with, which they can keep track of using a queue. For example, when customers are sending an email, message, or making a call, they can be added to a queue and their request will be dealt with when an operator is available.
• Processing orders: Queues are also used here so that orders are processed correctly and fairly, with the orders first added being dealt with first.
• Project management: A project usually has a lot of tasks within it, so someone can queue these to make sure they handle the most important tasks before the rest.

What Other Real-World Applications of Queues Are There?

There are some other applications of queues that you may have run into. These are:

• Buffering: Whenever you’re streaming, buffering is used to store some content in advance. It uses a queue as temporary storage to make playback seamless.
• Print spooling: You’ve likely encountered a print queue while printing. Printers use queues to order print jobs in the order they came in so that no data gets forgotten and people receive their printed documents fairly.
• Message queuing: We use apps like WhatsApp all the time. Sometimes, our connection drops out and our message doesn’t send. Queues can temporarily store messages so that when we do have a good connection, it can send them successfully.
• Managing traffic: Queues ensure that we can get traffic going again as soon as possible. When the light is red, a new queue of vehicles forms, and when the light turns green, the queue is released and vehicles can pass efficiently. We also use queues at airports, toll booths and parking garages. The principles are similar and work to make the passage of vehicles through entry and exit points faster.
• Theme parks: Waiting in line is hardly part of the fun of amusement parks. Queue systems are used to allow fair access to not only rides, but meet and greets, food stalls, and ticket collection. Virtual queues are even in place at some parks, where they add customers to a digital queue so they don’t need to physically wait in line.
• Healthcare: Whenever we have a health issue, we understandably want it to be checked out as soon as possible. They often do this with queues, which are used to check in patients and to schedule imaging, surgeries, and sample testing.

What Issues Can You Encounter With Queue?

While there’s a lot to love about the queue structure, we can occasionally run into some problems when using it. Here are some of the most frequent problems that can occur.

• Overflow: Queues typically have a fixed size, meaning they can become full. This can lead to overflow, where we need to add more elements but don’t have enough space. Overflow often occurs when we’re adding elements faster than they’re being removed. We can use dynamic resizing methods to overcome this or a circular buffer.
• Underflow: Similar to overflow, we can run into underflow problems when elements get removed faster than they’re added. We might try to remove an element when the queue is empty, which can cause technical issues. In this case, we can use null pointers to indicate an empty queue.
• Priority inversion: Where resources are held by a task that’s not as urgent, the task with higher priority can become blocked. This can be dealt with by using priority inheritance, meaning the lower-priority task’s priority is made equivalent to that of the higher-priority task so that the latter can be executed. We can also use ceiling priority, where we assign shared resources a priority limit so that a task that needs access can obtain it.
• Synchronization: When several processes are trying to access a queue structure, data can be corrupted if they’re not synchronized correctly. Clear guidelines are crucial for the system to avoid these issues.
• Memory problems: If elements are not properly removed from a queue, they’ll take up memory unnecessarily. Memory can also become fragmented into small amounts spread throughout a queue, which also wastes memory. We must use memory allocation carefully to avoid this, as well as track the size of the queue to ensure it isn’t becoming too large to handle.

Applications of Queue: Wrapping Up

In conclusion, queue has a lot of applications in the real world, and not just in the computer science industry. From healthcare and call centers to amusement parks and messaging apps, queues are essential for dealing with requests efficiently and preventing backlogs of any kind. We must take care to prevent any potential issues with queues, which could include things like priority inversion, memory mismanagement, queue overflow or underflow. Queues have been and will remain a crucial tool for management processes and data, and will probably only keep improving over time.