diff --git a/acceptor_unix.go b/acceptor_unix.go
index 1afad82b4..fe7d67cab 100644
--- a/acceptor_unix.go
+++ b/acceptor_unix.go
@@ -33,7 +33,7 @@ func (el *eventloop) accept0(fd int, _ netpoll.IOEvent, _ netpoll.IOFlags) error
 		nfd, sa, err := socket.Accept(fd)
 		if err != nil {
 			switch err {
-			case unix.EAGAIN: // the Accept queue has been drained, we can return now
+			case unix.EAGAIN: // the Accept queue has been drained out, we can return now
 				return nil
 			case unix.EINTR, unix.ECONNRESET, unix.ECONNABORTED:
 				// ECONNRESET or ECONNABORTED could indicate that a socket
@@ -93,16 +93,5 @@ func (el *eventloop) accept(fd int, ev netpoll.IOEvent, flags netpoll.IOFlags) e
 	}
 
 	c := newTCPConn(nfd, el, sa, el.listeners[fd].addr, remoteAddr)
-	addEvents := el.poller.AddRead
-	if el.engine.opts.EdgeTriggeredIO {
-		addEvents = el.poller.AddReadWrite
-	}
-	if err = addEvents(&c.pollAttachment, el.engine.opts.EdgeTriggeredIO); err != nil {
-		el.getLogger().Errorf("failed to register the accepted socket fd=%d to poller: %v", c.fd, err)
-		_ = unix.Close(c.fd)
-		c.release()
-		return err
-	}
-	el.connections.addConn(c, el.idx)
-	return el.open(c)
+	return el.register0(c)
 }
diff --git a/connection_bsd.go b/connection_bsd.go
index b24becffb..3223f01e4 100644
--- a/connection_bsd.go
+++ b/connection_bsd.go
@@ -39,14 +39,14 @@ func (c *conn) processIO(_ int, filter netpoll.IOEvent, flags netpoll.IOFlags) (
 	if flags&unix.EV_EOF != 0 && c.opened && err == nil {
 		switch filter {
 		case unix.EVFILT_READ:
-			// Receive the event of EVFILT_READ | EV_EOF, but the previous eventloop.read
+			// Received the event of EVFILT_READ|EV_EOF, but the previous eventloop.read
 			// failed to drain the socket buffer, so we make sure we get it done this time.
 			c.isEOF = true
 			err = el.read(c)
 		case unix.EVFILT_WRITE:
-			// On macOS, the kqueue in both LT and ET mode will notify with one event for the EOF
-			// of the TCP remote: EVFILT_READ|EV_ADD|EV_CLEAR|EV_EOF. But for some reason, two
-			// events will be issued in ET mode for the EOF of the Unix remote in this order:
+			// On macOS, the kqueue in either LT or ET mode will notify with one event for the
+			// EOF of the TCP remote: EVFILT_READ|EV_ADD|EV_CLEAR|EV_EOF. But for some reason,
+			// two events will be issued in ET mode for the EOF of the Unix remote in this order:
 			// 1) EVFILT_WRITE|EV_ADD|EV_CLEAR|EV_EOF, 2) EVFILT_READ|EV_ADD|EV_CLEAR|EV_EOF.
 			err = el.write(c)
 		default:
diff --git a/connection_linux.go b/connection_linux.go
index ac8376e4c..d14e1f32e 100644
--- a/connection_linux.go
+++ b/connection_linux.go
@@ -28,7 +28,7 @@ import (
 func (c *conn) processIO(_ int, ev netpoll.IOEvent, _ netpoll.IOFlags) error {
 	el := c.loop
 	// First check for any unexpected non-IO events.
-	// For these events we just close the corresponding connection directly.
+	// For these events we just close the connection directly.
 	if ev&netpoll.ErrEvents != 0 && ev&unix.EPOLLIN == 0 && ev&unix.EPOLLOUT == 0 {
 		c.outboundBuffer.Release() // don't bother to write to a connection with some unknown error
 		return el.close(c, io.EOF)
@@ -40,9 +40,9 @@ func (c *conn) processIO(_ int, ev netpoll.IOEvent, _ netpoll.IOFlags) error {
 	// offload the incoming traffic by writing all pending data back to the remotes
 	// before continuing to read and handle requests.
 	// 2. When the connection is dead, we need to try writing any pending data back
-	// to the remote and close the connection first.
+	// to the remote first and then close the connection.
 	//
-	// We perform eventloop.write for EPOLLOUT because it will take good care of either case.
+	// We perform eventloop.write for EPOLLOUT because it can take good care of either case.
 	if ev&(unix.EPOLLOUT|unix.EPOLLERR) != 0 {
 		if err := el.write(c); err != nil {
 			return err
@@ -61,8 +61,8 @@ func (c *conn) processIO(_ int, ev netpoll.IOEvent, _ netpoll.IOFlags) error {
 		if ev&unix.EPOLLIN == 0 { // unreadable EPOLLRDHUP, close the connection directly
 			return el.close(c, io.EOF)
 		}
-		// Received the event of EPOLLIN | EPOLLRDHUP, but the previous eventloop.read
-		// failed to drain the socket buffer, so we make sure we get it done this time.
+		// Received the event of EPOLLIN|EPOLLRDHUP, but the previous eventloop.read
+		// failed to drain the socket buffer, so we ensure to get it done this time.
 		c.isEOF = true
 		return el.read(c)
 	}
diff --git a/eventloop_unix.go b/eventloop_unix.go
index c0b326804..b7530a966 100644
--- a/eventloop_unix.go
+++ b/eventloop_unix.go
@@ -75,20 +75,20 @@ func (el *eventloop) register(itf interface{}) error {
 		c = ccb.c
 		defer ccb.cb()
 	}
+	return el.register0(c)
+}
 
