I export a function from d to c++ with extern(C++). The d code has a try catch statement on the highest level.Whenever the d code throws a exception the program aborts. I have c++ objects on the call stack and call the function in d. Then there is the d try catch statement and then the d exception throw.
The d code:
extern (C++) void ThrowEx() {
try {
throw new Exception("hello");
} catch (Exception ex) {
}
}
The c++ code:
extern "C" int rt_init();
void ThrowEx();
void func() {
rt_init();
ThrowEx();
}
When I change ThrowEx to not throw an exception everything works as expected. The d code gets executed and no error occurs.
When the program crashes the following output is generated:
dwarfeh(224) fatal error
uncaught exception
Related
In my iOS project, I use a C++ module. The C++ module throws exception for some cases and the Objective C++ wrapper fails to catch it. For instance
Here is my HelloWorld.h
#include <string>
using namespace std;
class HelloWorld{
public:
string helloWorld();
};
#endif
Implementation HelloWorld.cpp
#include "HelloWorld.h"
string HelloWorld::helloWorld(){
throw (std::runtime_error("runtime_error")); // Throwing exception to test
string s("Hello from CPP");
return s;
}
Objective C++ wrapper HelloWorldIOSWrapper.h
#import <Foundation/Foundation.h>
#interface HelloWorldIOSWrapper:NSObject
- (NSString*)getHello;
#end
#endif /* HelloWorldIOSWrapper_h */
Implementation HelloWorldIOSWrapper.mm
#import "HelloWorldIOSWrapper.h"
#include "HelloWorld.h"
#implementation HelloWorldIOSWrapper
- (NSString*)getHello{
try {
HelloWorld h;
NSString *text=[NSString stringWithUTF8String: h.helloWorld().c_str()];
return text;
} catch (const std::exception & e) {
NSLog(#"Error %s", e.what());
}
return nil;
}
#end
#import "HelloWorldIOSWrapper.h" is added to the Bridging-Header
And now, when I try to invoke getHello() from controller, app crashes leaving the below message in log
libc++abi: terminating with uncaught exception of type std::runtime_error: runtime_error
dyld4 config: DYLD_LIBRARY_PATH=/usr/lib/system/introspection DYLD_INSERT_LIBRARIES=/Developer/usr/lib/libBacktraceRecording.dylib:/Developer/usr/lib/libMainThreadChecker.dylib:/Developer/Library/PrivateFrameworks/DTDDISupport.framework/libViewDebuggerSupport.dylib
terminating with uncaught exception of type std::runtime_error: runtime_error
I expect that the exception must be caught in the wrapper, but, no idea why is it not caught leading to app crash. What do I miss?
C++ Interoperability
In 64-bit processes, Objective-C exceptions (NSException) and C++
exception are interoperable. Specifically, C++ destructors and
Objective-C #finally blocks are honored when the exception mechanism
unwinds an exception. In addition, default catch clauses—that is,
catch(...) and #catch(...)—can catch and rethrow any exception
On the other hand, an Objective-C catch clause taking a dynamically
typed exception object (#catch(id exception)) can catch any
Objective-C exception, but cannot catch any C++ exceptions. So, for
interoperability, use #catch(...) to catch every exception and #throw;
to rethrow caught exceptions. In 32-bit, #catch(...) has the same
effect as #catch(id exception).
#try {
}
#catch (...) {
}
I'm using LibJIT to JIT-compile a programming language. My compiler is written in C++, so I have a C++ program calling the LibJIT library, which is written in C.
In my C++ code I have some functions that throw exceptions, and sometimes these get triggered on the far side of a LibJIT-compiled function. That is, my C++ program uses LibJIT to compile a function, calls it, and the JIT-compiled function in turn calls a C++ function that throws an exception. But instead of the exception being propagated back through the JIT-compiled function to my handler, the runtime calls std::terminate.
