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/**
* Copyright 2012 (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/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <third_party/murmurhash3/MurmurHash3.h>
#include <boost/intrusive_ptr.hpp>
#include <boost/noncopyable.hpp>
#include "mongo/util/intrusive_counter.h"
#include "mongo/db/pipeline/value.h"
namespace mongo {
/** Helper class to make the position in a document abstract
* Warning: This is NOT guaranteed to be the ordered position.
* eg. the first field may not be at Position(0)
*/
class Position {
public:
// This represents "not found" similar to std::string::npos
Position() :index(static_cast<unsigned>(-1)) {}
bool found() const { return index != Position().index; }
bool operator == (Position rhs) const { return this->index == rhs.index; }
bool operator != (Position rhs) const { return !(*this == rhs); }
// For debugging and ASSERT_EQUALS in tests.
template <typename OStream>
friend OStream& operator<<(OStream& stream, Position p) { return stream << p.index; }
private:
explicit Position(size_t i) :index(i) {}
unsigned index;
friend class DocumentStorage;
friend class DocumentStorageIterator;
};
#pragma pack(1)
/** This is how values are stored in the DocumentStorage buffer
* Internal class. Consumers shouldn't care about this.
*/
class ValueElement : boost::noncopyable {
public:
Value val;
Position nextCollision; // Position of next field with same hashBucket
const int nameLen; // doesn't include '\0'
const char _name[1]; // pointer to start of name (use nameSD instead)
ValueElement* next() {
return align(plusBytes(sizeof(ValueElement) + nameLen));
}
const ValueElement* next() const {
return align(plusBytes(sizeof(ValueElement) + nameLen));
}
StringData nameSD() const { return StringData(_name, nameLen); }
// helpers for doing pointer arithmetic with this class
// Note: These don't dereference 'this' so they are safe to use with NULL
char* ptr() { return reinterpret_cast<char*>(this); }
const char* ptr() const { return reinterpret_cast<const char*>(this); }
const ValueElement* plusBytes(size_t bytes) const {
return reinterpret_cast<const ValueElement*>(ptr() + bytes);
}
ValueElement* plusBytes(size_t bytes) {
return reinterpret_cast<ValueElement*>(ptr() + bytes);
}
// Round number or pointer up to N-byte boundary. No change if already aligned.
template <typename T>
static T align(T size) {
const intmax_t ALIGNMENT = 8; // must be power of 2 and <= 16 (malloc alignment)
// Can't use c++ cast because of conversion between intmax_t and both ints and pointers
return (T)(((intmax_t)(size) + (ALIGNMENT-1)) & ~(ALIGNMENT-1));
}
private:
ValueElement(); // this class should never be constructed
~ValueElement(); // or destructed
};
// Real size is sizeof(ValueElement) + nameLen
#pragma pack()
BOOST_STATIC_ASSERT(sizeof(ValueElement) == (sizeof(Value) +
sizeof(Position) +
sizeof(int) +
1));
// This is an internal class for Document. See FieldIterator for the public version.
class DocumentStorageIterator {
public:
// DocumentStorage::iterator() and iteratorAll() are easier to use
DocumentStorageIterator(const ValueElement* first,
const ValueElement* end,
bool includeMissing)
: _first(first)
, _it(first)
, _end(end)
, _includeMissing(includeMissing) {
if (!_includeMissing)
skipMissing();
}
bool atEnd() const { return _it == _end; }
const ValueElement& get() const { return *_it; }
Position position() const { return Position(_it->ptr() - _first->ptr()); }
void advance() {
advanceOne();
if (!_includeMissing)
skipMissing();
}
const ValueElement* operator-> () { return _it; }
const ValueElement& operator* () { return *_it; }
private:
void advanceOne() {
_it = _it->next();
}
void skipMissing() {
while (!atEnd() && _it->val.missing()) {
advanceOne();
}
}
const ValueElement* _first;
const ValueElement* _it;
const ValueElement* _end;
bool _includeMissing;
};
/// Storage class used by both Document and MutableDocument
class DocumentStorage : public RefCountable {
public:
// Note: default constructor should zero-init to support emptyDoc()
DocumentStorage() : _buffer(NULL)
, _bufferEnd(NULL)
, _usedBytes(0)
, _numFields(0)
, _hashTabMask(0)
, _hasTextScore(false)
, _textScore(0)
{}
~DocumentStorage();
static const DocumentStorage& emptyDoc() {
static const char emptyBytes[sizeof(DocumentStorage)] = {0};
return *reinterpret_cast<const DocumentStorage*>(emptyBytes);
}
size_t size() const {
// can't use _numFields because it includes removed Fields
size_t count = 0;
for (DocumentStorageIterator it = iterator(); !it.atEnd(); it.advance())
count++;
return count;
}
/// Returns the position of the next field to be inserted
Position getNextPosition() const { return Position(_usedBytes); }
/// Returns the position of the named field (may be missing) or Position()
Position findField(StringData name) const;
// Document uses these
const ValueElement& getField(Position pos) const {
verify(pos.found());
return *(_firstElement->plusBytes(pos.index));
}
Value getField(StringData name) const {
Position pos = findField(name);
if (!pos.found())
return Value();
return getField(pos).val;
}
// MutableDocument uses these
ValueElement& getField(Position pos) {
verify(pos.found());
return *(_firstElement->plusBytes(pos.index));
}
Value& getField(StringData name) {
Position pos = findField(name);
if (!pos.found())
return appendField(name); // TODO: find a way to avoid hashing name twice
return getField(pos).val;
}
/// Adds a new field with missing Value at the end of the document
Value& appendField(StringData name);
/** Preallocates space for fields. Use this to attempt to prevent buffer growth.