+func (el *eventloop) register0(c *conn) error {
 	addEvents := el.poller.AddRead
 	if el.engine.opts.EdgeTriggeredIO {
 		addEvents = el.poller.AddReadWrite
 	}
-
 	if err := addEvents(&c.pollAttachment, el.engine.opts.EdgeTriggeredIO); err != nil {
 		_ = unix.Close(c.fd)
 		c.release()
 		return err
 	}
-
 	el.connections.addConn(c, el.idx)
-
 	if c.isDatagram && c.remote != nil {
 		return nil
 	}
diff --git a/eventloop_windows.go b/eventloop_windows.go
index 074318c58..ea0f87377 100644
--- a/eventloop_windows.go
+++ b/eventloop_windows.go
@@ -17,12 +17,13 @@ package gnet
 import (
 	"bytes"
 	"context"
+	"errors"
 	"runtime"
 	"strings"
 	"sync/atomic"
 	"time"
 
-	"github.com/panjf2000/gnet/v2/pkg/errors"
+	errorx "github.com/panjf2000/gnet/v2/pkg/errors"
 	"github.com/panjf2000/gnet/v2/pkg/logging"
 )
 
@@ -79,7 +80,7 @@ func (el *eventloop) run() (err error) {
 			err = v()
 		}
 
-		if err == errors.ErrEngineShutdown {
+		if errors.Is(err, errorx.ErrEngineShutdown) {
 			el.getLogger().Debugf("event-loop(%d) is exiting in terms of the demand from user, %v", el.idx, err)
 			break
 		} else if err != nil {
@@ -121,7 +122,7 @@ func (el *eventloop) read(c *conn) error {
 	case Close:
 		return el.close(c, nil)
 	case Shutdown:
-		return errors.ErrEngineShutdown
+		return errorx.ErrEngineShutdown
 	}
 	_, _ = c.inboundBuffer.Write(c.buffer.B)
 	c.buffer.Reset()
@@ -132,7 +133,7 @@ func (el *eventloop) read(c *conn) error {
 func (el *eventloop) readUDP(c *conn) error {
 	action := el.eventHandler.OnTraffic(c)
 	if action == Shutdown {
-		return errors.ErrEngineShutdown
+		return errorx.ErrEngineShutdown
 	}
 	c.release()
 	return nil
@@ -160,7 +161,7 @@ func (el *eventloop) ticker(ctx context.Context) {
 		case Shutdown:
 			if !shutdown {
 				shutdown = true
-				el.ch <- errors.ErrEngineShutdown
+				el.ch <- errorx.ErrEngineShutdown
 				el.getLogger().Debugf("stopping ticker in event-loop(%d) from Tick()", el.idx)
 			}
 		}
@@ -220,7 +221,7 @@ func (el *eventloop) handleAction(c *conn, action Action) error {
 	case Close:
 		return el.close(c, nil)
 	case Shutdown:
-		return errors.ErrEngineShutdown
+		return errorx.ErrEngineShutdown
 	default:
 		return nil
 	}
diff --git a/gnet_test.go b/gnet_test.go
index fec73ad16..11c7df997 100644
--- a/gnet_test.go
+++ b/gnet_test.go
@@ -1484,7 +1484,7 @@ func (s *simServer) OnTraffic(c Conn) (action Action) {
 	var packets [][]byte
 	for {
 		data, err := codec.Decode(c)
-		if err == errIncompletePacket {
+		if errors.Is(err, errIncompletePacket) {
 			break
 		}
 		if err != nil {
diff --git a/reactor_epoll_default.go b/reactor_epoll_default.go
index 83be6d525..4f150e6ec 100644
--- a/reactor_epoll_default.go
+++ b/reactor_epoll_default.go
@@ -18,13 +18,11 @@
 package gnet
 