Apparently the exception-handling mechanism needs each function in the call stack to implement some kind of exception support. When compiling C code, the -fexceptions flag tells the compiler (at least gcc) to include this support.
Is there a way to include this exception support in my LibJIT-generated functions?
I tried using the LibJIT instructions to set up a "catcher" block that rethrows all exceptions, but that didn't work; it looks like the LibJIT's exception-handling model is separate from the C++ model.
Obviously I don't really want to throw C++ exceptions into my language's code, and I'll have to figure out some other error-handling strategy. But I'm wondering if it's even possible to get it to work.
Here's a sample program that demonstrates the issue. I'm sorry it's this long but LibJIT is pretty low-level so you have to write a lot of code to get anything done. I'm compiling on Linux with clang 10.0.0.
#include <array>
#include <exception>
#include <iostream>
#include <string>
#include <jit/jit.h>
class ex : public std::exception {};
extern "C" int bad(int arg) {
std::cout << "Called with arg=" << arg << std::endl;
throw ex();
}
jit_function_t build_function(jit_context_t context) {
// The signature of the compiled function and "bad" are the same.
std::array<jit_type_t, 1> params{jit_type_int};
jit_type_t signature = jit_type_create_signature(jit_abi_cdecl, jit_type_int, params.data(), params.size(), 1);
jit_function_t function = jit_function_create(context, signature);
jit_value_t arg_value = jit_value_get_param(function, 0);
jit_value_t bad_value =
jit_value_create_nint_constant(function, jit_type_void_ptr, (reinterpret_cast<jit_nint>(bad)));
std::array<jit_value_t, 1> bad_args{arg_value};
jit_value_t result = jit_insn_call_indirect(function, bad_value, signature, bad_args.data(), bad_args.size(), 0);
jit_insn_return(function, result);
jit_function_compile(function);
return function;
}
int main(int argc, char* argv[]) {
// This exception will be caught:
try {
bad(7);
} catch (const ex&) {
std::cout << "Caught exception from direct call" << std::endl;
}
// Initialize libjit.
// We're single-threaded so not going to bother with jit_context_build_start/jit_context_build_end.
jit_init();
jit_context_t context = jit_context_create();
jit_function_t function = build_function(context);
// This one will not be caught, calls std::terminate instead:
try {
int (*closure)(int) = reinterpret_cast<int (*)(int)>(jit_function_to_closure(function));
closure(7);
} catch (const ex&) {
std::cout << "Caught exception from libjit call" << std::endl;
}
return 0;
}
Output:
Called with arg=7
Caught exception from direct call
Called with arg=7
terminate called after throwing an instance of 'ex'
what(): std::exception
Aborted
I wrote the following program:
// Example program
#include <iostream>
#include <string>
#include <exception>
struct A {
A() {
std::cout << "A ctor" << std::endl;
}
~A() {
std::cout << "A dtor" << std::endl;
try {
throw std::exception();
} catch (std::exception &e) {
std::cout << "Internal exception caught" << std::endl;
}
}
};
int main()
{
try {
A a;
throw std::exception();
} catch (std::exception &e) {
std::cout << "External exception caught" << std::endl;
}
}
The output I expected was:
A ctor
A dtor
Internal exception caught
External exception caught
And this is what I'm getting in GCC. But when I'm using Visual Studio (version 2013) the output I'm getting is:
A ctor
External exception caught
What's going on here?
MSVC2013 is wrong here and GCC is right. Unfortunately, I cannot find an appropriate reference from the standard now, but according to std::uncaught_exception:
For example, if stack unwinding causes a stack-allocated object to be
destructed, the destructor for that object could run code that throws
an exception as long as the exception is caught by some catch block
before escaping the destructor.
For more details see also "Throwing during stack unwinding" section here.
Finally, as it is mentioned by #StoryTeller, this behaviour is not reproducible with newer MSVC versions.
