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多态异常处理：如何捕获子类异常？

[英]Polymorphic exception handling: How to catch subclass exception?

 原文  2017-09-26 07:41:23  6   2    python/ c++/ exception/ boost/ boost-python

问题描述

I have the following simple hierarchy of two C++ exceptions: 我有以下两个C ++异常的简单层次结构： 

class LIB_EXP ClusterException : public std::exception {
public:
    ClusterException() { }
    ClusterException(const std::string& what) { init(what); }
    virtual const char* what() const throw() { return what_.c_str(); }
    virtual ~ClusterException() throw() {}
    virtual ClusterException* clone() { return new ClusterException(*this);  } 
protected:
    void init(const std::string& what) { what_ = what; }
private:
    std::string what_;
};

class LIB_EXP ClusterExecutionException : public ClusterException {
public:
    ClusterExecutionException(const std::string& jsonResponse);
    std::string getErrorType() const throw() { return errorType_; }
    std::string getClusterResponse() const throw() { return clusterResponse_; }
    virtual ~ClusterExecutionException() throw() {}
    virtual ClusterExecutionException* clone() { return new ClusterExecutionException(*this);  } 
private:
    std::string errorType_;
    std::string clusterResponse_;
};

I then export them to Python with Boost-Python as follows. 然后我使用Boost-Python将它们导出到Python，如下所示。 Note my use of the bases to make sure that the inheritance relationship is preserved in the translation: 请注意我使用bases来确保在转换中保留继承关系： 

class_<ClusterException> clusterException("ClusterException", no_init);
clusterException.add_property("message", &ClusterException::what);
clusterExceptionType = clusterException.ptr();
register_exception_translator<ClusterException>(&translateClusterException);

class_<ClusterExecutionException, bases<ClusterException> > clusterExecutionException("ClusterExecutionException", no_init);
clusterExecutionException.add_property("message", &ClusterExecutionException::what)
                         .add_property("errorType", &ClusterExecutionException::getErrorType)
                         .add_property("clusterResponse", &ClusterExecutionException::getClusterResponse);
clusterExecutionExceptionType = clusterExecutionException.ptr();
register_exception_translator<ClusterExecutionException>(&translateClusterExecutionException);

Then the exception translation method: 然后是异常翻译方法： 

static PyObject *clusterExceptionType = NULL;
static void translateClusterException(ClusterException const &exception) {
  assert(clusterExceptionType != NULL); 
  boost::python::object pythonExceptionInstance(exception);
  PyErr_SetObject(clusterExceptionType, pythonExceptionInstance.ptr());
}

static PyObject *clusterExecutionExceptionType = NULL;
static void translateClusterExecutionException(ClusterExecutionException const &exception) {
  assert(clusterExecutionExceptionType != NULL);
  boost::python::object pythonExceptionInstance(exception);
  PyErr_SetObject(clusterExecutionExceptionType, pythonExceptionInstance.ptr());
}

I created the following test C++ function that throws the exceptions: 我创建了以下测试C ++函数，抛出异常： 

static void boomTest(int exCase) {
  switch (exCase) {
    case 0:  throw ClusterException("Connection to server failed");
             break;
    case 1:  throw ClusterExecutionException("Error X while executing in the cluster");
             break;
    default: throw std::runtime_error("Unknown exception type");
  }
}

Finally the Python test code that calls my C++ boomTest : 最后调用我的C ++ boomTest的Python测试代码： 

import cluster
reload(cluster)
from cluster import ClusterException, ClusterExecutionException

def test_exception(exCase):
    try:
        cluster.boomTest(exCase)

    except ClusterException as ex:
        print 'Success! ClusterException gracefully handled:' \
            '\n message="%s"' % ex.message
    except ClusterExecutionException as ex:
        print 'Success! ClusterExecutionException gracefully handled:' \
            '\n message="%s"' \
            '\n errorType="%s"' \
            '\n clusterResponse="%s"' % (ex.message, ex.errorType, ex.clusterResponse)
    except:
        print 'Caught unknown exception: %s "%s"' % (sys.exc_info()[0], sys.exc_info()[1])

def main():
    print '\n************************ throwing ClusterException ***********************************************************************'
    test_exception(0)
    print '\n************************ throwing ClusterExecutionException **************************************************************'
    test_exception(1)
    print '\n************************ throwing std::runtime_error *********************************************************************'
    test_exception(2)

if __name__ == "__main__":
    main()

Up to here it all works. 到这里一切都有效。 However if I remove the ClusterExecutionException catch handler from Python then this exception will be caught and fallback to an unknown exception instead of being caught as its base ClusterException . 但是，如果我从Python中删除ClusterExecutionException catch处理程序， ClusterExecutionException捕获此异常并回ClusterException未知异常，而不是作为其基本ClusterException 。

