JSON serialized storage of properties table.

.vscode/settings.json

@@ -101,6 +101,8 @@
         "ranges": "cpp",
         "stop_token": "cpp",
         "version": "cpp",
-        "shared_mutex": "cpp"
+        "shared_mutex": "cpp",
+        "compare": "cpp",
+        "concepts": "cpp"
     }
 }

src/common/module.mk

@@ -33,6 +33,8 @@ MODULE_OBJS := \
 	src/common/sdl_blitter/QisBlitter.o \
 	src/common/sdl_blitter/BlitterFactory.o \
 	src/common/repository/KeyValueRepositoryPropertyFile.o \
+	src/common/repository/KeyValueRepositoryJsonFile.o \
+	src/common/repository/CompositeKVRJsonAdapter.o
 
 MODULE_DIRS += \
 	src/common

src/common/repository/CompositeKVRJsonAdapter.cxx

@@ -0,0 +1,77 @@
+//============================================================================
+//
+//   SSSS    tt          lll  lll
+//  SS  SS   tt           ll   ll
+//  SS     tttttt  eeee   ll   ll   aaaa
+//   SSSS    tt   ee  ee  ll   ll      aa
+//      SS   tt   eeeeee  ll   ll   aaaaa  --  "An Atari 2600 VCS Emulator"
+//  SS  SS   tt   ee      ll   ll  aa  aa
+//   SSSS     ttt  eeeee llll llll  aaaaa
+//
+// Copyright (c) 1995-2021 by Bradford W. Mott, Stephen Anthony
+// and the Stella Team
+//
+// See the file "License.txt" for information on usage and redistribution of
+// this file, and for a DISCLAIMER OF ALL WARRANTIES.
+//============================================================================
+
+#include <sstream>
+
+#include "CompositeKVRJsonAdapter.hxx"
+#include "repository/KeyValueRepositoryJsonFile.hxx"
+
+namespace {
+  class ProxyRepository : public KeyValueRepository {
+      public:
+        ProxyRepository(KeyValueRepositoryAtomic& kvr, const string& key)
+          : myKvr(kvr), myKey(key)
+        {}
+
+        std::map<string, Variant> load() override {
+          if (!myKvr.has(myKey)) return std::map<string, Variant>();
+
+          string serialized;
+          myKvr.get(myKey, serialized);
+
+          stringstream in{serialized};
+
+          return KeyValueRepositoryJsonFile::load(in);
+        }
+
+        bool save(const std::map<string, Variant>& values) override {
+          stringstream out;
+
+          if (!KeyValueRepositoryJsonFile::save(out, values)) return false;
+
+          return myKvr.save(myKey, out.str());
+        }
+
+      private:
+
+        KeyValueRepositoryAtomic& myKvr;
+        const string& myKey;
+    };
+}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+CompositeKVRJsonAdapter::CompositeKVRJsonAdapter(KeyValueRepositoryAtomic& kvr)
+  : myKvr(kvr)
+{}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+shared_ptr<KeyValueRepository> CompositeKVRJsonAdapter::get(const string& key)
+{
+  return make_shared<ProxyRepository>(myKvr, key);
+}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+bool CompositeKVRJsonAdapter::has(const string& key)
+{
+  return myKvr.has(key);
+}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+void CompositeKVRJsonAdapter::remove(const string& key)
+{
+  return myKvr.remove(key);
+}