The closest match in the standard I am able to find is the next (from the N3936 draft):
15.1 Throwing an exception [except.throw]
If the exception handling mechanism, after completing the
initialization of the exception object but before the activation of a
handler for the exception, calls a function that exits via an
exception, std::terminate is called.
So, formally, it is perfectly valid to call a function during stack unwinding process (including destructor) which might deal with exception, but if the exception inside such function is not caught by appropriate catch block then std::terminate must be called.
Situation
I want to create a Python language binding for a C++ API using SWIG. Some of the API functions may throw exceptions. The C++ application has a hierarchy of self-defined exceptions, like this example:
std::exception
-> API::Exception
-> API::NetworkException
-> API::TimeoutException
-> API::UnreachableException
-> API::InvalidAddressException
The desired behavior is as follows:
All exception types should have a matching Python class as wrapper. These wrapper classes should be valid Python exceptions.
When an API call throws a C++ exception, it should be caught. The corresponding Python exception (i.e. the wrapper class of the caught C++ exception) should be thrown.
This should be a dynamic process: the Python exception type is decided at runtime, only based on the runtime type of the caught C++ exception. This way, there is no need to describe the complete exception hierarchy in the SWIG interface file.
Problems and questions
Wrapper classes are no Python exceptions.
While SWIG creates wrapper classes for all self-defined exceptions (like for any other class), these classes are not Python exceptions. The wrapper of the base exception (API::Exception in the example) extends Object instead of BaseException, the Python class of which all exceptions in Python should be derived.
Furthermore, it doesn't seem possible to let SWIG add a parent class manually. Note this is possible when using SWIG with Java through the usage of %typemap(javabase) (see SWIG documentation for details).
How can the Python C API throw a user-defined exception?
The most common way to throw a Python exception from the Python C API is by calling PyErr_SetString [reference]. This is also shown in the demo application below.
But this is only trivial with the standard (built-in) exceptions of Python, because references to them are stored in global variables [reference] in the Python C API.
I know there is a method PyErr_NewException [reference] to get references to self-defined exceptions, but I didn't got this working.
How can the Python C API evaluate the C++ type at runtime and then find the corresponding Python wrapper class by name?
I assume a Python class can be searched by name at runtime, through the reflection part of the Python C API. Is this the way to go? And how is it done in practice?
Demo application
To experiment with this problem, I created a tiny C++ API with a single function that calculates the factorial of a number. It has a minimal self-defined exception hierarchy, consisting of only one class TooBigException.
Note this exception acts as the base exception in the general problem and the application should work with any subclass of it. This means the solution may only use the dynamic (i.e. runtime) type of the caught exception to rethrow it in Python (see below).
The full source code of the demo application is as follows:
// File: numbers.h
namespace numbers {
int fact(int n);
}
// File: numbers.cpp
#include "TooBigException.h"
namespace numbers {
int fact(int n) {
if (n > 10) throw TooBigException("Value too big", n);
else if (n <= 1) return 1;
else return n*fact(n-1);
}
}
// File: TooBigException.h
namespace numbers {
class TooBigException: public std::exception {
public:
explicit TooBigException(const std::string & inMessage,
const int inValue);
virtual ~TooBigException() throw() {}
virtual const char* what() const throw();
const std::string & message() const;
const int value() const;
private:
std::string mMessage;
int mValue;
};
}
// File: TooBigException.cpp
#include "TooBigException.h"
namespace numbers {
TooBigException::TooBigException(const std::string & inMessage, const int inValue):
std::exception(),
mMessage(inMessage),
mValue(inValue)
{
}
const char* TooBigException::what() const throw(){
return mMessage.c_str();
}
const std::string & TooBigException::message() const {
return mMessage;
}
const int TooBigException::value() const {
return mValue;
}
}
To get the Python binding I use the following SWIG interface file:
// File: numbers.i
%module numbers
%include "stl.i"
%include "exception.i"
%{
#define SWIG_FILE_WITH_INIT
#include "TooBigException.h"
#include "numbers.h"
%}
%exception {
try {
$action
}
catch (const numbers::TooBigException & e) {
// This catches any self-defined exception in the exception hierarchy,
// because they all derive from this base class.
