File handle left behind by C++ code in Linux

Question

I am trying to debug an issue in my code. I have a process A which runs continuously till I ask it to stop.

Inside A I do the following:

• mount partition /dev/sda1
• open() // creates an empty file X
• write() // write some bytes to it
• close() // close the file
• processFile() // Perform some operation
• remove() // remove file
• umount /dev/sda1

Note I test after each operation above if it was successful or not befor moving forward. When I do lsof | grep A it shows the file handle of X being owned by process A. I also see it has a (deleted). This prevents me from umounting the partition. Why is this happening and how can I get around this issue?

EDIT: Thanks all. Here is the snippet of the code:

tarFileDesc = _pSysCall->open("test.tar", O_CREAT | O_RDWR | O_APPEND, 0777);    
 if (0 > tarFileDesc)
  return false;

 ... some logging here

 // Write http stream to tar file, istr is an argument to my function     
 int read_buffer_size = 0;     
 buffer = new char[4096];     
 while (!istr.eof() && count < content_length)
 {      
    if ((content_length - count) >= 4096)
        read_buffer_size = 4096;
    else
        read_buffer_size = content_length - count;

    memset(buffer, 0, 4096);
    istr.read(buffer, read_buffer_size);
    std::streamsize in_bytes = istr.gcount();
    if (istr.fail() || istr.bad())
    {
        status = false;
        break;
    }

    if (write(tarFileDesc, buffer, in_bytes) != in_bytes)
    {
        status = false;
        break;
    }
    count += in_bytes;
}
// Cleanup buffer
delete[] buffer;

if ((0 > tarFileDesc) && (0 != close(tarFileDesc)))
    return false;   

if (0 != system("tar C /test -xvf test.tar"))
    return false;

if (0 != remove("test.tar"))
      return false;

Note I even tried just doing the open, close and remove. But I still see the handle being held by process.

Answer 1

The issue lies in these lines:

if ((0 > tarFileDesc) && (0 != close(tarFileDesc)))
    return false;   

This will only close the file descriptor if tarFileDesc < 0. What you mean is if tarFileDesc >= 0 then close it as it's a valid file descriptor, so try changing this code to:

if ((0 > tarFileDesc) || (0 != close(tarFileDesc)))
    return false;

This way you return false if the file descriptor is invalid, otherwise you return false if you're unable to close it.

Answer 2

Thanks all. Here is the snippet of the code:

tarFileDesc = _pSysCall->open("test.tar", O_CREAT | O_RDWR | O_APPEND, 0777);    
 if (0 > tarFileDesc)
  return false;

 ... some logging here

 // Write http stream to tar file, istr is an argument to my function     
 int read_buffer_size = 0;     
 buffer = new char[4096];     
 while (!istr.eof() && count < content_length)
 {      
    if ((content_length - count) >= 4096)
        read_buffer_size = 4096;
    else
        read_buffer_size = content_length - count;

    memset(buffer, 0, 4096);
    istr.read(buffer, read_buffer_size);
    std::streamsize in_bytes = istr.gcount();
    if (istr.fail() || istr.bad())
    {
        status = false;
        break;
    }

    if (write(tarFileDesc, buffer, in_bytes) != in_bytes)
    {
        status = false;
        break;
    }
    count += in_bytes;
}
// Cleanup buffer
delete[] buffer;

if ((0 > tarFileDesc) && (0 != close(tarFileDesc)))
    return false;   

if (0 != system("tar C /test -xvf test.tar"))
    return false;

if (0 != remove("test.tar"))
      return false;

Note I even tried just doing the open, close and remove. But I still see the handle being held by process.