132 lines
2.9 KiB
C++
132 lines
2.9 KiB
C++
/*
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----
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This file is part of SECONDO.
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Copyright (C) 2018, University in Hagen,
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Faculty of Mathematics and Computer Science,
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Database Systems for New Applications.
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SECONDO is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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SECONDO is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with SECONDO; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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----
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1 Operator ~headnp~
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Generic head operator without progress support
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*/
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#include "VTuple.h"
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#include "NestedList.h"
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#include "Operator.h"
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#include "Stream.h"
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#include "ListUtils.h"
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#include "StandardTypes.h"
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extern QueryProcessor* qp;
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namespace cstream{
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ListExpr headTM(ListExpr args){
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if(!nl->HasLength(args,2)){
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return listutils::typeError("2 args expected");
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}
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if(!listutils::isStream(nl->First(args))){
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return listutils::typeError("first arg must be a stream");
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}
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if(!CcInt::checkType(nl->Second(args))){
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return listutils::typeError("second arg must be of type int");
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}
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return nl->First(args);
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}
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class headInfo{
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public:
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headInfo(Word _stream, int count):stream(_stream), count(count){
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qp->Open(stream.addr);
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}
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~headInfo(){
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qp->Close(stream.addr);
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}
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int next(Word& result){
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if(count<=0){
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result.addr = 0;
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return CANCEL;
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}
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qp->Request(stream.addr, result);
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count--;
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return qp->Received(stream.addr)?YIELD: CANCEL;
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}
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private:
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Word stream;
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int count;
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};
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int headVM(Word* args, Word& result, int message,
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Word& local, Supplier s) {
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headInfo* li = (headInfo*) local.addr;
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switch(message){
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case OPEN : {
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if(li) delete li;
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CcInt* h = (CcInt*) args[1].addr;
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int n = h->IsDefined()?h->GetValue():0;
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local.addr = new headInfo(args[0],n);
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return 0;
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}
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case REQUEST: if(!li) return CANCEL;
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return li->next(result);
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case CLOSE: {
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if(li) {
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delete li;
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local.addr = 0;
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}
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return 0;
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}
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}
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return -1;
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}
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OperatorSpec headSpec(
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"stream(ANY) x int -> stream(ANY)",
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"_ head[_]",
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"Cuts a stream after a certain number of elements",
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"query receivestream('ais.txt',\"ais\") head[10] count"
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);
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Operator head_Op(
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"headnp",
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headSpec.getStr(),
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headVM,
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Operator::SimpleSelect,
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headTM
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);
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} // end of namespace
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