xsync: Add ContextMutex

Tends to be extremely useful.

xsync/xsync.go

@@ -0,0 +1,37 @@
+package xsync
+
+type ContextMutex struct {
+	ch chan struct{}
+}
+
+func NewContextMutex() *ContextMutex {
+	return &ContextMutex{
+		ch: make(chan struct{}, 1),
+	}
+}
+
+func (cm *ContextMutex) TryLock() bool {
+	select {
+	case cm.ch <- struct{}{}:
+		return true
+	default:
+		return false
+	}
+}
+
+func (cm *ContextMutex) Lock(ctx context.Context) error {
+	select {
+	case <-ctx.Done():
+		return fmt.Errorf("failed to acquire lock: %w", ctx.Err())
+	case cm.ch <- struct{}{}:
+		return nil
+	}
+}
+
+func (cm *ContextMutex) Unlock() {
+	select {
+	case <-cm.ch:
+	default:
+		panic("xsync.ContextMutex: Unlock before Lock")
+	}
+}