Queue Library

README.md

@@ -17,6 +17,13 @@ Pure Golang errors library with stacktrace support (for wrapping and formatting
 
 [See here](errors/README.md).
 
+## queue
+
+A Pure Golang low-level and simple queue library for thread-safe and unlimited-size generics in-memory message queue implementation (async enqueue and blocking dequeue supports).\
+The alternative way to communicate between goroutines compared to `channel`
+
+[See here](queue/README.md).
+
 ## address
 
 Ethereum address utilities package. (a [go-ethereum](https://github.com/ethereum/go-ethereum) helper library)

go.work

@@ -9,5 +9,6 @@ use (
 	./address
 	./errors
 	./fixedpoint
+	./queue
 	./utils
 )

queue/README.md

@@ -0,0 +1,24 @@
+[![GoDoc](https://godoc.org/github.com/Cleverse/go-utilities/queue?status.svg)](http://godoc.org/github.com/Cleverse/go-utilities/queue)
+[![Report card](https://goreportcard.com/badge/github.com/Cleverse/go-utilities/queue)](https://goreportcard.com/report/github.com/Cleverse/go-utilities/queue)
+
+# queue
+
+A Pure Golang thread-safe and unlimited-size generics in-memory message queue implementation
+that supports async enqueue and blocking dequeue. \
+It's alternative way to communicate between goroutines compared to `channel`
+
+> **Note:** \
+> This package is not intended to be used as a distributed message queue. For advanced use-cases like distributed queue, persistent message please use a message broker like Kafka, RabbitMQ, NATES or NSQ instead.
+>
+> And if your use-case requires a limited-size queue and blocking enqueue, please use a channel instead.
+
+This package is low-level and simple queue library, it's not a full-featured message queue. \
+You can build any advanced message queue on top of this queue (use this queue for under the hood)
+like an advance message queue like a single-producer with multiple-consumers queue,
+broadcast system, multiple topics queue or any other use-cases.
+
+## Installation
+
+```shell
+go get github.com/Cleverse/go-utilities/queue
+```

queue/go.mod

@@ -0,0 +1,3 @@
+module github.com/Cleverse/go-utilities/queue
+
+go 1.18

queue/queue.go

@@ -0,0 +1,159 @@
+// Package queue provides a Pure Golang thread-safe and unlimited-size generics in-memory message queue implementation
+// that supports async enqueue and blocking dequeue.
+// It's alternative way to communicate between goroutines compared to `channel`.
+// The implementation of this in-memory message queue uses sync.Cond instead of channel.
+//
+// This queue is low-level and simple library, it's not a full-featured message queue.
+// If your use-case requires a limited-size queue and blocking enqueue, please use a channel instead.
+// For advanced use-cases like distributed queue, persistent message please use a message broker like Kafka, RabbitMQ, NATES or NSQ instead.
+//
+// You can build any advanced message queue on top of this queue (use this queue for under the hood)
+// like an advance message queue like a single-producer with multiple-consumers queue,
+// broadcast system, multiple topics queue or any other use-cases.
+package queue
+
+import (
+	"sync"
+)
+
+// Queue a instance of thread-safe and unlimited-size generics in-memory message queue
+// and alternative way to communicate between goroutines compared to channel.
+type Queue[T comparable] struct {
+	cond     *sync.Cond
+	items    []T
+	mu       sync.RWMutex
+	isClosed bool
+}
+
+// New creates a new message queue.
+func New[T comparable]() *Queue[T] {
+	q := &Queue[T]{
+		items: make([]T, 0),
+	}
+	q.cond = sync.NewCond(&q.mu)
+	return q
+}
+
+// Close closes the queue.
+// queue will be permanent unusable after this method is called.
+func (q *Queue[T]) Close() {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+
+	q.isClosed = true
+	q.items = nil
+	q.cond.Broadcast()
+}
+
+// IsClosed returns true if the queue is closed.
+func (q *Queue[T]) IsClosed() bool {
+	q.mu.RLock()
+	defer q.mu.RUnlock()
+	return q.isClosed
+}
+
+// Enqueue adds an item to the end of the queue. returns the index of the item.
+func (q *Queue[T]) Enqueue(item T) (index int) {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+
+	if q.isClosed {
+		return -1
+	}
+
+	q.items = append(q.items, item)
+	q.cond.Signal()
+
+	return len(q.items) - 1
+}
+
+// Dequeue removes an item from the front of the queue.
+//
+// If the queue is empty, this method blocks(wait) until an item is available.
+//
+// returns second value as false if the queue is closed.
+func (q *Queue[T]) Dequeue() (val T, ok bool) {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+
+	for len(q.items) == 0 {
+		if q.isClosed {
+			return val, false
+		}
+		q.cond.Wait()
+	}
+
+	// Recheck the length of the queue after waking up from wait.
+	// or another goroutine might have dequeued the last item.
+	if q.isClosed || len(q.items) == 0 {
+		return val, false
+	}
+
+	item := q.items[0]
+	q.items = q.items[1:]
+
+	return item, true
+}
+
+// IsEmpty returns true if the queue is empty.
+func (q *Queue[T]) IsEmpty() bool {
+	q.mu.RLock()
+	defer q.mu.RUnlock()
+	return len(q.items) == 0
+}
+
+// IndexOf returns the index of the first item that matches the target.
+func (q *Queue[T]) IndexOf(target T) (index int) {
+	return q.IndexOfIter(func(item T) bool {
+		return item == target
+	})
+}
+
+// IndexOfIter returns the index of the first item that matches the callback.
+// If no item matches the callback, -1 is returned.
+func (q *Queue[T]) IndexOfIter(cb func(item T) bool) (index int) {
+	q.mu.RLock()
+	defer q.mu.RUnlock()
+	for i, item := range q.items {
+		if cb(item) {
+			return i
+		}
+	}
+	return -1
+}
+
+// Len returns the length of the queue.
+func (q *Queue[T]) Len() int {
+	q.mu.RLock()
+	defer q.mu.RUnlock()
+	return len(q.items)
+}
+
+// Items returns a copy of the all items in the queue.
+func (q *Queue[T]) Items() []T {
+	q.mu.RLock()
+	defer q.mu.RUnlock()
+	items := make([]T, len(q.items))
+	copy(items, q.items)
+	return items
+}
+
+// RemoveAt removes an item at the given index and returns the new size of the queue.
+func (q *Queue[T]) RemoveAt(index int) (size int) {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+	q.items = append(q.items[:index], q.items[index+1:]...)
+	return len(q.items)
+}
+
+// Clear removes all items from the queue and returns the size of the removed items.
+func (q *Queue[T]) Clear() (size int) {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+	size = len(q.items)
+
+	// clean up the slice without changing the capacity and allocation.
+	q.items = q.items[:0:cap(q.items)]
+
+	return size
+}

