gofherd

Herd of gophers at your service

Gofherd

Gofherd (gof-herd), is a small framework for running user defined functions with bounded parallelism. It's simple interface gives you a function which accepts tasks, allows you to define a function which has "processing logic" and gives you an output channel to read results from.

Gofherd provides:

• Bounded parallelism
  • You can configure number of gophers to run the tasks.
• Monitoring
  • Current state is exposed as Prometheus compatible metrics on /metrics
  • Metrics: gofherd_success_total, gofherd_retry_total, gofherd_failure_total
• Dynamic parallelism
  • Using GET/PATCH calls on /herd

Example

go get github.com/darshanime/gofherd

package main

import (
	"fmt"

	gf "github.com/darshanime/gofherd"
)

func LoadWork(herd *gf.Gofherd) {
	for i := 0; i < 10; i++ {
		w := gf.Work{ID: fmt.Sprintf("workdID:%d", i), Body: i}
		// blocking call, returns when work picked up by a goroutine
		herd.SendWork(w)
	}
	// done pushing all work, close input chan to indicate that
	herd.CloseInputChan()
}

// this is the signature of "processing logic" function
func ProcessWork(w *gf.Work) gf.Status {
	result := w.Body.(int) + 10
	// set the result after processing
	w.SetResult(result)
	return gf.Success
}

func ReviewOutput(outputChan <-chan gf.Work) {
	// output chan is closed when all results are received
	for work := range outputChan {
		fmt.Printf("%s, status: %s, result:%d\n", work.ID, work.Status(), work.Result())
	}
}

func main() {
	// passing "processing logic" when initializing work
	herd := gf.New(ProcessWork)
	// setting a herd size of 0
	herd.SetHerdSize(0)
	// disabling retries
	herd.SetMaxRetries(0)
	// bind on 127.0.0.1:5555
	herd.SetAddr("127.0.0.1:5555")
	go LoadWork(herd)
	herd.Start()
	ReviewOutput(herd.OutputChan())
}

Get current herd size: curl -XGET localhost:5555/herd

Now, we can increase the herd size using curl -XPATCH 127.0.0.1:5555/herd -d '{"num": 10}'

Output:

$ go run main.go
workdID:0, status: success, result:10
workdID:1, status: success, result:11
workdID:2, status: success, result:12
workdID:3, status: success, result:13
workdID:5, status: success, result:15
workdID:4, status: success, result:14
workdID:7, status: success, result:17
workdID:6, status: success, result:16
workdID:9, status: success, result:19
workdID:8, status: success, result:18

Specification

When initializing gofherd, it takes:

• processing logic function with the signature func ProcessWork(w *gf.Work) gf.Status The status can be one of:

const (
	// Success represents a successful processing outcome. It won't be retried.
	Success Status = iota
	// Retry represents a failed processing outcome, but is retriable. It will be retried for MaxRetries.
	Retry
	// Failure represents a failed processing outcome and should not be retried again.
	Failure
)

Each unit of "work" is defined as the struct:

type Work struct {
	ID     string
	retry  int64
	status Status
	Body   interface{}
	result interface{}
}

The ID field is used to track status of the work unit, retry count etc. The Body field can be anything that makes sense for the usecase at hand. It is for the input problem, there is a Result field which has the output answer.

For sending work, gf.SendWork can be used. It is a blocking call and will return when a member of the herd is accepts the work. On calling gf.OutputChan(), a receive only channel <-chan Work is returned which can be used to read the status for successfully processed work units. It will be closed by gofherd on completion.

Callbacks can be registered for Success, Retry and Failures. The corresponding function will be called when the processing work function returns with the assigned status. Make sure the callbacks are concurrent safe.

Logging

Gofherd accepts

type Logger interface {
	Printf(format string, v ...interface{})
}

Example Usage:

logger := log.New(os.Stdout, "gofherd:", log.Ldate|log.Ltime|log.Lshortfile)
herd.SetLogger(logger)

Deploying

There is a docker compose deployment at github.com/darshanime/gofherd-deploy you can refer to jumpstart your custom thing.

Contributing

Run the tests

go test -race -v ./...