Trying to understand locking in BoltDB

bolt_locking.go

package main

import "io/ioutil"
import "fmt"
import "github.com/boltdb/bolt"
import "sync"
import "time"


func update(id string, val string) func(*bolt.Tx) error {
  return func(tx *bolt.Tx) error {

    bkt := []byte(id)
    if tx.Bucket(bkt) == nil {
      tx.CreateBucket(bkt)
    }

    fmt.Println("Update enter")
    b := tx.Bucket(bkt)
    fmt.Println("Update bucket")
    b.Put([]byte("key"), []byte(val))
    fmt.Println("Update after put")
    return nil
  }
}

func view(id string) func(*bolt.Tx) error {
  return func(tx *bolt.Tx) error {
    fmt.Println("View enter")
    bkt := []byte(id)

    for i := 0; i < 5; i++ {
      b := tx.Bucket(bkt)
      fmt.Println("View after bucket", b)
      if b != nil {
        v := b.Get([]byte("key"))
        fmt.Println("View after get", string(v))
      }
      time.Sleep(time.Millisecond * 500)
    }
    fmt.Println("view end")
    return nil
  }
}


func main() {

  p, _ := ioutil.TempFile("", "test-bolt")
	db, err := bolt.Open(p.Name(), 0600, &bolt.Options{
		Timeout: time.Second * 5,
	})

  if err != nil {
    panic(err)
  }

  var wg sync.WaitGroup

  wg.Add(1)
  go func() {
    db.View(view("bkt-1"))
    wg.Done()
  }()

  time.Sleep(time.Second * 1)


  wg.Add(1)
  go func() {
    uperr := db.Update(update("bkt-1", "val-2"))
    fmt.Println("After update", "bkt-1", uperr)
    wg.Done()
  }()

  wg.Add(1)
  go func() {
    uperr := db.Update(update("bkt-2", "val-2"))
    fmt.Println("After update", "bkt-2", uperr)
    wg.Done()
  }()

  wg.Add(1)
  go func() {
    db.View(view("bkt-1"))
    wg.Done()
  }()

  wg.Wait()
}

c.go

package main

import "io/ioutil"
import "fmt"
import "github.com/boltdb/bolt"
import "sync"
import "time"


func update(prefix string, id string, val string) func(*bolt.Tx) error {
  fmt.Println(prefix, "Call update", id, val)
  return func(tx *bolt.Tx) error {

    bkt := []byte(id)
    if tx.Bucket(bkt) == nil {
      tx.CreateBucket(bkt)
    }

    fmt.Println(prefix, "Update enter", id)
    b := tx.Bucket(bkt)
    fmt.Println(prefix, "Update bucket", id)
    b.Put([]byte("key"), []byte(val))
    fmt.Println(prefix, "Update after put", id, val)
    return nil
  }
}

func view(id string, wait chan bool) func(*bolt.Tx) error {
  return func(tx *bolt.Tx) error {
    fmt.Println("___ View enter", id)
    bkt := []byte(id)

    if wait != nil {
      <-wait
    }

    b := tx.Bucket(bkt)
    fmt.Println("___ View after bucket", id, b)
    if b != nil {
      v := b.Get([]byte("key"))
      fmt.Println("___ View after get", id, string(v))
    }


    fmt.Println("___ View end", id)
    return nil
  }
}


func main() {

  p, _ := ioutil.TempFile("", "test-bolt")
	db, err := bolt.Open(p.Name(), 0600, &bolt.Options{
		Timeout: time.Second * 5,
	})

  if err != nil {
    panic(err)
  }

  var wg sync.WaitGroup

  wait := make(chan bool)

  wg.Add(1)
  go func() {
    db.View(view("bkt-1", wait))
    wg.Done()
  }()


  for i := 0; i < 3; i++ {
    time.Sleep(time.Millisecond)
    wg.Add(1)
    go func(i int) {
      uperr := db.Update(update(">", "bkt-1", fmt.Sprint(i)))
      if uperr != nil {
        panic(uperr)
      }
      wg.Done()
    }(i)
  }

  wg.Add(1)
  go func() {
    uperr := db.Update(update("++", "bkt-2", "val-2"))
    if uperr != nil {
      panic(uperr)
    }
    wg.Done()
  }()

  time.Sleep(time.Second * 5)
  fmt.Println("Closing")
  close(wait)

  wg.Wait()

  db.View(view("bkt-1", nil))
}

c_out.txt

___ View enter bkt-1
> Call update bkt-1 0
> Update enter bkt-1
> Update bucket bkt-1
> Update after put bkt-1 0
> Call update bkt-1 1
> Update enter bkt-1
> Update bucket bkt-1
> Update after put bkt-1 1
> Call update bkt-1 2
++ Call update bkt-2 val-2
Closing
___ View after bucket bkt-1 <nil>
___ View end bkt-1
> Update enter bkt-1
> Update bucket bkt-1
> Update after put bkt-1 2
++ Update enter bkt-2
++ Update bucket bkt-2
++ Update after put bkt-2 val-2
___ View enter bkt-1
___ View after bucket bkt-1 &{0x1283035 0xc42008c2a0 map[] 0x1283045 <nil> map[] 0.5}
___ View after get bkt-1 2
___ View end bkt-1

output.txt

View enter
View after bucket <nil>
View after bucket <nil>
View after bucket <nil>
Update enter
Update bucket
Update after put
View enter
View after bucket <nil>
After update bkt-1 <nil>
Update enter
Update bucket
Update after put
View after bucket <nil>
View after bucket <nil>
View after bucket <nil>
View after bucket <nil>
View after bucket <nil>
view end
View after bucket <nil>
view end
After update bkt-2 <nil>