Develop branch and Asio? about fiber HOT 13 CLOSED

2015-02-11 13:36 GMT+01:00 erakadjiev [email protected]:

Hello Oliver,

I contacted you a week ago to ask which development branch to use. I saw
that in the meantime develop became the one.

I just got around to starting to work with Boost Fiber. I built it with
modular Boost (which btw. wasn't trivial) and wanted to re-read the Asio
examples and start coding. I have to use Fibers together with Asio.
Unfortunately, I saw that yesterday you have first modified and then
deleted the Asio-related examples. Doesn't the integration with Asio work
anymore? If so, then what do you recommend? Can the Asio-related problems
be fixed easily? Or should I use an older commit or the old master branch?

Thank you very much!

Best regards,
Emil

the problem is that boost.fiber is C++14-only and some APIs are
incompatible - for instance boost.fiber uses std::exception_ptr and
boost.asio requires boost::exception_ptr

from fiber.

I'll commit a new version of asio examples soon - be aware that boost.fiber requires C++14

from fiber.

Thank you for the reply and the information!
The C++14 requirement would likely be an issue for me.
For now, I started using the master branch and I have a question regarding that: do the Asio-related things work there under C++11? I tried and got compilation errors, but maybe because I compiled the rest of Boost with C++03.

from fiber.

I just spent some time to try and fix the C++11 build issues in the master branch.

One problem was that forward is used without a namespace specifier and this causes conflicts in C++11. If all occurences are simply replaced with boost::forward, then this issue is solved.

The other problem is related to chrono. It requires a bit more work, because Boost Fiber interacts with Boost Thread and Boost Asio using chrono time_points, and there is a discrepancy between which type of chrono those libraries use. Boost Asio automatically switches to std::chrono if it detects a C++11 compiler flag, but Boost Thread has not been updated to do this, and also the master branch of Boost Fiber doesn't have support for std::chrono.
One solution is to recompile Boost Asio with BOOST_ASIO_DISABLE_STD_CHRONO.
The other one is to modify examples/asio/loop.hpp. In the timer_handler function, the return value of boost::fibers::detail::scheduler::instance()->next_wakeup() has to be converted from boost::chrono::time_point to std::chrono::time_point before passing it as a parameter to Asio's timer.expires_at(). I used a conversion based on to_time_t and from_time_t methods. Furthermore, in the run_service function, boost::chrono::seconds(0) has to be replaced with std::chrono::seconds(0), and the <boost/chrono/system_clocks.hpp> include has to be replaced with <chrono>.
For a nicer, more universal solution, conditional compilation using the BOOST_ASIO_HAS_STD_CHRONO macro should be used.

With those changes, the library compiles and the tests run successfully, but when I try to use Fibers in my code, I get a segfault (the coroutine call ( * f->callee_)( caller_, null_ptr) at the end of the resume method of fiber/detail/worker_fiber.hpp causes it).

from fiber.

Well, the code in master is 'deprecated' :/ I'm working on branch develop which will be merged into branch master soon. The issue related to boost.asio is already solved in branch develop - but unfortunately it requires some C++14 features.

from fiber.

It'd be the best if I could use the develop branch, but in my use-case I'm already running into issues due to C++03 and C++11 incompatibility, and I suppose that if I mix C++14 in, even more problems will pop up. That's why I'm trying to stick to the old master branch.

PS: I updated my previous comment, because when using the modified library in my code, I get a segfault.

from fiber.

Regarding the segfault: previously, I did the C++11 Fibers tests both with the current newest version of Modular Boost and the stable 1.57.0 version, and both with BOOST_ASIO_HAS_STD_CHRONO defined and not defined. I always got the segfault.

Now, I tried the develop branch with C++14, but again, I get a segfault. I noticed that the join() on the fiber that calls boost::fibers::asio::run_service returns almost immediately.

This implies that the problem is in my code, but I haven't identified yet what it is. It's nonetheless strange, that the code works perfectly when compiled with g++ myclass.cpp [...], but if I use -std=c++11 or -std=c++14, it segfaults. I'll keep looking for the problem.

from fiber.

With C++14 I managed to solve the segfault issue (but there is a different issue now).

I was spawning a main fiber that in turn spawned many other child fibers, and only some of those children were doing async Asio operations. As in the examples, after spawning the main fiber, I ran a fiber that called boost::fibers::asio::run_service (io_service.run()) and join()ed it. When processing was done, I called io_service.stop() from one of the child fibers.

