退出前如何确保goroutine完全运行

Question

I have a function calling a go routine that calls additional functions within it. However, those go routines are exiting before being completely finished. How would I make sure all the underlying code within the function (migrateUserHelper) runs before the exit. Here is my code below:

func MigrateUsers(){
  var wg sync.WaitGroup
  userCount:=10 //userDAO.GetUserCount()
  limitSize:=2
  count:=0
  divisor = userCount/limitSize
  for divisor>0{
      wg.Add(1)
      go migrateUserHelper(limitSize,&wg,count)
      divisor =divisor -1
      count=count +1
  }
  wg.Wait()
  fm.Println("DONE BATCHES")
 }
 func migrateUserHelper(limitSize int, count int, wg *sync.WaitGroup) 
 {
   defer wg.Done()
   fmt.Println("Start batch "+strconv.Itoa(count))
   users:= userDAO.GetUsers(limitSize)
   fmt.Println("Fetched Users for batch "+ strconv.Itoa(count))
   userDAO.BulkUpdateUsers(users)
  fmt.Println("Reconciled Users for batch "+ strconv.Itoa(count))
}

Im trying to update A LOT OF records in the database simultaneously in different go routines.

Thanks

Answer 1

The WaitGroup is a counting semaphore and can be used to count off goroutines as they finish their work, but for that, you need to set how many goroutines you are going to spawn. You can do that by calling the method Add:

package main

import (
    "fmt"
    "strconv"
    "sync"
)

func main() {
    migrateUsers()
}

func migrateUsers() {
    var wg sync.WaitGroup

    userCount := 10
    limitSize := 2
    count := 0
    divisor := userCount / limitSize
    wg.Add(divisor)

    for divisor > 0 {
        go migrateUserHelper(limitSize, count, &wg)
        divisor = divisor - 1
        count = count + 1
    }

    wg.Wait()
    fmt.Println("DONE BATCHES")
}

func migrateUserHelper(limitSize int, count int, wg *sync.WaitGroup) {
    defer wg.Done()
    fmt.Println("Start batch " + strconv.Itoa(count))
    fmt.Println("Fetched Users for batch " + strconv.Itoa(count))
    fmt.Println("Reconciled Users for batch " + strconv.Itoa(count))
}

playground.