src/common/repository/CompositeKVRJsonAdapter.hxx

@@ -0,0 +1,41 @@
+//============================================================================
+//
+//   SSSS    tt          lll  lll
+//  SS  SS   tt           ll   ll
+//  SS     tttttt  eeee   ll   ll   aaaa
+//   SSSS    tt   ee  ee  ll   ll      aa
+//      SS   tt   eeeeee  ll   ll   aaaaa  --  "An Atari 2600 VCS Emulator"
+//  SS  SS   tt   ee      ll   ll  aa  aa
+//   SSSS     ttt  eeeee llll llll  aaaaa
+//
+// Copyright (c) 1995-2021 by Bradford W. Mott, Stephen Anthony
+// and the Stella Team
+//
+// See the file "License.txt" for information on usage and redistribution of
+// this file, and for a DISCLAIMER OF ALL WARRANTIES.
+//============================================================================
+
+#ifndef COMPOSITE_KVR_JSON_ADAPTER_HXX
+#define COMPOSITE_KVR_JSON_ADAPTER_HXX
+
+#include "repository/CompositeKeyValueRepository.hxx"
+#include "repository/KeyValueRepository.hxx"
+#include "bspf.hxx"
+
+class CompositeKVRJsonAdapter : public CompositeKeyValueRepository {
+  public:
+
+    CompositeKVRJsonAdapter(KeyValueRepositoryAtomic& kvr);
+
+    shared_ptr<KeyValueRepository> get(const string& key) override;
+
+    bool has(const string& key) override;
+
+    void remove(const string& key) override;
+
+  private:
+
+    KeyValueRepositoryAtomic& myKvr;
+};
+
+#endif // COMPOSITE_KVR_JSON_ADAPTER_HXX

src/common/repository/KeyValueRepository.hxx

@@ -23,6 +23,11 @@
 #include "Variant.hxx"
 #include "bspf.hxx"
 
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Woverloaded-virtual"
+
+class KeyValueRepositoryAtomic;
+
 class KeyValueRepository
 {
   public:
@@ -33,9 +38,22 @@ class KeyValueRepository
 
     virtual bool save(const std::map<string, Variant>& values) = 0;
 
+    virtual KeyValueRepositoryAtomic* atomic() { return nullptr; }
+};
+
+class KeyValueRepositoryAtomic : public KeyValueRepository {
+  public:
+    virtual bool has(const string& key) = 0;
+
+    virtual bool get(const string& key, string& value) = 0;
+
     virtual bool save(const string& key, const Variant& value) = 0;
 
     virtual void remove(const string& key) = 0;
+
+    KeyValueRepositoryAtomic* atomic() override { return this; }
 };
 
+#pragma clang diagnostic pop
+
 #endif // KEY_VALUE_REPOSITORY_HXX

src/common/repository/KeyValueRepositoryConfigfile.hxx

@@ -21,7 +21,7 @@
 #include "FSNode.hxx"
 #include "KeyValueRepository.hxx"
 
-class KeyValueRepositoryConfigfile : public KeyValueRepository
+class KeyValueRepositoryConfigfile : public KeyValueRepositoryAtomic
 {
   public:
 
@@ -31,10 +31,6 @@ class KeyValueRepositoryConfigfile : public KeyValueRepository
 
     bool save(const std::map<string, Variant>& values) override;
 
-    bool save(const string& key, const Variant& value) override { return false; }
-
-    void remove(const string& key) override {}
-
   private:
 
     FilesystemNode myFile;

src/common/repository/KeyValueRepositoryFile.hxx

@@ -0,0 +1,99 @@
+//============================================================================
+//
+//   SSSS    tt          lll  lll
+//  SS  SS   tt           ll   ll
+//  SS     tttttt  eeee   ll   ll   aaaa
+//   SSSS    tt   ee  ee  ll   ll      aa
+//      SS   tt   eeeeee  ll   ll   aaaaa  --  "An Atari 2600 VCS Emulator"
+//  SS  SS   tt   ee      ll   ll  aa  aa
+//   SSSS     ttt  eeeee llll llll  aaaaa
+//
+// Copyright (c) 1995-2021 by Bradford W. Mott, Stephen Anthony
+// and the Stella Team
+//
+// See the file "License.txt" for information on usage and redistribution of
+// this file, and for a DISCLAIMER OF ALL WARRANTIES.
+//============================================================================
+
+#ifndef KEY_VALUE_REPOSITORY_FILE_HXX
+#define KEY_VALUE_REPOSITORY_FILE_HXX
+
+#include <sstream>
+
+#include "KeyValueRepository.hxx"
+#include "Logger.hxx"
+#include "FSNode.hxx"
+#include "bspf.hxx"
+
+template<class T>
+class KeyValueRepositoryFile : public KeyValueRepository {
+  public:
+    KeyValueRepositoryFile(const FilesystemNode& node);
+
+    std::map<string, Variant> load() override;
+
+    bool save(const std::map<string, Variant>& values) override;
+
+  protected:
+
+    const FilesystemNode& myNode;
+};
+
+///////////////////////////////////////////////////////////////////////////////
+// IMPLEMEMNTATION
+///////////////////////////////////////////////////////////////////////////////
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+template<class T>
+KeyValueRepositoryFile<T>::KeyValueRepositoryFile(const FilesystemNode& node)
+  : myNode(node)
+{}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+template<class T>
+std::map<string, Variant> KeyValueRepositoryFile<T>::load()
+{
+  if (!myNode.exists()) return std::map<string, Variant>();
+
+  stringstream in;
+
+  try {
+    myNode.read(in);
+    return T::load(in);
+  }
+  catch (const runtime_error& err) {
+    Logger::error(err.what());
+
+    return std::map<string, Variant>();
+  }
+  catch (...) {
+    return std::map<string, Variant>();
+  }
+}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+template<class T>
+bool KeyValueRepositoryFile<T>::save(const std::map<string, Variant>& values)
+{
+  if (values.size() == 0) return true;
+
+  stringstream out;
+
+  try {
+    T::save(out, values);
+    myNode.write(out);
+
+    return true;
+  }
+  catch (const runtime_error& err) {
+    Logger::error(err.what());
+
+    return false;
+  }
+  catch (...)
+  {
+    return false;
+  }
+}
+
+#endif // KEY_VALUE_REPOSITORY_FILE

