A small Go package providing a concurrent queue, on which consumers can wait for an item satisfying a given condition, and producers can add items to wake consumers.

Run go get hermannm.dev/condqueue to add it to your project!

Docs: pkg.go.dev/hermannm.dev/condqueue

Contents:

• Usage
• Maintainer's guide

In the example below, we have a simple message, which can either be of type success or error. A producer goroutine adds messages to the queue, while two consumer goroutines wait for a message type each.

import (
	"context"
	"fmt"
	"sync"

	"hermannm.dev/condqueue"
)

type Message struct {
	Type    string
	Content string
}

func main() {
	queue := condqueue.New[Message]()

	var wg sync.WaitGroup
	wg.Add(3)

	// Producer
	go func() {
		fmt.Println("[Producer] Adding success message...")
		queue.Add(Message{Type: "success", Content: "Great success!"})

		fmt.Println("[Producer] Adding error message...")
		queue.Add(Message{Type: "error", Content: "I've made a huge mistake"})

		wg.Done()
	}()

	// Consumer 1
	go func() {
		fmt.Println("[Consumer 1] Waiting for success...")

		msg, _ := queue.AwaitMatchingItem(context.Background(), func(candidate Message) bool {
			return candidate.Type == "success"
		})

		fmt.Printf("[Consumer 1] Received success message: %s\n", msg.Content)
		wg.Done()
	}()

	// Consumer 2
	go func() {
		fmt.Println("[Consumer 2] Waiting for errors...")

		msg, _ := queue.AwaitMatchingItem(context.Background(), func(candidate Message) bool {
			return candidate.Type == "error"
		})

		fmt.Printf("[Consumer 2] Received error message: %s\n", msg.Content)
		wg.Done()
	}()

	wg.Wait()
}

This gives the following output (the order may vary due to concurrency):

[Consumer 2] Waiting for errors...
[Producer] Adding success message...
[Producer] Adding error message...
[Consumer 2] Received error message: I've made a huge mistake
[Consumer 1] Waiting for success...
[Consumer 1] Received success message: Great success!

For more details on how to use condqueue, refer to the documentation.

• Run tests and linter (golangci-lint):

  go test ./... && golangci-lint run
  

• Add an entry to CHANGELOG.md (with the current date)
  • Remember to update the link section, and bump the version for the [Unreleased] link
• Create commit and tag for the release (update TAG variable in below command):

  TAG=vX.Y.Z && git commit -m "Release ${TAG}" && git tag -a "${TAG}" -m "Release ${TAG}" && git log --oneline -2
  

• Push the commit and tag:

  git push && git push --tags
  

  • Our release workflow will then create a GitHub release with the pushed tag's changelog entry