Decrypt Go: runtime.SetFinalizer

Effective Usage and Common Pitfalls

huizhou92

3 min read

·

Sep 6, 2024

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If we want to do some resource release before an object is GC, we can use returns.SetFinalizer. It’s like executing defer to free resources before a function returns. For example：

List 1: Using runtime.SetFinalizer

type MyStruct struct {  
     Name  string  
     Other *MyStruct  
 }
 ​
 func main() {  
     x := MyStruct{Name: "X"}  
     runtime.SetFinalizer(&x, func(x *MyStruct) {  
        fmt.Printf("Finalizer for %s is called\n", x.Name)  
     })  
     runtime.GC()  
     time.Sleep(1 * time.Second)  
     runtime.GC()  
 }

The official documentation explains that SetFinalizer associates a finalizer function with an object. When the garbage collector (GC) detects that an unreachable object has an associated finalizer, it will execute the finalizer and disassociate it. The object will be collected on the next GC cycle if it is unreachable and no longer has an associated finalizer.

Important Considerations

While runtime.SetFinalizer can be helpful, there are a few critical points to keep in mind:

• Deferred Execution: The SetFinalizer function will not execute until the object is selected for garbage collection. Therefore, avoid using SetFinalizer for…