如何在python 2.4中发出0.5秒后的警报信号

Question

我想让一段特定的python代码在in运行0.5秒后超时。因此，我打算在0.5秒后引发一个异常/信号，并优雅地处理它，然后继续执行其余的代码。

在python中，我知道signal.alarm()可以设置整秒的警报。有没有其他选择，我们可以在0.5秒后发出警报。其他帖子中建议的signal.setitimer()在python2.4中不可用，我需要使用python2.4？

Answer 1

从耐心等待的"守护进程"线程发出警报。在下面的代码中，snoozealarm通过SnoozeAlarm线程执行您想要的操作：

#! /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

您有两个选项：

1. 在有问题的代码运行时轮询time.time()或类似程序。显而易见，只有当代码在您的控制之下时，这才是可行的。

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以后版本的Python源代码中复制signal.getitimer()和signal.setitimer()的代码。它们只是名称相同的系统调用的薄包装。

   只有当您使用CPython并且您所在的环境允许您使用自定义C扩展时，此选项才可行。

   编辑：以下是从Python 2.7中的signalmodule.c复制的代码(适用Python许可证(：

   #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_VIRTUALn
   or ITIMER_PROF) to fire after value seconds and aftern
   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，使用类似的东西将其编译为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，你应该能够使用从Python导入它

   import itimer
   

   并呼叫CCD_ 11。