How Can I Control the Execution Order of Go Routines?

Go Routine Execution Order

This code showcases the concept of Go routine order of execution, where two concurrent "go" routines, or goroutines, are executed concurrently but without any guaranteed ordering.

The code defines a sum function that takes an integer array and a channel as inputs. This function calculates the sum of the integers in the array and sends the result to the provided channel.

In the main function, a channel c is created to facilitate communication between the goroutines. Two goroutines are launched, each executing the sum function with different input arrays and sending the result to c.

The program then receives the values sent by the goroutines from channel c and prints them. However, the order in which the goroutines complete is non-deterministic, so the output order may vary.

To control the execution order of goroutines, you can use various mechanisms like blocking channels or synchronization primitives provided by the standard library. Here are a few examples:

1. Blocking Channels:

In this modified version, the goroutines are executed sequentially by blocking the main routine until a value is received from the channel:

func main() {
    c := make(chan int)

    go sum([]int{1, 2, 3}, c)

    // Block until a value is received from c
    x := <-c
    fmt.Println(x)

    go sum([]int{4, 5, 6}, c)

    // Block until a value is received from c
    x = <-c
    fmt.Println(x)
}

2. Wait Group with Channels:

Another option is to use a wait group and a range over the channel to ensure that all goroutines have completed execution before processing the results:

func main() {
    c := make(chan int)
    wg := new(sync.WaitGroup)

    wg.Add(1)
    go sum([]int{1, 2, 3}, c, wg)
    wg.Wait()

    wg.Add(1)
    go sum([]int{4, 5, 6}, c, wg)
    wg.Wait()

    close(c)

    for x := range c {
        fmt.Println(x)
    }
}

These techniques allow you to control the execution order of goroutines to achieve desired behavior in your concurrent programs.

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