src/common/repository/KeyValueRepositoryJsonFile.cxx

@@ -0,0 +1,81 @@
+//============================================================================
+//
+//   SSSS    tt          lll  lll
+//  SS  SS   tt           ll   ll
+//  SS     tttttt  eeee   ll   ll   aaaa
+//   SSSS    tt   ee  ee  ll   ll      aa
+//      SS   tt   eeeeee  ll   ll   aaaaa  --  "An Atari 2600 VCS Emulator"
+//  SS  SS   tt   ee      ll   ll  aa  aa
+//   SSSS     ttt  eeeee llll llll  aaaaa
+//
+// Copyright (c) 1995-2021 by Bradford W. Mott, Stephen Anthony
+// and the Stella Team
+//
+// See the file "License.txt" for information on usage and redistribution of
+// this file, and for a DISCLAIMER OF ALL WARRANTIES.
+//============================================================================
+
+#include "repository/KeyValueRepositoryJsonFile.hxx"
+#include "Logger.hxx"
+#include "json_lib.hxx"
+
+using nlohmann::json;
+
+namespace {
+  json jsonIfValid(const string& s) {
+    json parsed = json::parse(s, nullptr, false);
+
+    return parsed.is_discarded() ? json(s) : parsed;
+  }
+}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+KeyValueRepositoryJsonFile::KeyValueRepositoryJsonFile(const FilesystemNode& node)
+  : KeyValueRepositoryFile<KeyValueRepositoryJsonFile>(node)
+{}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+std::map<string, Variant> KeyValueRepositoryJsonFile::load(istream& in)
+{
+  try {
+    std::map<string, Variant> map;
+
+    json deserialized = json::parse(in);
+
+    if (!deserialized.is_object()) {
+      Logger::error("KeyVallueRepositoryJsonFile: not an object");
+
+      return map;
+    }
+
+    for (const auto& [key, value] : deserialized.items())
+      map[key] = value.is_string() ? value.get<string>() : value.dump();
+
+    return map;
+  }
+  catch (const json::exception& err) {
+    Logger::error("KeyValueRepositoryJsonFile: error during deserialization: " + string(err.what()));
+
+    return std::map<string, Variant>();
+  }
+}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+bool KeyValueRepositoryJsonFile::save(ostream& out, const std::map<string, Variant>& values)
+{
+  try {
+    json serializedJson = json::object();
+
+    for (const auto& [key, value] : values)
+      serializedJson[key] = jsonIfValid(value.toString());
+
+    out << serializedJson.dump(2);
+
+    return true;
+  }
+  catch (const json::exception& err) {
+    Logger::error("KeyValueRepositoryJsonFile: error during serialization: "  + string(err.what()));
+
+    return false;
+  }
+}

