issue-433 avoid keeping all the allocated handles forever by using map

and uintptr of the allocated object.

c-bindings/c-bindings.go

@@ -82,7 +82,7 @@ func (i *importer) Import(importedFrom, importedPath string) (contents jsonnet.C
 	return i.contentCache[foundHere], foundHere, nil
 }
 
-var handles = handlesTable{}
+var handles = newHandlesTable()
 var versionString *C.char
 
 //export jsonnet_version
@@ -106,12 +106,12 @@ func jsonnet_make() *C.struct_JsonnetVm {
 		os.Exit(1)
 	}
 
-	return C.jsonnet_internal_make_vm_with_id(C.uint64_t(id))
+	return C.jsonnet_internal_make_vm_with_id(C.uintptr_t(id))
 }
 
 //export jsonnet_destroy
 func jsonnet_destroy(vmRef *C.struct_JsonnetVm) {
-	if err := handles.free(uint64(vmRef.id)); err != nil {
+	if err := handles.free(uintptr(vmRef.id)); err != nil {
 		fmt.Fprintln(os.Stderr, err.Error())
 		os.Exit(1)
 	}
@@ -120,7 +120,7 @@ func jsonnet_destroy(vmRef *C.struct_JsonnetVm) {
 }
 
 func getVM(vmRef *C.struct_JsonnetVm) *vm {
-	ref, err := handles.get(uint64(vmRef.id))
+	ref, err := handles.get(uintptr(vmRef.id))
 
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err.Error())
@@ -411,7 +411,7 @@ func jsonnet_json_destroy(vmRef *C.struct_JsonnetVm, v *C.struct_JsonnetJsonValu
 		jsonnet_json_destroy(vmRef, child)
 	}
 
-	if err := handles.free(uint64(v.id)); err != nil {
+	if err := handles.free(uintptr(v.id)); err != nil {
 		fmt.Fprintln(os.Stderr, err.Error())
 		os.Exit(1)
 	}
@@ -427,11 +427,11 @@ func createJSONValue(vmRef *C.struct_JsonnetVm, val interface{}) *C.struct_Jsonn
 		os.Exit(1)
 	}
 
-	return C.jsonnet_internal_make_json_with_id(C.uint64_t(id))
+	return C.jsonnet_internal_make_json_with_id(C.uintptr_t(id))
 }
 
 func getJSONValue(jsonRef *C.struct_JsonnetJsonValue) *jsonValue {
-	ref, err := handles.get(uint64(jsonRef.id))
+	ref, err := handles.get(uintptr(jsonRef.id))
 
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err.Error())

c-bindings/handles.go

@@ -2,11 +2,9 @@ package main
 
 import (
 	"errors"
-	"fmt"
+	"unsafe"
 )
 
-const maxID = (1 << 63) - 1
-
 // Because of Go GC, there are restrictions on keeping Go pointers in C.
 // We cannot just pass *jsonnet.VM/JsonValue to C. So instead we use "handle" structs in C
 // which refer to JsonnetVM/JsonnetJsonValue by a numeric id.
@@ -17,62 +15,45 @@ const maxID = (1 << 63) - 1
 
 // handlesTable is the set of active, valid Jsonnet allocated handles
 type handlesTable struct {
-	objects  []interface{}
+	handles map[uintptr]*handle
-	freedIDs []uint64
 }
 
-// errMaxNumberOfOpenHandles tells that there was an attempt to create more than maxID open handles
+type handle struct {
-var errMaxNumberOfOpenHandles = fmt.Errorf("maximum number of constructed Jsonnet handles exceeded (%d)", maxID)
+	ref interface{}
+}
 
 // errInvalidHandle tells that there was an attempt to dereference invalid handle ID
 var errInvalidHandle = errors.New("invalid handle ID was provided")
 
