c++协程连续循环导致栈溢出

Question

我在visual studio循环中的协程中遇到堆栈溢出异常，发现循环有一个错误阻止它终止但我想知道为什么堆栈溢出？协程甚至可能没有使用堆栈，而是使用堆，即使使用了堆栈，也根本没有任何递归调用

经过一些实验，我可以重现崩溃：

msvc 19.28
wsl 和 mingw64 上的 g++-10
clang-cl windows 上的 10 和 linux

此代码导致堆栈溢出：

#include <stdexcept>
#include <utility>
#include <cstdio>

#ifdef __clang__
#ifdef _WIN32
#pragma message "using clang coroutine header"
#include "clang-cl-coro.h"
#else
#pragma message "using coroutine experimental header"
#include <experimental/coroutine>
#endif

namespace std
{
    template<class P = void>
    using coroutine_handle = experimental::coroutine_handle<P>;

    using suspend_never = experimental::suspend_never;

    using suspend_always = experimental::suspend_always;

}

#else
#pragma message "using coroutine header"
#include <coroutine>
#endif

class vtask
{
    inline static size_t task_count = 0;

public:

    struct promise_type
    {
        inline static size_t promise_count = 0;

        std::coroutine_handle<> waiter;
        std::exception_ptr ex_ptr = nullptr;

        struct resume_waiter
        {
            inline static size_t awaiter_count = 0;

            std::coroutine_handle<> waiter;

            resume_waiter(std::coroutine_handle<> waiter) noexcept : waiter{ waiter }
            {
                ++awaiter_count;
                printf("[%zu] resume_waiter(std::coroutine_handle<> waiter)\n", awaiter_count);
            }

            ~resume_waiter()
            {
                --awaiter_count;
                printf("[%zu] ~resume_waiter()\n", awaiter_count);
            }

            bool await_ready() const noexcept { return false; }

            auto await_suspend(std::coroutine_handle<>) noexcept
            {
                return waiter;
            }

            void await_resume() const noexcept {}
        };

        promise_type()
        {
            ++promise_count;
            printf("[%zu] vtask::promise_type()\n", promise_count);

        }

        ~promise_type()
        {
            --promise_count;
            printf("[%zu] ~vtask::promise_type()\n", promise_count);
        }

        vtask get_return_object() { return { *this }; }

        constexpr std::suspend_always initial_suspend() noexcept { return {}; }

        resume_waiter final_suspend() const noexcept { return { waiter }; }

        void unhandled_exception() noexcept
        {
            ex_ptr = std::current_exception();
        }

        void return_void() const noexcept {}
    };

    vtask(promise_type& p) : coro{ std::coroutine_handle<promise_type>::from_promise(p) }
    {
        ++task_count;
        printf("[%zu] vtask(promise_type& p)\n", task_count);
    }

    vtask(vtask&& other) noexcept : coro{ std::exchange(other.coro, nullptr) }
    {
        ++task_count;
        printf("[%zu] vtask(vtask&& other)\n", task_count);
    }

    ~vtask()
    {
        if (coro)
            coro.destroy();
        --task_count;
        printf("[%zu] ~vtask()\n", task_count);
    }

    bool await_ready() const noexcept
    {
        return false;
    }

    void await_suspend(std::coroutine_handle<> waiter)
    {
        coro.promise().waiter = waiter;
        coro.resume();
    }

    void await_resume() noexcept {}

private:
    std::coroutine_handle<promise_type> coro;
};

struct detached_task
{
    struct promise_type
    {
        inline static size_t promise_count = 0;

        promise_type()
        {
            ++promise_count;
            printf("[%zu] detached_task::promise_type()\n", promise_count);
        }

        ~promise_type()
        {
            --promise_count;
            printf("[%zu] ~detached_task::promise_type()\n", promise_count);
        }

        detached_task get_return_object() { return {}; }

        std::suspend_never initial_suspend() noexcept { return {}; }

        std::suspend_never final_suspend() noexcept { return {}; }

        void unhandled_exception() noexcept
        {
            std::terminate();
        }

        constexpr void return_void() const noexcept {}
    };

    inline static size_t task_count = 0;

    detached_task()
    {
        ++task_count;
        printf("[%zu] detached_task()\n", task_count);
    }

    ~detached_task()
    {
        --task_count;
        printf("[%zu] ~detached_task()\n", task_count);
    }
};

vtask do_Whosebug() { co_return; }

detached_task Whosebug()
{
    for (;;)
        co_await do_Whosebug();
}

int main()
{
    Whosebug();
}

使用的命令行：

cl /std:c++latest coro-Whosebug.cpp /EHsc for msvc

g++ -std=c++20 coro-Whosebug.cpp -fcoroutines 用于 mingw64

clang-cl /std:c++latest coro-Whosebug.cpp /EHsc

g++-10 -std=c++20 coro-Whosebug.cpp -fcoroutines -o overflow.bug 在 wsl

clang++-10 -std=c++20 -stdlib=libc++ coro-Whosebug.cpp -o overflow-clang.bug 在 wsl

