blockchain_db: fix db txn ending too early

The db txn in add_block ending caused the entire overarching
batch txn to stop.
Also add a new guard class so a db txn can be stopped in the
face of exceptions.

Also use a read only db txn in init when the db itself is
read only, and do not save the max tx size in that case.

1 files changed, 52 insertions, 3 deletions

diff --git a/src/blockchain_db/blockchain_db.h b/src/blockchain_db/blockchain_db.h
index 2c40b5a78..567be6a65 100644
--- a/src/blockchain_db/blockchain_db.h
+++ b/src/blockchain_db/blockchain_db.h
@@ -770,9 +770,12 @@ public:
    */
   virtual void set_batch_transactions(bool) = 0;
 
-  virtual void block_txn_start(bool readonly=false) = 0;
-  virtual void block_txn_stop() = 0;
-  virtual void block_txn_abort() = 0;
+  virtual void block_wtxn_start() = 0;
+  virtual void block_wtxn_stop() = 0;
+  virtual void block_wtxn_abort() = 0;
+  virtual bool block_rtxn_start() const = 0;
+  virtual void block_rtxn_stop() const = 0;
+  virtual void block_rtxn_abort() const = 0;
 
   virtual void set_hard_fork(HardFork* hf);
 
@@ -1699,6 +1702,52 @@ public:
 
 };  // class BlockchainDB
 
+class db_txn_guard
+{
+public:
+  db_txn_guard(BlockchainDB *db, bool readonly): db(db), readonly(readonly), active(false)
+  {
+    if (readonly)
+    {
+      active = db->block_rtxn_start();
+    }
+    else
+    {
+      db->block_wtxn_start();
+      active = true;
+    }
+  }
+  virtual ~db_txn_guard()
+  {
+    if (active)
+      stop();
+  }
+  void stop()
+  {
+    if (readonly)
+      db->block_rtxn_stop();
+    else
+      db->block_wtxn_stop();
+    active = false;
+  }
+  void abort()
+  {
+    if (readonly)
+      db->block_rtxn_abort();
+    else
+      db->block_wtxn_abort();
+    active = false;
+  }
+
+private:
+  BlockchainDB *db;
+  bool readonly;
+  bool active;
+};
+
+class db_rtxn_guard: public db_txn_guard { public: db_rtxn_guard(BlockchainDB *db): db_txn_guard(db, true) {} };
+class db_wtxn_guard: public db_txn_guard { public: db_wtxn_guard(BlockchainDB *db): db_txn_guard(db, false) {} };
+
 BlockchainDB *new_db(const std::string& db_type);
 
 }  // namespace cryptonote