rocksdb/util/defer.h
Cheng Chang dafb568052 Add utility class Defer (#6382)
Summary:
Add a utility class `Defer` to defer the execution of a function until the Defer object goes out of scope.
Used in VersionSet:: ProcessManifestWrites as an example.
The inline comments for class `Defer` have more details.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6382

Test Plan: `make defer_test version_set_test && ./defer_test && ./version_set_test`

Differential Revision: D19797538

Pulled By: cheng-chang

fbshipit-source-id: b1a9b7306e4fd4f48ec2ab55783caa561a315f0f
2020-02-10 17:59:47 -08:00

53 lines
1.4 KiB
C++

// 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>
namespace rocksdb {
// 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:
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_;
};
} // namespace rocksdb