Signal channels

A signal channel is a channel that is used just for signaling. Signal channels will be illustrated using the signalChannel.go program with a rather unusual example that will be presented in five parts. The program executes four goroutines: when the first one is finished, it sends a signal to a signal channel by closing it, which will unblock the second goroutine. When the second goroutine finishes its job, it closes another channel that unblocks the remaining two goroutines. Note that signal channels are not the same as channels that carry the os.Signal values.

The first part of the program is the following:

package main 
 
import ( 
   "fmt" 
   "time" 
) 
 
func A(a, b chan struct{}) { 
   <-a 
   fmt.Println("A!") 
   time.Sleep(time.Second) 
   close(b) 
} 

The A() function is blocked by the channel defined in the a parameter. This means that until this channel is closed, the A() function cannot continue its execution. The last statement of the function closes the channel...