363 lines
11 KiB
C++
363 lines
11 KiB
C++
#include "lmdb-safe.hh"
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#include <fcntl.h>
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#include <sys/stat.h>
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#include <cstring>
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#include <map>
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#include <memory>
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#include <mutex>
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using namespace std;
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namespace LMDBSafe {
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MDBDbi::MDBDbi(MDB_env *env, MDB_txn *txn, const string_view dbname, unsigned int flags)
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{
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(void)env;
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// A transaction that uses this function must finish (either commit or abort) before any other transaction in the process may use this function.
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if (const auto rc = mdb_dbi_open(txn, dbname.empty() ? 0 : &dbname[0], flags, &d_dbi))
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throw LMDBError("Unable to open named database: ", rc);
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// Database names are keys in the unnamed database, and may be read but not written.
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}
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MDBEnv::MDBEnv(const char *fname, unsigned int flags, mdb_mode_t mode, MDB_dbi maxDBs)
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{
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mdb_env_create(&d_env);
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if (const auto rc = mdb_env_set_mapsize(d_env, 16ULL * 4096 * 244140ULL)) { // 4GB
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throw LMDBError("Setting map size: ", rc);
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}
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// Various other options may also need to be set before opening the handle, e.g. mdb_env_set_mapsize(), mdb_env_set_maxreaders(), mdb_env_set_maxdbs(),
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if (const auto rc = mdb_env_set_maxdbs(d_env, maxDBs)) {
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throw LMDBError("Setting maxdbs: ", rc);
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}
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// we need MDB_NOTLS since we rely on its semantics
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if (const auto rc = mdb_env_open(d_env, fname, flags | MDB_NOTLS, mode)) {
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// If this function fails, mdb_env_close() must be called to discard the MDB_env handle.
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mdb_env_close(d_env);
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throw LMDBError("Unable to open database file " + std::string(fname) + ": ", rc);
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}
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}
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void MDBEnv::incROTX()
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{
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std::lock_guard<std::mutex> l(d_countmutex);
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++d_ROtransactionsOut[std::this_thread::get_id()];
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}
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void MDBEnv::decROTX()
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{
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std::lock_guard<std::mutex> l(d_countmutex);
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--d_ROtransactionsOut[std::this_thread::get_id()];
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}
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void MDBEnv::incRWTX()
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{
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std::lock_guard<std::mutex> l(d_countmutex);
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++d_RWtransactionsOut[std::this_thread::get_id()];
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}
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void MDBEnv::decRWTX()
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{
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std::lock_guard<std::mutex> l(d_countmutex);
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--d_RWtransactionsOut[std::this_thread::get_id()];
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}
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int MDBEnv::getRWTX()
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{
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std::lock_guard<std::mutex> l(d_countmutex);
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return d_RWtransactionsOut[std::this_thread::get_id()];
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}
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int MDBEnv::getROTX()
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{
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std::lock_guard<std::mutex> l(d_countmutex);
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return d_ROtransactionsOut[std::this_thread::get_id()];
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}
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std::shared_ptr<MDBEnv> getMDBEnv(const char *fname, unsigned int flags, mdb_mode_t mode, MDB_dbi maxDBs)
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{
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struct Value {
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weak_ptr<MDBEnv> wp;
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unsigned int flags;
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};
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static std::map<tuple<dev_t, ino_t>, Value> s_envs;
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static std::mutex mut;
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struct stat statbuf;
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if (stat(fname, &statbuf)) {
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if (errno != ENOENT)
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throw LMDBError("Unable to stat prospective mdb database: " + string(strerror(errno)));
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else {
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std::lock_guard<std::mutex> l(mut);
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auto fresh = std::make_shared<MDBEnv>(fname, flags, mode, maxDBs);
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if (stat(fname, &statbuf))
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throw LMDBError("Unable to stat prospective mdb database: " + string(strerror(errno)));
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auto key = std::tie(statbuf.st_dev, statbuf.st_ino);
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s_envs[key] = { fresh, flags };
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return fresh;
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}
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}
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std::lock_guard<std::mutex> l(mut);
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auto key = std::tie(statbuf.st_dev, statbuf.st_ino);
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auto iter = s_envs.find(key);
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if (iter != s_envs.end()) {
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auto sp = iter->second.wp.lock();
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if (sp) {
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if (iter->second.flags != flags)
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throw LMDBError("Can't open mdb with differing flags");
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return sp;
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} else {
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s_envs.erase(iter); // useful if make_shared fails
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}
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}
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auto fresh = std::make_shared<MDBEnv>(fname, flags, mode, maxDBs);
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s_envs[key] = { fresh, flags };
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return fresh;
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}
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MDBDbi MDBEnv::openDB(const string_view dbname, unsigned int flags)
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{
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unsigned int envflags;
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mdb_env_get_flags(d_env, &envflags);
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/*
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This function must not be called from multiple concurrent transactions in the same process. A transaction that uses this function must finish (either commit or abort) before any other transaction in the process may use this function.
