Adding upstream version 18.2.2.upstream/18.2.2

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 82 insertions, 0 deletions

diff --git a/src/rocksdb/util/defer.h b/src/rocksdb/util/defer.h
new file mode 100644
index 000000000..f71e67ba9
--- /dev/null
+++ b/src/rocksdb/util/defer.h
@@ -0,0 +1,82 @@
+// 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).
+
+#pragma once
+
+#include <functional>
+
+#include "rocksdb/rocksdb_namespace.h"
+
+namespace ROCKSDB_NAMESPACE {
+
+// Defers the execution of the provided function until the Defer
+// object goes out of scope.
+//
+// Usage example:
+//
+// Status DeferTest() {
+//   Status s;
+//   Defer defer([&s]() {
+//     if (!s.ok()) {
+//       // do cleanups ...
+//     }
+//   });
+//   // do something ...
+//   if (!s.ok()) return;
+//   // do some other things ...
+//   return s;
+// }
+//
+// The above code ensures that cleanups will always happen on returning.
+//
+// Without the help of Defer, you can
+// 1. every time when !s.ok(), do the cleanup;
+// 2. instead of returning when !s.ok(), continue the work only when s.ok(),
+//    but sometimes, this might lead to nested blocks of "if (s.ok()) {...}".
+//
+// With the help of Defer, you can centralize the cleanup logic inside the
+// lambda passed to Defer, and you can return immediately on failure when
+// necessary.
+class Defer final {
+ public:
+  explicit Defer(std::function<void()>&& fn) : fn_(std::move(fn)) {}
+  ~Defer() { fn_(); }
+
+  // Disallow copy.
+  Defer(const Defer&) = delete;
+  Defer& operator=(const Defer&) = delete;
+
+ private:
+  std::function<void()> fn_;
+};
+
+// An RAII utility object that saves the current value of an object so that
+// it can be overwritten, and restores it to the saved value when the
+// SaveAndRestore object goes out of scope.
+template <typename T>
+class SaveAndRestore {
+ public:
+  // obj is non-null pointer to value to be saved and later restored.
+  explicit SaveAndRestore(T* obj) : obj_(obj), saved_(*obj) {}
+  // new_value is stored in *obj
+  SaveAndRestore(T* obj, const T& new_value)
+      : obj_(obj), saved_(std::move(*obj)) {
+    *obj = new_value;
+  }
+  SaveAndRestore(T* obj, T&& new_value) : obj_(obj), saved_(std::move(*obj)) {
+    *obj = std::move(new_value);
+  }
+  ~SaveAndRestore() { *obj_ = std::move(saved_); }
+
+  // No copies
+  SaveAndRestore(const SaveAndRestore&) = delete;
+  SaveAndRestore& operator=(const SaveAndRestore&) = delete;
+
+ private:
+  T* const obj_;
+  T saved_;
+};
+
+}  // namespace ROCKSDB_NAMESPACE