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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-21 11:54:28 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-21 11:54:28 +0000 |
commit | e6918187568dbd01842d8d1d2c808ce16a894239 (patch) | |
tree | 64f88b554b444a49f656b6c656111a145cbbaa28 /src/rocksdb/util/defer.h | |
parent | Initial commit. (diff) | |
download | ceph-e6918187568dbd01842d8d1d2c808ce16a894239.tar.xz ceph-e6918187568dbd01842d8d1d2c808ce16a894239.zip |
Adding upstream version 18.2.2.upstream/18.2.2
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'src/rocksdb/util/defer.h')
-rw-r--r-- | src/rocksdb/util/defer.h | 82 |
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 |