I have tried in Boost-Python while registering the exception translation of ClusterExecutionException to register it as its base ClusterException and then it gets caught "polymorphically" but then it won't be caught as a ClusterExecutionException . 我在Boost-Python中尝试了注册ClusterExecutionException的异常转换， ClusterExecutionException其注册为基本的ClusterException ，然后它被“多态”捕获，但它不会被捕获为ClusterExecutionException 。 How can make it so that ClusterExecutionException gets caught as both ClusterException and ClusterExecutionException ? 如何使ClusterExecutionException被捕获为ClusterException和ClusterExecutionException ？ I have tried of course registering this ClusterExecutionException exception as both ClusterException and ClusterExecutionException but it follows a last wins strategy, and only one works not both. 我当然尝试将此ClusterExecutionException异常作为ClusterException和ClusterExecutionException但它遵循最后一个获胜策略，并且只有一个不同时工作。

Is there any other way to solve this? 有没有其他方法可以解决这个问题？

UPDATE 1: The wholy grail of this problem is to find out on the C++ side the type of the except Python statement eg except ClusterException as ex: which is unknown once inside the C++ side. 更新1：这个问题的关键是要在C ++端找到except Python语句except ClusterException as ex:的类型，例如except ClusterException as ex:在C ++方面是未知的。 The exception translate by Boost.Python will call the translate function that corresponds to the dynamic type of the exception and the Python catch static type is not known. Boost.Python转换的异常将调用与异常的动态类型相对应的translate函数，并且Python catch静态类型未知。

UPDATE 2: As suggested changing the Python code to the following ie adding print(type(ex).__bases__) gives: 更新2：建议将Python代码更改为以下内容，即添加print(type(ex).__bases__)给出： 

def test_exception(exCase):
    try:
        cluster.boomTest(exCase)

    except ClusterException as ex:
        print(type(ex).__bases__)
        print 'Success! ClusterException gracefully handled:' \
            '\n message="%s"' % ex.message
    except ClusterExecutionException as ex:
        print(type(ex).__bases__)
        print 'Success! ClusterExecutionException gracefully handled:' \
            '\n message="%s"' \
            '\n errorType="%s"' \
            '\n clusterResponse="%s"' % (ex.message, ex.errorType, ex.clusterResponse)
    except:
        print 'Caught unknown exception: %s "%s"' % (sys.exc_info()[0], sys.exc_info()[1])

and the output: 和输出： 

************************ throwing ClusterException ***********************************************************************
(<type 'Boost.Python.instance'>,)
Success! ClusterException gracefully handled:
 message="Connection to server failed"

************************ throwing ClusterExecutionException **************************************************************
(<class 'cluster.ClusterException'>,)
Success! ClusterExecutionException gracefully handled:
 message="Error X while executing in the cluster"
 errorType="LifeCycleException"
 clusterResponse="{ "resultStatus": "Error", "errorType": "LifeCycleException", "errorMessage": "Error X while executing in the cluster" }"

Meaning that the inheritance relationship is "seen" from Python. 意味着继承关系是从Python“看到”的。 But the polymorphic handling still doesn't work. 但多态处理仍然无效。

UPDATE 3 This is the output of running VS dumpbin.exe : 更新3这是运行VS dumpbin.exe的输出：

The command I used is: 我使用的命令是： 

dumpbin.exe /EXPORTS /SYMBOLS C:\ClusterDK\x64\Debug\ClusterDK.dll > c:\temp\dumpbin.out

and the relevant parts of the output: 以及输出的相关部分： 

Microsoft (R) COFF/PE Dumper Version 11.00.50727.1
Copyright (C) Microsoft Corporation.  All rights reserved.

Dump of file C:\ClusterDK\x64\Debug\ClusterDK.dll

File Type: DLL

Section contains the following exports for ClusterDK.dll

00000000 characteristics
5A1689DA time date stamp Thu Nov 23 09:42:02 2017
    0.00 version
       1 ordinal base
      78 number of functions
      78 number of names

