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/**
* Copyright (C) 2008 10gen Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* This program 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 Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#pragma once
#include "../pch.h"
#include "jsobj.h"
#include "diskloc.h"
#include "matcher.h"
namespace mongo {
class NamespaceDetails;
class Record;
class CoveredIndexMatcher;
/* Query cursors, base class. This is for our internal cursors. "ClientCursor" is a separate
concept and is for the user's cursor.
WARNING concurrency: the vfunctions below are called back from within a
ClientCursor::ccmutex. Don't cause a deadlock, you've been warned.
*/
class Cursor : boost::noncopyable {
public:
virtual ~Cursor() {}
virtual bool ok() = 0;
bool eof() { return !ok(); }
virtual Record* _current() = 0;
virtual BSONObj current() = 0;
virtual DiskLoc currLoc() = 0;
virtual bool advance() = 0; /*true=ok*/
virtual BSONObj currKey() const { return BSONObj(); }
// DiskLoc the cursor requires for continued operation. Before this
// DiskLoc is deleted, the cursor must be incremented or destroyed.
virtual DiskLoc refLoc() = 0;
/* Implement these if you want the cursor to be "tailable" */
/* Request that the cursor starts tailing after advancing past last record. */
/* The implementation may or may not honor this request. */
virtual void setTailable() {}
/* indicates if tailing is enabled. */
virtual bool tailable() {
return false;
}
virtual void aboutToDeleteBucket(const DiskLoc& b) { }
/* optional to implement. if implemented, means 'this' is a prototype */
virtual Cursor* clone() {
return 0;
}
virtual BSONObj indexKeyPattern() {
return BSONObj();
}
virtual bool supportGetMore() = 0;
/* called after every query block is iterated -- i.e. between getMore() blocks
so you can note where we are, if necessary.
*/
virtual void noteLocation() { }
/* called before query getmore block is iterated */
virtual void checkLocation() { }
virtual bool supportYields() = 0;
/** Called before a ClientCursor yield. */
virtual bool prepareToYield() { noteLocation(); return supportYields(); }
/** Called after a ClientCursor yield. */
virtual void recoverFromYield() { checkLocation(); }
virtual string toString() { return "abstract?"; }
/* used for multikey index traversal to avoid sending back dups. see Matcher::matches().
if a multikey index traversal:
if loc has already been sent, returns true.
otherwise, marks loc as sent.
*/
virtual bool getsetdup(DiskLoc loc) = 0;
virtual bool isMultiKey() const = 0;
/**
* return true if the keys in the index have been modified from the main doc
* if you have { a : 1 , b : [ 1 , 2 ] }
* an index on { a : 1 } would not be modified
* an index on { b : 1 } would be since the values of the array are put in the index
* not the array
*/
virtual bool modifiedKeys() const = 0;
virtual BSONObj prettyIndexBounds() const { return BSONArray(); }
virtual bool capped() const { return false; }
virtual long long nscanned() = 0;
// The implementation may return different matchers depending on the
// position of the cursor. If matcher() is nonzero at the start,
// matcher() should be checked each time advance() is called.
// Implementations which generate their own matcher should return this
// to avoid a matcher being set manually.
// Note that the return values differ subtly here
// Used when we want fast matcher lookup
virtual CoveredIndexMatcher *matcher() const { return 0; }
// Used when we need to share this matcher with someone else
virtual shared_ptr< CoveredIndexMatcher > matcherPtr() const { return shared_ptr< CoveredIndexMatcher >(); }
// A convenience function for setting the value of matcher() manually
// so it may accessed later. Implementations which must generate
// their own matcher() should assert here.
virtual void setMatcher( shared_ptr< CoveredIndexMatcher > matcher ) {
massert( 13285, "manual matcher config not allowed", false );
}
virtual void explainDetails( BSONObjBuilder& b ) { return; }
};
// strategy object implementing direction of traversal.
class AdvanceStrategy {
public:
virtual ~AdvanceStrategy() { }
virtual DiskLoc next( const DiskLoc &prev ) const = 0;
};
const AdvanceStrategy *forward();
const AdvanceStrategy *reverse();
/* table-scan style cursor */
class BasicCursor : public Cursor {
public:
BasicCursor(DiskLoc dl, const AdvanceStrategy *_s = forward()) : curr(dl), s( _s ), _nscanned() {
incNscanned();
init();
}
BasicCursor(const AdvanceStrategy *_s = forward()) : s( _s ), _nscanned() {
init();
}
bool ok() { return !curr.isNull(); }
Record* _current() {
assert( ok() );
return curr.rec();
}
BSONObj current() {
Record *r = _current();
BSONObj j(r);
return j;
}
virtual DiskLoc currLoc() { return curr; }
virtual DiskLoc refLoc() { return curr.isNull() ? last : curr; }
bool advance();
virtual string toString() { return "BasicCursor"; }
virtual void setTailable() {
if ( !curr.isNull() || !last.isNull() )
tailable_ = true;
}
virtual bool tailable() { return tailable_; }
virtual bool getsetdup(DiskLoc loc) { return false; }
virtual bool isMultiKey() const { return false; }
virtual bool modifiedKeys() const { return false; }
virtual bool supportGetMore() { return true; }
virtual bool supportYields() { return true; }
virtual CoveredIndexMatcher *matcher() const { return _matcher.get(); }
virtual shared_ptr< CoveredIndexMatcher > matcherPtr() const { return _matcher; }
virtual void setMatcher( shared_ptr< CoveredIndexMatcher > matcher ) { _matcher = matcher; }
virtual long long nscanned() { return _nscanned; }
protected:
DiskLoc curr, last;
const AdvanceStrategy *s;
void incNscanned() { if ( !curr.isNull() ) { ++_nscanned; } }
private:
bool tailable_;
shared_ptr< CoveredIndexMatcher > _matcher;
long long _nscanned;
void init() { tailable_ = false; }
};
/* used for order { $natural: -1 } */
class ReverseCursor : public BasicCursor {
public:
ReverseCursor(DiskLoc dl) : BasicCursor( dl, reverse() ) { }
ReverseCursor() : BasicCursor( reverse() ) { }
virtual string toString() { return "ReverseCursor"; }
};
class ForwardCappedCursor : public BasicCursor, public AdvanceStrategy {
public:
ForwardCappedCursor( NamespaceDetails *nsd = 0, const DiskLoc &startLoc = DiskLoc() );
virtual string toString() {
return "ForwardCappedCursor";
}
virtual DiskLoc next( const DiskLoc &prev ) const;
virtual bool capped() const { return true; }
private:
NamespaceDetails *nsd;
};
class ReverseCappedCursor : public BasicCursor, public AdvanceStrategy {
public:
ReverseCappedCursor( NamespaceDetails *nsd = 0, const DiskLoc &startLoc = DiskLoc() );
virtual string toString() {
return "ReverseCappedCursor";
}
virtual DiskLoc next( const DiskLoc &prev ) const;
virtual bool capped() const { return true; }
private:
NamespaceDetails *nsd;
};
} // namespace mongo
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