1 files changed, 364 insertions, 0 deletions
diff --git a/ext/lmdb-safe/lmdb-safe.cc b/ext/lmdb-safe/lmdb-safe.cc
new file mode 100644
index 0000000..7a023fd
--- /dev/null
+++ b/ext/lmdb-safe/lmdb-safe.cc
@@ -0,0 +1,364 @@
+#include "lmdb-safe.hh"
+#include <fcntl.h>
+#include <mutex>
+#include <memory>
+#include <sys/stat.h>
+#include <string.h>
+#include <map>
+
+using std::string;
+using std::runtime_error;
+using std::tuple;
+using std::weak_ptr;
+
+static string MDBError(int rc)
+{
+  return mdb_strerror(rc);
+}
+
+MDBDbi::MDBDbi(MDB_env* env, MDB_txn* txn, const string_view dbname, int flags)
+{
+  // A transaction that uses this function must finish (either commit or abort) before any other transaction in the process may use this function.
+  
+  int rc = mdb_dbi_open(txn, dbname.empty() ? 0 : &dbname[0], flags, &d_dbi);
+  if(rc)
+    throw std::runtime_error("Unable to open named database: " + MDBError(rc));
+  
+  // Database names are keys in the unnamed database, and may be read but not written.
+}
+
+MDBEnv::MDBEnv(const char* fname, int flags, int mode)
+{
+  mdb_env_create(&d_env);
+  uint64_t mapsizeMB = (sizeof(long)==4) ? 100 : 16000;
+  // on 32 bit platforms, there is just no room for more
+  if(mdb_env_set_mapsize(d_env, mapsizeMB * 1048576))
+    throw std::runtime_error("setting map size");
+    /*
+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(),
+    */
+
+  mdb_env_set_maxdbs(d_env, 128);
+
+  // we need MDB_NOTLS since we rely on its semantics
+  if(int rc=mdb_env_open(d_env, fname, flags | MDB_NOTLS, mode)) {
+    // If this function fails, mdb_env_close() must be called to discard the MDB_env handle.
+    mdb_env_close(d_env);
+    throw std::runtime_error("Unable to open database file "+std::string(fname)+": " + MDBError(rc));
+  }
+
+  if ((flags & MDB_RDONLY) == 0) {
+    // Check for stale readers to prevent unbridled database growth.
+    // Only do this when in RW mode since it affects the file.
+    mdb_reader_check(d_env, nullptr);
+  }
+}
+
+void MDBEnv::incROTX()
+{
+  std::lock_guard<std::mutex> l(d_countmutex);
+  ++d_ROtransactionsOut[std::this_thread::get_id()];
+}
+
+void MDBEnv::decROTX()
+{
+  std::lock_guard<std::mutex> l(d_countmutex);
+  --d_ROtransactionsOut[std::this_thread::get_id()];
+}
+
+void MDBEnv::incRWTX()
+{
+  std::lock_guard<std::mutex> l(d_countmutex);
+  ++d_RWtransactionsOut[std::this_thread::get_id()];
+}
+
+void MDBEnv::decRWTX()
+{
+  std::lock_guard<std::mutex> l(d_countmutex);
+  --d_RWtransactionsOut[std::this_thread::get_id()];
+}
+
+int MDBEnv::getRWTX()
+{
+  std::lock_guard<std::mutex> l(d_countmutex);
+  return d_RWtransactionsOut[std::this_thread::get_id()];
+}
+int MDBEnv::getROTX()
+{
+  std::lock_guard<std::mutex> l(d_countmutex);
+  return d_ROtransactionsOut[std::this_thread::get_id()];
+}
+
+
+std::shared_ptr<MDBEnv> getMDBEnv(const char* fname, int flags, int mode)
+{
+  struct Value
+  {
+    weak_ptr<MDBEnv> wp;
+    int flags;
+  };
+  
+  static std::map<tuple<dev_t, ino_t>, Value> s_envs;
+  static std::mutex mut;
+  
+  struct stat statbuf;
+  if(stat(fname, &statbuf)) {
+    if(errno != ENOENT)
+      throw std::runtime_error("Unable to stat prospective mdb database: "+string(strerror(errno)));
+    else {
+      std::lock_guard<std::mutex> l(mut);
+      auto fresh = std::make_shared<MDBEnv>(fname, flags, mode);
+      if(stat(fname, &statbuf))
