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main.go
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main.go
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package main
import (
"fmt"
"math/rand"
"sync"
"time"
)
// Creating a cache, each Book will have an ID
var cache = map[int]Book{}
var rnd = rand.New(rand.NewSource(time.Now().UnixNano()))
func main() {
// Create a Wait Group, and save the pointer
wg := &sync.WaitGroup{}
// Create a Mutex, once against using a pointer
m := &sync.RWMutex{}
cacheCh := make(chan Book)
dbCh := make(chan Book)
for i := 0; i < 10; i++ {
// Fetch a random Book ID
id := rnd.Intn(10) + 1
// We've got 2 GoRoutines to wait for
wg.Add(2)
go func(id int, wg *sync.WaitGroup, m *sync.RWMutex, ch chan<- Book) {
// Query the cache, if found then print it out
if b, ok := queryCache(id, m); ok {
ch <- b // Pass the found Book to the cache channel
}
wg.Done()
}(id, wg, m, cacheCh)
go func(id int, wg *sync.WaitGroup, m *sync.RWMutex, ch chan<- Book) {
// Query the DB, if found then print it out
if b, ok := queryDatabase(id, m); ok {
m.Lock()
cache[id] = b
m.Unlock()
ch <- b
}
wg.Done()
}(id, wg, m, dbCh)
// Create on GoRoutine per query to handle response
go func(cacheCh, dbCh <-chan Book) {
select {
case b := <-cacheCh:
fmt.Println("Source: Cache")
fmt.Println(b)
<-dbCh // Wait to get the message from the DB Channel so we don't block
case b := <-dbCh:
fmt.Println("Source: Database")
fmt.Println(b)
}
}(cacheCh, dbCh)
time.Sleep(150 * time.Millisecond)
}
wg.Wait()
}
// Accepts the ID of the Book, and returns a true/false to whether it was found
func queryCache(id int, m *sync.RWMutex) (Book, bool) {
// Lock for Writes, however, allowing multiple reads is okay
m.RLock()
b, ok := cache[id]
m.RUnlock()
return b, ok
}
// Simulates running the query against the database - this method is slower than
// querying the cache
func queryDatabase(id int, m *sync.RWMutex) (Book, bool) {
time.Sleep(100 * time.Millisecond)
for _, b := range books {
if b.ID == id {
// Add the Book to the cache
m.Lock()
cache[id] = b
m.Unlock()
// Return the Book
return b, true
}
}
return Book{}, false
}