Question

我已经使用gcc 8.2.1在Linux下编译了以下虚拟程序：

#include <iostream>
#include <mutex>
#include <thread>

struct Foo
{
  void start() {
    thread = std::thread(&Foo::run, this);
  }

  void stop() {
    mutex.lock();
    done = true;
    mutex.unlock();

    thread.join();
  }

  void run() {
    bool tmp;

    for (;;) {
      mutex.lock();
      tmp = done;
      mutex.unlock();

      if (tmp)
        break;
    }
  }

  std::thread thread;
  std::mutex mutex;
  bool done;
};

int main()
{
  Foo foo;

  std::cout << "starting...\n";
  foo.start();

  std::cout << "stopping...\n";
  foo.stop();

  std::cout << "done\n";
}

如果随后在valgrind 3.14.0下运行它，则会收到以下警告：

==30060== Thread 2:
==30060== Conditional jump or move depends on uninitialised value(s)
==30060==    at 0x1095F3: Foo::run() (in /.../a.out)
==30060==    by 0x109AAE: void std::__invoke_impl<void, void (Foo::*)(), Foo*>(std::__invoke_memfun_deref, void (Foo::*&&)(), Foo*&&) (in /.../a.out)
==30060==    by 0x109771: std::__invoke_result<void (Foo::*)(), Foo*>::type std::__invoke<void (Foo::*)(), Foo*>(void (Foo::*&&)(), Foo*&&) (in /.../a.out)
==30060==    by 0x10A012: decltype (__invoke((_S_declval<0ul>)(), (_S_declval<1ul>)())) std::thread::_Invoker<std::tuple<void (Foo::*)(), Foo*> >::_M_invoke<0ul, 1ul>(std::_Index_tuple<0ul, 1ul>) (in /.../a.out)
==30060==    by 0x109FB8: std::thread::_Invoker<std::tuple<void (Foo::*)(), Foo*> >::operator()() (in /.../a.out)
==30060==    by 0x109F8D: std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (Foo::*)(), Foo*> > >::_M_run() (in /.../a.out)
==30060==    by 0x496A062: execute_native_thread_routine (thread.cc:80)
==30060==    by 0x4894A9C: start_thread (in /usr/lib/libpthread-2.28.so)
==30060==    by 0x4CD7A42: clone (in /usr/lib/libc-2.28.so)

我不确定是什么原因造成的，我已经编写了此代码段，以期诊断当前正在处理的更复杂的类中的错误（我无法在此处发布），并且在调用等效的时会产生异常Foo::stop()。 valgrind警告是否暗示我对C ++线程接口有严重的误解？并假设Foo::run实际上会做一些有用的事情，如何在保持Foo的界面不变的情况下修复该程序？

Answer 1

bool done;的初始值是多少？它是不确定的（有些垃圾值），因此可以在不调用run方法的情况下停止线程（stop。

done必须初始化：

  //...
  std::mutex mutex;
  bool done = false; // <--

C ++ 11多线程：Valgrind未初始化的值警告

1 个答案: