1 files changed, 181 insertions, 0 deletions
diff --git a/src/rocksdb/util/cleanable.cc b/src/rocksdb/util/cleanable.cc
new file mode 100644
index 000000000..89a7ab9be
--- /dev/null
+++ b/src/rocksdb/util/cleanable.cc
@@ -0,0 +1,181 @@
+//  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