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/**
* Copyright 2013 (c) 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/>.
*/
#include "mongo/pch.h"
#include "mongo/db/pipeline/document_source.h"
#include "mongo/db/cmdline.h"
namespace mongo {
const char DocumentSourceMergeCursors::name[] = "$mergeCursors";
const char* DocumentSourceMergeCursors::getSourceName() const {
return name;
}
void DocumentSourceMergeCursors::setSource(DocumentSource *pSource) {
/* this doesn't take a source */
verify(false);
}
DocumentSourceMergeCursors::DocumentSourceMergeCursors(
const CursorIds& cursorIds,
const intrusive_ptr<ExpressionContext> &pExpCtx)
: DocumentSource(pExpCtx)
, _cursorIds(cursorIds)
, _unstarted(true)
{}
intrusive_ptr<DocumentSource> DocumentSourceMergeCursors::create(
const CursorIds& cursorIds,
const intrusive_ptr<ExpressionContext> &pExpCtx) {
return new DocumentSourceMergeCursors(cursorIds, pExpCtx);
}
intrusive_ptr<DocumentSource> DocumentSourceMergeCursors::createFromBson(
BSONElement* pBsonElement,
const intrusive_ptr<ExpressionContext>& pExpCtx) {
massert(17026, string("Expected an Array, but got a ") + typeName(pBsonElement->type()),
pBsonElement->type() == Array);
CursorIds cursorIds;
BSONObj array = pBsonElement->embeddedObject();
BSONForEach(cursor, array) {
massert(17027, string("Expected an Object, but got a ") + typeName(cursor.type()),
cursor.type() == Object);
cursorIds.push_back(make_pair(ConnectionString(cursor["host"].String()),
cursor["id"].Long()));
}
return new DocumentSourceMergeCursors(cursorIds, pExpCtx);
}
Value DocumentSourceMergeCursors::serialize(bool explain) const {
vector<Value> cursors;
for (size_t i = 0; i < _cursorIds.size(); i++) {
cursors.push_back(Value(DOC("host" << Value(_cursorIds[i].first.toString())
<< "id" << _cursorIds[i].second)));
}
return Value(DOC(getSourceName() << Value(cursors)));
}
DocumentSourceMergeCursors::CursorAndConnection::CursorAndConnection(
ConnectionString host,
NamespaceString ns,
CursorId id)
: connection(host)
, cursor(connection.get(), ns, id, 0, 0)
{}
boost::optional<Document> DocumentSourceMergeCursors::getNext() {
if (_unstarted) {
_unstarted = false;
// open each cursor and send message asking for a batch
for (CursorIds::const_iterator it = _cursorIds.begin(); it !=_cursorIds.end(); ++it) {
_cursors.push_back(boost::make_shared<CursorAndConnection>(
it->first, pExpCtx->ns, it->second));
verify(_cursors.back()->connection->lazySupported());
_cursors.back()->cursor.initLazy(); // shouldn't block
}
// wait for all cursors to return a batch
// TODO need a way to keep cursors alive if some take longer than 10 minutes.
for (Cursors::const_iterator it = _cursors.begin(); it !=_cursors.end(); ++it) {
bool retry = false;
bool ok = (*it)->cursor.initLazyFinish(retry); // blocks here for first batch
uassert(17028,
"error reading response from " + _cursors.back()->connection->toString(),
ok);
verify(!retry);
}
_currentCursor = _cursors.begin();
}
// purge eof cursors and release their connections
while (!_cursors.empty() && !(*_currentCursor)->cursor.more()) {
(*_currentCursor)->connection.done();
_cursors.erase(_currentCursor);
_currentCursor = _cursors.begin();
}
if (_cursors.empty())
return boost::none;
BSONObj next = (*_currentCursor)->cursor.next();
uassert(17029, str::stream() << "Received error in response from "
<< (*_currentCursor)->connection->toString()
<< ": " << next,
!next.hasField("$err"));
// advance _currentCursor, wrapping if needed
if (++_currentCursor == _cursors.end())
_currentCursor = _cursors.begin();
return Document(next);
}
void DocumentSourceMergeCursors::dispose() {
_cursors.clear();
_currentCursor = _cursors.end();
}
}
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