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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
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