How to use boost context correctly
I want to implement a quest system for my game engine using fibers. After searching the web for a good fiber implementation, I found that Boost.Context is a good starting point.
Update 1 : I want to implement my own scheduling algorithm, so Boost.Fiber , Boost.Coroutine , Boost.Coroutine2 not suitable for my implementation.
After compiling boost for x64 architecture and trying to run a basic example from boost documentation , I got the following exception:
boost :: context :: detail :: forced_unwind in memory location
This is the code I was trying to run (Visual Studio 2015 version, Windows 7):
#include <iostream>
#include <boost\context\continuation.hpp>
namespace ctx=boost::context;
int main()
{
ctx::continuation source=ctx::callcc
(
[](ctx::continuation && sink)
{
int a=0;
int b=1;
for(;;)
{
sink=sink.resume(a);
auto next=a+b;
a=b;
b=next;
}
return std::move(sink);
}
);
for (int j=0;j<10;++j) {
std::cout << source.get_data<int>() << " ";
source=source.resume();
}
return 0;
}
The code worked correctly (correct output: 0 1 1 2 3 5 8 13 21 34 55), but when it finished the run I got an exception.
Update 2: Exception only happens for release build
I want to ask two questions regarding boost context:
1) What caused the stack erase exception and how to avoid it?
2) I found the acceleration documentation to be a bit shallow and couldn't find another tutorial on how to use boost context. Can you point me to some good sources / tutorials on context acceleration?
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First, the forced disconnect exception is documented (and this is what gives contextual RAII support).
Secondly, if you want to use Fibers built from Boost Context, use the existing libraries:
- Boost Fiber
- possibly also Boost Coroutine / Boost Coroutine
Update:
Testing with Boost 1.64.0 in Microsoft (R) C / C ++ Compiler Optimization Version 19.00.24215.1 for x64 I was unable to reproduce the behavior:
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After 0 is returned, the original object is not at the position to be destroyed.
Something like:
namespace ctx = boost::context;
int a;
bool stop = false;
{
ctx::continuation source = ctx::callcc(
[&stop, &a](ctx::continuation && sink) {
a = 0;
int b = 1;
for (;;) {
sink = sink.resume();
if (stop)
break;
int next = a + b;
a = b;
b = next;
}
return std::move(sink);
});
for (int j = 0; j < 10; ++j) {
std::cout << a << " ";
source = source.resume();
}
stop = true;
source.resume();
}
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If you are on Windows and the error only occurs in release mode, you may need to verify that the compiler flags are set correctly.
Hence :
Windows using fcontext_t: Disable global program optimization (/ GL) and change / EHsc (the compiler assumes that functions declared extern "C" never throw a C ++ exception) in / EHs (tells the compiler that functions are declared extern " C might throw an exception).
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