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/********************************************************************************
* *
* L o c k - F r e e Q u e u e *
* *
*********************************************************************************
* Copyright (C) 2012,2022 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 "fxmath.h"
#include "FXElement.h"
#include "FXArray.h"
#include "FXPtrList.h"
#include "FXAtomic.h"
#include "FXLFQueue.h"
/*
Notes:
- Core idea: reserve a slot, write it (or read it), then commit it.
- Only works with atomic memory operations; in this case we need compare-and-swap
on integer data types.
- Multiple threads can read from the queue, and multiple threads can write to
the queue.
- Push may fail if queue is full; pop may fail if queue is empty.
*/
using namespace FX;
/*******************************************************************************/
namespace FX {
// Create initially empty queue
FXLFQueue::FXLFQueue():whead(0),wtail(0),rhead(0),rtail(0){
}
// Create queue with initial size, which must be a power of two
FXLFQueue::FXLFQueue(FXuint sz):whead(0),wtail(0),rhead(0),rtail(0){
setSize(sz);
}
// Change size of queue (must be power of two); return true if success
FXbool FXLFQueue::setSize(FXuint sz){
if(sz&(sz-1)){ fxerror("FXLFQueue::setSize: bad argument: %u.\n",sz); }
if(items.no(sz)){
whead=wtail=rhead=rtail=0;
return true;
}
return false;
}
// Return used slots
FXuint FXLFQueue::getUsed() const {
return whead-rtail;
}
// Return free slots
FXuint FXLFQueue::getFree() const {
return getSize()+rtail-whead;
}
// If queue not full, can write if no other producers
FXbool FXLFQueue::isFull() const {
return (whead-rtail)>=getSize();
}
// If queue not empty, can read if no other consumers
FXbool FXLFQueue::isEmpty() const {
return (whead-rtail)<=0;
}
// Add item to queue, return true if success
FXbool FXLFQueue::push(FXptr ptr){
FXuint mask=getSize()-1;
FXuint w;
x:w=whead;
if(__likely((w-rtail)<=mask)){
if(__unlikely(!atomicBoolCas(&whead,w,w+1))) goto x;
items[w&mask]=ptr;
while(__unlikely(wtail!=w)){}
wtail=w+1;
return true;
}
return false;
}
// Remove item from queue, return true if success
FXbool FXLFQueue::pop(FXptr& ptr){
FXuint mask=getSize()-1;
FXuint r;
x:r=rhead;
if(__likely((wtail-r)>=1)){
if(__unlikely(!atomicBoolCas(&rhead,r,r+1))) goto x;
ptr=items[r&mask];
while(__unlikely(rtail!=r)){}
rtail=r+1;
return true;
}
return false;
}
// Destroy job queue
FXLFQueue::~FXLFQueue(){
}
}
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