Merge pull request #47 from semihbkgr/clear

Clear function

Author: alphadose

e2e_test.go

@@ -235,6 +235,30 @@ func TestIterator(t *testing.T) {
 	}
 }
 
+func TestClear(t *testing.T) {
+	m := New[int, any]()
+	for i := 0; i < 100; i++ {
+		m.Set(i, nil)
+	}
+	m.Clear()
+	if m.Len() != 0 {
+		t.Error("map size should be zero after clear")
+	}
+	if m.Fillrate() != 0 {
+		t.Error("fillrate should be zero after clear")
+	}
+	log := int(math.Log2(defaultSize))
+	expectedSize := uintptr(strconv.IntSize - log)
+	if m.metadata.Load().keyshifts != expectedSize {
+		t.Error("keyshift is not as expected after clear")
+	}
+	for i := 0; i < 100; i++ {
+		if _, ok := m.Get(i); ok {
+			t.Error("the entries should not be existing in the map after clear")
+		}
+	}
+}
+
 func TestMapParallel(t *testing.T) {
 	max := 10
 	dur := 2 * time.Second

map.go

@@ -46,11 +46,12 @@ type (
 
 	// Map implements the concurrent hashmap
 	Map[K hashable, V any] struct {
-		listHead *element[K, V] // Harris lock-free list of elements in ascending order of hash
-		hasher   func(K) uintptr
-		metadata atomicPointer[metadata[K, V]] // atomic.Pointer for safe access even during resizing
-		resizing atomicUint32
-		numItems atomicUintptr
+		listHead    *element[K, V] // Harris lock-free list of elements in ascending order of hash
+		hasher      func(K) uintptr
+		metadata    atomicPointer[metadata[K, V]] // atomic.Pointer for safe access even during resizing
+		resizing    atomicUint32
+		numItems    atomicUintptr
+		defaultSize uintptr
 	}
 
 	// used in deletion of map elements
@@ -64,11 +65,11 @@ type (
 func New[K hashable, V any](size ...uintptr) *Map[K, V] {
 	m := &Map[K, V]{listHead: newListHead[K, V]()}
 	m.numItems.Store(0)
-	if len(size) > 0 && size[0] != 0 {
-		m.allocate(size[0])
-	} else {
-		m.allocate(defaultSize)
+	m.defaultSize = defaultSize
+	if len(size) > 0 && size[0] > 0 {
+		m.defaultSize = size[0]
 	}
+	m.allocate(m.defaultSize)
 	m.setDefaultHasher()
 	return m
 }
@@ -350,6 +351,21 @@ func (m *Map[K, V]) Grow(newSize uintptr) {
 	}
 }
 
+// Clear the map by removing all entries in the map.
+// This operation resets the underlying metadata to its initial state.
+func (m *Map[K, V]) Clear() {
+	index := make([]*element[K, V], m.defaultSize)
+	header := (*reflect.SliceHeader)(unsafe.Pointer(&index))
+	newdata := &metadata[K, V]{
+		keyshifts: strconv.IntSize - log2(m.defaultSize),
+		data:      unsafe.Pointer(header.Data),
+		index:     index,
+	}
+	m.listHead.nextPtr.Store(nil)
+	m.metadata.Store(newdata)
+	m.numItems.Store(0)
+}
+
 // SetHasher sets the hash function to the one provided by the user
 func (m *Map[K, V]) SetHasher(hs func(K) uintptr) {
 	m.hasher = hs