守护进程 python 包装器“子进程 I/O 超时”，需要一些指导

Question

我不太熟悉在 Python 中创建守护进程的方式，因此当我尝试安装和运行第三方开源 TeX Python Wrapper 时，我遇到了一个我不明白也不太理解的错误。

我添加了一些打印来帮助调试。

有问题的称为 texdp.py

当我运行 mathrand 并调用 texdp 服务器启动时， 我收到以下错误

output_fds  {8: 'dvi', 5: 'log', 6: 'logfile', 7: 'err'}
input_fds  3
readable, writable [] [3]  outflds, inputflds:  [8, 5, 6, 7] [3]
pointer len_str:  0 63
folder fd:  7
readable, writable [5] []  outflds, inputflds:  [8, 5, 6, 7] []
pointer len_str:  63 63
folder fd:  7
readable, writable [5] []  outflds, inputflds:  [8, 5, 6, 7] []
pointer len_str:  63 63
folder fd:  5
readable, writable [] []  outflds, inputflds:  [8, 5, 6, 7] []
pointer len_str:  63 63
folder fd:  5
SUB IO ERROR: readable []  pointer == len_str: 63 , 63

Traceback (most recent call last):
  File "/usr/local/bin/mathtrand", line 18, in <module>
    server.start()
  File "/usr/local/lib/python2.6/dist-packages/mathtran/server.py", line 71, in start
    self.secplain.start()
  File "/usr/local/lib/python2.6/dist-packages/tex/texdp.py", line 159, in start
    self.process(self._params.start)
  File "/usr/local/lib/python2.6/dist-packages/tex/texdp.py", line 175, in process
    value = self._process(str + self._params.done, self._params.done_str)
  File "/usr/local/lib/python2.6/dist-packages/tex/texdp.py", line 210, in _process
    raise SubprocessError, 'subprocess I/O timed out'

负责的代码部分已附加并位于方法 def _process 中的第 200 行左右。

我不知道从哪里开始寻找，也不知道这个错误的真正含义是什么。 非常欢迎任何帮助。

https://texd.svn.sourceforge.net/ svnroot/texd/trunk/py/tex/texdp.py

# Copyright: (c) 2007 The Open University, Milton Keynes, UK
# License: GPL version 2 or (at your option) any later version.
# Author: Jonathan Fine <[email protected]>, <[email protected]>

"""Wrapper around TeX process, to handle input and output.

Further comments to go here.
"""

__version__ = '$Revision: 116 $'[11:-2]
# $Source$

# TODO:  Move interface instances to elsewhere.
# TODO:  error recovery, e.g. undefined control sequence.
# TODO:  Abnormal exit is leaving orphaned processes.
# TODO:  Refactor _process into tex.util, share with metapostdp.

import os                               # Create directories and fifos
from select import select               # Helps handle i/o to TeX process
from tex.util import make_nonblocking   # For non-blocking file descriptor
from tex.util import DaemonSubprocess
from tex.dviopcode import FNT_DEF1, FNT_DEF4
import signal


class SubprocessError(EnvironmentError):

    pass

# TODO:  This belongs elsewhere.
class Interface(object):
    """Stores useful, but format specific, constants."""

    def __init__(self, **kwargs):
        # TODO:  Be more specific about the parameters.
        self.__dict__ = kwargs


# TeX knows about these fonts, but Python does not yet know.
# This list created by command: $tex --ini '&plain' \\dump
preloaded_fonts = ( 'cmr10', 'cmr9', 'cmr8', 'cmr7', 'cmr6', 'cmr5',
                    'cmmi10', 'cmmi9', 'cmmi8', 'cmmi7', 'cmmi6',
                    'cmmi5', 'cmsy10', 'cmsy9', 'cmsy8', 'cmsy7',
                    'cmsy6', 'cmsy5', 'cmex10', 'cmss10', 'cmssq8',
                    'cmssi10', 'cmssqi8', 'cmbx10', 'cmbx9', 'cmbx8',
                    'cmbx7', 'cmbx6', 'cmbx5', 'cmtt10', 'cmtt9',
                    'cmtt8', 'cmsltt10', 'cmsl10', 'cmsl9', 'cmsl8',
                    'cmti10', 'cmti9', 'cmti8', 'cmti7', 'cmu10',
                    'cmmib10', 'cmbsy10', 'cmcsc10', 'cmssbx10',
                    'cmdunh10', 'cmr7 scaled 2074',
                    'cmtt10 scaled 1440', 'cmssbx10 scaled 1440',
                    'manfnt', )

