Why is input.Text() Evaluated Before a Go Routine Starts?

Why is input.Text() Evaluated in the Main Goroutine?

In Go, the arguments passed to a function invoked concurrently with the go keyword are evaluated immediately. This differs from regular function calls where argument evaluation occurs when the function is actually executed. In the case of echoServer, the argument input.Text() is evaluated in the main goroutine at the time the go statement is executed.

Reason for Immediate Evaluation

The immediate evaluation of function arguments in goroutines ensures the following:

• Correctness: The values of arguments are guaranteed to be available when the corresponding goroutine begins execution.
• Efficiency: Compiler-generated code is optimized to push argument values onto the stack, avoiding unnecessary copying and memory allocation.
• Determinism: The order of argument evaluation is consistent and predictable, allowing for deterministic behavior in concurrent environments.

Example Illustration

Consider the following example:

package main

import (
    "fmt"
    "time"
)

func main() {
    i := 1
    go func(i int) {
        fmt.Println(i) // => 1
        i++
    }(i)
    i++
}

If input.Text() evaluation occurred during the go statement execution, the value of i would be 2 due to the immediate evaluation. However, if it were evaluated during goroutine execution, the variable i would have been incremented and would have printed 3.

Conclusion

The immediate evaluation of function arguments in goroutines is an essential aspect of Go's concurrency model. It ensures the correctness, efficiency, and determinism of concurrent programs.

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