Started LDAP support

util/genpool/genpool.go

@@ -0,0 +1,113 @@
+package genpool
+
+import "errors"
+
+var (
+	ErrPoolClosed = errors.New("pool already closed")
+)
+
+type getResp[Item interface{}] struct {
+	Item *Item
+	err  error
+}
+
+type poolReq[Item interface{}] struct {
+	get chan<- getResp[Item]
+	ret *Item
+}
+
+type PoolManager[Item interface{}] interface {
+	Destroy(*Item)
+	Create() (*Item, error)
+	Validate(*Item) bool
+}
+
+type poolBackend[Item interface{}] struct {
+	manager PoolManager[Item]
+	pool    []*Item
+}
+
+func (b *poolBackend[Item]) run(ch <-chan poolReq[Item]) {
+	defer func() {
+		for _, item := range b.pool {
+			b.manager.Destroy(item)
+		}
+	}()
+	for req := range ch {
+		if req.get != nil {
+			// fetch an item
+			for {
+				if len(b.pool) > 0 {
+					item := b.pool[len(b.pool)-1]
+					b.pool = b.pool[:len(b.pool)-1]
+					if b.manager.Validate(item) {
+						req.get <- getResp[Item]{
+							Item: item,
+							err:  nil,
+						}
+						break
+					} else {
+						b.manager.Destroy(item)
+					}
+				} else {
+					// last item
+					item, err := b.manager.Create()
+					req.get <- getResp[Item]{
+						Item: item,
+						err:  err,
+					}
+					break
+				}
+			}
+		}
+		if req.ret != nil {
+			// return an item to the pool
+			if cap(b.pool) > len(b.pool) {
+				b.pool = append(b.pool, req.ret)
+			} else {
+				b.manager.Destroy(req.ret)
+			}
+		}
+	}
+
+}
+
+type Pool[Item interface{}] struct {
+	req chan<- poolReq[Item]
+}
+
+func NewPool[Item interface{}](manager PoolManager[Item], capacity int) Pool[Item] {
+	cmdChan := make(chan poolReq[Item])
+	backend := poolBackend[Item]{
+		manager: manager,
+		pool:    make([]*Item, 0, capacity),
+	}
+	go backend.run(cmdChan)
+	return Pool[Item]{
+		req: cmdChan,
+	}
+}
+
+func (p *Pool[Item]) Get() (*Item, error) {
+	retCh := make(chan getResp[Item])
+	p.req <- poolReq[Item]{
+		get: retCh,
+	}
+	item, ok := <-retCh
+	if ok {
+		return item.Item, item.err
+	} else {
+		return nil, ErrPoolClosed
+	}
+}
+
+func (p *Pool[Item]) Put(item *Item) {
+	p.req <- poolReq[Item]{
+		ret: item,
+	}
+}
+
+func (p *Pool[Item]) Close() {
+	close(p.req)
+	p.req = nil
+}