[#33] util: Define worker pool interface

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/util/worker_pool.go

@@ -0,0 +1,24 @@
+package util
+
+// WorkerPool represents the tool for control
+// the execution of go-routine pool.
+type WorkerPool interface {
+	// Submit queues a function for execution
+	// in a separate routine.
+	//
+	// Implementation must return any error encountered
+	// that prevented the function from being queued.
+	Submit(func()) error
+}
+
+// SyncWorkerPool represents synchronous worker pool.
+type SyncWorkerPool struct{}
+
+// Submit executes passed function immediately.
+//
+// Always returns nil.
+func (SyncWorkerPool) Submit(fn func()) error {
+	fn()
+
+	return nil
+}