[#901] util: implement Release for PseudWorkerPool

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

pkg/util/worker_pool.go

@@ -1,5 +1,10 @@
 package util
 
+import (
+	"github.com/panjf2000/ants/v2"
+	"go.uber.org/atomic"
+)
+
 // WorkerPool represents the tool for control
 // the execution of go-routine pool.
 type WorkerPool interface {
@@ -9,16 +14,41 @@ type WorkerPool interface {
 	// Implementation must return any error encountered
 	// that prevented the function from being queued.
 	Submit(func()) error
+
+	// Release releases worker pool resources. All `Submit` calls will
+	// finish with ErrPoolClosed. It doesn't wait until all submitted
+	// functions have returned so synchronization must be achieved
+	// via other means (e.g. sync.WaitGroup).
+	Release()
 }
 
-// PseudoWorkerPool represents pseudo worker pool which executes submitted job immediately in the caller's routine..
-type PseudoWorkerPool struct{}
+// pseudoWorkerPool represents pseudo worker pool which executes submitted job immediately in the caller's routine.
+type pseudoWorkerPool struct {
+	closed atomic.Bool
+}
+
+// ErrPoolClosed is returned when submitting task to a closed pool.
+var ErrPoolClosed = ants.ErrPoolClosed
+
+// NewPseudoWorkerPool returns new instance of a synchronous worker pool.
+func NewPseudoWorkerPool() WorkerPool {
+	return &pseudoWorkerPool{}
+}
 
 // Submit executes passed function immediately.
 //
 // Always returns nil.
-func (PseudoWorkerPool) Submit(fn func()) error {
+func (p *pseudoWorkerPool) Submit(fn func()) error {
+	if p.closed.Load() {
+		return ErrPoolClosed
+	}
+
 	fn()
 
 	return nil
 }
+
+// Release implements WorkerPool interface.
+func (p *pseudoWorkerPool) Release() {
+	p.closed.Store(true)
+}