ordinal hint RVA      name

      8    7 00004485 ??0ClusterException@cluster@@QEAA@AEBV01@@Z = @ILT+13440(??0ClusterException@cluster@@QEAA@AEBV01@@Z)
      9    8 00001659 ??0ClusterException@cluster@@QEAA@AEBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z = @ILT+1620(??0ClusterException@cluster@@QEAA@AEBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z)
     10    9 00001F1E ??0ClusterException@cluster@@QEAA@XZ = @ILT+3865(??0ClusterException@cluster@@QEAA@XZ)
     11    A 00004D4F ??0ClusterExecutionException@cluster@@QEAA@AEBV01@@Z = @ILT+15690(??0ClusterExecutionException@cluster@@QEAA@AEBV01@@Z)
     12    B 000010AA ??0ClusterExecutionException@cluster@@QEAA@AEBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z = @ILT+165(??0ClusterExecutionException@cluster@@QEAA@AEBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z)
     27   1A 000035D0 ??1ClusterException@cluster@@UEAA@XZ = @ILT+9675(??1ClusterException@cluster@@UEAA@XZ)
     28   1B 00003C7E ??1ClusterExecutionException@cluster@@UEAA@XZ = @ILT+11385(??1ClusterExecutionException@cluster@@UEAA@XZ)
     37   24 00002BD5 ??4ClusterException@cluster@@QEAAAEAV01@AEBV01@@Z = @ILT+7120(??4ClusterException@cluster@@QEAAAEAV01@AEBV01@@Z)
     38   25 000034D1 ??4ClusterExecutionException@cluster@@QEAAAEAV01@AEBV01@@Z = @ILT+9420(??4ClusterExecutionException@cluster@@QEAAAEAV01@AEBV01@@Z)
     46   2D 000D2220 ??_7ClusterException@cluster@@6B@ = ??_7ClusterException@cluster@@6B@ (const cluster::ClusterException::`vftable')
     47   2E 000D2248 ??_7ClusterExecutionException@cluster@@6B@ = ??_7ClusterExecutionException@cluster@@6B@ (const cluster::ClusterExecutionException::`vftable')
     52   33 00004BB5 ?clone@ClusterException@cluster@@UEAAPEAV12@XZ = @ILT+15280(?clone@ClusterException@cluster@@UEAAPEAV12@XZ)
     53   34 00004D31 ?clone@ClusterExecutionException@cluster@@UEAAPEAV12@XZ = @ILT+15660(?clone@ClusterExecutionException@cluster@@UEAAPEAV12@XZ)
     61   3C 00001D43 ?getErrorType@ClusterExecutionException@cluster@@QEBA?AV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@XZ = @ILT+3390(?getErrorType@ClusterExecutionException@cluster@@QEBA?AV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@XZ)
     69   44 0000480E ?init@ClusterException@cluster@@IEAAXAEBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z = @ILT+14345(?init@ClusterException@cluster@@IEAAXAEBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z)
     78   4D 000032FB ?what@ClusterException@cluster@@UEBAPEBDXZ = @ILT+8950(?what@ClusterException@cluster@@UEBAPEBDXZ)

Summary

    4000 .data
    5000 .idata
   12000 .pdata
   54000 .rdata
    2000 .reloc
    1000 .rsrc
   C9000 .text
    1000 .tls

2 个解决方案

解决方案1
 2  2017-10-04 10:03:36

My python skills are rusty and I haven't tested this, so this may need further improvements, but try adding the exception translation method to handle the base class exception type: 我的python技能生锈了，我还没有测试过，所以这可能需要进一步改进，但是尝试添加异常转换方法来处理基类异常类型： 

static PyObject *clusterExecutionAsClusterExceptionType = NULL;
static void translateClusterExecutionAsClusterException(ClusterException const &exception) {

  ClusterExecutionException* upcasted = dynamic_cast<ClusterExecutionException*>(&exception);
  if (upcasted)
  {
    assert(clusterExecutionAsClusterExceptionType != NULL);
    boost::python::object pythonExceptionInstance(*upcasted);
  PyErr_SetObject(clusterExecutionAsClusterExceptionType, pythonExceptionInstance.ptr());
  }
}

register_exception_translator<ClusterException>(&translateClusterExecutionAsClusterException);

解决方案2
 1  2017-10-06 09:28:30

I don't know about your C++ code. 我不知道你的C ++代码。 But there is small problem with your python code. 但是你的python代码有一个小问题。 Catch ClusterExecutionException before ClusterException . 在ClusterExecutionException之前捕获ClusterException 。 You should always put child exception handler before base exception. 您应该始终在基本异常之前放置子异常处理程序。

In test_exception if ClusterExecutionException raised it will be catch by ClusterException before it could reach ClusterExecutionException . 在test_exception如果ClusterExecutionException引发，它将被ClusterException捕获，然后才能到达ClusterExecutionException 。

code should be as below code 代码应该如下代码 

def test_exception(exCase):
    try:
        cluster.boomTest(exCase)

    except ClusterExecutionException as ex:
        print 'Success! ClusterExecutionException gracefully handled:' \
            '\n message="%s"' \
            '\n errorType="%s"' \
            '\n clusterResponse="%s"' % (ex.message, ex.errorType, ex.clusterResponse)
    except ClusterException as ex:
        print 'Success! ClusterException gracefully handled:' \
            '\n message="%s"' % ex.message
    except:
        print 'Caught unknown exception: %s "%s"' % (sys.exc_info()[0], sys.exc_info()[1])

now do I have tried in Boost-Python while registering the exception translation of ClusterExecutionException to register it as its base ClusterException , what you have mentioned in question. 现在I have tried in Boost-Python while registering the exception translation of ClusterExecutionException to register it as its base ClusterException ，这就是你所提到的问题。

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