这是 windows 上的 clang coro header:

#pragma once

namespace std { namespace experimental { inline namespace coroutines_v1 {

template <typename R, typename...> struct coroutine_traits {
  using promise_type = typename R::promise_type;
};

template <typename Promise = void> struct coroutine_handle;

template <> struct coroutine_handle<void> {
  static coroutine_handle from_address(void *addr) noexcept {
    coroutine_handle me;
    me.ptr = addr;
    return me;
  }
  void operator()() { resume(); }
  void *address() const { return ptr; }
  void resume() const { __builtin_coro_resume(ptr); }
  void destroy() const { __builtin_coro_destroy(ptr); }
  bool done() const { return __builtin_coro_done(ptr); }
  coroutine_handle &operator=(decltype(nullptr)) {
    ptr = nullptr;
    return *this;
  }
  coroutine_handle(decltype(nullptr)) : ptr(nullptr) {}
  coroutine_handle() : ptr(nullptr) {}
//  void reset() { ptr = nullptr; } // add to P0057?
  explicit operator bool() const { return ptr; }

protected:
  void *ptr;
};

template <typename Promise> struct coroutine_handle : coroutine_handle<> {
  using coroutine_handle<>::operator=;

  static coroutine_handle from_address(void *addr) noexcept {
    coroutine_handle me;
    me.ptr = addr;
    return me;
  }

  Promise &promise() const {
    return *reinterpret_cast<Promise *>(
        __builtin_coro_promise(ptr, alignof(Promise), false));
  }
  static coroutine_handle from_promise(Promise &promise) {
    coroutine_handle p;
    p.ptr = __builtin_coro_promise(&promise, alignof(Promise), true);
    return p;
  }
};

  template <typename _PromiseT>
  bool operator==(coroutine_handle<_PromiseT> const& _Left,
    coroutine_handle<_PromiseT> const& _Right) noexcept
  {
    return _Left.address() == _Right.address();
  }

  template <typename _PromiseT>
  bool operator!=(coroutine_handle<_PromiseT> const& _Left,
    coroutine_handle<_PromiseT> const& _Right) noexcept
  {
    return !(_Left == _Right);
  }

  template <typename _PromiseT>
  bool operator==(coroutine_handle<_PromiseT> const& _Left,
     std::nullptr_t) noexcept
  {
      return _Left.address() == nullptr;
  }

  template <typename _PromiseT>
  bool operator==(std::nullptr_t, coroutine_handle<_PromiseT> const& _Right) noexcept
  {
      return _Right.address() == nullptr;
  }

  template <typename _PromiseT>
  bool operator!=(coroutine_handle<_PromiseT> const& _Left,
     std::nullptr_t) noexcept
  {


    return !(_Left == nullptr);
  }

  template <typename _PromiseT>
  bool operator!=(std::nullptr_t, coroutine_handle<_PromiseT> const& _Right) noexcept
  {
      return _Right.address() != nullptr;
  }

struct suspend_always {
  bool await_ready() { return false; }
  void await_suspend(coroutine_handle<>) {}
  void await_resume() {}
};
struct suspend_never {
  bool await_ready() { return true; }
  void await_suspend(coroutine_handle<>) {}
  void await_resume() {}
};

}}}

在 windows 上，msvc 和 clang-cl 构建早期发生崩溃，但 mingw64 和 wsl 构建需要更多时间

我使用的 gcc 10.1 似乎有一个已知的错误，其中任务构造了两次，但一旦每次迭代都泄漏了一个任务就被销毁，这似乎导致了溢出

但是 clang 和 msvc 没有这个错误，它们也会崩溃！

编辑：尝试了 gcc 10.3 mingw64，它没有提到的 gcc 错误，但它也会导致堆栈溢出！有问题的编译器甚至更快！也许这种行为是预期的？

我搞不懂上面的代码哪里错了

Answer 1

问题出在这部分代码中：

void await_suspend(std::coroutine_handle<> waiter)
{
    coro.promise().waiter = waiter;
    coro.resume(); 
}

这种不对称传输导致计算器溢出并将代码更改为：

auto await_suspend(std::coroutine_handle<> waiter)
{
    coro.promise().waiter = waiter;
    return coro; 
}

解决了 clang 和 msvc 的问题，但 gcc 10.3 仍然崩溃，我认为它还不支持对称传输

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