小编Pau*_*ger的帖子

我有一个从套接字读取并生成数据的线程.每次操作后,线程都会检查一个std::atomic_bool标志,看它是否必须提前退出.

为了取消操作,我将取消标志设置为true,然后调用join()工作线程对象.

线程代码和取消函数看起来像这样:

std::thread work_thread;
std::atomic_bool cancel_requested{false};

void thread_func()
{
   while(! cancel_requested.load(std::memory_order_relaxed))
      process_next_element();

}

void cancel()
{
    cancel_requested.store(true, std::memory_order_relaxed);
    work_thread.join();
}

是std::memory_order_relaxed此,将原子变量的正确的内存顺序？

我已经构建了Boost 1.68（使用来自https://gist.github.com/sim642/29caef3cc8afaa273ce6的说明，并添加link=static,shared到b2命令行中还可以构建共享库。）

库似乎正确构建，并且我已经正确设置了BOOST_INCLUDEDIR和BOOST_LIBRARYDIR环境变量。

但是，当我将以下内容添加到时CMakeLists.txt：

find_package(Boost REQUIRED COMPONENTS system context coroutine thread random REQUIRED)

并生成MinGW Makefiles，出现以下错误：

CMake Error at C:/Users/pbelanger/AppData/Local/JetBrains/Toolbox/apps/CLion/ch-0/182.4129.15/bin/cmake/win/share/cmake-3.12/Modules/FindBoost.cmake:2044 (message):
  Unable to find the requested Boost libraries.

  Boost version: 1.68.0

  Boost include path: C:/boost/install/include/boost-1_68

  Could not find the following static Boost libraries:

          boost_system
          boost_context
          boost_coroutine
          boost_thread
          boost_random

  Some (but not all) of the required Boost libraries were found.  You may
  need to install these additional Boost libraries.  Alternatively, …

我目前正在为项目使用boost :: asio,并且必须将缓冲区发送到远程端点.我当前发送数据的算法如下所示:

void send_the_data(DataElement const& data)
{
    auto databuf = make_shared<std::vector<uint8_t>>(data.to_bytes());

    // lambda object holds a reference to the data to prevent early destruction. 
    asio::async_write(this->sock,
        asio::buffer(databuf),
        transfer_all(),
        [this, databuf](size_t bt, boost::system::error_code const& ec)
    {
        if(ec) this->handle_error(ec);
        else this->do_the_next_thing();

        assert(bt = databuf->size());
        // the destructor of this lambda should clean up the data buffer here,
        // after it has been handled. 
    });

}

我的逻辑是,shared_ptr的lambda捕获将阻止它在async_write完成之后被销毁,然后在处理程序执行后正确清理缓冲区.

但是,我很好奇,如果主要编译器或标准允许变量的捕获被忽略,如果在lambda的主体中没有引用它,这将导致未定义的行为(由于可能访问一个在async_write调用中悬空指针),或者如果标准保证不会省略所有值捕获.