Refactor: Move m_db pointers into BerkeleyDatabase

This is a refactoring change that doesn't affect behavior. The motivation
behind the change is give BerkeleyEnvironment objects access to
BerkeleyDatabase objects so it will be possible to simplify the duplicate
wallet check and more reliably avoid opening the same databases twice.

2 files changed, 29 insertions, 14 deletions

diff --git a/src/wallet/db.cpp b/src/wallet/db.cpp
index 74787eb5d2..b2404e2a85 100644
--- a/src/wallet/db.cpp
+++ b/src/wallet/db.cpp
@@ -90,13 +90,13 @@ void BerkeleyEnvironment::Close()
 
     fDbEnvInit = false;
 
-    for (auto& db : mapDb) {
+    for (auto& db : m_databases) {
         auto count = mapFileUseCount.find(db.first);
         assert(count == mapFileUseCount.end() || count->second == 0);
-        if (db.second) {
-            db.second->close(0);
-            delete db.second;
-            db.second = nullptr;
+        BerkeleyDatabase& database = db.second.get();
+        if (database.m_db) {
+            database.m_db->close(0);
+            database.m_db.reset();
         }
     }
 
@@ -463,7 +463,7 @@ BerkeleyBatch::BerkeleyBatch(BerkeleyDatabase& database, const char* pszMode, bo
         if (!env->Open(false /* retry */))
             throw std::runtime_error("BerkeleyBatch: Failed to open database environment.");
 
-        pdb = env->mapDb[strFilename];
+        pdb = database.m_db.get();
         if (pdb == nullptr) {
             int ret;
             std::unique_ptr<Db> pdb_temp = MakeUnique<Db>(env->dbenv.get(), 0);
@@ -508,7 +508,7 @@ BerkeleyBatch::BerkeleyBatch(BerkeleyDatabase& database, const char* pszMode, bo
             }
 
             pdb = pdb_temp.release();
-            env->mapDb[strFilename] = pdb;
+            database.m_db.reset(pdb);
 
             if (fCreate && !Exists(std::string("version"))) {
                 bool fTmp = fReadOnly;
@@ -563,12 +563,13 @@ void BerkeleyEnvironment::CloseDb(const std::string& strFile)
 {
     {
         LOCK(cs_db);
-        if (mapDb[strFile] != nullptr) {
+        auto it = m_databases.find(strFile);
+        assert(it != m_databases.end());
+        BerkeleyDatabase& database = it->second.get();
+        if (database.m_db) {
             // Close the database handle
-            Db* pdb = mapDb[strFile];
-            pdb->close(0);
-            delete pdb;
-            mapDb[strFile] = nullptr;
+            database.m_db->close(0);
+            database.m_db.reset();
         }
     }
 }
@@ -586,7 +587,7 @@ void BerkeleyEnvironment::ReloadDbEnv()
     });
 
     std::vector<std::string> filenames;
-    for (auto it : mapDb) {
+    for (auto it : m_databases) {
         filenames.push_back(it.first);
     }
     // Close the individual Db's
diff --git a/src/wallet/db.h b/src/wallet/db.h
index 8f96483a18..e9f89ac6cb 100644
--- a/src/wallet/db.h
+++ b/src/wallet/db.h
@@ -31,6 +31,8 @@ struct WalletDatabaseFileId {
     bool operator==(const WalletDatabaseFileId& rhs) const;
 };
 
+class BerkeleyDatabase;
+
 class BerkeleyEnvironment
 {
 private:
@@ -43,7 +45,7 @@ private:
 public:
     std::unique_ptr<DbEnv> dbenv;
     std::map<std::string, int> mapFileUseCount;
-    std::map<std::string, Db*> mapDb;
+    std::map<std::string, std::reference_wrapper<BerkeleyDatabase>> m_databases;
     std::unordered_map<std::string, WalletDatabaseFileId> m_fileids;
     std::condition_variable_any m_db_in_use;
 
@@ -115,6 +117,8 @@ public:
         nUpdateCounter(0), nLastSeen(0), nLastFlushed(0), nLastWalletUpdate(0)
     {
         env = GetWalletEnv(wallet_path, strFile);
+        auto inserted = env->m_databases.emplace(strFile, std::ref(*this));
+        assert(inserted.second);
         if (mock) {
             env->Close();
             env->Reset();
@@ -122,6 +126,13 @@ public:
         }
     }
 
+    ~BerkeleyDatabase() {
+        if (env) {
+            size_t erased = env->m_databases.erase(strFile);
+            assert(erased == 1);
+        }
+    }
+
     /** Return object for accessing database at specified path. */
     static std::unique_ptr<BerkeleyDatabase> Create(const fs::path& path)
     {
@@ -161,6 +172,9 @@ public:
     unsigned int nLastFlushed;
     int64_t nLastWalletUpdate;
 
+    /** Database pointer. This is initialized lazily and reset during flushes, so it can be null. */
+    std::unique_ptr<Db> m_db;
+
 private:
     /** BerkeleyDB specific */
     BerkeleyEnvironment *env;