src/common/repository/KeyValueRepositoryJsonFile.hxx

@@ -0,0 +1,36 @@
+//============================================================================
+//
+//   SSSS    tt          lll  lll
+//  SS  SS   tt           ll   ll
+//  SS     tttttt  eeee   ll   ll   aaaa
+//   SSSS    tt   ee  ee  ll   ll      aa
+//      SS   tt   eeeeee  ll   ll   aaaaa  --  "An Atari 2600 VCS Emulator"
+//  SS  SS   tt   ee      ll   ll  aa  aa
+//   SSSS     ttt  eeeee llll llll  aaaaa
+//
+// Copyright (c) 1995-2021 by Bradford W. Mott, Stephen Anthony
+// and the Stella Team
+//
+// See the file "License.txt" for information on usage and redistribution of
+// this file, and for a DISCLAIMER OF ALL WARRANTIES.
+//============================================================================
+
+#ifndef KEY_VALUE_REPOSITORY_JSON_FILE_HXX
+#define KEY_VALUE_REPOSITORY_JSON_FILE_HXX
+
+#include <istream>
+#include <ostream>
+
+#include "repository/KeyValueRepositoryFile.hxx"
+#include "bspf.hxx"
+
+class KeyValueRepositoryJsonFile : public KeyValueRepositoryFile<KeyValueRepositoryJsonFile> {
+  public:
+    KeyValueRepositoryJsonFile(const FilesystemNode& node);
+
+    static std::map<string, Variant> load(istream& in);
+
+    static bool save(ostream& out, const std::map<string, Variant>& values);
+};
+
+#endif // KEY_VALUE_REPOSITORY_JSON_FILE_HXX

src/common/repository/KeyValueRepositoryNoop.hxx

@@ -20,7 +20,7 @@
 
 #include "KeyValueRepository.hxx"
 
-class KeyValueRepositoryNoop : public KeyValueRepository
+class KeyValueRepositoryNoop : public KeyValueRepositoryAtomic
 {
   public:
 
@@ -28,6 +28,10 @@ class KeyValueRepositoryNoop : public KeyValueRepository
       return std::map<string, Variant>();
     }
 
+    bool has(const string& key) override { return false; }
+
+    bool get(const string& key, string& value) override { return false; }
+
     bool save(const std::map<string, Variant>& values) override { return false; }
 
     bool save(const string& key, const Variant& value) override { return false; }

src/common/repository/KeyValueRepositoryPropertyFile.cxx

@@ -8,20 +8,14 @@
 //  SS  SS   tt   ee      ll   ll  aa  aa
 //   SSSS     ttt  eeeee llll llll  aaaaa
 //
-// Copyright (c) 1995-2020 by Bradford W. Mott, Stephen Anthony
+// Copyright (c) 1995-2021 by Bradford W. Mott, Stephen Anthony
 // and the Stella Team
 //
 // See the file "License.txt" for information on usage and redistribution of
 // this file, and for a DISCLAIMER OF ALL WARRANTIES.
 //============================================================================
 
-#include <istream>
-#include <ostream>
-#include <sstream>
-#include <map>
-
 #include "repository/KeyValueRepositoryPropertyFile.hxx"
-#include "Logger.hxx"
 
 namespace {
 
@@ -77,30 +71,14 @@ namespace {
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 KeyValueRepositoryPropertyFile::KeyValueRepositoryPropertyFile(const FilesystemNode& node)
-  : myNode(node)
+  : KeyValueRepositoryFile<KeyValueRepositoryPropertyFile>(node)
 {}
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-std::map<string, Variant> KeyValueRepositoryPropertyFile::load()
+std::map<string, Variant> KeyValueRepositoryPropertyFile::load(istream& in)
 {
   std::map<string, Variant> map;
 
-  if (!myNode.exists()) return map;
-
-  stringstream in;
-
-  try {
-    myNode.read(in);
-  }
-  catch (const runtime_error& err) {
-    Logger::error(err.what());
-
-    return map;
-  }
-  catch (...) {
-    return map;
-  }
-
   // Loop reading properties
   string key, value;
   for(;;)
@@ -129,12 +107,8 @@ std::map<string, Variant> KeyValueRepositoryPropertyFile::load()
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-bool KeyValueRepositoryPropertyFile::save(const std::map<string, Variant>& values)
+bool KeyValueRepositoryPropertyFile::save(ostream& out, const std::map<string, Variant>& values)
 {
-  if (values.size() == 0) return true;
-
-  stringstream out;
-
   for (auto& [key, value]: values) {
     writeQuotedString(out, key);
     out.put(' ');
@@ -142,22 +116,5 @@ bool KeyValueRepositoryPropertyFile::save(const std::map<string, Variant>& value
     out.put('\n');
   }
 
