Blocking problem of golang unbuffered channel

done:=make(chan struct{})
c:=make(chan int)
go func() {
    defer close(done)
    for{
        s,ok:=<-c
        if !ok{
            //close(c)
            return
        }
        println(s)
    }
}()
for i:=0;i<1 ;iPP  {
    println("put")
    c<-i
}
println("main....")
//close(c)
<-done

clipboard.png
formax+1BcloseA

clipboard.png

Golang
May.12,2021

you can close channel, in both places, except that the conditional statement below 

        s,ok:=<-c
        if !ok{
            //close(c)
            return
        }

condition ! ok means that channel has been closed, and it is no longer meaningful to call close (c) at this time.
when channel is not closed, s, ok: = <-c enters a blocking state unless data arrives.

you can change it to this and exit the loop when there is no data 

    for {
        select {
        case s, ok := <-c:
            if ok {
                println(s)
                continue
            }
            break
        default:  // channel 
            break
        }
    }

go func s code <-c in a for endless loop, the first loop blocks here, waiting for the c semaphore.
main the for loop prints out put , and then sends a c signal to the go func . The program receives this signal and starts execution. if! ok means false so return, go func will not print 0 at this time. Enter the next loop, still blocking and waiting for the c semaphore.
while main goes to println ("main.") , so it can print out main.

.
  1. if there is no area B close (c) , then the go func protocol blocks the waiting c semaphore, while the main protocol blocks the waiting down semaphore, resulting in lockout! , and the close (c) in area A does not have a chance to get there, so return, will not go to defer, and will not go to close (down)
    2. .
  2. if region B has close (c) , then the main protocol is temporarily blocked waiting for the down semaphore. go func receives this c semaphore and continues to go. At this time, c has already close, so if! ok for true, at this time, you can go to return, to jump out of the for dead cycle, go to the defer function, go to close (down), and send a down semaphore to main, at this time main continues to go, and complete the whole process.

Previous: Group by is grouped by one field, but select has multiple fields?

Next: Cnpm start error reporting based on ant-design-pro

css mysql arrays josn react html typescript webpack npm sass R objective-c .net sql-server jquery python-3.x angularjs django angular excel regex iphone ajax linux xml pandas vba spring database wordpress string wpf xcode windows bash postgresql oracle multithreading eclipse list firebase algorithm macos forms image scala visual-studio azure bootstrap spring-boot react-native python-2.7 docker performance function winforms matlab powershell apache dataframe api sqlite numpy rest shell selenium flutter dart maven loops qt swing android-studio csv express file class tensorflow sorting codeigniter perl
© 2021 CodesHelper
Advertising Contact us About us
Menu