[feat] dataconv: SharedDict for concurrent access (#49)

* draft for shared dict

* limit

* move

* SD

* add tests

* cnt it

* SD

* custom fn

* udate test"
;

* fir orias

* callable type

* more errors

* for args cnt

* testing frozen

* remove unused code

* all attr tests

* check more equal

* not self

* noop self

* S unit

* lambda works'
tig

* unpacks

* clean pack things --- now focus on lint

* for comments

* for missing

* compare type

* unsupported operator

dataconv/share.go

@@ -0,0 +1,245 @@
+package dataconv
+
+import (
+	"fmt"
+	"sort"
+	"sync"
+
+	"go.starlark.net/starlark"
+	"go.starlark.net/syntax"
+)
+
+// SharedDict is a dictionary that can be shared among multiple Starlark threads.
+type SharedDict struct {
+	sync.RWMutex
+	dict   *starlark.Dict
+	frozen bool
+}
+
+const (
+	defaultSharedDictSize = 8
+)
+
+// NewSharedDict creates a new SharedDict instance.
+func NewSharedDict() *SharedDict {
+	return &SharedDict{
+		dict: starlark.NewDict(defaultSharedDictSize),
+	}
+}
+
+var (
+	_ starlark.Value      = (*SharedDict)(nil)
+	_ starlark.Comparable = (*SharedDict)(nil)
+	_ starlark.Mapping    = (*SharedDict)(nil)
+	_ starlark.HasAttrs   = (*SharedDict)(nil)
+	_ starlark.HasSetKey  = (*SharedDict)(nil)
+)
+
+func (s *SharedDict) String() string {
+	var v string
+	if s != nil && s.dict != nil {
+		v = s.dict.String()
+	}
+	return fmt.Sprintf("shared_dict(%s)", v)
+}
+
+// Type returns the type name of the SharedDict.
+func (s *SharedDict) Type() string {
+	return "shared_dict"
+}
+
+// Freeze prevents the SharedDict from being modified.
+func (s *SharedDict) Freeze() {
+	s.Lock()
+	defer s.Unlock()
+
+	s.frozen = true
+	if s.dict != nil {
+		s.dict.Freeze()
+	}
+}
+
+// Truth returns the truth value of the SharedDict.
+func (s *SharedDict) Truth() starlark.Bool {
+	s.RLock()
+	defer s.RUnlock()
+
+	return s != nil && s.dict != nil && s.dict.Truth()
+}
+
+// Hash returns the hash value of the SharedDict, actually it's not hashable.
+func (s *SharedDict) Hash() (uint32, error) {
+	return 0, fmt.Errorf("unhashable type: shared_dict")
+}
+
+// Get returns the value corresponding to the specified key, or not found if the mapping does not contain the key.
+// It implements the starlark.Mapping interface.
+func (s *SharedDict) Get(k starlark.Value) (v starlark.Value, found bool, err error) {
+	s.RLock()
+	defer s.RUnlock()
+
+	if s.dict != nil {
+		return s.dict.Get(k)
+	}
+	return nil, false, nil
+}
+
+// SetKey sets the value for the specified key, supports update using x[k]=v syntax, like a dictionary.
+// It implements the starlark.HasSetKey interface.
+func (s *SharedDict) SetKey(k, v starlark.Value) error {
+	s.Lock()
+	defer s.Unlock()
+
+	// basic check
+	if s.frozen {
+		return fmt.Errorf("frozen dict")
+	}
+
+	// maybe create the dictionary (perhaps this line is unreachable)
+	if s.dict == nil {
+		s.dict = starlark.NewDict(defaultSharedDictSize)
+	}
+
+	// check if the value is a shared dict -- reject it
+	if sd, ok := v.(*SharedDict); ok {
+		return fmt.Errorf("unsupported value: %s", sd.Type())
+	}
+	return s.dict.SetKey(k, v)
+}
+
+// Attr returns the value of the specified attribute, or (nil, nil) if the attribute is not found.
+// It implements the starlark.HasAttrs interface.
+func (s *SharedDict) Attr(name string) (starlark.Value, error) {
+	s.Lock()
+	defer s.Unlock()
+
+	// basic check
+	if s.dict == nil {
+		return nil, nil
+	}
+
+	var (
+		attr starlark.Value
+		err  error
+	)
