I tried some synchronization techniques to share state between goroutines and find out that incorrect variant (without sync) works slowly than same program with mutex.
Given the code:
package main
import (
"sync"
"time"
"fmt"
)
func main() {
var wg sync.WaitGroup
var mu sync.Mutex
hash := make(map[string]string)
hash["test"] = "string"
num := 40000000
wg.Add(num)
start := time.Now()
for i := 0; i < num; i++ {
go func() {
mu.Lock()
_, _ = hash["test"]
mu.Unlock()
wg.Done()
}()
}
wg.Wait()
fmt.Println(time.Since(start))
}
Perform on my laptop with 8 HT cores for 9-10 seconds. But if just remove sync it works for 11-12 seconds:
package main
import (
"sync"
"time"
"fmt"
)
func main() {
var wg sync.WaitGroup
hash := make(map[string]string)
hash["test"] = "string"
num := 40000000
wg.Add(num)
start := time.Now()
for i := 0; i < num; i++ {
go func() {
_, _ = hash["test"]
wg.Done()
}()
}
wg.Wait()
fmt.Println(time.Since(start))
}
A synced version is faster and unitizes CPU much higher. Question is why?
My thought is about how goroutines scheduled and overhead for context switching because of the more GOMAXPROCS the greater the gap between these two versions. But I can't explain the real reason for that that happens under the hood of the scheduler.
