Boost C++ Libraries

boost/interprocess/sync/detail/condition_algorithm_8a.hpp

//////////////////////////////////////////////////////////////////////////////
//
// (C) Copyright Ion Gaztanaga 2005-2011. Distributed under the Boost
// Software License, Version 1.0. (See accompanying file
// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
// See http://www.boost.org/libs/interprocess for documentation.
//
//////////////////////////////////////////////////////////////////////////////

#ifndef BOOST_INTERPROCESS_DETAIL_CONDITION_ALGORITHM_8A_HPP
#define BOOST_INTERPROCESS_DETAIL_CONDITION_ALGORITHM_8A_HPP

#include <boost/interprocess/detail/config_begin.hpp>
#include <boost/interprocess/detail/workaround.hpp>
#include <boost/interprocess/sync/scoped_lock.hpp>
#include <limits>

namespace boost {
namespace interprocess {
namespace ipcdetail {

////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////
//
// Condition variable algorithm taken from pthreads-win32 discussion.
//
// The algorithm was developed by Alexander Terekhov in colaboration with
// Louis Thomas.
//
//     Algorithm 8a / IMPL_SEM,UNBLOCK_STRATEGY == UNBLOCK_ALL
//
// semBlockLock - bin.semaphore
// semBlockQueue - semaphore
// mtxExternal - mutex or CS
// mtxUnblockLock - mutex or CS
// nWaitersGone - int
// nWaitersBlocked - int
// nWaitersToUnblock - int
//
// wait( timeout ) {
//
//   [auto: register int result          ]     // error checking omitted
//   [auto: register int nSignalsWasLeft ]
//   [auto: register int nWaitersWasGone ]
//
//   sem_wait( semBlockLock );
//   nWaitersBlocked++;
//   sem_post( semBlockLock );
//
//   unlock( mtxExternal );
//   bTimedOut = sem_wait( semBlockQueue,timeout );
//
//   lock( mtxUnblockLock );
//   if ( 0 != (nSignalsWasLeft = nWaitersToUnblock) ) {
//     if ( bTimedOut ) {                       // timeout (or canceled)
//       if ( 0 != nWaitersBlocked ) {
//         nWaitersBlocked--;
//       }
//       else {
//         nWaitersGone++;                     // count spurious wakeups.
//       }
//     }
//     if ( 0 == --nWaitersToUnblock ) {
//       if ( 0 != nWaitersBlocked ) {
//         sem_post( semBlockLock );           // open the gate.
//         nSignalsWasLeft = 0;                // do not open the gate
//                                             // below again.
//       }
//       else if ( 0 != (nWaitersWasGone = nWaitersGone) ) {
//         nWaitersGone = 0;
//       }
//     }
//   }
//   else if ( INT_MAX/2 == ++nWaitersGone ) { // timeout/canceled or
//                                             // spurious semaphore :-)
//     sem_wait( semBlockLock );
//     nWaitersBlocked -= nWaitersGone;     // something is going on here
//                                          //  - test of timeouts? :-)
//     sem_post( semBlockLock );
//     nWaitersGone = 0;
//   }
//   unlock( mtxUnblockLock );
//
//   if ( 1 == nSignalsWasLeft ) {
//     if ( 0 != nWaitersWasGone ) {
//       // sem_adjust( semBlockQueue,-nWaitersWasGone );
//       while ( nWaitersWasGone-- ) {
//         sem_wait( semBlockQueue );       // better now than spurious later
//       }
//     } sem_post( semBlockLock );          // open the gate
//   }
//
//   lock( mtxExternal );
//
//   return ( bTimedOut ) ? ETIMEOUT : 0;
// }
//
// signal(bAll) {
//
//   [auto: register int result         ]
//   [auto: register int nSignalsToIssue]
//
//   lock( mtxUnblockLock );
//
//   if ( 0 != nWaitersToUnblock ) {        // the gate is closed!!!
//     if ( 0 == nWaitersBlocked ) {        // NO-OP
//       return unlock( mtxUnblockLock );
//     }
//     if (bAll) {
//       nWaitersToUnblock += nSignalsToIssue=nWaitersBlocked;
//       nWaitersBlocked = 0;
//     }
//     else {
//       nSignalsToIssue = 1;
//       nWaitersToUnblock++;
//       nWaitersBlocked--;
//     }
//   }
//   else if ( nWaitersBlocked > nWaitersGone ) { // HARMLESS RACE CONDITION!
//     sem_wait( semBlockLock );                  // close the gate
//     if ( 0 != nWaitersGone ) {
//       nWaitersBlocked -= nWaitersGone;
//       nWaitersGone = 0;
//     }
//     if (bAll) {
//       nSignalsToIssue = nWaitersToUnblock = nWaitersBlocked;
//       nWaitersBlocked = 0;
//     }
//     else {
//       nSignalsToIssue = nWaitersToUnblock = 1;
//       nWaitersBlocked--;
//     }
//   }
//   else { // NO-OP
//     return unlock( mtxUnblockLock );
//   }
//
//   unlock( mtxUnblockLock );
//   sem_post( semBlockQueue,nSignalsToIssue );
//   return result;
// }
////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////


