opt: only enable SO_REUSEPORT on Linux and FreeBSD (#580)

Fixes #579

gnet.go

@@ -18,6 +18,7 @@ import (
 	"context"
 	"io"
 	"net"
+	"runtime"
 	"strings"
 	"sync"
 	"time"
@@ -463,6 +464,23 @@ func createListeners(addrs []string, opts ...Option) ([]*listener, *Options, err
 		options.WriteBufferCap = math.CeilToPowerOfTwo(wbc)
 	}
 
+	// SO_REUSEPORT enables duplicate address and port bindings across various
+	// Unix-like OSs, whereas there is platform-specific inconsistency:
+	// Linux implemented SO_REUSEPORT with load balancing for incoming connections
+	// while *BSD implemented it for only binding to the same address and port, which
+	// makes it pointless to enable SO_REUSEPORT on *BSD and Darwin for gnet with
+	// multiple event-loops because only the first event-loop will be constantly woken
+	// up to accept incoming connections and handle I/O events while the rest of event
+	// loops remain idle.
+	// Thus, we disable SO_REUSEPORT on *BSD and Darwin by default.
+	//
+	// Note that FreeBSD 12 introduced a new socket option named SO_REUSEPORT_LB
+	// with the capability of load balancing, it's the equivalent of Linux's SO_REUSEPORT.
+	goos := runtime.GOOS
+	if (options.Multicore || options.NumEventLoop > 1) && options.ReusePort && goos != "linux" && goos != "freebsd" {
+		options.ReusePort = false
+	}
+
 	// If there is UDP listener in the list, enable SO_REUSEPORT and disable edge-triggered I/O by default.
 	for i := 0; (!options.ReusePort || options.EdgeTriggeredIO) && i < len(addrs); i++ {
 		proto, _, err := parseProtoAddr(addrs[i])

internal/socket/sockopts_freebsd.go

@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2024 The Gnet Authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package socket
+
+import (
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+// SetReuseport enables SO_REUSEPORT_LB option on socket.
+func SetReuseport(fd, reusePort int) error {
+	return os.NewSyscallError("setsockopt", unix.SetsockoptInt(fd, unix.SOL_SOCKET, unix.SO_REUSEPORT_LB, reusePort))
+}

internal/socket/sockopts_posix.go

@@ -48,11 +48,6 @@ func SetSendBuffer(fd, size int) error {
 	return unix.SetsockoptInt(fd, unix.SOL_SOCKET, unix.SO_SNDBUF, size)
 }
 
-// SetReuseport enables SO_REUSEPORT option on socket.
-func SetReuseport(fd, reusePort int) error {
-	return os.NewSyscallError("setsockopt", unix.SetsockoptInt(fd, unix.SOL_SOCKET, unix.SO_REUSEPORT, reusePort))
-}
-
 // SetReuseAddr enables SO_REUSEADDR option on socket.
 func SetReuseAddr(fd, reuseAddr int) error {
 	return os.NewSyscallError("setsockopt", unix.SetsockoptInt(fd, unix.SOL_SOCKET, unix.SO_REUSEADDR, reuseAddr))

internal/socket/sockopts_unix1.go

@@ -0,0 +1,29 @@
+// Copyright (c) 2021 The Gnet Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build linux || dragonfly || netbsd || openbsd || darwin
+// +build linux dragonfly netbsd openbsd darwin
+
+package socket
+
+import (
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+// SetReuseport enables SO_REUSEPORT option on socket.
+func SetReuseport(fd, reusePort int) error {
+	return os.NewSyscallError("setsockopt", unix.SetsockoptInt(fd, unix.SOL_SOCKET, unix.SO_REUSEPORT, reusePort))
+}