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slice.h
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slice.h
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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
//
// Slice is a simple structure containing a pointer into some external
// storage and a size. The user of a Slice must ensure that the slice
// is not used after the corresponding external storage has been
// deallocated.
//
// Multiple threads can invoke const methods on a Slice without
// external synchronization, but if any of the threads may call a
// non-const method, all threads accessing the same Slice must use
// external synchronization.
#pragma once
#include <cassert>
#include <cstddef>
#include <cstdio>
#include <cstring>
#include <string>
#include <string_view> // RocksDB now requires C++17 support
#include "rocksdb/cleanable.h"
namespace ROCKSDB_NAMESPACE {
class Slice {
public:
// Create an empty slice.
Slice() : data_(""), size_(0) {}
// Create a slice that refers to d[0,n-1].
Slice(const char* d, size_t n) : data_(d), size_(n) {}
// Create a slice that refers to the contents of "s"
/* implicit */
Slice(const std::string& s) : data_(s.data()), size_(s.size()) {}
// Create a slice that refers to the same contents as "sv"
/* implicit */
Slice(const std::string_view& sv) : data_(sv.data()), size_(sv.size()) {}
// Create a slice that refers to s[0,strlen(s)-1]
/* implicit */
Slice(const char* s) : data_(s) { size_ = (s == nullptr) ? 0 : strlen(s); }
// Create a single slice from SliceParts using buf as storage.
// buf must exist as long as the returned Slice exists.
Slice(const struct SliceParts& parts, std::string* buf);
// Return a pointer to the beginning of the referenced data
const char* data() const { return data_; }
// Return the length (in bytes) of the referenced data
size_t size() const { return size_; }
// Return true iff the length of the referenced data is zero
bool empty() const { return size_ == 0; }
// Return the ith byte in the referenced data.
// REQUIRES: n < size()
char operator[](size_t n) const {
assert(n < size());
return data_[n];
}
// Change this slice to refer to an empty array
void clear() {
data_ = "";
size_ = 0;
}
// Drop the first "n" bytes from this slice.
void remove_prefix(size_t n) {
assert(n <= size());
data_ += n;
size_ -= n;
}
void remove_suffix(size_t n) {
assert(n <= size());
size_ -= n;
}
// Return a string that contains the copy of the referenced data.
// when hex is true, returns a string of twice the length hex encoded (0-9A-F)
std::string ToString(bool hex = false) const;
// Return a string_view that references the same data as this slice.
std::string_view ToStringView() const {
return std::string_view(data_, size_);
}
// Decodes the current slice interpreted as an hexadecimal string into result,
// if successful returns true, if this isn't a valid hex string
// (e.g not coming from Slice::ToString(true)) DecodeHex returns false.
// This slice is expected to have an even number of 0-9A-F characters
// also accepts lowercase (a-f)
bool DecodeHex(std::string* result) const;
// Three-way comparison. Returns value:
// < 0 iff "*this" < "b",
// == 0 iff "*this" == "b",
// > 0 iff "*this" > "b"
int compare(const Slice& b) const;
// Return true iff "x" is a prefix of "*this"
bool starts_with(const Slice& x) const {
return ((size_ >= x.size_) && (memcmp(data_, x.data_, x.size_) == 0));
}
bool ends_with(const Slice& x) const {
return ((size_ >= x.size_) &&
(memcmp(data_ + size_ - x.size_, x.data_, x.size_) == 0));
}
// Compare two slices and returns the first byte where they differ
size_t difference_offset(const Slice& b) const;
// private: make these public for rocksdbjni access
const char* data_;
size_t size_;
// Intentionally copyable
};
/**
* A Slice that can be pinned with some cleanup tasks, which will be run upon
* ::Reset() or object destruction, whichever is invoked first. This can be used
* to avoid memcpy by having the PinnableSlice object referring to the data
* that is locked in the memory and release them after the data is consumed.
*/
class PinnableSlice : public Slice, public Cleanable {
public:
PinnableSlice() { buf_ = &self_space_; }
explicit PinnableSlice(std::string* buf) { buf_ = buf; }
PinnableSlice(PinnableSlice&& other);
PinnableSlice& operator=(PinnableSlice&& other);
// No copy constructor and copy assignment allowed.
PinnableSlice(PinnableSlice&) = delete;
PinnableSlice& operator=(PinnableSlice&) = delete;
inline void PinSlice(const Slice& s, CleanupFunction f, void* arg1,
void* arg2) {
assert(!pinned_);
pinned_ = true;
data_ = s.data();
size_ = s.size();
RegisterCleanup(f, arg1, arg2);
assert(pinned_);
}
inline void PinSlice(const Slice& s, Cleanable* cleanable) {
assert(!pinned_);
pinned_ = true;
data_ = s.data();
size_ = s.size();
if (cleanable != nullptr) {
cleanable->DelegateCleanupsTo(this);
}
assert(pinned_);
}
inline void PinSelf(const Slice& slice) {
assert(!pinned_);
buf_->assign(slice.data(), slice.size());
data_ = buf_->data();
size_ = buf_->size();
assert(!pinned_);
}
inline void PinSelf() {
assert(!pinned_);
data_ = buf_->data();
size_ = buf_->size();
assert(!pinned_);
}
void remove_suffix(size_t n) {
assert(n <= size());
if (pinned_) {
size_ -= n;
} else {
buf_->erase(size() - n, n);
PinSelf();
}
}
void remove_prefix(size_t n) {
assert(n <= size());
if (pinned_) {
data_ += n;
size_ -= n;
} else {
buf_->erase(0, n);
PinSelf();
}
}
void Reset() {
Cleanable::Reset();
pinned_ = false;
size_ = 0;
}
inline std::string* GetSelf() { return buf_; }
inline bool IsPinned() const { return pinned_; }
private:
friend class PinnableSlice4Test;
std::string self_space_;
std::string* buf_;
bool pinned_ = false;
};
// A set of Slices that are virtually concatenated together. 'parts' points
// to an array of Slices. The number of elements in the array is 'num_parts'.
struct SliceParts {
SliceParts(const Slice* _parts, int _num_parts)
: parts(_parts), num_parts(_num_parts) {}
SliceParts() : parts(nullptr), num_parts(0) {}
const Slice* parts;
int num_parts;
};
inline bool operator==(const Slice& x, const Slice& y) {
return ((x.size() == y.size()) &&
(memcmp(x.data(), y.data(), x.size()) == 0));
}
inline bool operator!=(const Slice& x, const Slice& y) { return !(x == y); }
inline int Slice::compare(const Slice& b) const {
assert(data_ != nullptr && b.data_ != nullptr);
const size_t min_len = (size_ < b.size_) ? size_ : b.size_;
int r = memcmp(data_, b.data_, min_len);
if (r == 0) {
if (size_ < b.size_)
r = -1;
else if (size_ > b.size_)
r = +1;
}
return r;
}
inline size_t Slice::difference_offset(const Slice& b) const {
size_t off = 0;
const size_t len = (size_ < b.size_) ? size_ : b.size_;
for (; off < len; off++) {
if (data_[off] != b.data_[off]) break;
}
return off;
}
} // namespace ROCKSDB_NAMESPACE