使用helgrind提升asio http async_client示例警告：假阳性？

Question

运行helgrind中官方boos asio示例代码的示例时，会出现警告。这从文件boost/asio/detail/posix_event.hpp代码似乎是警告的原因：

// Signal the event and unlock the mutex. 
template <typename Lock> 
void signal_and_unlock(Lock& lock) 
{ 
    BOOST_ASSERT(lock.locked()); 
    signalled_ = true; 
    lock.unlock(); 
    ::pthread_cond_signal(&cond_); // Ignore EINVAL. 
} 

这里是Valgrind的全力输出/ helgrind：

jcm@Ubuntu:~/samples/async-client/build$ valgrind --tool=helgrind ./async-client stackoverflow.com error.html 
==2894== Helgrind, a thread error detector 
==2894== Copyright (C) 2007-2011, and GNU GPL'd, by OpenWorks LLP et al. 
==2894== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info 
==2894== Command: ./async-client stackoverflow.com error.html 
==2894== 
==2894== ---Thread-Announcement------------------------------------------ 
==2894== 
==2894== Thread #1 is the program's root thread 
==2894== 
==2894== ---------------------------------------------------------------- 
==2894== 
==2894== Thread #1: pthread_cond_{signal,broadcast}: dubious: associated lock is not held by any thread 
==2894== at 0x4C2C978: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so) 
==2894== by 0x4C2E5EA: pthread_cond_signal@* (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so) 
==2894== by 0x43FCB2: void boost::asio::detail::posix_event::signal_and_unlock<boost::asio::detail::scoped_lock<boost::asio::detail::posix_mutex> >(boost::asio::detail::scoped_lock<boost::asio::detail::posix_mutex>&) (in /home/jcm/samples/async-client/build/async-client) 
==2894== by 0x43B659: boost::asio::detail::task_io_service::wake_one_idle_thread_and_unlock(boost::asio::detail::scoped_lock<boost::asio::detail::posix_mutex>&) (in /home/jcm/samples/async-client/build/async-client) 
==2894== by 0x43B68A: boost::asio::detail::task_io_service::wake_one_thread_and_unlock(boost::asio::detail::scoped_lock<boost::asio::detail::posix_mutex>&) (in /home/jcm/samples/async-client/build/async-client) 
==2894== by 0x43B0B8: boost::asio::detail::task_io_service::post_immediate_completion(boost::asio::detail::task_io_service_operation*) (in /home/jcm/samples/async-client/build/async-client) 
==2894== by 0x43DBFD: boost::asio::detail::resolver_service_base::start_resolve_op(boost::asio::detail::task_io_service_operation*) (in /home/jcm/samples/async-client/build/async-client) 
==2894== by 0x442F86: void boost::asio::detail::resolver_service<boost::asio::ip::tcp>::async_resolve<boost::_bi::bind_t<void, boost::_mfi::mf2<void, client, boost::system::error_code const&, boost::asio::ip::basic_resolver_iterator<boost::asio::ip::tcp> >, boost::_bi::list3<boost::_bi::value<client*>, boost::arg<1> (*)(), boost::arg<2> (*)()> > >(std::shared_ptr<void>&, boost::asio::ip::basic_resolver_query<boost::asio::ip::tcp> const&, boost::_bi::bind_t<void, boost::_mfi::mf2<void, client, boost::system::error_code const&, boost::asio::ip::basic_resolver_iterator<boost::asio::ip::tcp> >, boost::_bi::list3<boost::_bi::value<client*>, boost::arg<1> (*)(), boost::arg<2> (*)()> >) (in /home/jcm/samples/async-client/build/async-client) 
==2894== by 0x44187E: void boost::asio::ip::resolver_service<boost::asio::ip::tcp>::async_resolve<boost::_bi::bind_t<void, boost::_mfi::mf2<void, client, boost::system::error_code const&, boost::asio::ip::basic_resolver_iterator<boost::asio::ip::tcp> >, boost::_bi::list3<boost::_bi::value<client*>, boost::arg<1> (*)(), boost::arg<2> (*)()> > >(std::shared_ptr<void>&, boost::asio::ip::basic_resolver_query<boost::asio::ip::tcp> const&, boost::_bi::bind_t<void, boost::_mfi::mf2<void, client, boost::system::error_code const&, boost::asio::ip::basic_resolver_iterator<boost::asio::ip::tcp> >, boost::_bi::list3<boost::_bi::value<client*>, boost::arg<1> (*)(), boost::arg<2> (*)()> >&&) (in /home/jcm/samples/async-client/build/async-client) 
==2894== by 0x44097E: void boost::asio::ip::basic_resolver<boost::asio::ip::tcp, boost::asio::ip::resolver_service<boost::asio::ip::tcp> >::async_resolve<boost::_bi::bind_t<void, boost::_mfi::mf2<void, client, boost::system::error_code const&, boost::asio::ip::basic_resolver_iterator<boost::asio::ip::tcp> >, boost::_bi::list3<boost::_bi::value<client*>, boost::arg<1> (*)(), boost::arg<2> (*)()> > >(boost::asio::ip::basic_resolver_query<boost::asio::ip::tcp> const&, boost::_bi::bind_t<void, boost::_mfi::mf2<void, client, boost::system::error_code const&, boost::asio::ip::basic_resolver_iterator<boost::asio::ip::tcp> >, boost::_bi::list3<boost::_bi::value<client*>, boost::arg<1> (*)(), boost::arg<2> (*)()> >&&) (in /home/jcm/samples/async-client/build/async-client) 
==2894== by 0x43E05F: client::client(boost::asio::io_service&, std::string const&, std::string const&) (in /home/jcm/samples/async-client/build/async-client) 
==2894== by 0x437018: main (in /home/jcm/samples/async-client/build/async-client) 
==2894== 
Response returned with status code 400 
==2894== 
==2894== For counts of detected and suppressed errors, rerun with: -v 
==2894== Use --history-level=approx or =none to gain increased speed, at 
==2894== the cost of reduced accuracy of conflicting-access information 
==2894== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 89 from 29) 

我似乎是错误的，我认为互斥量前解锁条件变量被发信号。如果这是误报，请让我知道为什么上述代码是正确的。

Answer 1

。假定lock是因为这是在匹配调用中使用pthread_cond_(timed)wait非常相同的pthread_mutex_t对象的包装对象，并行线程可以让你发出的信号，并以任何顺序解锁的大多数实现，因为pthread_cond_(timed)wait被定义为解锁条件变量并获取互斥锁作为原子操作 - 也就是说，它将不会成功返回，直到均为 CV已被发信号并且调用线程已获取互斥锁。

网上传言表明，没有人失败此操作不管它是什么样的顺序中，但一些线程调度程序都获得最大效率当信号后解锁发生被写入 - 和别人已经为最大效率时写解锁发生在信号之前，这意味着无论您如何编写它，您都无法赢得所有时间。就个人而言，如果我维护有问题的代码，我会改变命令，理由是它使helgrind高兴。你不想通过垃圾投诉来寻找真正的竞争条件。

而且，我添加“pthread_cond_signal应该同时使用CV和互斥体，就像pthread_cond_wait”，以便在我获得时间机器时修复POSIX API错误列表。