How to build a job queue in Go without external dependencies

Building a job queue in Go without relying on external dependencies is straightforward using the language's standard library. The tutorial outlines a simple yet powerful concurrent job queue implementation consisting of a fixed pool of workers processing tasks from a buffered channel.

Key features of this job queue include:

- A fixed pool of workers pulling from a buffered channel

- Non-blocking enqueue with error handling for a full queue

- Per-job retry with a configurable limit

- Graceful shutdown handling on SIGINT/SIGTERM without dropping jobs in-flight

- An error channel to capture worker failures without crashing the process

The implementation consists of around 150 lines of Go code without relying on any external libraries. The core components are:

1. The `Job` struct representing each task with its ID, payload, retries count, and maximum retry limit.

2. The `Handler` function type defining the processing logic for a job.

3. The `Queue` struct managing the job pool, workers, and error channel.

The queue creation function `New` initializes a buffered channel with a specified buffer size, sets up the worker goroutines, and returns a pointer to the queue. The `Enqueue` method attempts to add a job to the queue, returning an error if the queue is full. Worker goroutines continuously pull jobs from the channel, invoke the provided handler function, and handle retries as needed.

The `Stop` method gracefully shuts down the queue by closing the jobs channel and waiting for all workers to finish. Finally, the `Errors` method returns the channel capturing any worker errors.