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/********************************************************************************
* *
* B a r r i e r C l a s s *
* *
*********************************************************************************
* Copyright (C) 2004,2022 by Jeroen van der Zijp. All Rights Reserved. *
*********************************************************************************
* This library is free software; you can redistribute it and/or modify *
* it under the terms of the GNU Lesser General Public License as published by *
* the Free Software Foundation; either version 3 of the License, or *
* (at your option) any later version. *
* *
* This library is distributed in the hope that it will be useful, *
* but WITHOUT ANY WARRANTY; without even the implied warranty of *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
* GNU Lesser General Public License for more details. *
* *
* You should have received a copy of the GNU Lesser General Public License *
* along with this program. If not, see <http://www.gnu.org/licenses/> *
********************************************************************************/
#include "xincs.h"
#include "fxver.h"
#include "fxdefs.h"
#include "FXMutex.h"
#include "FXCondition.h"
#include "FXBarrier.h"
/*
Notes:
- Barrier synchronization primitive.
- Not using POSIX barriers, since they lack a few important features:
o Ability to adjust threshold on the fly.
o Obtain current threshold value.
o Unconditionally release all threads.
- Ability to change threshold is necessary to adjust number of threads based on
working conditions. For example, on busy machine one could reduce number of
threads working on a parallel problem until system load drops below some level.
- To release all blocked threads in case a program can't wait for all threads
to clock.
- Many scenarios are possible, and often necessary.
*/
using namespace FX;
namespace FX {
/*******************************************************************************/
// Initialize the barrier with initial threshold thr
FXBarrier::FXBarrier(FXuint thr):generation(0),thresh(FXMAX(thr,1)),count(0){
}
// Wait for all threads to hit the barrier
FXbool FXBarrier::wait(){
FXScopedMutex locker(mutex);
FXuint gen=generation;
if(++count>=thresh){
count=0;
generation++;
condition.broadcast();
return true;
}
while(gen==generation){
condition.wait(mutex);
}
return false;
}
// Change threshold, possibly releasing all waiting threads
FXbool FXBarrier::threshold(FXuint thr){
FXScopedMutex locker(mutex);
thresh=FXMAX(thr,1);
if(count>=thresh){
count=0;
generation++;
condition.broadcast();
return true;
}
return false;
}
// Release all waiting threads unconditionally
FXbool FXBarrier::release(){
FXScopedMutex locker(mutex);
if(count){
count=0;
generation++;
condition.broadcast();
return true;
}
return false;
}
// Delete the barrier
FXBarrier::~FXBarrier(){
}
}
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