 import (
-	"io"
+	"errors"
 	"runtime"
 
-	"golang.org/x/sys/unix"
-
 	"github.com/panjf2000/gnet/v2/internal/netpoll"
-	"github.com/panjf2000/gnet/v2/pkg/errors"
+	errorx "github.com/panjf2000/gnet/v2/pkg/errors"
 )
 
 func (el *eventloop) rotate() error {
@@ -34,7 +32,7 @@ func (el *eventloop) rotate() error {
 	}
 
 	err := el.poller.Polling(el.accept0)
-	if err == errors.ErrEngineShutdown {
+	if errors.Is(err, errorx.ErrEngineShutdown) {
 		el.getLogger().Debugf("main reactor is exiting in terms of the demand from user, %v", err)
 		err = nil
 	} else if err != nil {
@@ -52,57 +50,16 @@ func (el *eventloop) orbit() error {
 		defer runtime.UnlockOSThread()
 	}
 
-	err := el.poller.Polling(func(fd int, ev netpoll.IOEvent, _ netpoll.IOFlags) error {
+	err := el.poller.Polling(func(fd int, ev netpoll.IOEvent, flags netpoll.IOFlags) error {
 		c := el.connections.getConn(fd)
 		if c == nil {
 			// Somehow epoll notified with an event for a stale fd that is not in our connection set.
 			// We need to delete it from the epoll set.
 			return el.poller.Delete(fd)
 		}
-
-		// First check for any unexpected non-IO events.
-		// For these events we just close the corresponding connection directly.
-		if ev&netpoll.ErrEvents != 0 && ev&unix.EPOLLIN == 0 && ev&unix.EPOLLOUT == 0 {
-			c.outboundBuffer.Release() // don't bother to write to a connection with some unknown error
-			return el.close(c, io.EOF)
-		}
-		// Secondly, check for EPOLLOUT before EPOLLIN, the former has a higher priority
-		// than the latter regardless of the aliveness of the current connection:
-		//
-		// 1. When the connection is alive and the system is overloaded, we want to
-		// offload the incoming traffic by writing all pending data back to the remotes
-		// before continuing to read and handle requests.
-		// 2. When the connection is dead, we need to try writing any pending data back
-		// to the remote and close the connection first.
-		//
-		// We perform eventloop.write for EPOLLOUT because it will take good care of either case.
-		if ev&(unix.EPOLLOUT|unix.EPOLLERR) != 0 {
-			if err := el.write(c); err != nil {
-				return err
-			}
-		}
-		// Check for EPOLLIN before EPOLLRDHUP in case that there are pending data in
-		// the socket buffer.
-		if ev&(unix.EPOLLIN|unix.EPOLLERR) != 0 {
-			if err := el.read(c); err != nil {
-				return err
-			}
-		}
-		// Ultimately, check for EPOLLRDHUP, this event indicates that the remote has
-		// either closed connection or shut down the writing half of the connection.
-		if ev&unix.EPOLLRDHUP != 0 && c.opened {
-			if ev&unix.EPOLLIN == 0 { // unreadable EPOLLRDHUP, close the connection directly
-				return el.close(c, io.EOF)
-			}
-			// Received the event of EPOLLIN | EPOLLRDHUP, but the previous eventloop.read
-			// failed to drain the socket buffer, so we make sure we get it done this time.
-			c.isEOF = true
-			return el.read(c)
-		}
-		return nil
+		return c.processIO(fd, ev, flags)
 	})
-
-	if err == errors.ErrEngineShutdown {
+	if errors.Is(err, errorx.ErrEngineShutdown) {
 		el.getLogger().Debugf("event-loop(%d) is exiting in terms of the demand from user, %v", el.idx, err)
 		err = nil
 	} else if err != nil {
@@ -130,52 +87,10 @@ func (el *eventloop) run() error {
 			// Somehow epoll notified with an event for a stale fd that is not in our connection set.
