Question

我正在尝试创建一个范围的线程。

#include <iostream>
#include <thread>

class ScopedThread {
 public:
    template< class Function, class... Args>
    explicit ScopedThread( int id, Function&& f, Args&&... args)
        : m_thread( std::ref(f), std::forward<Args>(args)...)
        , id(std::move(id)) {
    }



    int getId() const { return id; }

    ~ScopedThread() { m_thread.join(); }
 private:
    std::thread m_thread;
    int id;

};

class Worker {
 public:
    Worker(int id): thd(id, &Worker::work, this) { }

    void work() {
       for( int i = 0; i < 10; i++)
        std::cout << "I am working" << std::endl;
    }


 private:
    ScopedThread thd;
};

int main() {
    Worker(1);
    Worker(2);
    Worker(3);
    Worker(4);
}

当我运行代码时，它会转储核心。

#0  0x00007ffcfbbc6380 in ?? ()
#1  0x00000000004026c9 in std::_Mem_fn<void (Worker::*)()>::operator()<, void>(Worker*) const (this=0x7f0b43551de0, __object=0x7ffcfbbc63c0)
    at /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/functional:601
#2  0x00000000004025cd in std::__invoke<void (Worker::*)(), Worker*> (__f=@0x7ffcfbbc6360: (void (Worker::*)(Worker * const)) 0x7ffcfbbc6380, this adjustment 4198629,
    __args=<unknown type in /home/asit/cpp/scope_thd, CU 0x0, DIE 0x2abf>) at /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/functional:247
#3  0x0000000000402532 in std::reference_wrapper<void (Worker::*)()>::operator()<Worker*>(Worker*&&) const (this=0x1b27048,
    __args=<unknown type in /home/asit/cpp/scope_thd, CU 0x0, DIE 0x57fb>) at /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/functional:467
#4  0x00000000004024d2 in std::_Bind_simple<std::reference_wrapper<void (Worker::*)()> (Worker*)>::_M_invoke<0ul>(std::_Index_tuple<0ul>) (this=0x1b27040)
    at /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/functional:1731
#5  0x0000000000402485 in std::_Bind_simple<std::reference_wrapper<void (Worker::*)()> (Worker*)>::operator()() (this=0x1b27040)
    at /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/functional:1720
#6  0x0000000000402119 in std::thread::_Impl<std::_Bind_simple<std::reference_wrapper<void (Worker::*)()> (Worker*)> >::_M_run() (this=0x1b27028)
    at /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/thread:115
#7  0x00007f0b44103a60 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#8  0x00007f0b43920184 in start_thread (arg=0x7f0b43552700) at pthread_create.c:312
#9  0x00007f0b4364d37d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111

有人能告诉我如何将成员函数和参数转发给底层的std :: thread类？我观察到，分段错误只出现在clang ++中，而不是gcc中。

我的目标是使包装类完全可以用std :: thread类替换。 Wrapper类为线程id获取一个新参数。

Answer 1

您实施ScopedThread时存在几个问题。

无需单独处理Function&& f。只需将其作为args...包的一部分处理。

无需移动id。

template< class... Args>
explicit ScopedThread( int id, Args&&... args)
    : m_thread( std::forward<Args>(args)...)
    , id(id) {
}

在调用.join()之前，您应该确保您的线程可以加入。
```
~ScopedThread() { if(m_thread.joinable()) m_thread.join(); }
```

应用这些更改prevents the segmentation fault on clang++。

罪魁祸首是std::ref(f) - 您正在创建一个临时reference_wrapper并将其传递给std::thread的构造函数，该构造函数使用std::invoke来调用它。

根据g++和 UndefinedBehaviorSanitizer ：

/ usr / local / gcc-head / include / c ++ / 7.0.1 / bits / invoke.h:73:46:

运行时错误：成员调用未对齐的地址0x7fff939ec8d3   输入'struct Worker'，需要8字节对齐

问题是您使用std::ref(f)创建对临时的引用，其中临时值为&Worker::work。

Copying f instead of using std::ref doesn't cause any segfault or UndefinedBehaviorSanitizer diagnostic.

Answer 2

我给研究此主题的人5美分。

我确实清理了代码并实现了已删除的构造函数：

class ScopedThread{
public:
    template<class ...Args>
    explicit ScopedThread(Args &&...args) : thread_(std::forward<Args>(args)...){}

    ScopedThread(ScopedThread &&other){
        thread_ = std::move(other.thread_);
    }

    ScopedThread &operator=(ScopedThread &&other){
        thread_ = std::move(other.thread_);
        return *this;
    }

    std::thread &operator*(){
        return thread_;
    }

    std::thread const &operator*() const{
        return thread_;
    }

    std::thread *operator->(){
        return & operator*();
    }

    std::thread const *operator->() const{
        return & operator*();
    }

    auto get_id() const{
        return thread_.get_id();
    }

    auto join(){
        if (thread_.joinable())
            thread_.join();
    }

    ~ScopedThread(){
        join();
    }

private:
    std::thread thread_;
};

用于std :: thread的scoped线程包装器

2 个答案: