Question

当我在socket()内调用std::thread()时，它返回套接字描述符1.调用std::cout而不是将终端文本发送到服务器。当我在调用cout << "";之前添加socket()时，会创建stdin / out / err for的描述符，socket()将返回3.

来自http://www.cplusplus.com/reference/iostream/cout/：

就静态初始化顺序而言，cout保证在不晚于第一次构造ios_base::Init类型的对象的情况下正确构造和初始化，并包含<iostream>计为具有静态持续时间的此类对象的至少一次初始化。

默认情况下，cout与stdout同步（请参阅ios_base::sync_with_stdio）。

std::cout应该已经初始化并同步到stdout，这解释了为什么std::cout将消息发送到服务器而不是终端。

我想知道调用std::thread()是否关闭新线程中的stdin / out / err描述符，或者这些描述符是否存在于线程中，因为线程没有创建通过终端或initd？

我使用GCC 4.8.2在RHEL 6.4上运行。我已在下面添加了我的客户端代码，并附加了cout << "";已注明完整性。

Client.cpp：

#include "Client.hpp"

#include <cstdlib>
#include <cstring>
#include <iostream>
#include <thread>
#include <vector>
#include <algorithm>
#include <sstream>
#include <functional>

#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <unistd.h>

using namespace std;

Client::Client( const string& hostname, const string& port ) {
    this->hostname = hostname;
    this->port = port;
}

Client::~Client() { close( fd ); }

void Client::operator()() {
    struct addrinfo hints;
    memset( &hints, 0, sizeof( struct addrinfo ) );

    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_flags = 0;
    hints.ai_protocol = 0;

    struct addrinfo *result;
    int ret = getaddrinfo( hostname.c_str(), port.c_str(), &hints, &result );
    if( ret != 0) {
        cerr << "getaddrinfo failed: " << gai_strerror( ret ) << endl;
        return;
    }

    // cout << ""; // prevents socket() from returning 1 and redefining cout

    struct addrinfo *rp = NULL;
    for( rp = result; rp != NULL; rp = rp->ai_next ) {
        fd = socket( rp->ai_family, rp->ai_socktype, rp->ai_protocol );
        if( fd == -1 ) {
            continue;   /* Error */
        }

        if( connect( fd, rp->ai_addr, rp->ai_addrlen ) != -1) {
            break;      /* Success */
        }

        close( fd );        /* Try again */
    }

    if( rp == NULL ) {
        cerr << "Failed to connect to " << hostname << ":" << port << endl;
        return;
    }

    freeaddrinfo( result );

    cout << "Starting echo client" << endl;

    int i = 0;
    do {
        stringstream ss;
        ss << "Thread " << this_thread::get_id() << ": Message #" << ++i;
        string str = ss.str();

        _send( str.c_str() );
        string msg = _recv();

        //cout << "Thread " << this_thread::get_id() << " received message: " << msg << endl;
    } while ( i < 10 );

    cout << "Stopping echo client" << endl;

    close( fd );
}

string Client::_recv( ) const {
    const int BUF_SIZE = 1024;
    char* buf = ( char * ) malloc( sizeof( char) * BUF_SIZE );
    memset( buf, '\0', sizeof( char ) * BUF_SIZE );

    int bytes = recv( fd, buf, BUF_SIZE, 0 );
    if( bytes < 0 ) {
        perror( "recv failed" );
    }

    string msg = string( buf );

    free( buf );

    return msg;
}

void Client::_send( const string buf ) const {
    if( send( fd, buf.c_str(), buf.length(), 0 ) < 0 ) {
        perror( "send failed" );
    }
}
void usage() {
    cerr << "Usage: client <hostname> <port>" << endl;
    cerr << "   hostname - server name listening for incoming connctions" << endl;
    cerr << "   port - internet port to listen for connections from" << endl;
}

int main( int argc, char* argv[] ) {
    if( argc < 3 ) {
        cerr << "Not enough arguments!" << endl;
        usage();
        return EXIT_FAILURE;
    }

    vector<thread> clients;
    for( int i = 0; i < 1; i++ ) {
        clients.push_back( thread( ( Client( argv[1], argv[2] ) ) ) );
    }

    for_each( clients.begin(), clients.end(), mem_fn( &thread::join ) );

    return EXIT_SUCCESS;
}

Client.hpp：

#ifndef __CLIENT_HPP__
#define __CLIENT_HPP__

#include <string>

class Client {
    private:
        int fd;
        std::string hostname;
        std::string port;
        std::string _recv( ) const;
        void _send( const std::string buf ) const;

    public:
        Client( const std::string& hostname, const std::string& port);
        ~Client();
        void operator()();
};

#endif

Answer 1

如果您不小心关闭了stdout，通常会发生这种情况，即存在虚假的close(1);。那么FD将合法地成为1号。这可能在程序的其他地方。

我已多次这样做，通常会在gdb找到并在close()设置断点。

你的析构函数看起来很可疑：

Client::~Client() { close( fd ); }

您不应该在构造函数中将fd设置为-1，并在关闭它的任何其他位置小心地将fd设置为-1，而不是这样做如果fd==-1关闭？目前创建Client并销毁它将关闭随机fd。

socket（）在std :: thread中返回文件描述符1

1 个答案: