opt: eliminate error logs when the service exits normally

Fixes #497

acceptor_windows.go

@@ -15,8 +15,12 @@
 package gnet
 
 import (
+	"errors"
 	"net"
 	"runtime"
+	"sync/atomic"
+
+	errorx "github.com/panjf2000/gnet/v2/pkg/errors"
 )
 
 func (eng *engine) listen() (err error) {
@@ -34,7 +38,15 @@ func (eng *engine) listen() (err error) {
 			n, addr, e := eng.ln.pc.ReadFrom(buffer[:])
 			if e != nil {
 				err = e
-				eng.opts.Logger.Errorf("failed to receive data from UDP fd due to error:%v", err)
+				if atomic.LoadInt32(&eng.beingShutdown) == 0 {
+					eng.opts.Logger.Errorf("failed to receive data from UDP fd due to error:%v", err)
+				} else if errors.Is(err, net.ErrClosed) {
+					err = errorx.ErrEngineShutdown
+					// TODO: errors.Join() is not supported until Go 1.20,
+					// 	we will uncomment this line after we bump up the
+					// 	minimal supported go version to 1.20.
+					// err = errors.Join(err, errorx.ErrEngineShutdown)
+				}
 				return
 			}
 
@@ -46,7 +58,13 @@ func (eng *engine) listen() (err error) {
 			tc, e := eng.ln.ln.Accept()
 			if e != nil {
 				err = e
-				eng.opts.Logger.Errorf("Accept() fails due to error: %v", err)
+				if atomic.LoadInt32(&eng.beingShutdown) == 0 {
+					eng.opts.Logger.Errorf("Accept() fails due to error: %v", err)
+				} else if errors.Is(err, net.ErrClosed) {
+					err = errorx.ErrEngineShutdown
+					// TODO: ditto.
+					// err = errors.Join(err, errorx.ErrEngineShutdown)
+				}
 				return
 			}
 			el := eng.eventLoops.next(tc.RemoteAddr())

engine_windows.go

@@ -16,6 +16,7 @@ package gnet
 
 import (
 	"context"
+	"errors"
 	"runtime"
 	"sync"
 	"sync/atomic"
@@ -33,8 +34,9 @@ type engine struct {
 		ctx    context.Context
 		cancel context.CancelFunc
 	}
-	inShutdown int32 // whether the engine is in shutdown
-	workerPool struct {
+	inShutdown    int32 // whether the engine is in shutdown
+	beingShutdown int32 // whether the engine is being shutdown
+	workerPool    struct {
 		*errgroup.Group
 
 		shutdownCtx context.Context
@@ -50,10 +52,11 @@ func (eng *engine) isInShutdown() bool {
 
 // shutdown signals the engine to shut down.
 func (eng *engine) shutdown(err error) {
-	if err != nil && err != errorx.ErrEngineShutdown {
+	if err != nil && !errors.Is(err, errorx.ErrEngineShutdown) {
 		eng.opts.Logger.Errorf("engine is being shutdown with error: %v", err)
 	}
 	eng.workerPool.shutdown()
+	atomic.StoreInt32(&eng.beingShutdown, 1)
 }
 
 func (eng *engine) closeEventLoops() {
@@ -100,7 +103,7 @@ func (eng *engine) stop(engine Engine) error {
 
 	eng.closeEventLoops()
 
-	if err := eng.workerPool.Wait(); err != nil {
+	if err := eng.workerPool.Wait(); err != nil && !errors.Is(err, errorx.ErrEngineShutdown) {
 		eng.opts.Logger.Errorf("engine shutdown error: %v", err)
 	}