* This is only valid to call before anything is added to the document.
*/
void reserveFields(size_t expectedFields);
/// This skips missing values
DocumentStorageIterator iterator() const {
return DocumentStorageIterator(_firstElement, end(), false);
}
/// This includes missing values
DocumentStorageIterator iteratorAll() const {
return DocumentStorageIterator(_firstElement, end(), true);
}
/// Shallow copy of this. Caller owns memory.
boost::intrusive_ptr<DocumentStorage> clone() const;
size_t allocatedBytes() const {
return !_buffer ? 0 : (_bufferEnd - _buffer + hashTabBytes());
}
/**
* Copies all metadata from source if it has any.
* Note: does not clear metadata from this.
*/
void copyMetaDataFrom(const DocumentStorage& source) {
if (source.hasTextScore()) {
setTextScore(source.getTextScore());
}
}
bool hasTextScore() const { return _hasTextScore; }
double getTextScore() const { return _textScore; }
void setTextScore(double score) {
_hasTextScore = true;
_textScore = score;
}
private:
/// Same as lastElement->next() or firstElement() if empty.
const ValueElement* end() const { return _firstElement->plusBytes(_usedBytes); }
/// Allocates space in _buffer. Copies existing data if there is any.
void alloc(unsigned newSize);
/// Call after adding field to _buffer and increasing _numFields
void addFieldToHashTable(Position pos);
// assumes _hashTabMask is (power of two) - 1
unsigned hashTabBuckets() const { return _hashTabMask + 1; }
unsigned hashTabBytes() const { return hashTabBuckets() * sizeof(Position); }
/// rehash on buffer growth if load-factor > .5 (attempt to keep lf < 1 when full)
bool needRehash() const { return _numFields*2 > hashTabBuckets(); }
/// Initialize empty hash table
void hashTabInit() { memset(_hashTab, -1, hashTabBytes()); }
static unsigned hashKey(StringData name) {
// TODO consider FNV-1a once we have a better benchmark corpus
unsigned out;
MurmurHash3_x86_32(name.rawData(), name.size(), 0, &out);
return out;
}
unsigned bucketForKey(StringData name) const {
return hashKey(name) & _hashTabMask;
}
/// Adds all fields to the hash table
void rehash() {
hashTabInit();
for (DocumentStorageIterator it = iteratorAll(); !it.atEnd(); it.advance())
addFieldToHashTable(it.position());
}
enum {
HASH_TAB_INIT_SIZE = 8, // must be power of 2
HASH_TAB_MIN = 4, // don't hash fields for docs smaller than this
// set to 1 to always hash
};
// _buffer layout:
// -------------------------------------------------------------------------------
// | ValueElement1 Name1 | ValueElement2 Name2 | ... FREE SPACE ... | Hash Table |
// -------------------------------------------------------------------------------
// ^ _buffer and _firstElement point here ^
// _bufferEnd and _hashTab point here ^
//
//
// When the buffer grows, the hash table moves to the new end.
union {
char* _buffer;
ValueElement* _firstElement;
};
union {
// pointer to "end" of _buffer element space and start of hash table (same position)
char* _bufferEnd;
Position* _hashTab; // table lazily initialized once _numFields == HASH_TAB_MIN
};
unsigned _usedBytes; // position where next field would start
unsigned _numFields; // this includes removed fields
unsigned _hashTabMask; // equal to hashTabBuckets()-1 but used more often
bool _hasTextScore; // When adding more metadata fields, this should become a bitvector
double _textScore;
// When adding a field, make sure to update clone() method
};
}
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