# Ship out a page that starts with a font def.
load_font_template = \
r'''%%
\begingroup
  \hoffset 0sp
  \voffset 0sp
  \setbox0\hbox{\font\tmp %s\relax\tmp M}%%
  \ht0 0sp
  \shipout\box 0
\endgroup
'''

secplain_load_font_template = \
r'''%%
\_begingroup
  \_hoffset 0sp
  \_voffset 0sp
  \_setbox0\_hbox{\_font\_tmp %s\_relax\_tmp M}%%
  \_ht0 0sp
  \_shipout\_box 0
\_endgroup
'''


plain = Interface(format='plain',
                  start = r'\shipout\hbox{}' '\n',
                  done = '\n' r'\immediate\write16{DONE}\read-1to\temp ' '\n',
                  done_str = 'DONE\n',
                  stop = '\end' '\n',
                  preloaded_fonts = preloaded_fonts,
                  load_font_template = load_font_template,
                  )

secplain = Interface(format='secplain',
                  start = r'\_shipout\_hbox{}' '\n',
                  done = '\n' r'\_immediate\_write16{DONE}\_read-1to\_temp ' '\n',
                  done_str = 'DONE\n',
                  stop = '\_end' '\n',
                  preloaded_fonts = preloaded_fonts,
                  load_font_template = secplain_load_font_template,
                  )



class Texdp(DaemonSubprocess):
    """Wrapper around TeX process that handles input and output.

    More comments go here.    
    """

    _fifos = ('texput.tex', 'texput.log', 'texput.dvi')

    def _make_args(self):

        # Don Knuth created plain.fmt, renamed by some to tex.fmt.
        fmt = self._params.format
        if fmt == 'plain' or fmt == 'tex':
            fmt = ''
        else:
            fmt = '--fmt=' + fmt

        # Build up the arguments list.
        args = ('tex', '--ipc',)
        args += ('--output-comment=""',) # Don't record time of run.
        if fmt:
            args += (fmt,)
        args += ('texput.tex',)
        return args

    def start(self):

        super(Texdp, self).start()      # Start the TeX process.

        # We will now initialise TeX, and conprocessnect to file descriptors.
        # We need to do some low-level input/output, in order to
        # manage long input strings.  Therefore, we use file
        # descriptors rather than file objects.

        # We map output fds to what will be a dictionary key.
        ofd = self._output_fd_dict = {}

        cwd = self._cwd                 # Shorthand.
        child = self._child 

        # For us, stdin and stdout are special.
        self._stdin = child.stdin.fileno()
        self._stdout = child.stdout.fileno()

        # Read stdout and stderr to 'log' and 'err' respectively.
        ofd[self._stdout] = 'log'
        ofd[child.stderr.fileno()] = 'err'

        # Open 'texput.tex', and block until it is available, which is
        # when TeX has started.  Then make 'texput.tex' non-blocking,
        # in case of a long write.
        self._texin = os.open(os.path.join(cwd, 'texput.tex'), os.O_WRONLY)
        make_nonblocking(self._texin)

        # Read 'texput.log' and 'texput.dvi' to 'logfile' and 'dvi'.
        for src, tgt in (('texput.log', 'logfile'), ('texput.dvi', 'dvi')):
            fd = os.open(os.path.join(cwd, src),
                         os.O_RDONLY|os.O_NONBLOCK)
            ofd[fd] = tgt

        # Ship out blank page, and initialise preloaded fonts.
        self.process(self._params.start)
        self._fontdefs = []
        for font_spec in self._params.preloaded_fonts:
            self.load_new_font(font_spec)

    def process(self, str):
        "Return dictionary with log, dvi, logfile and err entries."

        # TeX will read the data, following by the 'done' command.
        # The 'done' command will cause TeX to write the 'done_str',
        # which signals the end of the process.  It will also pause
        # TeX for input.

