Synchronized Data Access in Go
Here we use the built-in synchronization features of goroutines and channels to achieve synchronized access to shared state. This channel-based approach aligns with Go’s ideas of sharing memory by communicating and having each piece of data owned by exactly 1 goroutine.
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() {
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)
}
}()
}
time.Sleep(time.Second)
readOpsFinal := atomic.LoadUint64(&readOps)
fmt.Println("readOps:", readOpsFinal)
writeOpsFinal := atomic.LoadUint64(&writeOps)
fmt.Println("writeOps:", writeOpsFinal)
}