<TODO>
}
catch (const std::exception & e)
{
SWIG_exception(SWIG_RuntimeError, (std::string("C++ std::exception: ") + e.what()).c_str());
}
catch (...)
{
SWIG_exception(SWIG_UnknownError, "C++ anonymous exception");
}
}
%include "TooBigException.h"
%include "numbers.h"
So every call to the API is wrapped by a try-catch block. First exceptions of our base type are caught and handled. Then all other exceptions are caught and rethrown using the SWIG exception library.
Note any subclass of numbers::TooBigException is caught and the wrappers of their dynamic (i.e. runtime) type should be thrown, not the wrapper of their static (i.e. compile time) type, which is always TooBigException!
The project can be built easily by executing the following commands on a Linux machine:
$ swig -c++ -python numbers.i
$ g++ -fPIC -shared TooBigException.cpp numbers.cpp numbers_wrap.cxx \
-I/usr/include/python2.7 -o _numbers.so
Current implementation
My current implementation still (successfully) throws a fixed standard Python exception. The code <TODO> above is then replaced by:
PyErr_SetString(PyExc_Exception, (std::string("C++ self-defined exception ") + e.what()).c_str());
return NULL;
Which gives the following (expected) behavior in Python:
>>> import numbers
>>> fact(11)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
Exception: C++ self-defined exception Value too big
It looks like someone has answered your basic question over on the swig-user list...
%exception {
try {
$action
} catch (MyException &_e) {
SWIG_Python_Raise(SWIG_NewPointerObj(
(new MyException(static_cast<const MyException& >(_e))),
SWIGTYPE_p_MyException,SWIG_POINTER_OWN),
"MyException", SWIGTYPE_p_MyException);
SWIG_fail;
}
}
This does assume you have generated wrappers for your exception classes, I believe.
Example for your hierarchy
std::exception
-> API::Exception
-> API::NetworkException
-> API::TimeoutException
-> API::UnreachableException
-> API::InvalidAddressException
example.i:
%module example
%include "stl.i"
%include "exception.i"
%{
#define SWIG_FILE_WITH_INIT
#include "example.cpp"
%}
%{
#define CATCH_PE(Namespace,Exception) \
catch(const Namespace::Exception &e) \
{ \
SWIG_Python_Raise(SWIG_NewPointerObj(new Namespace::Exception(e), \
SWIGTYPE_p_##Namespace##__##Exception,SWIG_POINTER_OWN), \
#Exception, SWIGTYPE_p_##Namespace##__##Exception); \
SWIG_fail; \
} \
/**/
// should be in "derived first" order
#define FOR_EACH_EXCEPTION(ACTION) \
ACTION(API,UnreachableException) \
ACTION(API,TimeoutException) \
ACTION(API,InvalidAddressException) \
ACTION(API,NetworkException) \
ACTION(API,Exception) \
/**/
// In order to remove macros, need traits:
// http://swig.10945.n7.nabble.com/traits-based-access-to-swig-type-info-td12315.html
%}
%exception {
try {
$action
}
FOR_EACH_EXCEPTION(CATCH_PE)
catch (const std::exception & e)
{
SWIG_exception(SWIG_RuntimeError, (std::string("C++ std::exception: ") + e.what()).c_str());
}
catch (...)