 			// We need to delete it from the epoll set.
 			return el.poller.Delete(fd)
-
-		}
-
-		// First check for any unexpected non-IO events.
-		// For these events we just close the corresponding connection directly.
-		if ev&netpoll.ErrEvents != 0 && ev&unix.EPOLLIN == 0 && ev&unix.EPOLLOUT == 0 {
-			c.outboundBuffer.Release() // don't bother to write to a connection with some unknown error
-			return el.close(c, io.EOF)
-		}
-		// Secondly, check for EPOLLOUT before EPOLLIN, the former has a higher priority
-		// than the latter regardless of the aliveness of the current connection:
-		//
-		// 1. When the connection is alive and the system is overloaded, we want to
-		// offload the incoming traffic by writing all pending data back to the remotes
-		// before continuing to read and handle requests.
-		// 2. When the connection is dead, we need to try writing any pending data back
-		// to the remote and close the connection first.
-		//
-		// We perform eventloop.write for EPOLLOUT because it will take good care of either case.
-		if ev&(unix.EPOLLOUT|unix.EPOLLERR) != 0 {
-			if err := el.write(c); err != nil {
-				return err
-			}
 		}
-		// Check for EPOLLIN before EPOLLRDHUP in case that there are pending data in
-		// the socket buffer.
-		if ev&(unix.EPOLLIN|unix.EPOLLERR) != 0 {
-			if err := el.read(c); err != nil {
-				return err
-			}
-		}
-		// Ultimately, check for EPOLLRDHUP, this event indicates that the remote has
-		// either closed connection or shut down the writing half of the connection.
-		if ev&unix.EPOLLRDHUP != 0 && c.opened {
-			if ev&unix.EPOLLIN == 0 { // unreadable EPOLLRDHUP, close the connection directly
-				return el.close(c, io.EOF)
-			}
-			// Received the event of EPOLLIN | EPOLLRDHUP, but the previous eventloop.read
-			// failed to drain the socket buffer, so we make sure we get it done this time.
-			c.isEOF = true
-			return el.read(c)
-		}
-		return nil
+		return c.processIO(fd, ev, flags)
 	})
-
-	if err == errors.ErrEngineShutdown {
+	if errors.Is(err, errorx.ErrEngineShutdown) {
 		el.getLogger().Debugf("event-loop(%d) is exiting in terms of the demand from user, %v", el.idx, err)
 		err = nil
 	} else if err != nil {
diff --git a/reactor_epoll_ultimate.go b/reactor_epoll_ultimate.go
index 49e1477ba..2fd3dd693 100644
--- a/reactor_epoll_ultimate.go
+++ b/reactor_epoll_ultimate.go
@@ -18,9 +18,10 @@
 package gnet
 
 import (
+	"errors"
 	"runtime"
 
-	"github.com/panjf2000/gnet/v2/pkg/errors"
+	errorx "github.com/panjf2000/gnet/v2/pkg/errors"
 )
 
 func (el *eventloop) rotate() error {
@@ -30,7 +31,7 @@ func (el *eventloop) rotate() error {
 	}
 
 	err := el.poller.Polling()
-	if err == errors.ErrEngineShutdown {
+	if errors.Is(err, errorx.ErrEngineShutdown) {
 		el.getLogger().Debugf("main reactor is exiting in terms of the demand from user, %v", err)
 		err = nil
 	} else if err != nil {
@@ -49,7 +50,7 @@ func (el *eventloop) orbit() error {
 	}
 
 	err := el.poller.Polling()
-	if err == errors.ErrEngineShutdown {
+	if errors.Is(err, errorx.ErrEngineShutdown) {
 		el.getLogger().Debugf("event-loop(%d) is exiting in terms of the demand from user, %v", el.idx, err)
 		err = nil
 	} else if err != nil {
@@ -69,7 +70,7 @@ func (el *eventloop) run() error {
 	}
 
