Why Does My Go Code Produce a 'fatal error: all goroutines are asleep - deadlock!' Error with sync.WaitGroup?

"All Goroutines Asleep" Error When Using sync.WaitGroup

In your code, you are encountering a "fatal error: all goroutines are asleep - deadlock!" message. This occurs because you are passing a copy of the WaitGroup to each goroutine instead of a reference to the original.

As per the documentation, WaitGroup requires you to pass a pointer to the variable instead of the variable itself. When you pass the actual WaitGroup value, Go makes a copy, resulting in multiple WaitGroup instances with different counts.

The updated code should be:

import "sync"

func doWork(wg *sync.WaitGroup) error {
    defer wg.Done()
    // Do some heavy lifting... request URL's or similar
    return nil
}

func main() {
    wg := &sync.WaitGroup{}
    for i := 0; i < 10; i++ {
        wg.Add(1)
        go doWork(wg)
    }
    wg.Wait()
}

By passing a pointer, all goroutines reference the same WaitGroup. When they call Done(), it decrements the count in the original WaitGroup, resulting in the expected behavior.

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