Synchronization characteristics of Go concurrency primitives
Having defined a happened-before relationship, it is easy to lay the ground rules for the Go memory model.
Package initialization
If package A imports another package, B, then the completion of all init() functions in package B happens before the init() functions in package A begin.
The following program always prints B initializing before A initializing:
package B
import "fmt"
func init() {
fmt.Println("B initializing")
}
---
package A
import (
"fmt"
"B"
)
func init() {
fmt.Println("A initializing")
}
This extends to the main package as well: all packages directly or indirectly imported by the main package of a program complete their init() functions before main() starts. If an init() function creates a goroutine, there is no guarantee that the goroutine will finish before main() starts...