+        throw std::runtime_error("Unable to stat prospective mdb database: "+string(strerror(errno)));
+      auto key = std::tie(statbuf.st_dev, statbuf.st_ino);
+      s_envs[key] = {fresh, flags};
+      return fresh;
+    }
+  }
+
+  std::lock_guard<std::mutex> l(mut);
+  auto key = std::tie(statbuf.st_dev, statbuf.st_ino);
+  auto iter = s_envs.find(key);
+  if(iter != s_envs.end()) {
+    auto sp = iter->second.wp.lock();
+    if(sp) {
+      if(iter->second.flags != flags)
+        throw std::runtime_error("Can't open mdb with differing flags");
+
+      return sp;
+    }
+    else {
+      s_envs.erase(iter); // useful if make_shared fails
+    }
+  }
+
+  auto fresh = std::make_shared<MDBEnv>(fname, flags, mode);
+  s_envs[key] = {fresh, flags};
+  
+  return fresh;
+}
+
+
+MDBDbi MDBEnv::openDB(const string_view dbname, int flags)
+{
+  unsigned int envflags;
+  mdb_env_get_flags(d_env, &envflags);
+  /*
+    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.
+  */
+  std::lock_guard<std::mutex> l(d_openmut);
+  
+  if(!(envflags & MDB_RDONLY)) {
+    auto rwt = getRWTransaction();
+    MDBDbi ret = rwt->openDB(dbname, flags);
+    rwt->commit();
+    return ret;
+  }
+
+  MDBDbi ret;
+  {
+    auto rwt = getROTransaction(); 
+    ret = rwt->openDB(dbname, flags);
+  }
+  return ret;
+}
+
+MDBRWTransactionImpl::MDBRWTransactionImpl(MDBEnv *parent, MDB_txn *txn):
+  MDBROTransactionImpl(parent, txn)
+
+{
+
+}
+
+MDB_txn *MDBRWTransactionImpl::openRWTransaction(MDBEnv *env, MDB_txn *parent, int flags)
+{
+  MDB_txn *result;
+  if(env->getROTX() || env->getRWTX())
+    throw std::runtime_error("Duplicate RW transaction");
+
+  if(int rc=mdb_txn_begin(env->d_env, parent, flags, &result))
+    throw std::runtime_error("Unable to start RW transaction: "+std::string(mdb_strerror(rc)));
+
+  env->incRWTX();
+  return result;
+}
+
+MDBRWTransactionImpl::MDBRWTransactionImpl(MDBEnv* parent, int flags):
+  MDBRWTransactionImpl(parent, openRWTransaction(parent, nullptr, flags))
+{
+}
+
+MDBRWTransactionImpl::~MDBRWTransactionImpl()
+{
+  abort();
+}
+
+void MDBRWTransactionImpl::commit()
+{
+  closeRORWCursors();
+  if (!d_txn) {
+    return;
+  }
+
+  if(int rc = mdb_txn_commit(d_txn)) {
+    throw std::runtime_error("committing: " + std::string(mdb_strerror(rc)));
+  }
+  environment().decRWTX();
+  d_txn = nullptr;
+}
+
+void MDBRWTransactionImpl::abort()
+{
+  closeRORWCursors();
+  if (!d_txn) {
+    return;
+  }
+
+  mdb_txn_abort(d_txn);
+  // prevent the RO destructor from cleaning up the transaction itself
+  environment().decRWTX();
+  d_txn = nullptr;
+}
+
+MDBROTransactionImpl::MDBROTransactionImpl(MDBEnv *parent, MDB_txn *txn):
+  d_parent(parent),
+  d_cursors(),
+  d_txn(txn)
+{
+
+}
+
+MDB_txn *MDBROTransactionImpl::openROTransaction(MDBEnv *env, MDB_txn *parent, int flags)
+{
+  if(env->getRWTX())
+    throw std::runtime_error("Duplicate RO transaction");
+  
+  /*
+    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. */
+  MDB_txn *result = nullptr;
+
+  if(int rc=mdb_txn_begin(env->d_env, parent, MDB_RDONLY | flags, &result))
+    throw std::runtime_error("Unable to start RO transaction: "+string(mdb_strerror(rc)));
+
+  env->incROTX();
+
+  return result;
+}
+
+void MDBROTransactionImpl::closeROCursors()
+{
+  // we need to move the vector away to ensure that the cursors don’t mess with our iteration.
+  std::vector<MDBROCursor*> buf;
+  std::swap(d_cursors, buf);
+  for (auto &cursor: buf) {
+    cursor->close();
+  }
+}
+
+MDBROTransactionImpl::MDBROTransactionImpl(MDBEnv *parent, int flags):
+    MDBROTransactionImpl(parent, openROTransaction(parent, nullptr, flags))
+{
+
+}
+
+MDBROTransactionImpl::~MDBROTransactionImpl()
+{
+  // this is safe because C++ will not call overrides of virtual methods in destructors.
+  commit();
+}
+
+void MDBROTransactionImpl::abort()
+{
+  closeROCursors();
+  // 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).
+  if (d_txn) {
+    d_parent->decROTX();
+    mdb_txn_abort(d_txn); // this appears to work better than abort for r/o database opening
+    d_txn = nullptr;
+  }
+}
+
+void MDBROTransactionImpl::commit()
+{
+  closeROCursors();
+  // 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).
+  if (d_txn) {
+    d_parent->decROTX();
+    mdb_txn_commit(d_txn); // this appears to work better than abort for r/o database opening
+    d_txn = nullptr;
+  }
+}
+
+
+
+void MDBRWTransactionImpl::clear(MDB_dbi dbi)
+{
+  if(int rc = mdb_drop(d_txn, dbi, 0)) {
+    throw runtime_error("Error clearing database: " + MDBError(rc));
+  }
+}
+
+MDBRWCursor MDBRWTransactionImpl::getRWCursor(const MDBDbi& dbi)
+{
+  MDB_cursor *cursor;
+  int rc= mdb_cursor_open(d_txn, dbi, &cursor);
+  if(rc) {
+    throw std::runtime_error("Error creating RO cursor: "+std::string(mdb_strerror(rc)));
+  }
+  return MDBRWCursor(d_rw_cursors, cursor);
+}
+
+MDBRWCursor MDBRWTransactionImpl::getCursor(const MDBDbi &dbi)
+{
+  return getRWCursor(dbi);
+}
+
+MDBRWTransaction MDBRWTransactionImpl::getRWTransaction()
+{
+  MDB_txn *txn;
+  if (int rc = mdb_txn_begin(environment(), *this, 0, &txn)) {
+    throw std::runtime_error(std::string("failed to start child transaction: ")+mdb_strerror(rc));
+  }
+  // we need to increase the counter here because commit/abort on the child transaction will decrease it
+  environment().incRWTX();
+  return MDBRWTransaction(new MDBRWTransactionImpl(&environment(), txn));
+}
+
+MDBROTransaction MDBRWTransactionImpl::getROTransaction()
+{
+  return getRWTransaction();
+}
+
+MDBROTransaction MDBEnv::getROTransaction()
+{
+  return MDBROTransaction(new MDBROTransactionImpl(this));
+}
+MDBRWTransaction MDBEnv::getRWTransaction()
+{
+  return MDBRWTransaction(new MDBRWTransactionImpl(this));
+}
+
+
+void MDBRWTransactionImpl::closeRWCursors()
+{
+  decltype(d_rw_cursors) buf;
+  std::swap(d_rw_cursors, buf);
+  for (auto &cursor: buf) {
+    cursor->close();
+  }
+}
+
+MDBROCursor MDBROTransactionImpl::getCursor(const MDBDbi& dbi)
+{
+  return getROCursor(dbi);
+}
+
+MDBROCursor MDBROTransactionImpl::getROCursor(const MDBDbi &dbi)
+{
+  MDB_cursor *cursor;
+  int rc= mdb_cursor_open(d_txn, dbi, &cursor);
+  if(rc) {
+    throw std::runtime_error("Error creating RO cursor: "+std::string(mdb_strerror(rc)));
+  }
+  return MDBROCursor(d_cursors, cursor);
+}