        # TODO: I do not know why the pause is required, but it is.
        # Remove it here and in the _params, and the program hangs.

        value = self._process(str + self._params.done, self._params.done_str)
        self._child.stdin.write('\n')   # TeX is paused for input.
        return value

    def _process(self, str, done_str):

        # Write str, and read output, until we are done.  Then gather
        # up the accumulated output, and return as a dictionary.  The
        # input string might be long.  Later, we might allow writing to
        # stdin, in response to errors.

        # Initialisation.
        print "output_fds ", self._output_fd_dict
        output_fds = self._output_fd_dict.keys()
        print "input_fds ", self._texin
        input_fds = [self._texin]

        accumulator = {}
        for fd in output_fds:
            accumulator[fd] = []

        pointer, len_str = 0, len(str)

        # The main input/ouput loop.
        # TOD0: magic number, timeout.
        done = False
        while not done:
            readable, writable = select(output_fds, input_fds, [], 0.1)[0:2]
            print "readable, writable", readable, writable, " outflds, inputflds: ", output_fds, input_fds
            print "pointer len_str: ", pointer, len_str
            print "folder fd: ", fd
            if not readable and pointer == len_str:
                print "SUB IO ERROR: readable", readable, " pointer == len_str:", pointer, ",", len_str
                os.kill(self._child.pid, signal.SIGKILL)
                self._child.wait()
                raise SubprocessError, 'subprocess I/O timed out'

            if pointer != len_str and writable:
                written = os.write(self._texin, str[pointer:pointer+4096])
                pointer += written
                if pointer == len_str:
                    input_fds = []

            for fd in readable:
                if self._child.poll() is not None:
                    raise SubprocessError, 'read from terminated subprocess'

                tmp = os.read(fd, 4096)
                if fd == self._stdout:
                    if tmp.endswith(done_str):
                        tmp = tmp[:-len(done_str)]
                        done = True
                accumulator[fd].append(tmp)

        if pointer != len_str:
            raise SystemError, "TeX said 'done' before end of input."

        # Join accumulated output, create and return ouput dictionary.
        value = {}
        for fd, name in self._output_fd_dict.items():
            value[name] = ''.join(accumulator[fd])
        return value

    def load_new_font(self, font_spec):
        """Tell both TeX and Python about a new font.

        Raises an exception if the font is not new.
        """

        # Ask TeX to load font, and ship out page that uses it.
        command mathtran= self._params.load_font_template % font_spec
        dvi = self.process(command)['dvi']

        bytes = dvi[45:-1]                  # Page body.
        opcode = ord(bytes[0])              # First opcode.

        # The first opcode should be a fontdef, which we extract.
        if FNT_DEF1 <= opcode <= FNT_DEF4:
            body_len = (2 + (opcode - FNT_DEF1)
                        + 12                # Checksum, scale, design size.
                        + 2)                # Length of 'area' and font name.

            name_len = ord(bytes[body_len - 2]) \
                       + ord(bytes[body_len - 1])

            fontdef = bytes[:body_len + name_len]
            self._fontdefs.append(fontdef)
            return

        else:
            raise ValueError, "font '%s' not new or not found" % font_spec

Answer 1

超时基于 select 调用。

readable, writable = select(output_fds, input_fds, [], 0.1)[0:2]

超时为 0.1 秒。 这合适吗？

变量名含糊不清（“指针”在 Python 中没有什么意义）。 然而，如果 0.1 秒内没有任何反应，则会引发“超时”。

---

奇怪的是，这个程序打开文件来与子进程通信。 与子进程“共享”文件是很奇怪的。

通常我们会做两件事之一——使用管道与子进程主动通信或使用文件让子进程自行运行。

这是一个更简单的设计。

1. 将输入放入输入文件。

2. 运行 Tex 守护程序子进程，直到它完成或者您厌倦了等待它。

   运行

3. 如果你厌倦了等待它，那就杀死它。

   其他

   • 通过等待函数查看状态

   • 读取输出文件。

这几乎就是您所需要的。 并且不会有神秘的“暂停”，没有低级 I/O，没有非阻塞 I/O。

如果由于某种原因您需要与子进程通信，那么您应该考虑用管道替换文件（管道不共享，并且可能更适合您正在做的事情。）