如何在0.5秒后在python 2.4中发出警报

Question

我希望在运行0.5秒后超时一段特定的python代码.所以我打算在0.5秒后引发一个异常/信号,并优雅地处理它并继续其余的代码.

在python我知道signal.alarm()可以设置整数秒的警报.是否有任何替代方案,我们可以在0.5秒后生成警报.signal.setitimer()正如其他帖子中所建议的那样在python2.4中不可用,我需要使用python2.4来达到这个目的吗？

Answer 1

从耐心等待的"守护程序"线程中提醒警报.在下面的代码中,snoozealarm通过SnoozeAlarm线程做你想要的:

#! /usr/bin/env python

import os
import signal
import threading
import time

class SnoozeAlarm(threading.Thread):
  def __init__(self, zzz):
    threading.Thread.__init__(self)
    self.setDaemon(True)
    self.zzz = zzz

  def run(self):
    time.sleep(self.zzz)
    os.kill(os.getpid(), signal.SIGALRM)

def snoozealarm(i):
  SnoozeAlarm(i).start()

def main():
  snoozealarm(0.5)
  while True:
    time.sleep(0.05)
    print time.time()


if __name__ == '__main__':
  main()

Answer 2

您有两个选择：

1. time.time()在有问题的代码运行时进行轮询或类似操作。显然，只有当该代码在您的控制之下时，这才可行。

2. 正如 pajton 所提到的，您可以编写一个 C 扩展来调用系统调用setitimer()。这并不太难，因为您可以简单地从更高版本的 Python 的源代码中signal.getitimer()复制代码。signal.setitimer()它们只是同名系统调用的薄包装。

   仅当您使用 CPython 并且处于允许您使用自定义 C 扩展的环境中时，此选项才可行。

   编辑：这是从signalmodule.cPython 2.7复制的代码（Python的许可证适用）：

   #include "Python.h"
   #include <sys/time.h>
   
   static PyObject *ItimerError;
   
   /* auxiliary functions for setitimer/getitimer */
   static void
   timeval_from_double(double d, struct timeval *tv)
   {
       tv->tv_sec = floor(d);
       tv->tv_usec = fmod(d, 1.0) * 1000000.0;
   }
   
   Py_LOCAL_INLINE(double)
   double_from_timeval(struct timeval *tv)
   {
       return tv->tv_sec + (double)(tv->tv_usec / 1000000.0);
   }
   
   static PyObject *
   itimer_retval(struct itimerval *iv)
   {
       PyObject *r, *v;
   
       r = PyTuple_New(2);
       if (r == NULL)
       return NULL;
   
       if(!(v = PyFloat_FromDouble(double_from_timeval(&iv->it_value)))) {
       Py_DECREF(r);
       return NULL;
       }
   
       PyTuple_SET_ITEM(r, 0, v);
   
       if(!(v = PyFloat_FromDouble(double_from_timeval(&iv->it_interval)))) {
       Py_DECREF(r);
       return NULL;
       }
   
       PyTuple_SET_ITEM(r, 1, v);
   
       return r;
   }
   
   static PyObject *
   itimer_setitimer(PyObject *self, PyObject *args)
   {
       double first;
       double interval = 0;
       int which;
       struct itimerval new, old;
   
       if(!PyArg_ParseTuple(args, "id|d:setitimer", &which, &first, &interval))
       return NULL;
   
       timeval_from_double(first, &new.it_value);
       timeval_from_double(interval, &new.it_interval);
       /* Let OS check "which" value */
       if (setitimer(which, &new, &old) != 0) {
       PyErr_SetFromErrno(ItimerError);
       return NULL;
       }
   
       return itimer_retval(&old);
   }
   
   PyDoc_STRVAR(setitimer_doc,
   "setitimer(which, seconds[, interval])\n\
   \n\
   Sets given itimer (one of ITIMER_REAL, ITIMER_VIRTUAL\n\
   or ITIMER_PROF) to fire after value seconds and after\n\
   that every interval seconds.\n\
   The itimer can be cleared by setting seconds to zero.\n\
   \n\
   Returns old values as a tuple: (delay, interval).");
   
   static PyObject *
   itimer_getitimer(PyObject *self, PyObject *args)
   {
       int which;
       struct itimerval old;
   
       if (!PyArg_ParseTuple(args, "i:getitimer", &which))
       return NULL;
   
       if (getitimer(which, &old) != 0) {
       PyErr_SetFromErrno(ItimerError);
       return NULL;
       }
   
       return itimer_retval(&old);
   }
   
   PyDoc_STRVAR(getitimer_doc,
   "getitimer(which)\n\
   \n\
   Returns current value of given itimer.");
   
   static PyMethodDef itimer_methods[] = {
       {"setitimer",       itimer_setitimer, METH_VARARGS, setitimer_doc},
       {"getitimer",       itimer_getitimer, METH_VARARGS, getitimer_doc},
       {NULL,                      NULL}           /* sentinel */
   };
   
   PyMODINIT_FUNC
   inititimer(void)
   {
       PyObject *m, *d, *x;
       int i;
       m = Py_InitModule3("itimer", itimer_methods, 0);
       if (m == NULL)
           return;
   
       d = PyModule_GetDict(m);
   
   #ifdef ITIMER_REAL
       x = PyLong_FromLong(ITIMER_REAL);
       PyDict_SetItemString(d, "ITIMER_REAL", x);
       Py_DECREF(x);
   #endif
   #ifdef ITIMER_VIRTUAL
       x = PyLong_FromLong(ITIMER_VIRTUAL);
       PyDict_SetItemString(d, "ITIMER_VIRTUAL", x);
       Py_DECREF(x);
   #endif
   #ifdef ITIMER_PROF
       x = PyLong_FromLong(ITIMER_PROF);
       PyDict_SetItemString(d, "ITIMER_PROF", x);
       Py_DECREF(x);
   #endif
   
       ItimerError = PyErr_NewException("itimer.ItimerError",
                                        PyExc_IOError, NULL);
       if (ItimerError != NULL)
           PyDict_SetItemString(d, "ItimerError", ItimerError);
   }
   

   将此代码保存为itimermodule.c，使用类似的方法将其编译为 C 扩展

   gcc -I /usr/include/python2.4 -fPIC -o itimermodule.o -c itimermodule.c
   gcc -shared -o itimer.so itimermodule.o -lpython2.4
   

   现在，如果你幸运的话，你应该能够使用以下命令从 Python 导入它：

   import itimer
   

   并致电itimer.setitimer().