为什么 condition_variable_any 需要一个由 shared_ptr 管理的互斥量？

Question

std::conditional_variable_any 的实现需要（在 gcc and clang 中）std::shared_ptr。

在 wait 方法中，互斥量的生命周期将延长到本地范围。

template<typename _Lock>
  void
  wait(_Lock& __lock)
  {
shared_ptr<mutex> __mutex = _M_mutex; // <-- Extend lifetime of mutex.
unique_lock<mutex> __my_lock(*__mutex);
_Unlock<_Lock> __unlock(__lock);
// *__mutex must be unlocked before re-locking __lock so move
// ownership of *__mutex lock to an object with shorter lifetime.
unique_lock<mutex> __my_lock2(std::move(__my_lock));
_M_cond.wait(__my_lock2);
  }

我想知道，为什么我们需要这个？只要 conditional_variable_any 对象存在，互斥量就存在。 std::mutex 还不够吗？

Answer 1

此错误报告中添加了代码：https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54352

解释如下：https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54185

The c11 standard (draft 3337, paragraph 30.5.1.5) states that condition_variable may be destructed even if not all wait() calls have returned, so long as all of those calls are blocking on the associated lock rather than on *this.

因此必须延长生命周期以防止在互斥体仍在使用时破坏它。

为什么 condition_variable_any 需要一个由 shared_ptr 管理的互斥量？

Why does condition_variable_any needs a mutex managed by a shared_ptr?

c++

multithreading

mutex

resource-management