util: add waitmap for target synchronization

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

util/waitmap/waitmap.go

@@ -0,0 +1,74 @@
+package waitmap
+
+import (
+	"context"
+	"sync"
+)
+
+type Map struct {
+	mu sync.RWMutex
+	m  map[string]interface{}
+	ch map[string]chan struct{}
+}
+
+func New() *Map {
+	return &Map{
+		m:  make(map[string]interface{}),
+		ch: make(map[string]chan struct{}),
+	}
+}
+
+func (m *Map) Set(key string, value interface{}) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	m.m[key] = value
+
+	if ch, ok := m.ch[key]; ok {
+		if ch != nil {
+			close(ch)
+		}
+	}
+	m.ch[key] = nil
+}
+
+func (m *Map) Get(ctx context.Context, keys ...string) (map[string]interface{}, error) {
+	if len(keys) == 0 {
+		return map[string]interface{}{}, nil
+	}
+
+	if len(keys) > 1 {
+		out := make(map[string]interface{})
+		for _, key := range keys {
+			mm, err := m.Get(ctx, key)
+			if err != nil {
+				return nil, err
+			}
+			out[key] = mm[key]
+		}
+		return out, nil
+	}
+
+	key := keys[0]
+	m.mu.Lock()
+	ch, ok := m.ch[key]
+	if !ok {
+		ch = make(chan struct{})
+		m.ch[key] = ch
+	}
+
+	if ch != nil {
+		m.mu.Unlock()
+		select {
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		case <-ch:
+			m.mu.Lock()
+		}
+	}
+
+	res := m.m[key]
+	m.mu.Unlock()
+
+	return map[string]interface{}{key: res}, nil
+}