Quick start

This program creates a worker, binds a queue to it and adds two jobs. Press Run to run it on the Go Playground. Press Edit to change it, then Run again (or Ctrl+Enter, Cmd+Enter on a Mac).

package main

import (
	"fmt"
	"time"

	"github.com/goptics/varmq"
)

func main() {
	worker := varmq.NewWorker(func(j varmq.Job[int]) {
		fmt.Printf("Processing %d\n", j.Data())
		time.Sleep(1 * time.Second)
	}) // default concurrency is 1
	defer worker.WaitUntilIdle()
	queue := worker.BindQueue()

	queue.Add(1)
	queue.Add(2)
}

It prints Processing 1, then Processing 2 once the first job’s one-second sleep is over, then Program exited.

Line by line

worker := varmq.NewWorker(func(j varmq.Job[int]) {
	fmt.Printf("Processing %d\n", j.Data())
	time.Sleep(1 * time.Second)
}) // default concurrency is 1

NewWorker builds a worker around a function that handles one job. The job type is generic: a Job[int] carries an int, which Data() returns. With no concurrency argument the worker runs one job at a time, which is why Processing 2 waits for the first job to finish.

defer worker.WaitUntilIdle()

WaitUntilIdle blocks until the worker has no jobs left and is idle. Deferring it stops main from returning until both jobs are done. Without it, main would return right after the two Add calls and the program would exit before the jobs ran.

queue := worker.BindQueue()

BindQueue creates a first-in, first-out queue and binds it to this worker. Jobs added to it go to this worker and no other.

queue.Add(1)
queue.Add(2)

Add puts a job in the queue and returns immediately, without waiting for the job to run. It returns a handle to the job and true. It returns false if the queue did not take the job, for example because the queue is full or closed. This example ignores both. Jobs covers them.

Try it

Press Edit and pass a concurrency of 2 as the last argument to NewWorker:

}, 2)

Run it again: both jobs now start together, so their two lines appear at the same moment, in either order. The timeline below shows both runs. Switch the concurrency and drag the time slider.

Next: workers and queues.