With C++03 (master, Boost 1.57) this worked correctly.
With C++11 (master, Boost 1.57) and C++14 (develop, Boost 1.58) it led to a segfault, because the join() on the io_service runner fiber returned almost immediately and the subsequent cleanup code was executed prematurely.

I replaced the spawning of fibers that don't do Asio operations (most importantly that of the main fiber) with normal fiber creation. This way, in C++14 the processing completed successfully without segfault.

However, my program doesn't terminate now. The join() on the io_service running fiber doesn't return, even though, io_service.stop() has been called and the internal timer used by the fiber is not active anymore.
Also, the C++11 version still segfaults.

from fiber.

I was getting nowhere with the C++/Boost/Fiber version problem debugging, because I didn't know if my code is wrong or the libraries, so I decided to build and run the included Asio examples (I should have done this earlier).

Here are the results:

Compilation was successful in all cases. I directly used g++ (not Boost Build) version 4.9.2 on 64-bit Ubuntu 14.04.1.
I used no/-std=c++11/-std=c++14 flag, for C++03/C++11/C++14 respectively.
To switch between the various Boost distributions, I used symlinks as /usr/local/include/boost for the headers, and specified the location of the respective library files on the command line (-L/... and -Wl,-rpath=/...).

Have you tried running the examples recently? Do you see different behavior?
If no, then the conclusion is that, currently, Fibers with Asio work only in the master branch with C++03.

from fiber.

With branch master of boost.asio all asio examples work as expected (branch develop C++14)

from fiber.

Thanks for the reply!

I'm also using Boost Asio master (commit 092171c). I tried the examples built using Boost Build, and they indeed work. They are statically linked, while I was linking Boost Fiber and the other required libraries dynamically. It turned out that this is what leads to the subtle failures.

So the result of g++ -std=c++14 echo_server.cpp -o echo_server -lboost_fiber -lboost_context -lboost_thread -lboost_system is that the server compiles, starts, but never gets a successful connection.
By adding -static (and -pthread), that is g++ -std=c++14 -static -pthread echo_server.cpp -o echo_server -lboost_fiber -lboost_context -lboost_thread -lboost_system, the server works well.
The echo_client works both with static and dynamic linking.

What is the correct way to compile applications using Boost Fiber? It would be good to add a short note in the readme about this.

PS: if I add -fsplit-stack -DBOOST_USE_SEGMENTED_STACKS to the g++ command, the compilation fails. Just -fsplit-stack works. By skimming through the errors, it seems that -DBOOST_USE_SEGMENTED_STACKS invalidates the -std=c++14 flag.

from fiber.

using shared libraries works for me - changed Jamfile.v2 to shared + put libboost_context.so in search path + tell the linked to use libboost_context.so -> asio examples do work

using segmented stacks requires to apply property segmented-stacks=on

from fiber.

I'm not going to use Boost Build for my application, and I'm not familiar with it either, so I'd like to make this work with g++ directly.

However, I tried what happens if I use Boost Build for the examples. As you wrote, they work.
I realized that by default the debug variant is built with b2, while with g++ I was using release libs. After trying both, it seems the debug shared library of Boost Fiber works, the release doesn't.

To reproduce:

0. Pre-built Boost library dependencies are in linker search path
1. cd /modboost-folder/libs/fiber/examples
2. Change Jamfile.v2:

   -      <link>static
   +      <link>shared
   +      <linkflags>-lboost_context
   +      <linkflags>-lboost_thread
   

3. debug build:

   • b2 toolset=gcc cxxflags="-std=c++14" address-model=64 architecture=x86 debug
     cd /modboost-folder/bin.v2/libs/fiber/examples/gcc-4.9.2/debug/address-model-64/architecture-x86/threading-multi/asio

   • In one terminal ./echo_server 1234, in another ./echo_client 127.0.0.1 1234
   • Works
4. release build

   • b2 toolset=gcc cxxflags="-std=c++14" address-model=64 architecture=x86 release
     cd /modboost-folder/bin.v2/libs/fiber/examples/gcc-4.9.2/release/address-model-64/architecture-x86/threading-multi/asio

   • In one terminal ./echo_server 1234, in another ./echo_client 127.0.0.1 1234
   • Doesn't work

from fiber.