-  writeQuotedString(out, "");
-  out.put('\n');
-  out.put('\n');
-
-  try {
-    myNode.write(out);
-
   return true;
-  }
-  catch (const runtime_error& err) {
-    Logger::error(err.what());
-
-    return false;
-  }
-  catch (...)
-  {
-    return false;
-  }
 }

src/common/repository/KeyValueRepositoryPropertyFile.hxx

@@ -8,7 +8,7 @@
 //  SS  SS   tt   ee      ll   ll  aa  aa
 //   SSSS     ttt  eeeee llll llll  aaaaa
 //
-// Copyright (c) 1995-2020 by Bradford W. Mott, Stephen Anthony
+// Copyright (c) 1995-2021 by Bradford W. Mott, Stephen Anthony
 // and the Stella Team
 //
 // See the file "License.txt" for information on usage and redistribution of
@@ -18,25 +18,19 @@
 #ifndef KEY_VALUE_REPOSITORY_PROPERTY_FILE_HXX
 #define KEY_VALUE_REPOSITORY_PROPERTY_FILE_HXX
 
-#include "repository/KeyValueRepository.hxx"
+#include <istream>
-#include "FSNode.hxx"
+#include <ostream>
+
+#include "repository/KeyValueRepositoryFile.hxx"
 #include "bspf.hxx"
 
-class KeyValueRepositoryPropertyFile : public KeyValueRepository {
+class KeyValueRepositoryPropertyFile : public KeyValueRepositoryFile<KeyValueRepositoryPropertyFile> {
   public:
     KeyValueRepositoryPropertyFile(const FilesystemNode& node);
 
-    std::map<string, Variant> load() override;
+    static std::map<string, Variant> load(istream& in);
 
-    bool save(const std::map<string, Variant>& values) override;
+    static bool save(ostream& out, const std::map<string, Variant>& values);
-
-    bool save(const string& key, const Variant& value) override { return false; }
-
-    void remove(const string& key) override {}
-
-  private:
-
-    const FilesystemNode& myNode;
 };
 
-#endif
+#endif // KEY_VALUE_REPOSITORY_PROPERTY_FILE_HXX

src/common/repository/sqlite/AbstractKeyValueRepositorySqlite.cxx

@@ -40,6 +40,47 @@ std::map<string, Variant> AbstractKeyValueRepositorySqlite::load()
   return values;
 }
 
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+bool AbstractKeyValueRepositorySqlite::has(const string& key)
+{
+  try {
+    SqliteStatement& stmt{stmtCount(key)};
+
+    if (!stmt.step()) throw new SqliteError("count failed");
+
+    const bool result = stmt.columnInt(0) != 0;
+    stmt.reset();
+
+    return result;
+  }
+  catch (const SqliteError& err) {
+    Logger::error(err.what());
+
+    return false;
+  }
+}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+bool AbstractKeyValueRepositorySqlite::get(const string& key, string& value)
+{
+  try {
+    SqliteStatement& stmt{stmtSelectOne(key)};
+
+    if (!stmt.step()) return false;
+    value = stmt.columnText(0);
+
+    stmt.reset();
+
+    return true;
+  }
+  catch (const SqliteError& err) {
+    Logger::error(err.what());
+
+    return false;
+  }
+}
+
+
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 bool AbstractKeyValueRepositorySqlite::save(const std::map<string, Variant>& values)
 {

src/common/repository/sqlite/AbstractKeyValueRepositorySqlite.hxx

@@ -6,10 +6,14 @@
 #include "SqliteDatabase.hxx"
 #include "SqliteStatement.hxx"
 
-class AbstractKeyValueRepositorySqlite : public KeyValueRepository
+class AbstractKeyValueRepositorySqlite : public KeyValueRepositoryAtomic
 {
   public:
 