-// make registers the new object as a handle and returns the corresponding ID
+func newHandlesTable() handlesTable {
-func (h *handlesTable) make(obj interface{}) (uint64, error) {
+	return handlesTable{
-	var id uint64
+		handles: make(map[uintptr]*handle),
-
-	if len(h.freedIDs) > 0 {
-		id, h.freedIDs = h.freedIDs[len(h.freedIDs)-1], h.freedIDs[:len(h.freedIDs)-1]
-		h.objects[id-1] = obj
-	} else {
-		id = uint64(len(h.objects) + 1)
-
-		if id > maxID {
-			return 0, errMaxNumberOfOpenHandles
-		}
-
-		h.objects = append(h.objects, obj)
 	}
+}
 
+// make registers the new object as a handle and returns the corresponding ID
+func (h *handlesTable) make(obj interface{}) (uintptr, error) {
+	entry := &handle{ref: obj}
+	id := uintptr(unsafe.Pointer(entry))
+	h.handles[id] = entry
 	return id, nil
 }
 
-// free marks the given handle ID as unused
+// free removes an object with the given ID
-func (h *handlesTable) free(id uint64) error {
+func (h *handlesTable) free(id uintptr) error {
-	if err := h.ensureValidID(id); err != nil {
+	if _, ok := h.handles[id]; !ok {
-		return err
+		return errInvalidHandle
 	}
 
-	h.objects[id-1] = nil
+	delete(h.handles, id)
-	h.freedIDs = append(h.freedIDs, id)
-
 	return nil
 }
 
 // get returns the corresponding object for the provided ID
-func (h *handlesTable) get(id uint64) (interface{}, error) {
+func (h *handlesTable) get(id uintptr) (interface{}, error) {
-	if err := h.ensureValidID(id); err != nil {
+	if _, ok := h.handles[id]; !ok {
-		return nil, err
+		return nil, errInvalidHandle
 	}
 
-	return h.objects[id-1], nil
+	return h.handles[id].ref, nil
-}
-
-// ensureValidID returns an error if the given handle ID is invalid, otherwise returns nil
-func (h *handlesTable) ensureValidID(id uint64) error {
-	if id == 0 || uint64(id) > uint64(len(h.objects)) {
-		return errInvalidHandle
-	}
-
-	return nil
 }

c-bindings/internal.h

@@ -3,17 +3,17 @@
 #include <stdint.h>
 
 struct JsonnetVm {
-    uint64_t id;
+    uintptr_t id;
 };
 
-struct JsonnetVm *jsonnet_internal_make_vm_with_id(uint64_t id);
+struct JsonnetVm *jsonnet_internal_make_vm_with_id(uintptr_t id);
 void jsonnet_internal_free_vm(struct JsonnetVm *x);
 
 struct JsonnetJsonValue {
-    uint64_t id;
+    uintptr_t id;
 };
 
-struct JsonnetJsonValue *jsonnet_internal_make_json_with_id(uint64_t id);
+struct JsonnetJsonValue *jsonnet_internal_make_json_with_id(uintptr_t id);
 void jsonnet_internal_free_json(struct JsonnetJsonValue *x);
 
 typedef struct JsonnetJsonValue *JsonnetNativeCallback(void *ctx,

c-bindings/libjsonnet.cpp

@@ -6,7 +6,7 @@ extern "C" {
     #include "internal.h"
 }
 
-struct JsonnetVm *jsonnet_internal_make_vm_with_id(uint64_t id) {
+struct JsonnetVm *jsonnet_internal_make_vm_with_id(uintptr_t id) {
     JsonnetVm *vm = new JsonnetVm();
     vm->id = id;
     return vm;
@@ -16,7 +16,7 @@ void jsonnet_internal_free_vm(struct JsonnetVm *x) {
     delete(x);
 }
 
-struct JsonnetJsonValue *jsonnet_internal_make_json_with_id(uint64_t id) {
+struct JsonnetJsonValue *jsonnet_internal_make_json_with_id(uintptr_t id) {
     JsonnetJsonValue *json = new JsonnetJsonValue();
     json->id = id;
     return json;