如何在0.5秒後在python 2.4中發出警報

Question

我想在運行0.5秒後超時一段特定的python代碼。所以我打算在0.5秒後發出一個異常/信號，並且正常處理它並繼續處理其餘的代碼。

在python我知道signal.alarm()可以設置整數秒的警報。在0.5秒後我們可以產生報警嗎？ signal.setitimer()在其他文章中建議不在python2.4中可用，我需要爲此使用python2.4？

Answer 1

你有兩個選擇：

1. 輪詢time.time()或在有問題的代碼運行類似。如果該代碼在您的控制之下，這是明顯可行的。

2. 正如pajton所述，您可以編寫一個C擴展名來調用系統調用setitimer()。這並不難，因爲您可以簡單地複製源自更高版本Python的源代碼signal.getitimer()和signal.setitimer()。它們僅僅是同名系統調用的簡單包裝。

   如果您使用CPython並且您處於允許使用自定義C擴展的環境中，則此選項纔可行。

   編輯：這裏是signalmodule.c in Python 2.7複製的代碼（Python的許可適用）：

   #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); 
   } 
   

   這段代碼保存爲itimermodule.c，使用類似

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

   把它編譯成一個C擴展現在，如果你幸運的話，你應該可以使用

   import itimer 
   

   並致電itimer.setitimer()。

Answer 2

提高耐心等待的「守護進程」線程的警報。在下面的代碼，snoozealarm你想要做什麼通過SnoozeAlarm螺紋：

#! /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()