stateful-goroutines.go

//
// gobyexample.com
// stateful-goroutines.go
//
package main

import (
	"fmt"
	"math/rand"
	"sync/atomic"
	"time"
)

//
// In this example our state will be owned by a single goroutine.
//
//  This will guarantee that the data is never corrupted with concurrent access.
//
// In order to read or write that state, other goroutines will send messages
// to the owning goroutine and receive corresponding replies.
//
// These readOp and writeOp structs encapsulate those requests
// and a way for the owning goroutine to respond.
//
type readOp struct {
	key  int
	resp chan int
}
type writeOp struct {
	key  int
	val  int
	resp chan bool
}

func main() {
	// As before we'll count how many operations we perform
	var readOps uint64
	var writeOps uint64

	//
	// The reads and writes channels will be used by other
	// goroutines to issue read and write requests, respectively.
	//
	reads := make(chan readOp)
	writes := make(chan writeOp)

	//
	// Here is the goroutine that owns the state,
	// which is a map as in the previous example but
	// now private to the stateful goroutine.
	//
	// This goroutine repeatedly selects on the reads and writes channels,
	// responding to requests as they arrive.
	//
	// A response is executed by first performing the requested operation and
	// then sending a value on the response channel resp to indicate success
	//(and the desired value in the case of reads).
	//
	go func() {
		var state = make(map[int]int)
		for {
			select {
			case read := <-reads:
				read.resp <- state[read.key]
			case write := <-writes:
				state[write.key] = write.val
				write.resp <- true
			}
		}
	}()

	//
	// This starts 100 goroutines to issue reads to the state-owning goroutine
	// via the reads channel.
	//
	// Each read requires constructing a readOp, sending it over the reads channel,
	// and the receiving the result over the provided resp channel.
	//
	for r := 0; r < 100; r++ {
		go func() {
			for {
				read := readOp{
					key:  rand.Intn(5),
					resp: make(chan int)}
				reads <- read
				<-read.resp
				atomic.AddUint64(&readOps, 1)
				time.Sleep(time.Millisecond)
			}
		}()
	}

	//
	// We start 10 writes as well, using a similar approach
	//
	for w := 0; w < 10; w++ {
		go func() {
			for {
				write := writeOp{
					key:  rand.Intn(5),
					val:  rand.Intn(100),
					resp: make(chan bool)}
				writes <- write
				<-write.resp
				atomic.AddUint64(&writeOps, 1)
				time.Sleep(time.Millisecond)
			}
		}()
	}
	//
	// Let the goroutines work for a second.
	//
	time.Sleep(time.Second)

	//
	// Finally, capture and report the op counts.
	//
	readOpsFinal := atomic.LoadUint64(&readOps)
	fmt.Println("readOps:", readOpsFinal)
	writeOpsFinal := atomic.LoadUint64(&writeOps)
	fmt.Println("writeOps:", writeOpsFinal)

}