From 236fe841100ef0ee1feee2fa84d440ee6e74b04c Mon Sep 17 00:00:00 2001
From: GouJie <507762441@qq.com>
Date: Sat, 20 Jan 2024 00:17:15 +0800
Subject: [PATCH] bugfix: Resolved a concurrency issue with ClientCounter.
 Previously, directly decrementing ClientCounter in multiple goroutines
 (ClientCounter--) could lead to data races and inconsistencies. Now, by using
 atomic.AddInt32(&ClientCounter, -1), we ensure safe updates to the counter,
 maintaining its accuracy and stability even in high concurrency scenarios.

---
 tcp/echo_test.go | 35 +++++++++++++++++++++++++++++++++++
 tcp/server.go    |  5 +++--
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/tcp/echo_test.go b/tcp/echo_test.go
index 1bc211c8..ef2bd5cc 100644
--- a/tcp/echo_test.go
+++ b/tcp/echo_test.go
@@ -51,3 +51,38 @@ func TestListenAndServe(t *testing.T) {
 	closeChan <- struct{}{}
 	time.Sleep(time.Second)
 }
+
+func TestClientCounter(t *testing.T) {
+	var err error
+	closeChan := make(chan struct{})
+	listener, err := net.Listen("tcp", ":0")
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	addr := listener.Addr().String()
+	go ListenAndServe(listener, MakeEchoHandler(), closeChan)
+
+	sleepUntil := time.Now().Add(3 * time.Second)
+	subtime := func() time.Duration {
+		return sleepUntil.Sub(time.Now())
+	}
+
+	for i := 0; i < 1000; i++ {
+		go func() {
+			conn, err := net.Dial("tcp", addr)
+			if err != nil {
+				t.Errorf(err.Error())
+			}
+			defer conn.Close()
+
+			time.Sleep(subtime())
+		}()
+		time.Sleep(5 * time.Microsecond)
+	}
+
+	time.Sleep(3 * time.Second)
+	if ClientCounter != 0 {
+		t.Errorf("client counter error: %d", ClientCounter)
+	}
+}
diff --git a/tcp/server.go b/tcp/server.go
index e381de17..b74de25d 100644
--- a/tcp/server.go
+++ b/tcp/server.go
@@ -11,6 +11,7 @@ import (
 	"os"
 	"os/signal"
 	"sync"
+	"sync/atomic"
 	"syscall"
 	"time"
 
@@ -26,7 +27,7 @@ type Config struct {
 }
 
 // ClientCounter Record the number of clients in the current Godis server
-var ClientCounter int
+var ClientCounter int32
 
 // ListenAndServeWithSignal binds port and handle requests, blocking until receive stop signal
 func ListenAndServeWithSignal(cfg *Config, handler tcp.Handler) error {
@@ -88,7 +89,7 @@ func ListenAndServe(listener net.Listener, handler tcp.Handler, closeChan <-chan
 		go func() {
 			defer func() {
 				waitDone.Done()
-				ClientCounter--
+				atomic.AddInt32(&ClientCounter, -1)
 			}()
 			handler.Handle(ctx, conn)
 		}()