1 files changed, 138 insertions, 0 deletions
diff --git a/src/lmdb/database.h b/src/lmdb/database.h
new file mode 100644
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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
+