+    bool has(const string& key) override;
+
+    bool get(const string& key, string& value) override;
+
     std::map<string, Variant> load() override;
 
     bool save(const std::map<string, Variant>& values) override;
@@ -23,6 +27,8 @@ class AbstractKeyValueRepositorySqlite : public KeyValueRepository
     virtual SqliteStatement& stmtInsert(const string& key, const string& value) = 0;
     virtual SqliteStatement& stmtSelect() = 0;
     virtual SqliteStatement& stmtDelete(const string& key) = 0;
+    virtual SqliteStatement& stmtCount(const string& key) = 0;
+    virtual SqliteStatement& stmtSelectOne(const string& key) = 0;
     virtual SqliteDatabase& database() = 0;
 };
 

src/common/repository/sqlite/CompositeKeyValueRepositorySqlite.cxx

@@ -35,15 +35,15 @@ shared_ptr<KeyValueRepository> CompositeKeyValueRepositorySqlite::get(const stri
 bool CompositeKeyValueRepositorySqlite::has(const string& key)
 {
   try {
-    myStmtCount->reset();
+    myStmtCountSet->reset();
-    myStmtCount->bind(1, key.c_str());
+    myStmtCountSet->bind(1, key.c_str());
 
-    if (!myStmtCount->step())
+    if (!myStmtCountSet->step())
       throw new SqliteError("count failed");
 
-    Int32 rowCount = myStmtCount->columnInt(0);
+    Int32 rowCount = myStmtCountSet->columnInt(0);
 
-    myStmtCount->reset();
+    myStmtCountSet->reset();
 
     return rowCount > 0;
   } catch (const SqliteError& err) {
@@ -78,9 +78,11 @@ void CompositeKeyValueRepositorySqlite::initialize()
 
   myStmtInsert = make_unique<SqliteStatement>(myDb, "INSERT OR REPLACE INTO `" + myTableName + "` VALUES (?, ?, ?)");
   myStmtSelect = make_unique<SqliteStatement>(myDb, "SELECT `key2`, `VALUE` FROM `" + myTableName + "` WHERE `key1` = ?");
-  myStmtCount = make_unique<SqliteStatement>(myDb, "SELECT COUNT(*) FROM `" + myTableName + "` WHERE `key1` = ?");
+  myStmtCountSet = make_unique<SqliteStatement>(myDb, "SELECT COUNT(*) FROM `" + myTableName + "` WHERE `key1` = ?");
   myStmtDelete = make_unique<SqliteStatement>(myDb, "DELETE FROM `" + myTableName + "` WHERE `key1` = ? AND `key2` = ?");
   myStmtDeleteSet = make_unique<SqliteStatement>(myDb, "DELETE FROM `" + myTableName + "` WHERE `key1` = ?");
+  myStmtSelectOne = make_unique<SqliteStatement>(myDb, "SELECT `value` FROM `" + myTableName + "` WHERE `key1` = ? AND `key2` = ?");
+  myStmtCount = make_unique<SqliteStatement>(myDb, "SELECT COUNT(`key1`) FROM `" + myTableName + "` WHERE `key1` = ? AND `key2` = ?");
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
@@ -121,6 +123,25 @@ SqliteStatement& CompositeKeyValueRepositorySqlite::ProxyRepository::stmtDelete(
     .bind(2, key.c_str());
 }
 
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+SqliteStatement& CompositeKeyValueRepositorySqlite::ProxyRepository::stmtSelectOne(const string& key)
+{
+  myRepo.myStmtSelectOne->reset();
+
+  return (*myRepo.myStmtSelectOne)
+    .bind(1, myKey.c_str())
+    .bind(2, key.c_str());
+}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+SqliteStatement& CompositeKeyValueRepositorySqlite::ProxyRepository::stmtCount(const string& key)
+{
+  myRepo.myStmtCount->reset();
+
+  return (*myRepo.myStmtCount)
+    .bind(1, myKey.c_str())
+    .bind(2, key.c_str());
+}
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 SqliteDatabase& CompositeKeyValueRepositorySqlite::ProxyRepository::database()

src/common/repository/sqlite/CompositeKeyValueRepositorySqlite.hxx

@@ -49,6 +49,8 @@ class CompositeKeyValueRepositorySqlite : public CompositeKeyValueRepository {
         SqliteStatement& stmtInsert(const string& key, const string& value) override;
         SqliteStatement& stmtSelect() override;
         SqliteStatement& stmtDelete(const string& key) override;
+        SqliteStatement& stmtCount(const string& key) override;
+        SqliteStatement& stmtSelectOne(const string& key) override;
         SqliteDatabase& database() override;
 
