Blocking Behaviour of GoRoutines in Golang

Question

Given the following pseudo-code:

func main() {
  go runFuncOne()
}

func runFuncOne() bool {
  runFuncTwo() 
  return true
}

func runFuncTwo() bool {
  // Do some heavy work
  return true
}

Would runFuncTwo only be blocking to runFuncOne (the calling goroutine) or would runFuncTwo also block main() as it is not itself running as a goroutine?

My assumption is that main() will open a thread within which runFuncOne() and runFuncTwo() will then operate. Any work performed within runFuncTwo() will then only block this instance of runFuncOne()?

Answer 1

runFuncTwo blocks runFuncOne only, as both are running in a separate Go routine.

Note though that main() will therefore continue and exit, causing the program to exit. To avoid this and all runFuncTwo to complete, you should use a sync.WaitGroup.

Answer 2

The Go Programming Language Specification

Go statements

The function value and parameters are evaluated as usual in the calling goroutine, but unlike with a regular call, program execution does not wait for the invoked function to complete. Instead, the function begins executing independently in a new goroutine. When the function terminates, its goroutine also terminates. If the function has any return values, they are discarded when the function completes.

func main() {
  go runFuncOne()
}

main will invoke runFuncOne() as a goroutine and then exit the program immediately, terminating runFuncOne() without waiting for it to complete.

func runFuncOne() bool {
  runFuncTwo() 
  return true
}

func runFuncTwo() bool {
  // Do some heavy work
  return true
}

runFuncOne() makes a function call to runFuncTwo() so it will wait for runFuncTwo() to complete.

Answer 3

Can also use a channel for synchronization:

package main

import (
    "fmt"
    "time"
)

func main() {
    var ch chan int = make(chan int)
    go runFuncOne(ch)
    fmt.Println("Waiting..")
    fmt.Println(<-ch)
}

func runFuncOne(ch chan int) {
    runFuncTwo(ch)
    ch <- 1
}

func runFuncTwo(ch chan int) bool {
    time.Sleep(1 * time.Second)
    fmt.Println("Done working..")
    return true
}

https://play.golang.org/p/h1S4TSdT0w

Return type of runFuncOne won't be of consequence if you are calling it with a go routine.