queue/queue_test.go

@@ -0,0 +1,143 @@
+package queue
+
+import (
+	"sync"
+	"testing"
+	"time"
+)
+
+func TestEnqueueDequeue(t *testing.T) {
+	expecteds := []string{"a", "b", "c", "d", "e"}
+
+	q := New[string]()
+	for expectedIndex, v := range expecteds {
+		actualIndex := q.Enqueue(v)
+		if expectedIndex != actualIndex {
+			t.Errorf("index should be equal to the expected value, expected: %d, actual: %d", expectedIndex, actualIndex)
+		}
+	}
+
+	for _, expected := range expecteds {
+		actual, ok := q.Dequeue()
+		if !ok {
+			t.Errorf("item should be dequeued")
+		}
+		if expected != actual {
+			t.Errorf("item should be equal to the expected value, expected: %s, actual: %s", expected, actual)
+		}
+	}
+}
+
+func TestAsyncEnqueueDequeue(t *testing.T) {
+	expected := "A"
+	q := New[string]()
+	go func() {
+		time.Sleep(3 * time.Second)
+		q.Enqueue(expected)
+	}()
+
+	// expected to block until enqueue
+	actual, ok := q.Dequeue()
+	if !ok {
+		t.Errorf("item should be dequeued")
+	}
+	if expected != actual {
+		t.Errorf("item should be equal to the expected value, expected: %s, actual: %s", expected, actual)
+	}
+}
+
+func TestCloseConcurrency(t *testing.T) {
+	var (
+		q  = New[int]()
+		wg sync.WaitGroup
+	)
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		if _, ok := q.Dequeue(); ok {
+			t.Error("should not dequeue from an empty queue")
+		}
+	}()
+
+	time.Sleep(1 * time.Second)
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		q.Close()
+	}()
+	wg.Wait()
+
+	actualIndex := q.Enqueue(1)
+	actualItem, ok := q.Dequeue()
+
+	if actualIndex != -1 {
+		t.Errorf("should not enqueue to a closed queue")
+	}
+	if actualItem != 0 {
+		t.Errorf("should not dequeue from a closed queue")
+	}
+	if ok {
+		t.Errorf("should not dequeue from a closed queue")
+	}
+}
+
+func TestClear(t *testing.T) {
+	q := New[int]()
+
+	expectedSize := 10
+	for i := 0; i < expectedSize; i++ {
+		q.Enqueue(i)
+	}
+
+	itemsCap := cap(q.items)
+	actualSize := q.Clear()
+
+	if q.Len() != 0 {
+		t.Errorf("queue size should be zero")
+	}
+	if expectedSize != actualSize {
+		t.Errorf("flushed size should be equal to the enqueued size")
+	}
+	if itemsCap != cap(q.items) {
+		t.Errorf("capacity should not change after flush")
+	}
+}
+
+func TestRemoveAt(t *testing.T) {
+	q := New[int]()
+	size := 10
+	expected := make([]int, 0, size)
+
+	for i := 0; i < size; i++ {
+		value := i + 1
+		expected = append(expected, value)
+		q.Enqueue(value)
+	}
+
+	removeValue := 5
+	removeIndex := q.IndexOf(removeValue)
+	newSize := q.RemoveAt(removeIndex)
+
+	// assert.Equal(t, size-1, newSize, "new size should be equal to the old size minus 1")
+	// assert.Equal(t, -1, q.IndexOf(removedValue), "index of removed item should be -1")
+	if size-1 != newSize {
+		t.Errorf("new size should be equal to the old size minus 1")
+	}
+	if -1 != q.IndexOf(removeValue) {
+		t.Errorf("index of removed item should be -1")
+	}
+
+	for i := 0; i < q.Len(); i++ {
+		item, ok := q.Dequeue()
+		if !ok {
+			t.Errorf("item should be dequeued")
+		}
+		if i != removeIndex && expected[i] != item {
+			t.Errorf("item should be equal to the expected value, expected: %d, actual: %d", expected[i], item)
+		}
+		if removeValue == item {
+			t.Errorf("removed item should not be in the queue")
+		}
+	}
+}