阻塞IO下的echo实验

代码分析

echo代码位置：recipes-master/tpc/echo.cc echo_client.cc
服务端代码

int main(int argc, char* argv[])
{InetAddress listenAddr(3007);Acceptor acceptor(listenAddr);printf("Accepting... Ctrl-C to exit\n");int count = 0;bool nodelay = argc > 1 && strcmp(argv[1], "-D") == 0;while (true){TcpStreamPtr tcpStream = acceptor.accept();printf("accepted no. %d client\n", ++count);if (nodelay)tcpStream->setTcpNoDelay(true);// 一个线程处理一个客户端连接// C++11 doesn't allow capturing unique_ptr in lambda, C++14 allows.std::thread thr([count] (TcpStreamPtr stream) {printf("thread for no. %d client started.\n", count);char buf[4096];int nr = 0;while ( (nr = stream->receiveSome(buf, sizeof(buf))) > 0){int nw = stream->sendAll(buf, nr);if (nw < nr){break;}}printf("thread for no. %d client ended.\n", count);}, std::move(tcpStream));thr.detach();}
}

服务端的逻辑主要就是，建立连接，每次读取4096个字节，然后这些数据再返回给客户端。

客户端

int main(int argc, const char* argv[])
{if (argc < 3){printf("Usage: %s hostname message_length [scp]\n", argv[0]);return 0;}const int len = atoi(argv[2]);InetAddress addr(3007);if (!InetAddress::resolve(argv[1], &addr)){printf("Unable to resolve %s\n", argv[1]);return 0;}printf("connecting to %s\n", addr.toIpPort().c_str());TcpStreamPtr stream(TcpStream::connect(addr));if (!stream){printf("Unable to connect %s\n", addr.toIpPort().c_str());perror("");return 0;}printf("connected, sending %d bytes\n", len);// 发送数据std::string message(len, 'S');int nw = stream->sendAll(message.c_str(), message.size());printf("sent %d bytes\n", nw);if (argc > 3){for (char cmd : std::string(argv[3])){if (cmd == 's')  // shutdown{printf("shutdown write\n");stream->shutdownWrite();}else if (cmd == 'p') // pause{printf("sleeping for 10 seconds\n");::sleep(10);printf("done\n");}else if (cmd == 'c') // close{printf("close without reading response\n");return 0;}else{printf("unknown command '%c'\n", cmd);}}}// 返回数据std::vector<char> receive(len);int nr = stream->receiveAll(receive.data(), receive.size());printf("received %d bytes\n", nr);if (nr != nw){printf("!!! Incomplete response !!!\n");}
}

客户端的逻辑主要就是，建立连接，发送数据，数据发送完再接收读取返回的数据。

测试

客户端在测试20m的数据时出现了阻塞，此时服务端也阻塞当中

[wang@localhost tpc]$ ./echo_client ip 2048000
connecting to 192.168.1.104:3007
connected, sending 2048000 bytes
# ... 客户端阻塞

[wang@localhost tpc]$ ./echo
Accepting... Ctrl-C to exit
accepted no. 1 client
thread for no. 1 client started.
# ... 服务端阻塞

排查问题

查看Recv-Q和Send-Q

服务端

[wang@localhost ~]$ netstat -tpn | grep '3007\|^[AP]'
(Not all processes could be identified, non-owned process infowill not be shown, you would have to be root to see it all.)
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp   536080 260640 192.168.1.104:3007      192.168.1.105:56412     ESTABLISHED 5985/./ech

客户端

[wang@localhost ~]$ netstat -tpn | grep '3007\|^[AP]'
(Not all processes could be identified, non-owned process infowill not be shown, you would have to be root to see it all.)
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp   261264 307992 192.168.1.105:56412     192.168.1.104:3007      ESTABLISHED 12526/./echo_client