refactor: internal package

internal/sandbox/semaphore.go

@@ -0,0 +1,45 @@
+package sandbox
+
+import "errors"
+
+var ErrBusy = errors.New("busy")
+
+// A Semaphore manages a limited number of tokens
+// that can be acquired or released.
+type Semaphore struct {
+	tokens chan struct{}
+}
+
+// NewSemaphore creates a new semaphore of the specified size.
+func NewSemaphore(size int) *Semaphore {
+	tokens := make(chan struct{}, size)
+	for i := 0; i < size; i++ {
+		tokens <- struct{}{}
+	}
+	return &Semaphore{tokens}
+}
+
+// Acquire acquires a token. Returns ErrBusy if no tokens are available.
+func (q *Semaphore) Acquire() error {
+	select {
+	case <-q.tokens:
+		return nil
+	default:
+		return ErrBusy
+	}
+}
+
+// Release releases a token.
+func (q *Semaphore) Release() {
+	select {
+	case q.tokens <- struct{}{}:
+		return
+	default:
+		return
+	}
+}
+
+// Size returns the size of the semaphore.
+func (q *Semaphore) Size() int {
+	return len(q.tokens)
+}