ceph/src/rocksdb/include/rocksdb/slice.h

   1 // Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
   2 //  This source code is licensed under both the GPLv2 (found in the
   3 //  COPYING file in the root directory) and Apache 2.0 License
   4 //  (found in the LICENSE.Apache file in the root directory).
   5 // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
   6 // Use of this source code is governed by a BSD-style license that can be
   7 // found in the LICENSE file. See the AUTHORS file for names of contributors.
   8 //
   9 // Slice is a simple structure containing a pointer into some external
  10 // storage and a size.  The user of a Slice must ensure that the slice
  11 // is not used after the corresponding external storage has been
  12 // deallocated.
  13 //
  14 // Multiple threads can invoke const methods on a Slice without
  15 // external synchronization, but if any of the threads may call a
  16 // non-const method, all threads accessing the same Slice must use
  17 // external synchronization.
  18
  19 #pragma once
  20
  21 #include <cassert>
  22 #include <cstddef>
  23 #include <cstdio>
  24 #include <cstring>
  25 #include <string>
  26 #include <string_view>  // RocksDB now requires C++17 support
  27
  28 #include "rocksdb/cleanable.h"
  29
  30 namespace ROCKSDB_NAMESPACE {
  31
  32 class Slice {
  33  public:
  34   // Create an empty slice.
  35   Slice() : data_(""), size_(0) {}
  36
  37   // Create a slice that refers to d[0,n-1].
  38   Slice(const char* d, size_t n) : data_(d), size_(n) {}
  39
  40   // Create a slice that refers to the contents of "s"
  41   /* implicit */
  42   Slice(const std::string& s) : data_(s.data()), size_(s.size()) {}
  43
  44   // Create a slice that refers to the same contents as "sv"
  45   /* implicit */
  46   Slice(const std::string_view& sv) : data_(sv.data()), size_(sv.size()) {}
  47
  48   // Create a slice that refers to s[0,strlen(s)-1]
  49   /* implicit */
  50   Slice(const char* s) : data_(s) { size_ = (s == nullptr) ? 0 : strlen(s); }
  51
  52   // Create a single slice from SliceParts using buf as storage.
  53   // buf must exist as long as the returned Slice exists.
  54   Slice(const struct SliceParts& parts, std::string* buf);
  55
  56   // Return a pointer to the beginning of the referenced data
  57   const char* data() const { return data_; }
  58
  59   // Return the length (in bytes) of the referenced data
  60   size_t size() const { return size_; }
  61
  62   // Return true iff the length of the referenced data is zero
  63   bool empty() const { return size_ == 0; }
  64
  65   // Return the ith byte in the referenced data.
  66   // REQUIRES: n < size()
  67   char operator[](size_t n) const {
  68     assert(n < size());
  69     return data_[n];
  70   }
  71
  72   // Change this slice to refer to an empty array
  73   void clear() {
  74     data_ = "";
  75     size_ = 0;
  76   }
  77
  78   // Drop the first "n" bytes from this slice.
  79   void remove_prefix(size_t n) {
  80     assert(n <= size());
  81     data_ += n;
  82     size_ -= n;
  83   }
  84
  85   void remove_suffix(size_t n) {
  86     assert(n <= size());
  87     size_ -= n;
  88   }
  89
  90   // Return a string that contains the copy of the referenced data.
  91   // when hex is true, returns a string of twice the length hex encoded (0-9A-F)
  92   std::string ToString(bool hex = false) const;
  93
  94   // Return a string_view that references the same data as this slice.
  95   std::string_view ToStringView() const {
  96     return std::string_view(data_, size_);
  97   }
  98
  99   // Decodes the current slice interpreted as an hexadecimal string into result,
 100   // if successful returns true, if this isn't a valid hex string
 101   // (e.g not coming from Slice::ToString(true)) DecodeHex returns false.
 102   // This slice is expected to have an even number of 0-9A-F characters
 103   // also accepts lowercase (a-f)
 104   bool DecodeHex(std::string* result) const;
 105
 106   // Three-way comparison.  Returns value:
 107   //   <  0 iff "*this" <  "b",
 108   //   == 0 iff "*this" == "b",
 109   //   >  0 iff "*this" >  "b"
 110   int compare(const Slice& b) const;
 111
 112   // Return true iff "x" is a prefix of "*this"
 113   bool starts_with(const Slice& x) const {
 114     return ((size_ >= x.size_) && (memcmp(data_, x.data_, x.size_) == 0));
 115   }
 116
 117   bool ends_with(const Slice& x) const {
 118     return ((size_ >= x.size_) &&
 119             (memcmp(data_ + size_ - x.size_, x.data_, x.size_) == 0));
 120   }
 121
 122   // Compare two slices and returns the first byte where they differ
 123   size_t difference_offset(const Slice& b) const;
 124
 125   // private: make these public for rocksdbjni access
 126   const char* data_;
 127   size_t size_;
 128
 129   // Intentionally copyable
 130 };
 131
 132 /**
 133  * A Slice that can be pinned with some cleanup tasks, which will be run upon
 134  * ::Reset() or object destruction, whichever is invoked first. This can be used
 135  * to avoid memcpy by having the PinnableSlice object referring to the data
 136  * that is locked in the memory and release them after the data is consumed.
