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Avoid overflow when running out of IDs 

* Throw an exception instead
* Add function that allows re-using lower IDs instead
* Move functions to query IDs to read-only operations
This commit is contained in:
Martchus 2022-04-15 19:18:35 +02:00
parent 7689f0ebd6
commit bb985870f0
2 changed files with 58 additions and 20 deletions
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11
lmdb-typed.cc
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@ -2,15 +2,4 @@
namespace LMDBSafe {
IDType MDBGetMaxID(MDBRWTransaction &txn, MDBDbi &dbi)
{
auto cursor = txn->getRWCursor(dbi);
MDBOutVal maxidval, maxcontent;
auto maxid = IDType(0);
if (!cursor.get(maxidval, maxcontent, MDB_LAST)) {
maxid = maxidval.get<IDType>();
}
return maxid;
}
} // namespace LMDBSafe

67
lmdb-typed.hh
View File

@ -13,14 +13,6 @@ namespace LMDBSafe {
*/
using IDType = std::uint32_t;
/*!
* \brief Returns the highest ID used in a database. Returns 0 for an empty DB.
* \remarks
* This makes us start everything at ID "1", which might make it possible to
* treat id 0 as special.
*/
LMDB_SAFE_EXPORT IDType MDBGetMaxID(MDBRWTransaction &txn, MDBDbi &dbi);
/*!
* \brief Converts \a t to an std::string.
*
@ -298,6 +290,63 @@ public:
return stat.ms_entries;
}
/*!
* \brief Returns the highest ID or 0 if the database is empty.
*/
IDType maxID()
{
auto cursor = (*d_parent.d_txn)->getCursor(d_parent.d_parent->d_main);
MDBOutVal idval, maxcontent;
auto id = IDType(0);
if (!cursor.get(idval, maxcontent, MDB_LAST)) {
id = idval.get<IDType>();
}
return id;
}
/*!
* \brief Returns the next highest ID in the database.
* \remarks Never returns 0 so it can be used as special "no such ID" value.
* \throws Throws LMDBError when running out of IDs.
*/
IDType nextID()
{
const auto id = maxID();
if (id < std::numeric_limits<IDType>::max()) {
return id + 1;
}
throw LMDBError("Running out of IDs");
}
/*!
* \brief Returns an ID not used in the database so far.
* \remarks
* - Lower IDs are reused but an extensive search for "gabs" is avoided.
* - Never returns 0 so it can be used as special "no such ID" value.
* \throws Throws LMDBError when running out of IDs.
*/
IDType newID()
{
auto cursor = (*d_parent.d_txn)->getCursor(d_parent.d_parent->d_main);
MDBOutVal idval, maxcontent;
auto id = IDType(1);
if (!cursor.get(idval, maxcontent, MDB_FIRST)) {
id = idval.get<IDType>();
}
if (id > 1) {
return id - 1;
}
if (!cursor.get(idval, maxcontent, MDB_LAST)) {
id = idval.get<IDType>();
} else {
id = 0;
}
if (id < std::numeric_limits<IDType>::max()) {
return id + 1;
}
throw LMDBError("Running out of IDs");
}
//! Get item with id, from main table directly
bool get(IDType id, T &t)
{
@ -798,7 +847,7 @@ public:
{
unsigned int flags = 0;
if (!id) {
id = MDBGetMaxID(*d_txn, d_parent->d_main) + 1;
id = this->nextID();
flags = MDB_APPEND;
}
(*d_txn)->put(d_parent->d_main, id, serToString(t), flags);