 	err := el.poller.Polling()
-	if err == errors.ErrEngineShutdown {
+	if errors.Is(err, errorx.ErrEngineShutdown) {
 		el.getLogger().Debugf("event-loop(%d) is exiting in terms of the demand from user, %v", el.idx, err)
 		err = nil
 	} else if err != nil {
diff --git a/reactor_kqueue_default.go b/reactor_kqueue_default.go
index 19ca75602..7426c74e0 100644
--- a/reactor_kqueue_default.go
+++ b/reactor_kqueue_default.go
@@ -19,13 +19,11 @@
 package gnet
 
 import (
-	"io"
+	"errors"
 	"runtime"
 
-	"golang.org/x/sys/unix"
-
 	"github.com/panjf2000/gnet/v2/internal/netpoll"
-	"github.com/panjf2000/gnet/v2/pkg/errors"
+	errorx "github.com/panjf2000/gnet/v2/pkg/errors"
 )
 
 func (el *eventloop) rotate() error {
@@ -35,7 +33,7 @@ func (el *eventloop) rotate() error {
 	}
 
 	err := el.poller.Polling(el.accept0)
-	if err == errors.ErrEngineShutdown {
+	if errors.Is(err, errorx.ErrEngineShutdown) {
 		el.getLogger().Debugf("main reactor is exiting in terms of the demand from user, %v", err)
 		err = nil
 	} else if err != nil {
@@ -53,46 +51,18 @@ func (el *eventloop) orbit() error {
 		defer runtime.UnlockOSThread()
 	}
 
-	err := el.poller.Polling(func(fd int, filter netpoll.IOEvent, flags netpoll.IOFlags) (err error) {
+	err := el.poller.Polling(func(fd int, filter netpoll.IOEvent, flags netpoll.IOFlags) error {
 		c := el.connections.getConn(fd)
 		if c == nil {
 			// This might happen when the connection has already been closed,
 			// the file descriptor will be deleted from kqueue automatically
 			// as documented in the manual pages, So we just print a warning log.
 			el.getLogger().Warnf("received event[fd=%d|filter=%d|flags=%d] of a stale connection from event-loop(%d)", fd, filter, flags, el.idx)
-			return
-		}
-
-		switch filter {
-		case unix.EVFILT_READ:
-			err = el.read(c)
-		case unix.EVFILT_WRITE:
-			err = el.write(c)
-		}
-		// EV_EOF indicates that the remote has closed the connection.
-		// We check for EV_EOF after processing the read/write event
-		// to ensure that nothing is left out on this event filter.
-		if flags&unix.EV_EOF != 0 && c.opened && err == nil {
-			switch filter {
-			case unix.EVFILT_READ:
-				// Receive the event of EVFILT_READ | EV_EOF, but the previous eventloop.read
-				// failed to drain the socket buffer, so we make sure we get it done this time.
-				c.isEOF = true
-				err = el.read(c)
-			case unix.EVFILT_WRITE:
-				// On macOS, the kqueue in both LT and ET mode will notify with one event for the EOF
-				// of the TCP remote: EVFILT_READ|EV_ADD|EV_CLEAR|EV_EOF. But for some reason, two
-				// events will be issued in ET mode for the EOF of the Unix remote in this order:
-				// 1) EVFILT_WRITE|EV_ADD|EV_CLEAR|EV_EOF, 2) EVFILT_READ|EV_ADD|EV_CLEAR|EV_EOF.
-				err = el.write(c)
-			default:
-				c.outboundBuffer.Release() // don't bother to write to a connection with some unknown error
-				err = el.close(c, io.EOF)
-			}
+			return nil
 		}
-		return
+		return c.processIO(fd, filter, flags)
 	})
-	if err == errors.ErrEngineShutdown {
+	if errors.Is(err, errorx.ErrEngineShutdown) {
 		el.getLogger().Debugf("event-loop(%d) is exiting in terms of the demand from user, %v", el.idx, err)
 		err = nil
 	} else if err != nil {
@@ -111,7 +81,7 @@ func (el *eventloop) run() error {
 		defer runtime.UnlockOSThread()
 	}
 
