| Basic sends and receives on channels are blocking. However, we can use `select` with a `default` clause to implement _non-blocking_ sends, receives, and even non-blocking multi-way `select`s. | ||
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 available on `messages` then `select` will take the `<-messages` `case` with that value. If not it will immediately take the `default` case. | 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` cannot be sent to the `messages` channel, because the channel has no buffer and there is no receiver. Therefore the `default` case is selected. | 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` clause to implement a multi-way non-blocking select. Here we attempt non-blocking receives on both `messages` and `signals`. | 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) |
no message received no message sent |
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default: |
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fmt.Println("no activity") |
no activity |
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} |
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} |