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Subject: Re: [Boost-users] [context] Crash in case of exception from a context
From: Tamas.Ruszkai_at_[hidden]
Date: 2015-03-11 03:33:35

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)
                std::cout << "Greetings from context f1" << std::endl;
                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_at_[hidden]>
To: "boost-users_at_[hidden]" <boost-users_at_[hidden]>,
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_at_[hidden]>

On Tue, Mar 10, 2015 at 10:32 AM, <Tamas.Ruszkai_at_[hidden]>

> 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
> "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
> that addresses exactly this problem. "), but somehow I still have the
> thing in 1.57. Is there some special preprocessor flag (#define) that I
> 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."


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