queue

The queue package provides thread-safe generic implementations in Go for the following data structures: BlockingQueue, PriorityQueue, CircularQueue and Linked Queue.

A queue is a sequence of entities that is open at both ends where the elements are added (enqueued) to the tail (back) of the queue and removed (dequeued) from the head (front) of the queue.

The implementations are designed to be easy-to-use and provide a consistent API, satisfying the Queue interface provided by this package. .

Benchmarks and Example tests can be found in this package.

• queue
  • Installation
  • Import
  • Usage
    • Queue Interface
    • Blocking Queue
    • Priority Queue
    • Circular Queue
    • Linked Queue
  • Benchmarks

Installation

To add this package as a dependency to your project, run:

go get -u github.com/adrianbrad/queue

Import

To use this package in your project, you can import it as follows:

import "github.com/adrianbrad/queue"

Usage

Queue Interface

// Queue is a generic queue interface, defining the methods that all queues must implement.
type Queue[T comparable] interface {
	// Get retrieves and removes the head of the queue.
	Get() (T, error)

	// Offer inserts the element to the tail of the queue.
	Offer(T) error

	// Reset sets the queue to its initial state.
	Reset()

	// Contains returns true if the queue contains the element.
	Contains(T) bool

	// Peek retrieves but does not remove the head of the queue.
	Peek() (T, error)

	// Size returns the number of elements in the queue.
	Size() int

	// IsEmpty returns true if the queue is empty.
	IsEmpty() bool

	// Iterator returns a channel that will be filled with the elements
	Iterator() <-chan T

	// Clear removes all elements from the queue.
	Clear() []T
}

Blocking Queue

Blocking queue is a FIFO ordered data structure. Both blocking and non-blocking methods are implemented. Blocking methods wait for the queue to have available items when dequeuing, and wait for a slot to become available in case the queue is full when enqueuing. The non-blocking methods return an error if an element cannot be added or removed. Implemented using sync.Cond from the standard library.

package main

import (
	"fmt"

	"github.com/adrianbrad/queue"
)

func main() {
	elems := []int{2, 3}

	blockingQueue := queue.NewBlocking(elems, queue.WithCapacity(3))

	containsTwo := blockingQueue.Contains(2)
	fmt.Println(containsTwo) // true

	size := blockingQueue.Size()
	fmt.Println(size) // 2

	empty := blockingQueue.IsEmpty()
	fmt.Println(empty) // false

	if err := blockingQueue.Offer(1); err != nil {
		// handle err
	}

	elem, err := blockingQueue.Get()
	if err != nil {
		// handle err
	}

	fmt.Println("elem: ", elem) // elem: 2
}

Priority Queue

Priority Queue is a data structure where the order of the elements is given by a comparator function provided at construction. Implemented using container/heap standard library package.

package main

import (
	"fmt"

	"github.com/adrianbrad/queue"
)

func main() {
	elems := []int{2, 3, 4}

	priorityQueue := queue.NewPriority(
		elems, 
		func(elem, otherElem int) bool { return elem < otherElem },
        )

	containsTwo := priorityQueue.Contains(2)
	fmt.Println(containsTwo) // true

	size := priorityQueue.Size()
	fmt.Println(size) // 3

	empty := priorityQueue.IsEmpty()
	fmt.Println(empty) // false

	if err := priorityQueue.Offer(1); err != nil {
		// handle err
	}

	elem, err := priorityQueue.Get()
	if err != nil {
		// handle err
	}

	fmt.Printf("elem: %d\n", elem) // elem: 1
}

Circular Queue

Circular Queue is a fixed size FIFO ordered data structure. When the queue is full, adding a new element to the queue overwrites the oldest element.

Example: We have the following queue with a capacity of 3 elements: [1, 2, 3]. If the tail of the queue is set to 0, as if we just added the element 3, the next element to be added to the queue will overwrite the element at index 0. So, if we add the element 4, the queue will look like this: [4, 2, 3]. If the head of the queue is set to 0, as if we never removed an element yet, then the next element to be removed from the queue will be the element at index 0, which is 4.

package main

import (
  "fmt"

  "github.com/adrianbrad/queue"
)

func main() {
  elems := []int{2, 3, 4}

  circularQueue := queue.NewCircular(elems, 3)

  containsTwo := circularQueue.Contains(2)
  fmt.Println(containsTwo) // true

  size := circularQueue.Size()
  fmt.Println(size) // 3

  empty := circularQueue.IsEmpty()
  fmt.Println(empty) // false

  if err := circularQueue.Offer(1); err != nil {
    // handle err
  }

  elem, err := circularQueue.Get()
  if err != nil {
    // handle err
  }

  fmt.Printf("elem: %d\n", elem) // elem: 1
}

Linked Queue

A linked queue, implemented as a singly linked list, offering O(1) time complexity for enqueue and dequeue operations. The queue maintains pointers to both the head (front) and tail (end) of the list for efficient operations without the need for traversal.

package main

import (
  "fmt"

  "github.com/adrianbrad/queue"
)

func main() {
  elems := []int{2, 3, 4}

  circularQueue := queue.NewLinked(elems)

  containsTwo := circularQueue.Contains(2)
  fmt.Println(containsTwo) // true

  size := circularQueue.Size()
  fmt.Println(size) // 3

  empty := circularQueue.IsEmpty()
  fmt.Println(empty) // false

  if err := circularQueue.Offer(1); err != nil {
    // handle err
  }

  elem, err := circularQueue.Get()
  if err != nil {
    // handle err
  }

  fmt.Printf("elem: %d\n", elem) // elem: 2
}

Benchmarks

Results as of October 2023.

BenchmarkBlockingQueue/Peek-8           84873882                13.98 ns/op            0 B/op          0 allocs/op
BenchmarkBlockingQueue/Get_Offer-8      27135865                47.00 ns/op           44 B/op          0 allocs/op
BenchmarkBlockingQueue/Offer-8          53750395                25.40 ns/op           43 B/op          0 allocs/op
BenchmarkCircularQueue/Peek-8           86001980                13.76 ns/op            0 B/op          0 allocs/op
BenchmarkCircularQueue/Get_Offer-8      32379159                36.83 ns/op            0 B/op          0 allocs/op
BenchmarkCircularQueue/Offer-8          63956366                18.77 ns/op            0 B/op          0 allocs/op
BenchmarkLinkedQueue/Peek-8             1000000000              0.4179 ns/op           0 B/op          0 allocs/op
BenchmarkLinkedQueue/Get_Offer-8        61257436                18.48 ns/op           16 B/op          1 allocs/op
BenchmarkLinkedQueue/Offer-8            38975062                30.74 ns/op           16 B/op          1 allocs/op
BenchmarkPriorityQueue/Peek-8           86633734                14.02 ns/op            0 B/op          0 allocs/op
BenchmarkPriorityQueue/Get_Offer-8      29347177                39.88 ns/op            0 B/op          0 allocs/op
BenchmarkPriorityQueue/Offer-8          40117958                31.37 ns/op           54 B/op          0 allocs/op