// Required interface for ConditionMembers
// class ConditionMembers
// {
//    typedef implementation_defined semaphore_type;
//    typedef implementation_defined mutex_type;
//    typedef implementation_defined integer_type;
//
//    integer_type    &get_nwaiters_blocked()
//    integer_type    &get_nwaiters_gone()
//    integer_type    &get_nwaiters_to_unblock()
//    semaphore_type  &get_sem_block_queue()
//    semaphore_type  &get_sem_block_lock()
//    mutex_type      &get_mtx_unblock_lock()
// };
//
template<class ConditionMembers>
class condition_algorithm_8a
{
   private:
   condition_algorithm_8a();
   ~condition_algorithm_8a();
   condition_algorithm_8a(const condition_algorithm_8a &);
   condition_algorithm_8a &operator=(const condition_algorithm_8a &);

   typedef typename ConditionMembers::semaphore_type  semaphore_type;
   typedef typename ConditionMembers::mutex_type      mutex_type;
   typedef typename ConditionMembers::integer_type    integer_type;

   // nwaiters_blocked == 0
   // nwaiters_gone() == 0
   // nwaiters_to_unblock == 0
   // sem_block_queue() == initial count 0
   // sem_block_lock() == initial count 1
   // mtx_unblock_lock (unlocked)

   public:
   template<class InterprocessMutex>
   static bool wait  (ConditionMembers &data, bool timeout_enabled, const boost::posix_time::ptime &abs_time, InterprocessMutex &mut);
   static void signal(ConditionMembers &data, bool broadcast);
};

template<class ConditionMembers>
inline void condition_algorithm_8a<ConditionMembers>::signal(ConditionMembers &data, bool broadcast)
{
   integer_type nsignals_to_issue;

   {
      scoped_lock<mutex_type> locker(data.get_mtx_unblock_lock());

      if ( 0 != data.get_nwaiters_to_unblock() ) {        // the gate is closed!!!
         if ( 0 == data.get_nwaiters_blocked() ) {        // NO-OP
            //locker's destructor triggers data.get_mtx_unblock_lock().unlock()
            return;
         }
         if (broadcast) {
            data.get_nwaiters_to_unblock() += nsignals_to_issue = data.get_nwaiters_blocked();
            data.get_nwaiters_blocked() = 0;
         }
         else {
            nsignals_to_issue = 1;
            data.get_nwaiters_to_unblock()++;
            data.get_nwaiters_blocked()--;
         }
      }
      else if ( data.get_nwaiters_blocked() > data.get_nwaiters_gone() ) { // HARMLESS RACE CONDITION!
         data.get_sem_block_lock().wait();                      // close the gate
         if ( 0 != data.get_nwaiters_gone() ) {
            data.get_nwaiters_blocked() -= data.get_nwaiters_gone();
            data.get_nwaiters_gone() = 0;
         }
         if (broadcast) {
            nsignals_to_issue = data.get_nwaiters_to_unblock() = data.get_nwaiters_blocked();
            data.get_nwaiters_blocked() = 0;
         }
         else {
            nsignals_to_issue = data.get_nwaiters_to_unblock() = 1;
            data.get_nwaiters_blocked()--;
         }
      }
      else { // NO-OP
         //locker's destructor triggers data.get_mtx_unblock_lock().unlock()
         return;
      }
      //locker's destructor triggers data.get_mtx_unblock_lock().unlock()
   }
   data.get_sem_block_queue().post(nsignals_to_issue);
}