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*/
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std::lock_guard<std::mutex> l(d_openmut);
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if (!(envflags & MDB_RDONLY)) {
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auto rwt = getRWTransaction();
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MDBDbi ret = rwt->openDB(dbname, flags);
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rwt->commit();
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return ret;
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}
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MDBDbi ret;
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{
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auto rwt = getROTransaction();
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ret = rwt->openDB(dbname, flags);
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}
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return ret;
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}
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MDBRWTransactionImpl::MDBRWTransactionImpl(MDBEnv *parent, MDB_txn *txn)
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: MDBROTransactionImpl(parent, txn)
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{
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}
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MDB_txn *MDBRWTransactionImpl::openRWTransaction(MDBEnv *env, MDB_txn *parent, unsigned int flags)
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{
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MDB_txn *result;
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if (env->getRWTX())
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throw LMDBError("Duplicate RW transaction");
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for (int tries = 0; tries < 3; ++tries) { // it might happen twice, who knows
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if (int rc = mdb_txn_begin(env->d_env, parent, flags, &result)) {
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if (rc == MDB_MAP_RESIZED && tries < 2) {
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// "If the mapsize is increased by another process (..) mdb_txn_begin() will return MDB_MAP_RESIZED.
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// call mdb_env_set_mapsize with a size of zero to adopt the new size."
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mdb_env_set_mapsize(env->d_env, 0);
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continue;
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}
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throw LMDBError("Unable to start RW transaction: ", rc);
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}
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break;
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}
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env->incRWTX();
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return result;
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}
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MDBRWTransactionImpl::MDBRWTransactionImpl(MDBEnv *parent, unsigned int flags)
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: MDBRWTransactionImpl(parent, openRWTransaction(parent, nullptr, flags))
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{
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}
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MDBRWTransactionImpl::~MDBRWTransactionImpl()
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{
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MDBRWTransactionImpl::abort();
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}
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void MDBRWTransactionImpl::commit()
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{
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closeRORWCursors();
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if (!d_txn) {
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return;
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}
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if (const auto rc = mdb_txn_commit(d_txn)) {
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throw LMDBError("Committing transaction: ", rc);
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}
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environment().decRWTX();
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d_txn = nullptr;
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}
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void MDBRWTransactionImpl::abort()
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{
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closeRORWCursors();
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if (!d_txn) {
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return;
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}
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mdb_txn_abort(d_txn);
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// prevent the RO destructor from cleaning up the transaction itself
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environment().decRWTX();
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d_txn = nullptr;
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}
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MDBROTransactionImpl::MDBROTransactionImpl(MDBEnv *parent, MDB_txn *txn)
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: d_parent(parent)
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, d_cursors()
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, d_txn(txn)
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{
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}
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MDB_txn *MDBROTransactionImpl::openROTransaction(MDBEnv *env, MDB_txn *parent, unsigned int flags)
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{
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if (env->getRWTX())
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throw LMDBError("Duplicate RO transaction");
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/*
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A transaction and its cursors must only be used by a single thread, and a thread may only have a single transaction at a time. If MDB_NOTLS is in use, this does not apply to read-only transactions. */
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MDB_txn *result = nullptr;
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for (int tries = 0; tries < 3; ++tries) { // it might happen twice, who knows
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if (const auto rc = mdb_txn_begin(env->d_env, parent, MDB_RDONLY | flags, &result)) {
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if (rc == MDB_MAP_RESIZED && tries < 2) {
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// "If the mapsize is increased by another process (..) mdb_txn_begin() will return MDB_MAP_RESIZED.
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// call mdb_env_set_mapsize with a size of zero to adopt the new size."
