photofloat/scanner/floatapp/process.py

from flask import Response
import subprocess
import os
import sys


class ProcessWrapper(object):
    def __init__(self, process, done):
        self.process = process
        self.done = done

    def close(self):
        self.done()
        if self.process.returncode is not None:
            return
        self.process.stdout.close()
        self.process.terminate()
        self.process.wait()

    def __iter__(self):
        return self

    def __del__(self):
        self.close()

    def next(self):
        try:
            data = self.process.stdout.readline()
        except:
            self.close()
            raise StopIteration()
        if data:
            return data
        self.close()
        raise StopIteration()


def send_process(args, pid_file):
    def setup_proc():
        f = open(pid_file, "w")
        f.write(str(os.getpid()))
        f.close()
        os.close(0)
        os.dup2(1, 2)

    def tear_down_proc():
        try:
            os.unlink(pid_file)
        except:
            pass

    if os.path.exists(pid_file):
        f = open(pid_file, "r")
        pid = f.read()
        f.close()
        if os.path.exists("/proc/%s/status" % pid):
            return Response(
                "Scanner is already running.\n", mimetype="text/plain")

    process = subprocess.Popen(
        args, close_fds=True, stdout=subprocess.PIPE, preexec_fn=setup_proc)
    response = ProcessWrapper(process, tear_down_proc)
    return Response(response, direct_passthrough=True, mimetype="text/plain")