Question

Is it possible to make the garbage collector in Go handle and release memory allocated through C code? I apologize, I haven’t used C and cgo before so my examples may need some clarification.

Lets say you’ve got some C library that you’d like to use and this library allocates some memory that needs to be freed manually. What I’d like to do is something like this:

package stuff

/*
#include <stuff.h>
*/
import "C"

type Stuff C.Stuff

func NewStuff() *Stuff {
    stuff := Stuff(C.NewStuff()) // Allocate memory

    // define the release function for the runtime to call
    // when this object has no references to it (to release memory)   
    // In this case it's stuff.Free()     

    return stuff

}

func (s Stuff) Free() {
    C.Free(C.Stuff(s)) // Release memory
}

Is there any way for the garbage collector to call Stuff.Free() when there are no references to *Stuff in the Go runtime?

Am I making sense here?

Perhaps a more direct question is: Is it possible to make the runtime automatically handle the cleanup of C allocated memory by writing a function that the runtime calls when there are zero references to that object?

Answer 1

There exists the runtime.SetFinalizer function, but it cannot be used on any object allocated by C code.

However, you can create a Go object for each C object that needs to be freed automatically:

type Stuff struct {
    cStuff *C.Stuff
}

func NewStuff() *Stuff {
    s := &Stuff{C.NewStuff()}
    runtime.SetFinalizer(s, (*Stuff).Free)
    return s
}

func (s *Stuff) Free() {
    C.Free(s.cStuff)
}