Implement SetFinalizer for latest tinygo dev (#5)

Author: anuraaga

.github/workflows/ci.yaml

@@ -40,13 +40,9 @@ jobs:
       - run: go run mage.go check
   build-tinygodev:
     runs-on: ubuntu-22.04
-    container: ghcr.io/tinygo-org/tinygo/tinygo-dev:sha-e0a5fc255522933f651a89c071ebd531ad634e7b
+    container: ghcr.io/tinygo-org/tinygo/tinygo-dev:sha-f6df2761187f1975e35eb43461d735d6e325df85
     steps:
       - uses: actions/checkout@v3
-      - uses: actions/setup-go@v3
-        with:
-          go-version: '^1.20.0'
-          cache: true
 
       - run: |
           go install github.com/wasilibs/tools/cmd/wasmtime@c93d2e477ab3c1eb7f5303c66a35c84a21d06dbd

finalizer.go

@@ -0,0 +1,59 @@
+//go:build nottinygc_finalizer
+
+package nottinygc
+
+/*
+void GC_register_finalizer(void* obj, void* fn, void* cd, void** ofn, void** ocn);
+void onFinalizer(void* obj, void* fn);
+void* malloc(unsigned int long);
+void free(void* ptr);
+*/
+import "C"
+import "unsafe"
+
+var finalizers = map[uintptr]interface{}{}
+
+//go:linkname SetFinalizer runtime.SetFinalizer
+func SetFinalizer(obj interface{}, finalizer interface{}) {
+	finKey := uintptr((*_interface)(unsafe.Pointer(&finalizer)).value)
+	finalizers[finKey] = finalizer
+
+	in := (*_interface)(unsafe.Pointer(&obj))
+
+	rf := (*registeredFinalizer)(C.malloc(C.ulong(unsafe.Sizeof(registeredFinalizer{}))))
+	rf.typecode = in.typecode
+	rf.finKey = finKey
+
+	C.GC_register_finalizer(in.value, C.onFinalizer, unsafe.Pointer(rf), nil, nil)
+}
+
+//export onFinalizer
+func onFinalizer(obj unsafe.Pointer, data unsafe.Pointer) {
+	defer C.free(data)
+
+	rf := (*registeredFinalizer)(data)
+	finalizer := finalizers[rf.finKey]
+	delete(finalizers, rf.finKey)
+
+	var in interface{}
+	inFields := (*_interface)(unsafe.Pointer(&in))
+	inFields.typecode = rf.typecode
+	inFields.value = obj
+
+	switch f := finalizer.(type) {
+	case func(interface{}):
+		f(in)
+	default:
+		panic("currently only finalizers of the form func(interface{}) are supported")
+	}
+}
+
+type _interface struct {
+	typecode uintptr
+	value    unsafe.Pointer
+}
+
+type registeredFinalizer struct {
+	typecode uintptr
+	finKey   uintptr
+}

finalizer_test.go

@@ -0,0 +1,45 @@
+//go:build nottinygc_finalizer
+
+package nottinygc
+
+import (
+	"runtime"
+	"testing"
+)
+
+func TestFinalizer(t *testing.T) {
+	finalized := 0
+	allocFinalized(10, func() {
+		finalized++
+	})
+
+	runtime.GC()
+
+	if finalized == 0 {
+		t.Errorf("finalizer not called")
+	}
+}
+
+//go:noinline
+func allocFinalized(num int, cb func()) {
+	f := &finalized{
+		a: 100,
+		b: "foo",
+	}
+
+	runtime.SetFinalizer(f, func(f interface{}) {
+		cb()
+	})
+
+	// Recurse to create some more stack frames or else the shadow stack
+	// may still not have been reset, causing GC to find the inaccessible
+	// pointers.
+	if num > 1 {
+		allocFinalized(num-1, cb)
+	}
+}
+
+type finalized struct {
+	a int
+	b string
+}

magefiles/magefile.go

@@ -4,14 +4,25 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 
 	"github.com/magefile/mage/mg"
 	"github.com/magefile/mage/sh"
 )
 
 // Test runs unit tests
 func Test() error {
-	return sh.RunV("tinygo", "test", "-gc=custom", "-tags=custommalloc", "-target=wasi", "-v", "-scheduler=none", "./...")
+	v, err := sh.Output("tinygo", "version")
+	if err != nil {
+		return fmt.Errorf("invoking tinygo: %w", err)
+	}
+
+	tags := []string{"custommalloc"}
+	if strings.HasSuffix(v, "tinygo version 0.28.") {
+		tags = append(tags, "nottinygc_finalizer")
+	}
+
+	return sh.RunV("tinygo", "test", "-gc=custom", fmt.Sprintf("-tags='%s'", strings.Join(tags, " ")), "-target=wasi", "-v", "-scheduler=none", "./...")
 }
 
 func Format() error {