Question

我需要编写一个C ++代码，它接受某个输入并打印相应的输出。此代码旨在使用Python子进程模块运行。无论输入和输出如何，我都需要确保Python代码不会因C ++代码遇到的运行时错误而过早终止。 C ++代码的基本特性如下

int main()
{
  /*The pointer is initialized to NULL to simulate a segmentation fault
    Also the n is meant for simulating input.*/
  int *p=NULL,n;   
  cin>>n;
  cout<<*p<<endl;  //This causes a segmentation fault.
}

运行它的Python代码如下：

from subprocess import *
from signal import *

def handler(signum,frame):
    raise RuntimeError("Runtime Error")

call(["g++","try.cpp"])
a = Popen(["stdbuf","-i0","-o0","-e0","./a.out"],stdin = PIPE,stdout = PIPE)
try:
    #Handler for signal due to termination of child process
    signal(SIGCHLD,handler)    
    a.stdin.write("1\n")
    temp = a.stdout.readline()
except RuntimeError as e:
    print e
    print a.returncode   

#Returncode of process killed due to SIGSEGV is -11
    if a.returncode == -11:   
        print "Segmentation Fault Occurred"

这就是问题所在。即使C ++代码遇到分段错误，也会调用信号处理程序，引发RuntimeError，但Popen对象的返回码为none，表示进程仍然存在。
现在，如果对except块进行了以下更改：

a.wait()
print a.returncode        
if a.returncode == -11:   
    print "Segmentation Fault Occurred"

问题已解决。输出显示Popen对象的返回码为-11，并且“分段故障发生”显示在屏幕上。
如果我尝试模拟由于被零除的浮点异常，则会发生相同的情况为什么会这样？

Answer 1

来自文档

Popen.wait（）等待子进程终止。设置并返回returncode属性。

因此，在调用returncode之前，wait不会设置。

或者，您可以执行非阻止检查以查看是否使用poll终止了流程，如果已终止，也会设置returncode。

Popen.poll（）检查子进程是否已终止。设置并返回returncode属性。

请注意，您并非真正需要signal电话（不确定它是否可以在Windows上移植）。代码可以简化为：

a = Popen(["stdbuf","-i0","-o0","-e0","./a.out"],stdin = PIPE,stdout = PIPE)
a.stdin.write("1\n")
a.stdin.flush()
temp = a.stdout.readline()
if temp:
    # do something
    print("output "+temp)
else:
    # empty string: recieved process has ended, probably unexpectedly
    # because it should have printed something
    pass

returncode = a.wait()

#Returncode of process killed due to SIGSEGV is -11
if returncode  == -11:   
    print("Segmentation Fault Occurred")

请注意，您必须a.stdin.flush()以确保输入到达c ++程序。

为什么由于分段错误而导致的子进程被立即杀死？

1 个答案: