ceph/src/rocksdb/util/cleanable.cc

   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 //
   6 // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
   7 // Use of this source code is governed by a BSD-style license that can be
   8 // found in the LICENSE file. See the AUTHORS file for names of contributors.
   9
  10 #include "rocksdb/cleanable.h"
  11
  12 #include <atomic>
  13 #include <cassert>
  14 #include <utility>
  15
  16 namespace ROCKSDB_NAMESPACE {
  17
  18 Cleanable::Cleanable() {
  19   cleanup_.function = nullptr;
  20   cleanup_.next = nullptr;
  21 }
  22
  23 Cleanable::~Cleanable() { DoCleanup(); }
  24
  25 Cleanable::Cleanable(Cleanable&& other) noexcept { *this = std::move(other); }
  26
  27 Cleanable& Cleanable::operator=(Cleanable&& other) noexcept {
  28   assert(this != &other);  // https://stackoverflow.com/a/9322542/454544
  29   cleanup_ = other.cleanup_;
  30   other.cleanup_.function = nullptr;
  31   other.cleanup_.next = nullptr;
  32   return *this;
  33 }
  34
  35 // If the entire linked list was on heap we could have simply add attach one
  36 // link list to another. However the head is an embeded object to avoid the cost
  37 // of creating objects for most of the use cases when the Cleanable has only one
  38 // Cleanup to do. We could put evernything on heap if benchmarks show no
  39 // negative impact on performance.
  40 // Also we need to iterate on the linked list since there is no pointer to the
  41 // tail. We can add the tail pointer but maintainin it might negatively impact
  42 // the perforamnce for the common case of one cleanup where tail pointer is not
  43 // needed. Again benchmarks could clarify that.
  44 // Even without a tail pointer we could iterate on the list, find the tail, and
  45 // have only that node updated without the need to insert the Cleanups one by
  46 // one. This however would be redundant when the source Cleanable has one or a
  47 // few Cleanups which is the case most of the time.
  48 // TODO(myabandeh): if the list is too long we should maintain a tail pointer
  49 // and have the entire list (minus the head that has to be inserted separately)
  50 // merged with the target linked list at once.
  51 void Cleanable::DelegateCleanupsTo(Cleanable* other) {
  52   assert(other != nullptr);
  53   if (cleanup_.function == nullptr) {
  54     return;
  55   }
  56   Cleanup* c = &cleanup_;
  57   other->RegisterCleanup(c->function, c->arg1, c->arg2);
  58   c = c->next;
  59   while (c != nullptr) {
  60     Cleanup* next = c->next;
  61     other->RegisterCleanup(c);
  62     c = next;
  63   }
  64   cleanup_.function = nullptr;
  65   cleanup_.next = nullptr;
  66 }
  67
  68 void Cleanable::RegisterCleanup(Cleanable::Cleanup* c) {
  69   assert(c != nullptr);
  70   if (cleanup_.function == nullptr) {
  71     cleanup_.function = c->function;
  72     cleanup_.arg1 = c->arg1;
  73     cleanup_.arg2 = c->arg2;
  74     delete c;
  75   } else {
  76     c->next = cleanup_.next;
  77     cleanup_.next = c;
  78   }
  79 }
  80
  81 void Cleanable::RegisterCleanup(CleanupFunction func, void* arg1, void* arg2) {
  82   assert(func != nullptr);
  83   Cleanup* c;
  84   if (cleanup_.function == nullptr) {
  85     c = &cleanup_;
  86   } else {
  87     c = new Cleanup;
  88     c->next = cleanup_.next;
  89     cleanup_.next = c;
  90   }
  91   c->function = func;
  92   c->arg1 = arg1;
  93   c->arg2 = arg2;
  94 }
  95
  96 struct SharedCleanablePtr::Impl : public Cleanable {
  97   std::atomic<unsigned> ref_count{1};  // Start with 1 ref
  98   void Ref() { ref_count.fetch_add(1, std::memory_order_relaxed); }
  99   void Unref() {
 100     if (ref_count.fetch_sub(1, std::memory_order_relaxed) == 1) {
 101       // Last ref
 102       delete this;
 103     }
 104   }
 105   static void UnrefWrapper(void* arg1, void* /*arg2*/) {
 106     static_cast<SharedCleanablePtr::Impl*>(arg1)->Unref();
 107   }
 108 };
 109
 110 void SharedCleanablePtr::Reset() {
 111   if (ptr_) {
 112     ptr_->Unref();
 113     ptr_ = nullptr;
 114   }
 115 }
 116
 117 void SharedCleanablePtr::Allocate() {
 118   Reset();
 119   ptr_ = new Impl();
 120 }
 121
 122 SharedCleanablePtr::SharedCleanablePtr(const SharedCleanablePtr& from) {
 123   *this = from;
 124 }
 125
 126 SharedCleanablePtr::SharedCleanablePtr(SharedCleanablePtr&& from) noexcept {
 127   *this = std::move(from);
 128 }
 129
 130 SharedCleanablePtr& SharedCleanablePtr::operator=(
 131     const SharedCleanablePtr& from) {
 132   if (this != &from) {
 133     Reset();
 134     ptr_ = from.ptr_;
 135     if (ptr_) {
 136       ptr_->Ref();
 137     }
 138   }
 139   return *this;
 140 }
 141
 142 SharedCleanablePtr& SharedCleanablePtr::operator=(
 143     SharedCleanablePtr&& from) noexcept {
 144   assert(this != &from);  // https://stackoverflow.com/a/9322542/454544
 145   Reset();
 146   ptr_ = from.ptr_;
 147   from.ptr_ = nullptr;
 148   return *this;
 149 }
 150
 151 SharedCleanablePtr::~SharedCleanablePtr() { Reset(); }
 152
 153 Cleanable& SharedCleanablePtr::operator*() {
 154   return *ptr_;  // implicit upcast
 155 }
 156
 157 Cleanable* SharedCleanablePtr::operator->() {
 158   return ptr_;  // implicit upcast
 159 }
 160
 161 Cleanable* SharedCleanablePtr::get() {
 162   return ptr_;  // implicit upcast
 163 }
 164
 165 void SharedCleanablePtr::RegisterCopyWith(Cleanable* target) {
 166   if (ptr_) {
 167     // "Virtual" copy of the pointer
 168     ptr_->Ref();
 169     target->RegisterCleanup(&Impl::UnrefWrapper, ptr_, nullptr);
 170   }
 171 }
 172
 173 void SharedCleanablePtr::MoveAsCleanupTo(Cleanable* target) {
 174   if (ptr_) {
 175     // "Virtual" move of the pointer
 176     target->RegisterCleanup(&Impl::UnrefWrapper, ptr_, nullptr);
 177     ptr_ = nullptr;
 178   }
 179 }
 180
 181 }  // namespace ROCKSDB_NAMESPACE