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Discrete-event simulation in C++20 using coroutines

License: MIT License

C++ 94.56% CMake 5.44%

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youcannotburnmyshadow chenyuho liuq abdelhak-khemiri ajunlonglive efokken-abb rodrigues-mariana invictuswingssrl thewaffler

simcpp20's Issues

memory leaks

Do you know anything more about the memory leaks?

I would like to use your code but don't really know, how much I should worry about the leaks. Do they only happen at program termination, after which the OS will reclaim everything regardless or can they accumulate?
In the end, if I use your project, I'm prepared to find and fix the leaks but it's rather opaque to me right now.

Memory leaks

If an event awaited by a process is never triggered, the process coroutine will stay suspended until the program exits. This means that all events referenced by the process and the process are leaked. Example:

#include <cstdio>

#include "fschuetz04/simcpp20.hpp"

simcpp20::event<> process(simcpp20::simulation<> &sim) {
  printf("[%.0f] start\n", sim.now());
  co_await sim.event();
  printf("[%.0f] end\n", sim.now());
}

int main() {
  simcpp20::simulation<> sim;
  process(sim);
  sim.run();
}

In this case, the event created in process is never triggered, so a memory leak occurs.

Add yield

Just a suggestion for a possible enhancement (I'm sure you already thought of it, but just in case): It might be possible to also support yield events from coroutines.

Latest changes

I tried the latest changes, things seem to work, then I tried your example, 'value_process'.
I think before it displayed 42, now it crashes, somewhere in event::process, on a call on resume: promise->process_handle().resume().

There is a null pointer access violation, I guess that could be overcome by checking the 'address' of the handle, but I'm not sure it will entirely solve the problem.

Adding this:

if (!promise->process_handle().address())
        continue;

in the for loop before checking the promise avoids the crash, but still does not work ok, as expected, nothing is displayed.

clang

Hi!

I forked your repository (my only repository actually) and found that clang now works more or less out of the box, except for ping-pong, where clang apparently fails
to recognize some template magic. Maybe you understand more from the error message, if you're interested.

FAILED: examples/CMakeFiles/ping_pong.dir/ping_pong.cpp.o
ccache /usr/bin/clang++ -D_GLIBCXX_DEBUG -I/home/user/git/simcpp20/include -g -stdlib=libc++ -fsanitize=address -fno-omit-frame-pointer -fsanitize=undefined -O0 -Werror -pedantic-errors -pedantic -Wall -Wextra -Wcast-align -Wcast-qual -Wctor-dtor-privacy -Wundef -Wdisabled-optimization -Wformat=2 -Winit-self -Wmissing-include-dirs -Wold-style-cast -Woverloaded-virtual -Wredundant-decls -Wsign-promo -Wstrict-overflow=5 -Wunused -Wno-error=unused-parameter -Wno-error=unused -Wno-error=unused-variable -Wno-error=unused-value -Wdelete-non-virtual-dtor -Wno-error=undef -Wunreachable-code -fcolor-diagnostics -Wno-error=unused-private-field -Wno-error=unknown-warning-option -std=c++20 -MD -MT examples/CMakeFiles/ping_pong.dir/ping_pong.cpp.o -MF examples/CMakeFiles/ping_pong.dir/ping_pong.cpp.o.d -o examples/CMakeFiles/ping_pong.dir/ping_pong.cpp.o -c /home/user/git/simcpp20/examples/ping_pong.cpp
In file included from /home/user/git/simcpp20/examples/ping_pong.cpp:6:
In file included from /home/user/git/simcpp20/include/fschuetz04/simcpp20.hpp:6:
In file included from /home/user/git/simcpp20/include/fschuetz04/simcpp20/simulation.hpp:16:
/home/user/git/simcpp20/include/fschuetz04/simcpp20/value_event.hpp:194:31: error: no matching constructor for initialization of 'ev_type'
    casted_data->value_ = new Value(std::forward<Args>(args)...);
                              ^     ~~~~~~~~~~~~~~~~~~~~~~~~
/home/user/git/simcpp20/include/fschuetz04/simcpp20/value_event.hpp:44:5: note: in instantiation of function template specialization 'simcpp20::value_event<ev_type>::set_value<simcpp20::value_event<ev_type> &>' requested here
    set_value(std::forward<Args>(args)...);
    ^
/home/user/git/simcpp20/examples/ping_pong.cpp:21:17: note: in instantiation of function template specialization 'simcpp20::value_event<ev_type>::trigger<simcpp20::value_event<ev_type> &>' requested here
    their_event.trigger(my_event);
                ^
/home/user/git/simcpp20/examples/ping_pong.cpp:10:8: note: candidate constructor (the implicit copy constructor) not viable: no known conversion from 'simcpp20::value_event<ev_type>' to 'const ev_type' for 1st argument
struct ev_type {
       ^
/home/user/git/simcpp20/examples/ping_pong.cpp:10:8: note: candidate constructor (the implicit move constructor) not viable: no known conversion from 'simcpp20::value_event<ev_type>' to 'ev_type' for 1st argument
/home/user/git/simcpp20/examples/ping_pong.cpp:10:8: note: candidate constructor (the implicit default constructor) not viable: requires 0 arguments, but 1 was provided
In file included from /home/user/git/simcpp20/examples/ping_pong.cpp:6:
In file included from /home/user/git/simcpp20/include/fschuetz04/simcpp20.hpp:6:
/home/user/git/simcpp20/include/fschuetz04/simcpp20/simulation.hpp:67:8: error: no matching member function for call to 'set_value'
    ev.set_value(std::forward<Args>(args)...);
    ~~~^~~~~~~~~
/home/user/git/simcpp20/examples/ping_pong.cpp:28:25: note: in instantiation of function template specialization 'simcpp20::simulation<double>::timeout<ev_type, simcpp20::value_event<ev_type> &>' requested here
  auto ping_event = sim.timeout<ev_type>(0, pong_event);
                        ^
/home/user/git/simcpp20/include/fschuetz04/simcpp20/value_event.hpp:192:36: note: candidate template ignored: substitution failure [with Args = <simcpp20::value_event<ev_type> &>]
  template <typename... Args> void set_value(Args &&...args) const {
                                   ^
2 errors generated.
ninja: build stopped: subcommand failed.

Double Free of std::coroutine_handle

Apparently, when using the value_event class the system incurs in a double free error when exiting the program (i.e., all processes have been stopped).

value_process(64525,0x100f6c580) malloc: *** error for object 0x600001844050: pointer being freed was not allocated

Unfortunately I cannot go too much in depth for debugging, but it seems that the error is related to the following destructor (and possibly to this phenomenon) in event.hpp:

 class data {
  public:
    ...
    /// Destructor.
    virtual ~data() {
      for (auto &handle : handles_) {
        handle.destroy();
      }
    }
}

A possible workaround might be to use a std::suspend_always instead of a std::suspend_never for the final_suspend method, however I am not able to understand the implications for the simulation.

My system is a MacOS 12.3.1 running on Arm M1 Pro. The code has been compiled with g++-11 (Homebrew GCC 11.2.0_3) 11.2.0.

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