-	err := el.poller.Polling(func(fd int, filter netpoll.IOEvent, flags netpoll.IOFlags) (err error) {
+	err := el.poller.Polling(func(fd int, filter netpoll.IOEvent, flags netpoll.IOFlags) error {
 		c := el.connections.getConn(fd)
 		if c == nil {
 			if _, ok := el.listeners[fd]; ok {
@@ -121,39 +91,11 @@ func (el *eventloop) run() error {
 			// the file descriptor will be deleted from kqueue automatically
 			// as documented in the manual pages, So we just print a warning log.
 			el.getLogger().Warnf("received event[fd=%d|filter=%d|flags=%d] of a stale connection from event-loop(%d)", fd, filter, flags, el.idx)
-			return
-		}
-
-		switch filter {
-		case unix.EVFILT_READ:
-			err = el.read(c)
-		case unix.EVFILT_WRITE:
-			err = el.write(c)
-		}
-		// EV_EOF indicates that the remote has closed the connection.
-		// We check for EV_EOF after processing the read/write event
-		// to ensure that nothing is left out on this event filter.
-		if flags&unix.EV_EOF != 0 && c.opened && err == nil {
-			switch filter {
-			case unix.EVFILT_READ:
-				// Receive the event of EVFILT_READ | EV_EOF, but the previous eventloop.read
-				// failed to drain the socket buffer, so we make sure we get it done this time.
-				c.isEOF = true
-				err = el.read(c)
-			case unix.EVFILT_WRITE:
-				// On macOS, the kqueue in both LT and ET mode will notify with one event for the EOF
-				// of the TCP remote: EVFILT_READ|EV_ADD|EV_CLEAR|EV_EOF. But for some reason, two
-				// events will be issued in ET mode for the EOF of the Unix remote in this order:
-				// 1) EVFILT_WRITE|EV_ADD|EV_CLEAR|EV_EOF, 2) EVFILT_READ|EV_ADD|EV_CLEAR|EV_EOF.
-				err = el.write(c)
-			default:
-				c.outboundBuffer.Release() // don't bother to write to a connection with some unknown error
-				err = el.close(c, io.EOF)
-			}
+			return nil
 		}
-		return
+		return c.processIO(fd, filter, flags)
 	})
-	if err == errors.ErrEngineShutdown {
+	if errors.Is(err, errorx.ErrEngineShutdown) {
 		el.getLogger().Debugf("event-loop(%d) is exiting in terms of the demand from user, %v", el.idx, err)
 		err = nil
 	} else if err != nil {
diff --git a/reactor_kqueue_ultimate.go b/reactor_kqueue_ultimate.go
index e09c296df..93b998625 100644
--- a/reactor_kqueue_ultimate.go
+++ b/reactor_kqueue_ultimate.go
@@ -19,9 +19,10 @@
 package gnet
 
 import (
+	"errors"
 	"runtime"
 
-	"github.com/panjf2000/gnet/v2/pkg/errors"
+	errorx "github.com/panjf2000/gnet/v2/pkg/errors"
 )
 
 func (el *eventloop) rotate() error {
@@ -31,7 +32,7 @@ func (el *eventloop) rotate() error {
 	}
 
 	err := el.poller.Polling()
-	if err == errors.ErrEngineShutdown {
+	if errors.Is(err, errorx.ErrEngineShutdown) {
 		el.getLogger().Debugf("main reactor is exiting in terms of the demand from user, %v", err)
 		err = nil
 	} else if err != nil {
@@ -50,7 +51,7 @@ func (el *eventloop) orbit() error {
 	}
 
 	err := el.poller.Polling()
-	if err == errors.ErrEngineShutdown {
+	if errors.Is(err, errorx.ErrEngineShutdown) {
 		el.getLogger().Debugf("event-loop(%d) is exiting in terms of the demand from user, %v", el.idx, err)
 		err = nil
 	} else if err != nil {
@@ -70,7 +71,7 @@ func (el *eventloop) run() error {
 	}
 
 	err := el.poller.Polling()
-	if err == errors.ErrEngineShutdown {
+	if errors.Is(err, errorx.ErrEngineShutdown) {
 		el.getLogger().Debugf("event-loop(%d) is exiting in terms of the demand from user, %v", el.idx, err)
 		err = nil
 	} else if err != nil {