template<class ConditionMembers>
template<class InterprocessMutex>
inline bool condition_algorithm_8a<ConditionMembers>::wait
   (ConditionMembers &data, bool tout_enabled, const boost::posix_time::ptime &abs_time, InterprocessMutex &mtxExternal)
{
   //Initialize to avoid warnings
   integer_type nsignals_was_left = 0;
   integer_type nwaiters_was_gone = 0;

   data.get_sem_block_lock().wait();
   ++data.get_nwaiters_blocked();
   data.get_sem_block_lock().post();

   struct scoped_unlock
   {
      InterprocessMutex & mut;
      scoped_unlock(InterprocessMutex & m)
         : mut(m)
      {  m.unlock();  }

      ~scoped_unlock()
      {  mut.lock();  }
   } unlocker(mtxExternal);


   bool bTimedOut = tout_enabled ? !data.get_sem_block_queue().timed_wait(abs_time) : (data.get_sem_block_queue().wait(), false);

   {
      scoped_lock<mutex_type> locker(data.get_mtx_unblock_lock());
      if ( 0 != (nsignals_was_left = data.get_nwaiters_to_unblock()) ) {
         if ( bTimedOut ) {                       // timeout (or canceled)
            if ( 0 != data.get_nwaiters_blocked() ) {
               data.get_nwaiters_blocked()--;
            }
            else {
               data.get_nwaiters_gone()++;                     // count spurious wakeups.
            }
         }
         if ( 0 == --data.get_nwaiters_to_unblock() ) {
            if ( 0 != data.get_nwaiters_blocked() ) {
               data.get_sem_block_lock().post();          // open the gate.
               nsignals_was_left = 0;          // do not open the gate below again.
            }
            else if ( 0 != (nwaiters_was_gone = data.get_nwaiters_gone()) ) {
               data.get_nwaiters_gone() = 0;
            }
         }
      }
      else if ( (std::numeric_limits<integer_type>::max)()/2
                == ++data.get_nwaiters_gone() ) { // timeout/canceled or spurious semaphore :-)
         data.get_sem_block_lock().wait();
         data.get_nwaiters_blocked() -= data.get_nwaiters_gone();       // something is going on here - test of timeouts? :-)
         data.get_sem_block_lock().post();
         data.get_nwaiters_gone() = 0;
      }
      //locker's destructor triggers data.get_mtx_unblock_lock().unlock()
   } 

   if ( 1 == nsignals_was_left ) {
      if ( 0 != nwaiters_was_gone ) {
         // sem_adjust( data.get_sem_block_queue(),-nwaiters_was_gone );
         while ( nwaiters_was_gone-- ) {
            data.get_sem_block_queue().wait();       // better now than spurious later
         }
      }
      data.get_sem_block_lock().post(); // open the gate
   }

   //mtxExternal.lock(); called from unlocker

   return ( bTimedOut ) ? false : true;
}

}  //namespace ipcdetail
}  //namespace interprocess
}  //namespace boost

#include <boost/interprocess/detail/config_end.hpp>

#endif   //BOOST_INTERPROCESS_DETAIL_CONDITION_ALGORITHM_8A_HPP