Fix #2601 misuses of LMDB API #2602
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Only open DBI once, doesn't need closing. Never reuse a txn handle after commit. Use MDB_RDONLY for txns that aren't doing any writes
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Hello @hyc , I finally had a chance to look at this in detail and one thing I wondered about: There is a new member variable 'MDB_dbi m_dbi;' in the LMDB class -- which makes sense. MDB_dbi is typedef'd to 'unsigned int', which means m_dbi is undefined initially. The LMDB constructor will initialize it with a successful call to mdb_dbi_open. But what if it fails? The return code from mdb_dbi_open isn't checked and we proceed as if it had been successful. I had a look at both the LMDB documentation and (a brief) skim of the code and it doesn't look like a failure condition within mdb_dbi_open will result in the MDB_dbi out-parameter being updated to a special value or anything (that might have been checked for in subsequent calls to other functions). Thoughts? |
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The default dbi, which is what your code uses, always exists and is always valid, so the mdb_dbi_open call will never fail. |
Only open DBI once, doesn't need closing.
Never reuse a txn handle after commit.
Use MDB_RDONLY for txns that aren't doing any writes