add bulk deletion feature

Author: alphadose

README.md

@@ -41,19 +41,21 @@ func main() {
 
 	mep.Set(2, "two")
 	mep.Set(3, "three")
+	mep.Set(4, "four")
 
 	// ForEach loop to iterate over all key-value pairs and execute the given lambda
 	mep.ForEach(func(key int, value string) bool {
 		fmt.Printf("Key -> %d | Value -> %s\n", key, value)
 		return true // return `true` to continue iteration and `false` to break iteration
 	})
 
-	// delete values
-	mep.Del(1)
-	mep.Del(2)
-	mep.Del(3)
+	mep.Del(1) // delete a value
 	mep.Del(0) // delete is safe even if a key doesn't exists
 
+	// bulk deletion is supported too in the same API call
+	// has better performance than deleting keys one by one
+	mep.Del(2, 3, 4)
+
 	if mep.Len() == 0 {
 		println("cleanup complete")
 	}

e2e_test.go

@@ -102,14 +102,12 @@ func TestDelete(t *testing.T) {
 	m.Set(1, cat)
 	m.Set(2, tiger)
 	m.Del(0)
-	m.Del(3)
+	m.Del(3, 4, 5)
 	if m.Len() != 2 {
 		t.Error("map should contain exactly two elements.")
 	}
 
-	m.Del(1)
-	m.Del(1)
-	m.Del(2)
+	m.Del(1, 2, 1)
 
 	if m.Len() != 0 {
 		t.Error("map should be empty.")

examples/concurrent_deletion.go

@@ -1,3 +1,6 @@
+// from bug https://github.com/alphadose/haxmap/issues/14
+// fixed in v1.0.1 and above
+
 package main
 
 import (

examples/simple.go

@@ -12,6 +12,7 @@ func main() {
 
 	// set a value (overwrites existing value if present)
 	mep.Set(1, "one")
+
 	// get the value and print it
 	val, ok := mep.Get(1)
 	if ok {
@@ -20,19 +21,21 @@ func main() {
 
 	mep.Set(2, "two")
 	mep.Set(3, "three")
+	mep.Set(4, "four")
 
 	// ForEach loop to iterate over all key-value pairs and execute the given lambda
 	mep.ForEach(func(key int, value string) bool {
 		fmt.Printf("Key -> %d | Value -> %s\n", key, value)
-		return true
+		return true // return `true` to continue iteration and `false` to break iteration
 	})
 
-	// delete values
-	mep.Del(1)
-	mep.Del(2)
-	mep.Del(3)
+	mep.Del(1) // delete a value
 	mep.Del(0) // delete is safe even if a key doesn't exists
 
+	// bulk deletion is supported too in the same API call
+	// has better performance than deleting keys one by one
+	mep.Del(2, 3, 4)
+
 	if mep.Len() == 0 {
 		println("cleanup complete")
 	}

map.go

@@ -2,6 +2,7 @@ package haxmap
 
 import (
 	"reflect"
+	"sort"
 	"strconv"
 	"sync/atomic"
 	"unsafe"
@@ -49,6 +50,12 @@ type (
 		resizing atomicUint32
 		numItems atomicUintptr
 	}
+
+	// used in deletion of map elements
+	deletionRequest[K hashable] struct {
+		keyHash uintptr
+		key     K
+	}
 )
 
 // New returns a new HashMap instance with an optional specific initialization size
@@ -64,48 +71,42 @@ func New[K hashable, V any](size ...uintptr) *Map[K, V] {
 	return m
 }
 
-// Del lazily deletes the key from the map
-// does nothing if key is absemt
-func (m *Map[K, V]) Del(key K) {
-	var (
-		h    = m.hasher(key)
-		elem = m.metadata.Load().indexElement(h)
-	)
-
-loop:
-	for ; elem != nil; elem = elem.next() {
-		if elem.keyHash == h && elem.key == key {
-			break loop
-		}
-		if elem.keyHash > h {
-			return
-		}
-	}
-	if elem == nil {
+// Del deletes key/keys from the map
+// Bulk deletion is more efficient than deleting keys one by one
+func (m *Map[K, V]) Del(keys ...K) {
+	if len(keys) == 0 {
 		return
 	}
-	// mark node for deletion
-	elem.remove()
-
-	for iter := m.listHead.next(); iter != nil; iter = iter.next() {
+	var (
+		size = len(keys)
+		delQ = make([]deletionRequest[K], size)
+		elem = m.listHead.next()
+		iter = 0
+	)
+	for idx := 0; idx < size; idx++ {
+		delQ[idx].keyHash, delQ[idx].key = m.hasher(keys[idx]), keys[idx]
 	}
 
-	// remove node from map index if exists
-	for {
-		data := m.metadata.Load()
-		index := elem.keyHash >> data.keyshifts
-		ptr := (*unsafe.Pointer)(unsafe.Pointer(uintptr(data.data) + index*intSizeBytes))
-
-		next := elem.next()
-		if next != nil && elem.keyHash>>data.keyshifts != index {
-			next = nil // do not set index to next item if it's not the same slice index
+	// sort in ascending order of keyhash
+	sort.Slice(delQ, func(i, j int) bool {
+		return delQ[i].keyHash < delQ[j].keyHash
+	})
+
+	for elem != nil && iter < size {
+		if elem.keyHash == delQ[iter].keyHash && elem.key == delQ[iter].key {
+			elem.remove() // mark node for deletion
+			m.removeItemFromIndex(elem)
+			iter++
+			elem = elem.next()
+		} else if elem.keyHash > delQ[iter].keyHash {
+			iter++
+		} else {
+			elem = elem.next()
 		}
-		atomic.CompareAndSwapPointer(ptr, unsafe.Pointer(elem), unsafe.Pointer(next))
+	}
 
-		if data == m.metadata.Load() { // check that no resize happened
-			m.numItems.Add(marked)
-			return
-		}
+	// iterate list from start to end to remove the marked nodes
+	for iter := m.listHead; iter != nil; iter = iter.next() {
 	}
 }
 
@@ -218,6 +219,26 @@ func (m *Map[K, V]) fillIndexItems(mapData *metadata[K, V]) {
 	}
 }
 
+// removeItemFromIndex removes an item from the map index
+func (m *Map[K, V]) removeItemFromIndex(item *element[K, V]) {
+	for {
+		data := m.metadata.Load()
+		index := item.keyHash >> data.keyshifts
+		ptr := (*unsafe.Pointer)(unsafe.Pointer(uintptr(data.data) + index*intSizeBytes))
+
+		next := item.next()
+		if next != nil && item.keyHash>>data.keyshifts != index {
+			next = nil // do not set index to next item if it's not the same slice index
+		}
+		atomic.CompareAndSwapPointer(ptr, unsafe.Pointer(item), unsafe.Pointer(next))
+
+		if data == m.metadata.Load() { // check that no resize happened
+			m.numItems.Add(marked)
+			return
+		}
+	}
+}
+
 // grow to the new size
 func (m *Map[K, V]) grow(newSize uintptr) {
 	for {