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//////////////////////////////////////////////////////////////////////////////
//
// (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
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