Adding classes, functions, and utilities for common LMDB operations.

1 files changed, 95 insertions, 0 deletions

diff --git a/src/lmdb/transaction.h b/src/lmdb/transaction.h
new file mode 100644
index 000000000..cdd80696c
--- /dev/null
+++ b/src/lmdb/transaction.h
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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 <lmdb.h>
+#include <memory>
+
+#include "lmdb/error.h"
+
+//! Uses C++ type system to differentiate between cursors
+#define MONERO_CURSOR(name)                                    \
+    struct close_ ## name : ::lmdb::close_cursor {};           \
+    using name = std::unique_ptr< MDB_cursor, close_ ## name >;
+
+namespace lmdb
+{
+    struct abort_txn
+    {
+        void operator()(MDB_txn* ptr) const noexcept
+        {
+            if (ptr)
+                mdb_txn_abort(ptr);
+        }
+    };
+
+    /*!
+        Only valid if used via `create_read_txn()`. Decrements active count in
+        associated `context`, and aborts a LMDB transaction (`mdb_txn_abort`).
+    */
+    struct release_read_txn
+    { 
+        void operator()(MDB_txn* ptr) const noexcept;
+        // implementation in database.cpp
+    };
+
+    /*!
+        Only valid if used via `create_write_txn()`. Decrements active count in
+        associated `context`, and aborts a LMDB transaction (`mdb_txn_abort`).
+    */
+    struct abort_write_txn
+    {
+        void operator()(MDB_txn* ptr) const noexcept
+        {
+            release_read_txn{}(ptr);
+        }
+    };
+
+    struct close_cursor
+    {
+        void operator()(MDB_cursor* ptr) const noexcept
+        {
+            if (ptr)
+                mdb_cursor_close(ptr);
+        }
+    };
+
+    template<typename D>
+    inline expect<std::unique_ptr<MDB_cursor, D>>
+    open_cursor(MDB_txn& txn, MDB_dbi tbl) noexcept
+    {
+        MDB_cursor* cur = nullptr;
+        MONERO_LMDB_CHECK(mdb_cursor_open(&txn, tbl, &cur));
+        return std::unique_ptr<MDB_cursor, D>{cur};
+    }
+
+    // The below use the C++ type system to designate `MDB_txn` status.
+
+    using suspended_txn = std::unique_ptr<MDB_txn, abort_txn>;
+    using read_txn = std::unique_ptr<MDB_txn, release_read_txn>;
+    using write_txn = std::unique_ptr<MDB_txn, abort_write_txn>;
+} // lmdb