当同一进程使用 FIFO 的两端时无法重新打开 FIFO

Question

在单个进程上使用 FIFO 时，看起来两端打开后关闭，无法重复使用 FIFO。任何重新打开封闭端的尝试都失败或返回的文件描述符无用。

是否可以解决此问题，或者我们是否必须保持 FIFO 的两端打开，直到我们完全确定不再需要它为止？

下面是一些测试代码，显示并尝试重新打开 FIFO 的关闭写入端：

#include <iostream>
#include <cstdio>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

using namespace std;

int main(int argc, const char **argv)
{
      cout << "Creating an instance of a named pipe..." << endl;
      mode_t prevMask = umask(0);
      if (mknod("my_pipe", S_IFIFO | 0666, 0))
         return -1;
      umask(prevMask);

      cout << "Opening Read end..." << endl;
      int fdM = open("my_pipe", O_RDONLY | O_NONBLOCK);
      if (fdM == -1)
         return -1;

      cout << "Opening Write end..." << endl;
      int fdS = open("my_pipe", O_WRONLY | O_NONBLOCK);
      if (fdS == -1)
         return -1;

      cout << "Sending data to pipe..." << endl;
      const char *data = "Hello my friend!";
      ssize_t NbOfBytesWritten = write(fdS, data, strlen(data));
      if (NbOfBytesWritten < 0)
         return -1;
      cout << "Number of bytes sent: " << NbOfBytesWritten << endl;

      cout << "Closing Write end..." << endl;
      if (close(fdS))
         return -1;

      cout << "Reopening Write end..." << endl;
      fdS = open("my_pipe", O_WRONLY | O_NONBLOCK);
      if (fdS == -1)
      {
         cout << "open() - failed("<< errno << "): " << strerror(errno) << '.';
         remove("my_pipe");
         return -1;
      }

      cout << "Sending some more data to pipe..." << endl;
      data = "What's up?";
      NbOfBytesWritten = write(fdS, data, strlen(data));
      if (NbOfBytesWritten < 0)
         return -1;
      cout << "Number of bytes sent: " << NbOfBytesWritten << endl;

      cout << "Reading data from pipe..." << endl;
      char buff[128];
      ssize_t numBytesRead = read(fdM, buff, 127);
      if (NbOfBytesWritten < 0)
         return -1;
      buff[numBytesRead] = '[=10=]'; // null terminate the string
      cout << "Number of bytes read: " << numBytesRead << endl;
      cout << "Message: " << buff << endl;

      cout << "Closing Write end..." << endl;
      if (close(fdS))
         return -1;

      cout << "Closing Read end..." << endl;
      if (close(fdM))
         return -1;

      cout << "Deleting pipe..." << endl;
      if (remove("my_pipe"))
         return -1;

   return 0;
}

这是输出：

Creating an instance of a named pipe...
Opening Read end...
Opening Write end...
Sending data to pipe...
Number of bytes sent: 16
Closing Write end...
Reopening Write end...
open() - failed(6): No such device or address.

我还测试了类似的代码，试图重新打开一个关闭的读端（而写端保持打开状态）。在这种情况下，open() 函数成功，但使用 open() 返回的文件描述符的 read() 函数失败并显示：发送时出现通信错误。 (70)

编辑：

我正在使用 CYGWIN。

Answer 1

您的代码在 Linux 上运行良好。我认为您运行遇到的问题是 CYGWIN 上的命名管道不能很好地工作并且无法遵循 POSIX 语义。参见 FIFO (named pipe) is broken on Cygwin。可能和你有同样的问题。

当同一进程使用 FIFO 的两端时无法重新打开 FIFO

Cannot reopen FIFO when the same process uses both ends of the FIFO

c++

unix

named-pipes

fifo