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diff --git a/src/rocksdb/util/cleanable.cc b/src/rocksdb/util/cleanable.cc
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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.
+
+#include "rocksdb/cleanable.h"
+
+#include <atomic>
+#include <cassert>
+#include <utility>
+
+namespace ROCKSDB_NAMESPACE {
+
+Cleanable::Cleanable() {
+ cleanup_.function = nullptr;
+ cleanup_.next = nullptr;
+}
+
+Cleanable::~Cleanable() { DoCleanup(); }
+
+Cleanable::Cleanable(Cleanable&& other) noexcept { *this = std::move(other); }
+
+Cleanable& Cleanable::operator=(Cleanable&& other) noexcept {
+ assert(this != &other); // https://stackoverflow.com/a/9322542/454544
+ cleanup_ = other.cleanup_;
+ other.cleanup_.function = nullptr;
+ other.cleanup_.next = nullptr;
+ return *this;
+}
+
+// If the entire linked list was on heap we could have simply add attach one
+// link list to another. However the head is an embeded object to avoid the cost
+// of creating objects for most of the use cases when the Cleanable has only one
+// Cleanup to do. We could put evernything on heap if benchmarks show no
+// negative impact on performance.
+// Also we need to iterate on the linked list since there is no pointer to the
+// tail. We can add the tail pointer but maintainin it might negatively impact
+// the perforamnce for the common case of one cleanup where tail pointer is not
+// needed. Again benchmarks could clarify that.
+// Even without a tail pointer we could iterate on the list, find the tail, and
+// have only that node updated without the need to insert the Cleanups one by
+// one. This however would be redundant when the source Cleanable has one or a
+// few Cleanups which is the case most of the time.
+// TODO(myabandeh): if the list is too long we should maintain a tail pointer
+// and have the entire list (minus the head that has to be inserted separately)
+// merged with the target linked list at once.
+void Cleanable::DelegateCleanupsTo(Cleanable* other) {
+ assert(other != nullptr);
+ if (cleanup_.function == nullptr) {
+ return;
+ }
+ Cleanup* c = &cleanup_;
+ other->RegisterCleanup(c->function, c->arg1, c->arg2);
+ c = c->next;
+ while (c != nullptr) {
+ Cleanup* next = c->next;
+ other->RegisterCleanup(c);
+ c = next;
+ }
+ cleanup_.function = nullptr;
+ cleanup_.next = nullptr;
+}
+
+void Cleanable::RegisterCleanup(Cleanable::Cleanup* c) {
+ assert(c != nullptr);
+ if (cleanup_.function == nullptr) {
+ cleanup_.function = c->function;
+ cleanup_.arg1 = c->arg1;
+ cleanup_.arg2 = c->arg2;
+ delete c;
+ } else {
+ c->next = cleanup_.next;
+ cleanup_.next = c;
+ }
+}
+
+void Cleanable::RegisterCleanup(CleanupFunction func, void* arg1, void* arg2) {
+ assert(func != nullptr);
+ Cleanup* c;
+ if (cleanup_.function == nullptr) {
+ c = &cleanup_;
+ } else {
+ c = new Cleanup;
+ c->next = cleanup_.next;
+ cleanup_.next = c;
+ }
+ c->function = func;
+ c->arg1 = arg1;
+ c->arg2 = arg2;
+}
+
+struct SharedCleanablePtr::Impl : public Cleanable {
+ std::atomic<unsigned> ref_count{1}; // Start with 1 ref
+ void Ref() { ref_count.fetch_add(1, std::memory_order_relaxed); }
+ void Unref() {
+ if (ref_count.fetch_sub(1, std::memory_order_relaxed) == 1) {
+ // Last ref
+ delete this;
+ }
+ }
+ static void UnrefWrapper(void* arg1, void* /*arg2*/) {
+ static_cast<SharedCleanablePtr::Impl*>(arg1)->Unref();
+ }
+};
+
+void SharedCleanablePtr::Reset() {
+ if (ptr_) {
+ ptr_->Unref();
+ ptr_ = nullptr;
+ }
+}
+
+void SharedCleanablePtr::Allocate() {
+ Reset();
+ ptr_ = new Impl();
+}
+
+SharedCleanablePtr::SharedCleanablePtr(const SharedCleanablePtr& from) {
+ *this = from;
+}
+
+SharedCleanablePtr::SharedCleanablePtr(SharedCleanablePtr&& from) noexcept {
+ *this = std::move(from);
+}
+
+SharedCleanablePtr& SharedCleanablePtr::operator=(
+ const SharedCleanablePtr& from) {
+ if (this != &from) {
+ Reset();
+ ptr_ = from.ptr_;
+ if (ptr_) {
+ ptr_->Ref();
+ }
+ }
+ return *this;
+}
+
+SharedCleanablePtr& SharedCleanablePtr::operator=(
+ SharedCleanablePtr&& from) noexcept {
+ assert(this != &from); // https://stackoverflow.com/a/9322542/454544
+ Reset();
+ ptr_ = from.ptr_;
+ from.ptr_ = nullptr;
+ return *this;
+}
+
+SharedCleanablePtr::~SharedCleanablePtr() { Reset(); }
+
+Cleanable& SharedCleanablePtr::operator*() {
+ return *ptr_; // implicit upcast
+}
+
+Cleanable* SharedCleanablePtr::operator->() {
+ return ptr_; // implicit upcast
+}
+
+Cleanable* SharedCleanablePtr::get() {
+ return ptr_; // implicit upcast
+}
+
+void SharedCleanablePtr::RegisterCopyWith(Cleanable* target) {
+ if (ptr_) {
+ // "Virtual" copy of the pointer
+ ptr_->Ref();
+ target->RegisterCleanup(&Impl::UnrefWrapper, ptr_, nullptr);
+ }
+}
+
+void SharedCleanablePtr::MoveAsCleanupTo(Cleanable* target) {
+ if (ptr_) {
+ // "Virtual" move of the pointer
+ target->RegisterCleanup(&Impl::UnrefWrapper, ptr_, nullptr);
+ ptr_ = nullptr;
+ }
+}
+
+} // namespace ROCKSDB_NAMESPACE