 137  */
 138 class PinnableSlice : public Slice, public Cleanable {
 139  public:
 140   PinnableSlice() { buf_ = &self_space_; }
 141   explicit PinnableSlice(std::string* buf) { buf_ = buf; }
 142
 143   PinnableSlice(PinnableSlice&& other);
 144   PinnableSlice& operator=(PinnableSlice&& other);
 145
 146   // No copy constructor and copy assignment allowed.
 147   PinnableSlice(PinnableSlice&) = delete;
 148   PinnableSlice& operator=(PinnableSlice&) = delete;
 149
 150   inline void PinSlice(const Slice& s, CleanupFunction f, void* arg1,
 151                        void* arg2) {
 152     assert(!pinned_);
 153     pinned_ = true;
 154     data_ = s.data();
 155     size_ = s.size();
 156     RegisterCleanup(f, arg1, arg2);
 157     assert(pinned_);
 158   }
 159
 160   inline void PinSlice(const Slice& s, Cleanable* cleanable) {
 161     assert(!pinned_);
 162     pinned_ = true;
 163     data_ = s.data();
 164     size_ = s.size();
 165     if (cleanable != nullptr) {
 166       cleanable->DelegateCleanupsTo(this);
 167     }
 168     assert(pinned_);
 169   }
 170
 171   inline void PinSelf(const Slice& slice) {
 172     assert(!pinned_);
 173     buf_->assign(slice.data(), slice.size());
 174     data_ = buf_->data();
 175     size_ = buf_->size();
 176     assert(!pinned_);
 177   }
 178
 179   inline void PinSelf() {
 180     assert(!pinned_);
 181     data_ = buf_->data();
 182     size_ = buf_->size();
 183     assert(!pinned_);
 184   }
 185
 186   void remove_suffix(size_t n) {
 187     assert(n <= size());
 188     if (pinned_) {
 189       size_ -= n;
 190     } else {
 191       buf_->erase(size() - n, n);
 192       PinSelf();
 193     }
 194   }
 195
 196   void remove_prefix(size_t n) {
 197     assert(n <= size());
 198     if (pinned_) {
 199       data_ += n;
 200       size_ -= n;
 201     } else {
 202       buf_->erase(0, n);
 203       PinSelf();
 204     }
 205   }
 206
 207   void Reset() {
 208     Cleanable::Reset();
 209     pinned_ = false;
 210     size_ = 0;
 211   }
 212
 213   inline std::string* GetSelf() { return buf_; }
 214
 215   inline bool IsPinned() const { return pinned_; }
 216
 217  private:
 218   friend class PinnableSlice4Test;
 219   std::string self_space_;
 220   std::string* buf_;
 221   bool pinned_ = false;
 222 };
 223
 224 // A set of Slices that are virtually concatenated together.  'parts' points
 225 // to an array of Slices.  The number of elements in the array is 'num_parts'.
 226 struct SliceParts {
 227   SliceParts(const Slice* _parts, int _num_parts)
 228       : parts(_parts), num_parts(_num_parts) {}
 229   SliceParts() : parts(nullptr), num_parts(0) {}
 230
 231   const Slice* parts;
 232   int num_parts;
 233 };
 234
 235 inline bool operator==(const Slice& x, const Slice& y) {
 236   return ((x.size() == y.size()) &&
 237           (memcmp(x.data(), y.data(), x.size()) == 0));
 238 }
 239
 240 inline bool operator!=(const Slice& x, const Slice& y) { return !(x == y); }
 241
 242 inline int Slice::compare(const Slice& b) const {
 243   assert(data_ != nullptr && b.data_ != nullptr);
 244   const size_t min_len = (size_ < b.size_) ? size_ : b.size_;
 245   int r = memcmp(data_, b.data_, min_len);
 246   if (r == 0) {
 247     if (size_ < b.size_)
 248       r = -1;
 249     else if (size_ > b.size_)
 250       r = +1;
 251   }
 252   return r;
 253 }
 254
 255 inline size_t Slice::difference_offset(const Slice& b) const {
 256   size_t off = 0;
 257   const size_t len = (size_ < b.size_) ? size_ : b.size_;
 258   for (; off < len; off++) {
 259     if (data_[off] != b.data_[off]) break;
 260   }
 261   return off;
 262 }
 263
 264 }  // namespace ROCKSDB_NAMESPACE