void ProgramOutputMultiplexer::appendLine(int port, ProcessId pid, const char* line) {
    stdx::lock_guard<stdx::mutex> lk(mongoProgramOutputMutex);
    uassert(28695, "program is terminating", !mongo::inShutdown());
    stringstream buf;
    string name = registry.programName(pid);
    if (port > 0)
        buf << name << port << "| " << line;
    else
        buf << name << pid << "| " << line;
    printf("%s\n", buf.str().c_str());  // cout << buf.str() << endl;
    fflush(stdout);  // not implicit if stdout isn't directly outputting to a console.
    _buffer << buf.str() << endl;
}

# Use unbuffered I/O pipes to avoid adding delay between when the subprocess writes output
# and when the LoggerPipe thread reads it.
buffer_size = 0

# Close file descriptors in the child process before executing the program. This prevents
# file descriptors that were inherited due to multiple calls to fork() -- either within one
# thread, or concurrently from multiple threads -- from causing another subprocess to wait
# for the completion of the newly spawned child process. Closing other file descriptors
# isn't supported on Windows when stdout and stderr are redirected.
close_fds = (sys.platform != "win32")

with _POPEN_LOCK:
    self._process = subprocess.Popen(self.args,
                                     bufsize=buffer_size,
                                     stdout=subprocess.PIPE,
                                     stderr=subprocess.PIPE,
                                     close_fds=close_fds,
                                     env=self.env,
                                     creationflags=creation_flags)