go-weak

This is my weak reference implementation using generics. It was inspired by the implementation of ivanrad.

Basically the next step is to implement a concurrent weak hash map, as proposed by the following still open ticket #43615.

Another implementation of a weak map was done by shyiko.

Warning

This code relies upon features of the garbage collector that may be changed in future go versions!

Implementation details

The implementation is different from the one ivanrad and others have made, because I think that one problem must be solved. When we restore the pointer while the GC is running, there will be a write-barrier so that the restored pointer would be flagged as black as soon as it is created (when I understand the latest version of the GC right). The problem is now a chicken egg one, we need to be sure that the uintptr is valid before we restore it. This implementation solves this problem by ensuring in the finalizer that, when concurrently a Get() is executing, the last valid reference given to the finalizer is rescued until all concurrent Get()'s are done.

This code should be thread safe, but the referee, the value being referred, may not be, so be careful!

Usage

The usage requires go 1.18 and is quite simple:

package main

import (
	"fmt"
	"github.com/xeus2001/go-weak/pkg/weak"
)

type Point struct {
	x int32
	y int32
}

func demo() {
	point := Point{10, 20}
	weakRef := weak.NewRef[Point](&point)
	p := weakRef.Get()
	if p != nil {
		fmt.Sprintf("Pointer is: %d, %d", (*p).x, (*p).y)
	}
}

Test

I added a small make file and increased the test coverage to 100%. Do make test and then make test-result. Due to the nature of one of the concurrent tests, it is possible that one branch is not entered; even while this is unlikely, you may need to execute the test multiple times to get a 100% test coverage (at least for me, it works every time).