Re: [Boost-bugs] [Boost C++ Libraries] #7461: detail::win32::ReleaseSemaphore may be called with count_to_release equal to 0

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #7461: detail::win32::ReleaseSemaphore may be called with count_to_release equal to 0
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-10-10 23:21:24

#7461: detail::win32::ReleaseSemaphore may be called with count_to_release equal
to 0
-----------------------------------------------------+----------------------
  Reporter:  Jesper Storm Bache <jsbache@…>          |       Owner:  viboes  
      Type:  Bugs                                    |      Status:  assigned
 Milestone:  To Be Determined                        |   Component:  thread  
   Version:  Boost 1.51.0                            |    Severity:  Problem 
Resolution:                                          |    Keywords:          
-----------------------------------------------------+----------------------

Comment (by viboes):

 Hi,

 I don't know how the tool you are using has deduced such an issue.

 The count_to_release parameter seems to be always > 0.

 Please let me know if I'm missing something.

 Either it is called with 1


 {{{
                     for(generation_list::iterator it=generations.begin(),
                             end=generations.end();
                         it!=end;++it)
                     {
                         (*it)->release(1);
                     }
 }}}

 or with the contents of waiters.

 {{{
             void release_waiters()
             {
                 release(detail::interlocked_read_acquire(&waiters));
             }
 }}}

 This variable is initialized as follows


 {{{
                 waiters(1),notified(false),references(0)

 }}}


 and updated by


 {{{
             void add_waiter()
             {
                 BOOST_INTERLOCKED_INCREMENT(&waiters);
             }

             void remove_waiter()
             {
                 BOOST_INTERLOCKED_DECREMENT(&waiters);
             }
 }}}


 But remove_waiter is always called after add_waiter



 {{{
             entry_ptr get_wait_entry()
             {
                 boost::lock_guard<boost::mutex>
 internal_lock(internal_mutex);

                 if(!wake_sem)
                 {
 wake_sem=detail::win32::create_anonymous_semaphore(0,LONG_MAX);
                     BOOST_ASSERT(wake_sem);
                 }

 detail::interlocked_write_release(&total_count,total_count+1);
                 if(generations.empty() ||
 generations.back()->is_notified())
                 {
                     entry_ptr new_entry(new list_entry(wake_sem));
                     generations.push_back(new_entry);
                     return new_entry;
                 }
                 else
                 {
                     generations.back()->add_waiter();
                     return generations.back();
                 }
             }

             struct entry_manager
             {
                 entry_ptr const entry;

                 BOOST_THREAD_NO_COPYABLE(entry_manager)
                 entry_manager(entry_ptr const& entry_):
                     entry(entry_)
                 {}

                 ~entry_manager()
                 {
                     entry->remove_waiter();
                 }

                 list_entry* operator->()
                 {
                     return entry.get();
                 }
             };


         protected:
             template<typename lock_type>
             bool do_wait(lock_type& lock,timeout abs_time)
             {
                 relocker<lock_type> locker(lock);

                 entry_manager entry(get_wait_entry());

                 locker.unlock();

                 bool woken=false;
                 while(!woken)
                 {
                     if(!entry->wait(abs_time))
                     {
                         return false;
                     }

                     woken=entry->woken();
                 }
                 return woken;
             }
 }}}

 Any deep explanation of on which circumstances this issue appear is
 welcome.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/7461#comment:3>
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