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# default math.rand.source is thread save while rand.new source is not

## Default math rand.Source is thread save while rand.New is not

Default pacakge rand uses Source that is thread safe with default seed `1`

we can use the pacakge's method to have thread safe random number generation

```go
package main

import (
  "fmt"
  "math/rand"
  "time"
)

func main() {
  seed := time.Now().UnixNano()
  rand.Seed(seed)
  fmt.Println(rand.Int63())
}
```

But the `rand.NewSource()` offers thread unsafe implementation. One of the reason to choose the unsafe implementation to avoid synchronization, especially when you have only single go routine.

```go
package main

import (
  "fmt"
  "math/rand"
  "time"
)

func main() {
  seed := time.Now().UnixNano()
  r := rand.New(rand.NewSource(seed))
  fmt.Println(r.Int63())
}
```