Re: [Boost-users] [context] Crash in case of exception from a context

11 Mar 2015

      ...
I use boost::context to implement cooperative multitasking. At the 
moment I
use boost 1.57 on Windows 7 with VisualStudio 2013.
Everything works fine until I throw an exception from a context created 
by
"boost::context::make_fcontext(.......)".
This guy metioned in his blogpost, that this problem was solved in boost
1.53 ("Boost 1.53 has updated and fixed version of boost::context
Actually the exception never leaves the stack frame of the context, 
because I have put a try catch block inside the context-function as it was 
recommended. - If I got the docs right

Here is a small demo. This crashes from V2013 standard C++ unit test.
When I step on the exception throwing line (the exception type does not 
matter) then I get the "First-chance exception at 0x71E026A2 (clr.dll) in 
vstest.executionengine.x86.exe: 0x80000001: Not implemented (parameters: 
0x00000001, 0x0644AC84)." exception and when I pass it to the system then 
a lot of  "0xC0000005: Access violation" exceptions.
I have also played around with the stack size, but it does not seem to 
have any effect.

void fException()
{
        std::cout << "I am still ok" << std::endl;
        throw int(42); // The crash occurs here
}

void f1(intptr_t)
{
        try
        {
                std::cout << "Greetings from context f1" << std::endl;
                fException();
                std::cout << "Never reach this" << std::endl;
        }
        catch (...)
        {
                std::cout << "Exception caught" << std::endl;
        }
}

void test()
{
        std::size_t size(512*1024);
        char* stack1((char*)std::malloc(size));
        void* stackPointer1(stack1 + size);

        boost::context::fcontext_t fcm, fc1;

        fc1 = boost::context::make_fcontext(stackPointer1, size, f1);
        std::cout << "Greetings from main thread stack" << std::endl;
        boost::context::jump_fcontext(&fcm, fc1, 0);
}

From:   Nat Goodspeed <nat@lindenlab.com>
To:     "boost-users@lists.boost.org" <boost-users@lists.boost.org>, 
Date:   10.03.2015 17:40
Subject:        Re: [Boost-users] [context] Crash in case of exception 
from a  context
Sent by:        "Boost-users" <boost-users-bounces@lists.boost.org>

On Tue, Mar 10, 2015 at 10:32 AM,  <Tamas.Ruszkai@leica-geosystems.com> 
wrote:

library
...
that addresses exactly this problem. "), but somehow I still have the 
same
thing in 1.57. Is there some special preprocessor flag (#define) that I 
have
to activate to get this fix?
That contradicts what the Boost 1.57 documentation itself says [0]:

"Exceptions in context-function
If the context-function emits an exception, the behaviour is undefined.

(!) Important
context-function should wrap the code in a try/catch block."

[0] 
http://www.boost.org/doc/libs/1_57_0/libs/context/doc/html/context/context.h...

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Re: [Boost-users] [context] Crash in case of exception from a context

Tamas.Ruszkai＠leica-geosystems.com