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