How to Avoid Deadlocks When Using Go's sync.WaitGroup?

Troubleshooting Deadlock Errors When Using sync.WaitGroup

When working with concurrent Go routines, handling synchronization is crucial to avoid deadlocks. One such scenario occurs when trying to coordinate multiple goroutines and wait for their completion using sync.WaitGroup. However, sometimes, you may encounter the error: "fatal error: all goroutines are asleep - deadlock!".

This error stems from an incorrect usage of sync.WaitGroup. In the provided code snippet:

import "sync"

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

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

The issue lies in passing the sync.WaitGroup object directly to the doWork function. When passing a value by value, a copy of the object is created, which leads to unexpected behavior.

The fix involves passing a pointer to the sync.WaitGroup instead:

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, each goroutine will reference the same WaitGroup object, ensuring that Done() is called on the intended instance. This resolves the deadlock issue and allows the program to execute without errors.

Remember, when using sync.WaitGroup to synchronize goroutines, always pass a pointer to the object to ensure consistent behavior and avoid potential deadlocks.

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