+	// try to get the new custom builtin
+	if b, ok := customSharedDictMethods[name]; ok {
+		attr = b.BindReceiver(s.dict)
+	} else {
+		// get the builtin from the original dict
+		attr, err = s.dict.Attr(name)
+	}
+
+	// convert to builtin
+	if attr == nil || err != nil {
+		return attr, err
+	}
+	btl, ok := attr.(*starlark.Builtin)
+	if !ok {
+		return nil, fmt.Errorf("unsupported attribute: %s", name)
+	}
+
+	// wrap the builtin
+	return starlark.NewBuiltin(name, func(thread *starlark.Thread, b *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
+		// lock the shared dict
+		s.Lock()
+		defer s.Unlock()
+
+		// call the original builtin
+		return btl.CallInternal(thread, args, kwargs)
+	}), nil
+}
+
+// AttrNames returns a new slice containing the names of all the attributes of the SharedDict.
+// It implements the starlark.HasAttrs interface.
+func (s *SharedDict) AttrNames() []string {
+	if s.dict != nil {
+		names := s.dict.AttrNames()
+		for cn := range customSharedDictMethods {
+			names = append(names, cn)
+		}
+		sort.Strings(names)
+		return names
+	}
+	return nil
+}
+
+// CompareSameType compares the SharedDict with another value of the same type.
+// It implements the starlark.Comparable interface.
+func (s *SharedDict) CompareSameType(op syntax.Token, y_ starlark.Value, depth int) (bool, error) {
+	// if they are the same object, they are equal
+	if s == y_ {
+		switch op {
+		case syntax.EQL:
+			return true, nil
+		case syntax.NEQ:
+			return false, nil
+		default:
+			return false, fmt.Errorf("unsupported operator: %s", op)
+		}
+	}
+
+	// scan the type
+	y := y_.(*SharedDict)
+
+	// lock both objects
+	s.RLock()
+	defer s.RUnlock()
+	y.RLock()
+	defer y.RUnlock()
+
+	// compare the underlying dictionaries
+	if s.dict != nil && y.dict != nil {
+		return s.dict.CompareSameType(op, y.dict, depth)
+	} else if s.dict == nil && y.dict == nil {
+		// both are nil, they are equal, aha! (nil == nil)
+		return true, nil
+	}
+
+	// one is nil, the other is not, they are not equal
+	switch op {
+	case syntax.EQL:
+		return false, nil
+	case syntax.NEQ:
+		return true, nil
+	default:
+		return false, fmt.Errorf("unsupported operator: %s", op)
+	}
+}
+
+var (
+	customSharedDictMethods = map[string]*starlark.Builtin{
+		"len":     starlark.NewBuiltin("len", shardDictLen),
+		"perform": starlark.NewBuiltin("perform", shardDictPerform),
+	}
+)
+
+// shardDictLen returns the length of the underlying dictionary.
+func shardDictLen(_ *starlark.Thread, b *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
+	if err := starlark.UnpackPositionalArgs(b.Name(), args, kwargs, 0); err != nil {
+		return nil, err
+	}
+	l := b.Receiver().(*starlark.Dict).Len()
+	return starlark.MakeInt(l), nil
+}
+
+// shardDictPerform calls the given function with the underlying receiver dictionary, and returns the result.
+// The function must be callable, like def perform(fn).
+func shardDictPerform(thread *starlark.Thread, b *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
+	// get the perform function
+	var pr starlark.Value
+	if err := starlark.UnpackArgs(b.Name(), args, kwargs, "fn", &pr); err != nil {
+		return nil, err
+	}
+
+	// get the receiver
+	d := b.Receiver().(*starlark.Dict)
+
+	// call the function with the receiver
+	switch pr := pr.(type) {
+	case starlark.Callable:
+		return pr.CallInternal(thread, starlark.Tuple{d}, nil)
+	default:
+		return nil, fmt.Errorf("%s: not callable type: %s", b.Name(), pr.Type())
+	}
+}