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50 lines
1.3 KiB
Go
50 lines
1.3 KiB
Go
// Basic sends and receives on channels are blocking.
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// However, we can use `select` with a `default` clause to
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// implement _non-blocking_ sends, receives, and even
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// non-blocking multi-way `select`s.
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package main
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import "fmt"
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func main() {
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messages := make(chan string)
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signals := make(chan bool)
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// Here's a non-blocking receive. If a value is
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// available on `messages` then `select` will take
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// the `<-messages` `case` with that value. If not
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// it will immediately take the `default` case.
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select {
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case msg := <-messages:
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fmt.Println("received message", msg)
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default:
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fmt.Println("no message received")
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}
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// A non-blocking send works similarly. Here `msg`
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// cannot be sent to the `messages` channel, because
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// the channel has no buffer and there is no receiver.
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// Therefore the `default` case is selected.
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msg := "hi"
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select {
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case messages <- msg:
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fmt.Println("sent message", msg)
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default:
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fmt.Println("no message sent")
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}
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// We can use multiple `case`s above the `default`
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// clause to implement a multi-way non-blocking
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// select. Here we attempt non-blocking receives
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// on both `messages` and `signals`.
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select {
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case msg := <-messages:
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fmt.Println("received message", msg)
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case sig := <-signals:
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fmt.Println("received signal", sig)
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default:
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fmt.Println("no activity")
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}
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}
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