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authorLee Clagett <code@leeclagett.com>2018-09-26 23:54:27 -0400
committerLee Clagett <code@leeclagett.com>2019-03-19 17:52:26 +0000
commit0c7e7bce18558ea04e120b5fddcf4d22c0abc785 (patch)
tree5211e26db0ebe41908dc37780ce6f993e9471b6f /src/lmdb/database.h
parentMerge pull request #5201 (diff)
downloadmonero-0c7e7bce18558ea04e120b5fddcf4d22c0abc785.tar.xz
Adding classes, functions, and utilities for common LMDB operations.
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+// Copyright (c) 2018, The Monero Project
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+// conditions and the following disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+// of conditions and the following disclaimer in the documentation and/or other
+// materials provided with the distribution.
+//
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+// used to endorse or promote products derived from this software without specific
+// prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#pragma once
+
+#include <atomic>
+#include <cstddef>
+#include <lmdb.h>
+#include <memory>
+#include <type_traits>
+
+#include "common/expect.h"
+#include "lmdb/error.h"
+#include "lmdb/transaction.h"
+
+namespace lmdb
+{
+ //! Closes LMDB environment handle.
+ struct close_env
+ {
+ void operator()(MDB_env* ptr) const noexcept
+ {
+ if (ptr)
+ mdb_env_close(ptr);
+ }
+ };
+
+ using environment = std::unique_ptr<MDB_env, close_env>;
+
+ //! \return LMDB environment at `path` with a max of `max_dbs` tables.
+ expect<environment> open_environment(const char* path, MDB_dbi max_dbs) noexcept;
+
+ //! Context given to LMDB.
+ struct context
+ {
+ std::atomic<std::size_t> active;
+ std::atomic_flag lock;
+ };
+
+ //! Manages a LMDB environment for safe memory-map resizing. Thread-safe.
+ class database
+ {
+ environment env;
+ context ctx;
+
+ //! \return The LMDB environment associated with the object.
+ MDB_env* handle() const noexcept { return env.get(); }
+
+ expect<write_txn> do_create_txn(unsigned int flags) noexcept;
+
+ public:
+ database(environment env);
+
+ database(database&&) = delete;
+ database(database const&) = delete;
+
+ virtual ~database() noexcept;
+
+ database& operator=(database&&) = delete;
+ database& operator=(database const&) = delete;
+
+ /*!
+ Resize the memory map for the LMDB environment. Will block until
+ all reads/writes on the environment complete.
+ */
+ expect<void> resize() noexcept;
+
+ //! \return A read only LMDB transaction, reusing `txn` if provided.
+ expect<read_txn> create_read_txn(suspended_txn txn = nullptr) noexcept;
+
+ //! \return `txn` after releasing context.
+ expect<suspended_txn> reset_txn(read_txn txn) noexcept;
+
+ //! \return A read-write LMDB transaction.
+ expect<write_txn> create_write_txn() noexcept;
+
+ //! Commit the read-write transaction.
+ expect<void> commit(write_txn txn) noexcept;
+
+ /*!
+ Create a write transaction, pass it to `f`, then try to commit
+ the write if `f` succeeds.
+
+ \tparam F must be callable with signature `expect<T>(MDB_txn&)`.
+ \param f must be re-startable if `lmdb::error(MDB_MAP_FULL)`.
+
+ \return The result of calling `f`.
+ */
+ template<typename F>
+ typename std::result_of<F(MDB_txn&)>::type try_write(F f, unsigned attempts = 3)
+ {
+ for (unsigned i = 0; i < attempts; ++i)
+ {
+ expect<write_txn> txn = create_write_txn();
+ if (!txn)
+ return txn.error();
+
+ MONERO_PRECOND(*txn != nullptr);
+ const auto wrote = f(*(*txn));
+ if (wrote)
+ {
+ MONERO_CHECK(commit(std::move(*txn)));
+ return wrote;
+ }
+ if (wrote != lmdb::error(MDB_MAP_FULL))
+ return wrote;
+
+ txn->reset();
+ MONERO_CHECK(this->resize());
+ }
+ return {lmdb::error(MDB_MAP_FULL)};
+ }
+ };
+} // lmdb
+