{
SWIG_exception(SWIG_UnknownError, "C++ anonymous exception");
}
}
%include "example.cpp"
example.cpp:
#include <exception>
#include <stdexcept>
namespace API
{
struct Exception: std::exception
{
virtual const char* what() const throw()
{
return "It is API::Exception";
}
};
struct NetworkException: Exception
{
virtual const char* what() const throw()
{
return "It is API::NetworkException";
}
};
struct TimeoutException: NetworkException
{
virtual const char* what() const throw()
{
return "It is API::TimeoutException";
}
};
struct UnreachableException: NetworkException
{
virtual const char* what() const throw()
{
return "It is API::UnreachableException";
}
};
struct InvalidAddressException: Exception
{
virtual const char* what() const throw()
{
return "It is API::InvalidAddressException";
}
};
inline void select(int i)
{
switch(i)
{
case 0: throw Exception();
case 1: throw NetworkException();
case 2: throw TimeoutException();
case 3: throw UnreachableException();
case 4: throw InvalidAddressException();
default: throw std::runtime_error("It is std::runtime_error");
}
}
}
Build:
swig -c++ -python example.i &&
g++ -fPIC -shared -lpython2.7 example.cpp example_wrap.cxx -I/usr/include/python2.7 -o _example.so
test.py:
#!/usr/bin/env python2.7
from exceptions import BaseException
from example import *
def catch(i):
try:
select(i)
except UnreachableException as e:
print "Caught UnreachableException"
print e.what()
print e
except TimeoutException as e:
print "Caught TimeoutException"
print e.what()
print e
except InvalidAddressException as e:
print "Caught InvalidAddressException"
print e.what()
print e
except NetworkException as e:
print "Caught NetworkException"
print e.what()
print e
except Exception as e:
print "Caught Exception"
print e.what()
print e
except BaseException as e:
print "Caught BaseException"
print str(e)
print "_"*16
for i in xrange(6):
catch(i)
Output is:
Caught Exception
It is API::Exception
<example.Exception; proxy of <Swig Object of type 'API::Exception *' at 0x7f9f54a02120> >
________________
Caught NetworkException
It is API::NetworkException
<example.NetworkException; proxy of <Swig Object of type 'API::NetworkException *' at 0x7f9f54a02120> >
________________
Caught TimeoutException
It is API::TimeoutException
<example.TimeoutException; proxy of <Swig Object of type 'API::TimeoutException *' at 0x7f9f54a02120> >
________________
Caught UnreachableException
It is API::UnreachableException
<example.UnreachableException; proxy of <Swig Object of type 'API::UnreachableException *' at 0x7f9f54a02120> >
________________
Caught InvalidAddressException
It is API::InvalidAddressException
<example.InvalidAddressException; proxy of <Swig Object of type 'API::InvalidAddressException *' at 0x7f9f54a02120> >
________________
Caught BaseException
C++ std::exception: It is std::runtime_error
________________
Based on answer in maillist.
I'm trying to play with handling unexpected exceptions, but cannot make it to work. This is example from: C++ Reference
// set_unexpected example
#include <iostream>
#include <exception>
using namespace std;
void myunexpected () {
cerr << "unexpected called\n";
throw 0; // throws int (in exception-specification)
}
void myfunction () throw (int) {
throw 'x'; // throws char (not in exception-specification)
}
int main (void) {
set_unexpected (myunexpected);
try {
myfunction();
}
catch (int) { cerr << "caught int\n"; }
catch (...) { cerr << "caught other exception (non-compliant compiler?)\n"; }
return 0;
}
They say that output should be:
Output:
unexpected called
caught int
Which doesn't happen when I try it. My output is:
caught other exception (non-compliant compiler?)
I'm using VS2010 sp1
Documentation of unexpected says:
The C++ Standard requires that unexpected is called when a function throws an exception that is not on its throw list. The current implementation does not support this.
So the answer is that VC10 is a non-compliant compiler.
Visual Studio does not implement the standard correctly. See this MSDN page. The int is parsed, but not used.
Visual C++ always issues Warning C4290 when function has exception specifiers. From the same article in MSDN: "A function is declared using exception specification, which Visual C++ accepts but does not implement." So, this compiler does not comply with standard.