我想通过包装来自C ++ 11的std :: thread类来使用自己的Thread实现，这样我就可以处理所需的异常。
这是我的包装类：
#include <Types.hpp>
#include <thread>
#include <exception>
#include <functional>
class Thread
{
private:
std::exception_ptr exceptionPtr;
std::thread thread;
public:
using Id = std::thread::id;
using NativeHandleType = std::thread::native_handle_type;
Thread() noexcept = default;
Thread(Thread &&t) noexcept :
exceptionPtr(std::move(t.exceptionPtr)),
thread(std::move(t.thread))
{
}
Thread &operator =(Thread &&t) noexcept
{
exceptionPtr = std::move(t.exceptionPtr);
thread = std::move(t.thread);
return *this;
}
template<typename Callable, typename... Args>
Thread(Callable &&f, Args &&... args) :
exceptionPtr(nullptr),
thread([&](Callable &&f, Args &&... args)
{
try
{
std::once_flag flag;
std::call_once(flag, f, args...);
}
catch (...)
{
exceptionPtr = std::current_exception();
}
}, f, args...)
{
if (exceptionPtr != nullptr)
{
std::rethrow_exception(exceptionPtr);
}
}
bool joinable() const noexcept
{
return thread.joinable();
}
void join()
{
thread.join();
}
void detach()
{
thread.detach();
}
Id getId() const noexcept
{
return thread.get_id();
}
NativeHandleType nativeHandle()
{
return thread.native_handle();
}
static uint32_t hardwareConcurrency() noexcept
{
return std::thread::hardware_concurrency();
}
static void wait(Time t)
{
std::this_thread::sleep_for(t);
}
};
如果没有参数，则效果很好：
Thread([&]() { /* do something */ }).detach();
...但是如果我尝试传递可变参数：
Thread(&GUI::refreshTask, this, refreshDelay).detach();
...我在编译时出错：
buildroot-2014.02 / output / host / usr / i586-buildroot-linux-uclibc / include / c ++ / 4.8.2 / functional：在'struct std :: _ Bind_simple）的实例中（std :: chrono :: duration>）; Args = {CRH :: GUI const，std :: chrono :: duration>＆}] :: ____ lambda1（void（CRH :: GUI :: ）（std :: chrono :: duration>），CRH :: GUI，std :: chrono :: duration>）>'：buildroot-2014.02 / output / host / usr / i586-buildroot-linux-uclibc / include / c ++ / 4.8.2 / thread：137：47：需要'std :: thread :: thread（_Callable &&，_Args && ...）[with _Callable = CRH :: Thread :: Thread（Callable &&，Args && ...）[with Callable = void（CRH :: GUI :: ）（std :: chrono ::持续时间>）; Args = {CRH :: GUI const，std :: chrono :: duration>＆}] :: __ lambda1; _Args = {void（CRH :: GUI :: ＆）（std :: chrono :: duration>），CRH :: GUIconst＆，std :: chrono :: duration>＆}]]'/home/cyril/Documents/crh-2016/src/robot2/../core/Thread.hpp:72:30：要求来自'CRH :: Thread： ：Thread（Callable &&，Args && ...）[with Callable = void（CRH :: GUI :: ）（std :: chrono :: duration>）; Args = {CRH :: GUI const，std :: chrono :: duration>＆}]'src / core / GUI.cpp：90：57：从此处需要buildroot-2014.02 / output / host / usr / i586-buildroot- linux-uclibc / include / c ++ / 4.8.2 / functional：1697：61：错误：在'class std :: result_of）（std :: chrono :: duration>）中没有名为'type'的类型; Args = {CRH :: GUI const，std :: chrono :: duration>＆}] :: __ lambda1（void（CRH :: GUI :: ）（std :: chrono :: duration>），CRH :: GUI，std :: chrono :: duration>）>'typedef typename result_of <_Callable（_Args ...）> :: type result_type; ^ buildroot-2014.02 / output / host / usr / i586-buildroot-linux-uclibc / include / c ++ / 4.8.2 / functional：1727：9：错误：'class std :: result_of）中没有名为'type'的类型（ std :: chrono :: duration>）; Args = {CRH :: GUI const，std :: chrono :: duration>＆}] :: ____ lambda1（void（CRH :: GUI :: ）（std :: chrono :: duration>），CRH :: GUI，std :: chrono :: duration>）>'_M_invoke（_Index_tuple <_Indices ...>）
可能会更清楚一点……但是对于GCC来说，它的要求太高了。
任何想法如何解决此问题？
解
#include <Types.hpp>
#include <thread>
#include <exception>
#include <functional>
class Thread
{
private:
std::exception_ptr exceptionPtr;
std::thread thread;
public:
using Id = std::thread::id;
using NativeHandleType = std::thread::native_handle_type;
Thread() noexcept = default;
Thread(Thread &&t) noexcept :
exceptionPtr(std::move(t.exceptionPtr)),
thread(std::move(t.thread))
{
}
Thread &operator =(Thread &&t) noexcept
{
exceptionPtr = std::move(t.exceptionPtr);
thread = std::move(t.thread);
return *this;
}
template<typename Callable, typename... Args>
Thread(Callable &&f, Args &&... args) :
exceptionPtr(nullptr),
thread([&](typename std::decay<Callable>::type &&f, typename std::decay<Args>::type &&... args)
{
try
{
std::bind(f, args...)();
}
catch (...)
{
exceptionPtr = std::current_exception();
}
}, std::forward<Callable>(f), std::forward<Args>(args)...)
{
}
bool joinable() const noexcept
{
return thread.joinable();
}
void join()
{
thread.join();
if (exceptionPtr != nullptr)
{
std::rethrow_exception(exceptionPtr);
}
}
void detach()
{
thread.detach();
}
Id getId() const noexcept
{
return thread.get_id();
}
NativeHandleType nativeHandle()
{
return thread.native_handle();
}
static uint32_t hardwareConcurrency() noexcept
{
return std::thread::hardware_concurrency();
}
static void wait(Time t)
{
std::this_thread::sleep_for(t);
}
};
Callable并且Args是转发引用，因此模板参数推导可以使它们成为左值引用或纯类型，具体取决于参数表达式的值类别。
这意味着当您在lambda的声明中重用推导的类型时：
thread([&](Callable&& f, Args&&... args)
引用折叠起作用，对于左值参数refreshDelay，它Args成为左值引用。
但是，std::thread存储接收到的参数的衰变副本，然后将其从其内部存储移至实际的处理程序，从而将存储的对象转换为xvalue。这就是错误告诉您的内容：处理程序无法与线程尝试传递的参数一起调用。
相反，您可以按以下方式实现它：
template <typename Callable, typename... Args>
Thread(Callable&& f, Args&&... args)
: exceptionPtr(nullptr)
, thread([] (typename std::decay<Callable>::type&& f
, typename std::decay<Args>::type&&... args)
{
// (...)
}
, std::forward<Callable>(f), std::forward<Args>(args)...)
{
// (...)
}
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我来说两句