Add channel_->tie() in Connector::connecting() to fix lifetime safety

[Louisyoung7]

Fix: Add channel_->tie() in Connector::connecting()

Problem

The FIXME comments in Connector::connecting() indicate potential dangling
pointer issues when Channel callbacks execute:

// channel_->tie(shared_from_this()); is not working,
// as channel_ is not managed by shared_ptr

If Connector is destroyed while Channel is handling events, callbacks like
handleWrite() / handleError() would access a dangling this pointer.

Solution

Since TcpClient manages Connector via shared_ptr<Connector> and Connector
inherits std::enable_shared_from_this, we can safely call
channel_->tie(shared_from_this()) to extend Connector's lifetime until
Channel finishes handling events.

Testing

Regression tests pass:
louis@louis-VMware-Virtual-Platform:~/OpenSourceProjects/Net/muduo/build$ cd /home/louis/OpenSourceProjects/Net/muduo/build && ./bin/tcpclient_reg1 2>&1
20260509 09:09:21.672204Z 606126 INFO TcpClient::TcpClient[TcpClient] - connector 0x64BC591356F0 - TcpClient.cc:60
20260509 09:09:21.672236Z 606126 INFO TcpClient::connect[TcpClient] - connecting to 127.0.0.1:2 - TcpClient.cc:87
20260509 09:09:21.772421Z 606126 WARN fd = 6 Channel::handle_event() POLLHUP - Channel.cc:71
20260509 09:09:21.772446Z 606126 ERROR Connector::handleError state=1 - Connector.cc:166
20260509 09:09:21.772470Z 606126 INFO Connector::retry - Retry connecting to 127.0.0.1:2 in 500 milliseconds. - Connector.cc:179
20260509 09:09:21.772532Z 606126 INFO timeout - TcpClient_reg1.cc:14
20260509 09:09:22.672373Z 606126 INFO TcpClient::TcpClient[TcpClient] - connector 0x64BC591356F0 - TcpClient.cc:64
louis@louis-VMware-Virtual-Platform:/OpenSourceProjects/Net/muduo/build$ cd /home/louis/OpenSourceProjects/Net/muduo/build && ./bin/tcpclient_reg2 2>&1 && ./bin/tcpclient_reg3 2>&1
20260509 09:09:27.463890Z 606556 DEBUG EventLoop EventLoop created 0x7FFE710C1DB0 in thread 606556 - EventLoop.cc:77
20260509 09:09:27.464049Z 606557 DEBUG Connector ctor[0x7D4594000B80] - Connector.cc:26
20260509 09:09:27.464066Z 606557 INFO TcpClient::TcpClient[TcpClient] - connector 0x7D4594000B80 - TcpClient.cc:60
20260509 09:09:27.464068Z 606557 INFO TcpClient::connect[TcpClient] - connecting to 127.0.0.1:1234 - TcpClient.cc:87
20260509 09:09:27.464160Z 606556 WARN fd = 6 Channel::handle_event() POLLHUP - Channel.cc:71
20260509 09:09:27.464176Z 606556 ERROR Connector::handleError state=1 - Connector.cc:166
20260509 09:09:27.464190Z 606556 INFO Connector::retry - Retry connecting to 127.0.0.1:1234 in 500 milliseconds. - Connector.cc:179
20260509 09:09:27.964343Z 606556 WARN fd = 6 Channel::handle_event() POLLHUP - Channel.cc:71
20260509 09:09:27.964366Z 606556 ERROR Connector::handleError state=1 - Connector.cc:166
20260509 09:09:27.964380Z 606556 INFO Connector::retry - Retry connecting to 127.0.0.1:1234 in 1000 milliseconds. - Connector.cc:179
20260509 09:09:28.464158Z 606557 INFO TcpClient::~TcpClient[TcpClient] - connector 0x7D4594000B80 - TcpClient.cc:64
20260509 09:09:28.964432Z 606556 DEBUG startInLoop do not connect - Connector.cc:45
20260509 09:09:29.464367Z 606556 DEBUG ~Connector dtor[0x7D4594000B80] - Connector.cc:30
20260509 09:09:30.463957Z 606556 DEBUG ~EventLoop EventLoop 0x7FFE710C1DB0 of thread 606556 destructs in thread 606556 - EventLoop.cc:95
20260509 09:09:30.466203Z 606723 DEBUG EventLoop EventLoop created 0x7650EC5EE980 in thread 606723 - EventLoop.cc:77
20260509 09:09:30.466287Z 606722 DEBUG Connector ctor[0x5B761DAA24B0] - Connector.cc:26
20260509 09:09:30.466312Z 606722 INFO TcpClient::TcpClient[TcpClient] - connector 0x5B761DAA24B0 - TcpClient.cc:60
20260509 09:09:30.466322Z 606722 INFO TcpClient::connect[TcpClient] - connecting to 127.0.0.1:1234 - TcpClient.cc:87
20260509 09:09:30.466413Z 606723 WARN fd = 6 Channel::handle_event() POLLHUP - Channel.cc:71
20260509 09:09:30.466424Z 606723 ERROR Connector::handleError state=1 - Connector.cc:166
20260509 09:09:30.466436Z 606723 INFO Connector::retry - Retry connecting to 127.0.0.1:1234 in 500 milliseconds. - Connector.cc:179
20260509 09:09:30.966427Z 606722 INFO TcpClient::~TcpClient[TcpClient] - connector 0x5B761DAA24B0 - TcpClient.cc:64
20260509 09:09:30.966583Z 606723 DEBUG startInLoop do not connect - Connector.cc:45
20260509 09:09:31.966521Z 606723 DEBUG ~Connector dtor[0x5B761DAA24B0] - Connector.cc:30
20260509 09:09:31.966588Z 606723 DEBUG ~EventLoop EventLoop 0x7650EC5EE980 of thread 606723 destructs in thread 606723 - EventLoop.cc:95

Diff

diff --git a/muduo/net/Connector.cc b/muduo/net/Connector.cc
index 0b492ad..3fb947f 100644
--- a/muduo/net/Connector.cc
+++ b/muduo/net/Connector.cc
@@ -130,10 +130,11 @@ void Connector::connecting(int sockfd)
   setState(kConnecting);
   assert(!channel_);
   channel_.reset(new Channel(loop_, sockfd));
+  channel_->tie(shared_from_this());
   channel_->setWriteCallback(
-      std::bind(&Connector::handleWrite, this)); // FIXME: unsafe
+      std::bind(&Connector::handleWrite, this));
   channel_->setErrorCallback(
-      std::bind(&Connector::handleError, this)); // FIXME: unsafe
+      std::bind(&Connector::handleError, this));
 
   // channel_->tie(shared_from_this()); is not working,
   // as channel_ is not managed by shared_ptr
@@ -146,7 +147,7 @@ int Connector::removeAndResetChannel()
   channel_->remove();
   int sockfd = channel_->fd();
   // Can't reset channel_ here, because we are inside Channel::handleEvent
-  loop_->queueInLoop(std::bind(&Connector::resetChannel, this)); // FIXME: unsafe
+  loop_->queueInLoop(std::bind(&Connector::resetChannel, this));
   return sockfd;
 }