從套接字接收線程中的消息

Question

我正在編寫套接字程序並在線程中接收消息。 但是我遇到了細分錯誤。 當我直接接收而不啟動線程時，就沒有這樣的問題（顯示在注釋部分）。

在下面的代碼中，我直接接收並將其發送給客戶端。部分代碼如下所示：

if (acceptor->start() == 0)
    {
        while (1)
        {
            stream = acceptor->accept();
            if (stream != NULL)
            {
                /*
                ssize_t len;
                char line[256];
                while ((len = stream->receive(line, sizeof(line))) > 0) {
                    line[len] = 0;
                    printf("received - %s\n", line);
                    stream->send(line, len);
                */    
                pthread_t sniffer_thread;
                if( pthread_create( &sniffer_thread, NULL, connection_handler,NULL) < 0)
                {
                     perror("could not create thread");
                     return 1;
                }
                //Now join the thread , so that we dont terminate before the thread
                pthread_join( sniffer_thread , NULL);
             }
                delete stream;
          }
       }
    exit(0);

現在，我在線程函數中收到了同樣的消息。 顯示分段錯誤。

代碼如下所示。

void *connection_handler(void *arg)
{
    TCPStream* stream = NULL;
    ssize_t len;
    char line[256];
    while ((len = stream->receive(line, sizeof(line))) > 0)
    {
        line[len] = 0;
        printf("received - %s\n", line);
        stream->send(line, len);
    }
}

Valgrind輸出的一部分是

==5163== Memcheck, a memory error detector
==5163== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==5163== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info
==5163== Command: ./appdownload 9999 192.5.60
==5163== 
==5163== Thread 2:
==5163== Invalid read of size 4
==5163==    at 0x401975: TCPStream::receive(char*, unsigned long, int) (tcpstream.cpp:30)
==5163==    by 0x40177B: connection_handler(void*) (appdownload.cpp:68)
==5163==    by 0x4E3F181: start_thread (pthread_create.c:312)
==5163==    by 0x566947C: clone (clone.S:111)
==5163==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
==5163== 
==5163== 
==5163== Process terminating with default action of signal 11 (SIGSEGV)
==5163==  Access not within mapped region at address 0x0
==5163==    at 0x401975: TCPStream::receive(char*, unsigned long, int) (tcpstream.cpp:30)
==5163==    by 0x40177B: connection_handler(void*) (appdownload.cpp:68)
==5163==    by 0x4E3F181: start_thread (pthread_create.c:312)
==5163==    by 0x566947C: clone (clone.S:111)
==5163==  If you believe this happened as a result of a stack
==5163==  overflow in you`enter code here`r program's main thread (unlikely but
==5163==  possible), you can try to increase the size of the
==5163==  main thread stack using the --main-stacksize= flag.
==5163==  The main thread stack size used in this run was 8388608.

Answer 1

TCPStream* stream = NULL; // HERE
ssize_t len;
char line[256];
while ((len = stream->receive(line, sizeof(line))) > 0) // HERE

您在NULL指針上調用receive 。 Valgrind告訴您：

==5163== Thread 2:
==5163== Invalid read of size 4
==5163==    at 0x401975: TCPStream::receive(char*, unsigned long, int) (tcpstream.cpp:30) // HERE
==5163==    by 0x40177B: connection_handler(void*) (appdownload.cpp:68)
==5163==    by 0x4E3F181: start_thread (pthread_create.c:312)
==5163==    by 0x566947C: clone (clone.S:111)
==5163==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
              //  ^- HERE

如果需要將TCPStream*從主線程傳遞到新線程函數，則可以使用pthread_create第4個參數：

pthread_create（）函數在調用過程中啟動一個新線程。 新線程通過調用start_routine（）開始執行。 arg作為start_routine（）的唯一參數傳遞。 （來源： man pthread_create ）

主線程：

TCPStream *stream = acceptor->accept();
(...)
pthread_create( &sniffer_thread, NULL, connection_handler, stream)
                                                      //   ^^^^^^

工作線程：

void *connection_handler(void *arg)
{
    TCPStream* stream = (TCPStream *)arg;
    //                  ^^^^^^^^^^^^^^^^

Answer 2

顯示了valgrind跟蹤之后，很明顯，您只是在null指針上調用了receive 。

---

嗯，讓我們看看。

char line[256];                                              // 256 bytes space
while ((len = stream->receive(line, sizeof(line))) > 0)      // receive up to 256 bytes
{
    line[len] = 0;                                           // put 257th byte in

我猜您可能會再為0使用一個字節-嘗試接收最大為sizeof(line)-1字節。

或僅使用std::vector ，然后push_back 0。