FIFO管道中的数据丢失？

Question

I have a python process writing to a named pipe, and a C++ program reads it. (I create the pipes in C++). Well, it seems to work fine. However, sometimes I notice that there's loss of data. The data is not detected by the reader! Am I doing something wrong?

Here's how I am creating the pipes:

void create_pipes(string pipename){

    char * cstr1 = new char [pipename.length()+1];
    strcpy (cstr1, pipename.c_str());

    cout << "Creating " << pipename << " pipe..." << endl;
    unlink (cstr1); // Delete pipe
    int result = mkfifo (cstr1, S_IRUSR| S_IWUSR);  // Create Pipe
    if( result == -1 ){
         cout << "There was en error creating the pipe! " << result << endl;
         //return 0;
    }
    else
        cout << "Pipe created!" << endl;
}

Now, I have a thread that reads the pipe like this:

     int fd = open(cstr1, O_RDONLY);  // Open the pipe


    while( running_threads ){

        if(!read(fd, buf, MAX_BUF))
            continue;
        string line(buf);
        if( buf != "" ){
            //cout << line;
            pipe_r.DECODE_PIPE_DATA(line);
        }
    }

    cout << "Thread terminated" << endl;

    close(fd);

In python I'm simply writing the data to the pipe by doing this:

def write_pipe(file_string):
    while True:
        try:
            pipe.write(file_string)
            pipe.flush()
            break
        except:
            print "Error while writing to pipe"
            continue

What could be causing my problem? The python program writes the data into the pipe successfully; But the c++ program sometimes will not read the pipe. Can this be caused by the python process writing data faster than the c++ program before it could actually read it? What should I do?

Thanks.

Answer 1

buf is not guaranteed to be terminated, nor is it guaranteed to not have '\\0' characters embedded in it from the code you posted. This should work better, but may still fail if the Python code embeds a '\\0' in the data it writes:

while( running_threads )
{
    ssize_t bytesRead = read(fd, buf, MAX_BUF);
    if ( bytesRead < 0 )
         break;
    else if ( bytesRead == 0 )
         continue;

    string line( buf, static_cast<size_t>(bytesRead) );

And your code doesn't properly handle an error condition should read() return -1.