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mdb_env_set_mapsize(env->d_env, 0);
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continue;
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}
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throw LMDBError("Unable to start RO transaction: ", rc);
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}
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break;
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}
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env->incROTX();
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return result;
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}
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void MDBROTransactionImpl::closeROCursors()
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{
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// we need to move the vector away to ensure that the cursors don’t mess with our iteration.
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std::vector<MDBROCursor *> buf;
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std::swap(d_cursors, buf);
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for (auto &cursor : buf) {
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cursor->close();
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}
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}
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MDBROTransactionImpl::MDBROTransactionImpl(MDBEnv *parent, unsigned int flags)
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: MDBROTransactionImpl(parent, openROTransaction(parent, nullptr, flags))
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{
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}
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MDBROTransactionImpl::~MDBROTransactionImpl()
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{
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// this is safe because C++ will not call overrides of virtual methods in destructors.
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MDBROTransactionImpl::commit();
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}
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void MDBROTransactionImpl::abort()
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{
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closeROCursors();
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// if d_txn is non-nullptr here, either the transaction object was invalidated earlier (e.g. by moving from it), or it is an RW transaction which has already cleaned up the d_txn pointer (with an abort).
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if (d_txn) {
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d_parent->decROTX();
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mdb_txn_abort(d_txn); // this appears to work better than abort for r/o database opening
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d_txn = nullptr;
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}
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}
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void MDBROTransactionImpl::commit()
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{
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closeROCursors();
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// if d_txn is non-nullptr here, either the transaction object was invalidated earlier (e.g. by moving from it), or it is an RW transaction which has already cleaned up the d_txn pointer (with an abort).
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if (d_txn) {
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d_parent->decROTX();
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if (const auto rc = mdb_txn_commit(d_txn)) { // this appears to work better than abort for r/o database opening
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throw LMDBError("Error comitting transaction: ", rc);
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}
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d_txn = nullptr;
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}
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}
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void MDBRWTransactionImpl::clear(MDB_dbi dbi)
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{
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if (const auto rc = mdb_drop(d_txn, dbi, 0)) {
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throw LMDBError("Error clearing database: ", rc);
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}
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}
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MDBRWCursor MDBRWTransactionImpl::getRWCursor(const MDBDbi &dbi)
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{
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MDB_cursor *cursor;
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;
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if (const auto rc = mdb_cursor_open(d_txn, dbi, &cursor)) {
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throw LMDBError("Error creating RO cursor: ", rc);
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}
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return MDBRWCursor(d_rw_cursors, cursor);
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}
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MDBRWCursor MDBRWTransactionImpl::getCursor(const MDBDbi &dbi)
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{
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return getRWCursor(dbi);
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}
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MDBRWTransaction MDBRWTransactionImpl::getRWTransaction()
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{
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MDB_txn *txn;
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if (const auto rc = mdb_txn_begin(environment(), *this, 0, &txn)) {
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throw LMDBError("Failed to start child transaction: ", rc);
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}
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// we need to increase the counter here because commit/abort on the child transaction will decrease it
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environment().incRWTX();
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return MDBRWTransaction(new MDBRWTransactionImpl(&environment(), txn));
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}
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MDBROTransaction MDBRWTransactionImpl::getROTransaction()
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{
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return getRWTransaction();
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}
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MDBROTransaction MDBEnv::getROTransaction()
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{
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return MDBROTransaction(new MDBROTransactionImpl(this));
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}
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MDBRWTransaction MDBEnv::getRWTransaction()
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{
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return MDBRWTransaction(new MDBRWTransactionImpl(this));
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}
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void MDBRWTransactionImpl::closeRWCursors()
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{
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decltype(d_rw_cursors) buf;
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std::swap(d_rw_cursors, buf);
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for (auto &cursor : buf) {
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cursor->close();
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}
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}
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MDBROCursor MDBROTransactionImpl::getCursor(const MDBDbi &dbi)
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{
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return getROCursor(dbi);
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}
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MDBROCursor MDBROTransactionImpl::getROCursor(const MDBDbi &dbi)
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{
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MDB_cursor *cursor;
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if (const auto rc = mdb_cursor_open(d_txn, dbi, &cursor)) {
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throw LMDBError("Error creating RO cursor: ", rc);
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}
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return MDBROCursor(d_cursors, cursor);
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}
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} // namespace LMDBSafe
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