Example use of Cond.Wait

cond_wait.go

package main

import (
    "fmt"
    "sync"
    "time"
)

func waitForSignal() {
    var m sync.Mutex
    c := sync.NewCond(&m)
    for i := 0; i < 10; i++ {
        go func(i int){
            m.Lock()
            fmt.Println(i, "waiting")
            c.Wait()
            fmt.Println(i, "got a signal")
            m.Unlock()
        }(i)
    }
    fmt.Println("waiting for things to start")
    time.Sleep(1 * time.Second)
    fmt.Println("sending a signal which will awaken 1 goroutine")
    c.Signal()
}

func waitForBroadcast() {
    var m sync.Mutex
    c := sync.NewCond(&m)
    for i := 10; i < 20; i++ {
        go func(i int){
            m.Lock()
            fmt.Println(i, "waiting")
            c.Wait()
            fmt.Println(i, "got a signal")
            m.Unlock()
        }(i)
    }
    fmt.Println("waiting for things to start")
    time.Sleep(1 * time.Second)
    fmt.Println("sending a broadcast which will awaken all goroutines")
    c.Broadcast()
}

func main() {
    waitForSignal()
    fmt.Println("waiting to make sure no others signal")
    time.Sleep(1 * time.Second)
    waitForBroadcast()
    fmt.Println("\n\nsleeping to trigger a context switch...")
    time.Sleep(500 * time.Millisecond)
    fmt.Println("all 10-20 should have gotten that signal")
}