|  | exceptions and resource deallocation | | |
| | | Vasilis |  |
|  Posted: Tue Jul 29, 2008 4:23 pm Post subject: exceptions and resource deallocation |  |
| |  | |
Dear list,
I have problems understanding what exactly goes on during stack
unwinding and resource deallocation. Here is my sample code:
#include <memory>
class exception{};
class dummy{};
void f ( int a ) {
if ( a == 7 )
throw exception();
}
int main() {
std::auto_ptr<dummy> temp( new dummy() );
f ( 7 );
return 1;
}
//sample code end
Now, i must admit, with great surprise, feeding this to valgrind, i
get back a byte leaked, besides a mysterious error that has to do with
the exception throwing itself:
==15040== 1 bytes in 1 blocks are still reachable in loss record 1 of
2
==15040== at 0x4022AA7: operator new(unsigned) (vg_replace_malloc.c:
163)
==15040== by 0x80485FB: main (example.cpp:13)
==15040==
==15040==
==15040== 81 bytes in 1 blocks are still reachable in loss record 2 of
2
==15040== at 0x402239B: malloc (vg_replace_malloc.c:149)
==15040== by 0x40EF371: __cxa_allocate_exception (in /usr/lib/
libstdc++.so.6.0.
==15040== by 0x80485C9: f(int) (example.cpp:9)
==15040== by 0x8048618: main (example.cpp:14)
==15040==
==15040== LEAK SUMMARY:
==15040== definitely lost: 0 bytes in 0 blocks.
==15040== possibly lost: 0 bytes in 0 blocks.
==15040== still reachable: 82 bytes in 2 blocks.
==15040== suppressed: 0 bytes in 0 blocks.
//valgrind output terminates here.
I am not worried at all by the second leak. The first one surprises
me.
Isn't this all about smart pointers? resource deallocation on
exception throwing? What's wrong?
Thank you all,
vasilis.
--
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| |
| | | Pete Becker | |
| | Posted: Tue Jul 29, 2008 8:59 pm Post subject: Re: exceptions and resource deallocation | |
On 2008-07-29 06:23:35 -0400, Vasilis <VASILI3000@hotmail.com> said:
| Quote: |
#include <memory
class exception{};
class dummy{};
void f ( int a ) {
if ( a == 7 )
throw exception();
}
int main() {
std::auto_ptr<dummy> temp( new dummy() );
f ( 7 );
return 1;
}
//sample code end
|
Nobody caught the exception, so the implementation calls
std::terminate(), and it's implementation-defined whether the stack is
unwound before that call. Add try and catch blocks to main, and catch
the exception.
--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)
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| |
| | | Mathias Gaunard | |
| | Posted: Tue Jul 29, 2008 9:28 pm Post subject: Re: exceptions and resource deallocation | |
On 29 juil, 18:23, Vasilis <VASILI3...@hotmail.com> wrote:
| Quote: | Dear list,
I have problems understanding what exactly goes on during stack
unwinding and resource deallocation. Here is my sample code:
#include <memory
class exception{};
class dummy{};
void f ( int a ) {
if ( a == 7 )
throw exception();
}
int main() {
std::auto_ptr<dummy> temp( new dummy() );
f ( 7 );
return 1;}
|
The destructor of auto_ptr will not be called here, because the
program will abort before that.
Try
int main()
{
try
{
std::auto_ptr<dummy> temp(new dummy());
f(7);
}
catch(...)
{
std::cerr << "An unknown exception occured!" << std::endl;
}
}
--
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| |
| | | David Abrahams | |
| | Posted: Wed Jul 30, 2008 5:32 am Post subject: Re: exceptions and resource deallocation | |
on Tue Jul 29 2008, Vasilis <VASILI3000-AT-hotmail.com> wrote:
| Quote: | Dear list,
I have problems understanding what exactly goes on during stack
unwinding and resource deallocation. Here is my sample code:
#include <memory
class exception{};
class dummy{};
void f ( int a ) {
if ( a == 7 )
throw exception();
}
int main() {
std::auto_ptr<dummy> temp( new dummy() );
f ( 7 );
return 1;
}
//sample code end
Now, i must admit, with great surprise, feeding this to valgrind, i
get back a byte leaked, besides a mysterious error that has to do with
the exception throwing itself:
|
The rules say that if you let an exception escape your program without
catching it, the compiler is allowed (but not required) to skip
unwinding and any associated destructors. That's what's happening to
you.
HTH,
--
Dave Abrahams
BoostPro Computing
LINK
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| |
| | | Vasilis | |
| | Posted: Wed Jul 30, 2008 10:28 am Post subject: Re: exceptions and resource deallocation | |
On Jul 29, 9:32 pm, David Abrahams <d...@boostpro.com> wrote:
| Quote: | The rules say that if you let an exception escape your program without
catching it, the compiler is allowed (but not required) to skip
unwinding and any associated destructors. That's what's happening to
you.
I didn't know that the compiler was not required to unwind the stack |
on exit. true is that
if i catch the exception there is no memory leak.
thank you all,
Vasilis.
--
[ See LINK for info about ]
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| |
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