       private:
@@ -71,9 +73,11 @@ class CompositeKeyValueRepositorySqlite : public CompositeKeyValueRepository {
 
     unique_ptr<SqliteStatement> myStmtInsert;
     unique_ptr<SqliteStatement> myStmtSelect;
-    unique_ptr<SqliteStatement> myStmtCount;
+    unique_ptr<SqliteStatement> myStmtCountSet;
     unique_ptr<SqliteStatement> myStmtDelete;
     unique_ptr<SqliteStatement> myStmtDeleteSet;
+    unique_ptr<SqliteStatement> myStmtSelectOne;
+    unique_ptr<SqliteStatement> myStmtCount;
 
    private:
 

src/common/repository/sqlite/KeyValueRepositorySqlite.cxx

@@ -53,6 +53,24 @@ SqliteStatement& KeyValueRepositorySqlite::stmtDelete(const string& key)
     .bind(1, key.c_str());
 }
 
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+SqliteStatement& KeyValueRepositorySqlite::stmtCount(const string& key)
+{
+  myStmtCount->reset();
+
+  return (*myStmtCount)
+    .bind(1, key.c_str());
+}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+SqliteStatement& KeyValueRepositorySqlite::stmtSelectOne(const string& key)
+{
+  myStmtSelectOne->reset();
+
+  return (*myStmtSelectOne)
+    .bind(1, key.c_str());
+}
+
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 SqliteDatabase& KeyValueRepositorySqlite::database()
 {
@@ -67,6 +85,8 @@ void KeyValueRepositorySqlite::initialize()
   );
 
   myStmtInsert = make_unique<SqliteStatement>(myDb, "INSERT OR REPLACE INTO `" + myTableName + "` VALUES (?, ?)");
-  myStmtSelect = make_unique<SqliteStatement>(myDb, "SELECT `key`, `VALUE` FROM `" + myTableName + "`");
+  myStmtSelect = make_unique<SqliteStatement>(myDb, "SELECT `key`, `value` FROM `" + myTableName + "`");
   myStmtDelete = make_unique<SqliteStatement>(myDb, "DELETE FROM `" + myTableName + "` WHERE `key` = ?");
+  myStmtSelectOne = make_unique<SqliteStatement>(myDb, "SELECT `value` FROM `" + myTableName + "` WHERE `key` = ?");
+  myStmtCount = make_unique<SqliteStatement>(myDb, "SELECT COUNT(`key`) FROM `" + myTableName + "` WHERE `key` = ?");
 }

src/common/repository/sqlite/KeyValueRepositorySqlite.hxx

@@ -37,6 +37,8 @@ class KeyValueRepositorySqlite : public AbstractKeyValueRepositorySqlite
     SqliteStatement& stmtSelect() override;
     SqliteStatement& stmtDelete(const string& key) override;
     SqliteDatabase& database() override;
+    SqliteStatement& stmtCount(const string& key) override;
+    SqliteStatement& stmtSelectOne(const string& key) override;
 
   private:
 
@@ -46,6 +48,8 @@ class KeyValueRepositorySqlite : public AbstractKeyValueRepositorySqlite
     unique_ptr<SqliteStatement> myStmtInsert;
     unique_ptr<SqliteStatement> myStmtSelect;
     unique_ptr<SqliteStatement> myStmtDelete;
+    unique_ptr<SqliteStatement> myStmtSelectOne;
+    unique_ptr<SqliteStatement> myStmtCount;
 
   private:
 

src/common/repository/sqlite/SettingsDb.cxx

@@ -36,8 +36,10 @@ bool SettingsDb::initialize()
     mySettingsRepository = make_unique<KeyValueRepositorySqlite>(*myDb, "settings");
     mySettingsRepository->initialize();
 
-    myPropertyRepository = make_unique<CompositeKeyValueRepositorySqlite>(*myDb, "properties");
+    myPropertyRepositoryHost = make_unique<KeyValueRepositorySqlite>(*myDb, "properties");
-    myPropertyRepository->initialize();
+    myPropertyRepositoryHost->initialize();
+
+    myPropertyRepository = make_unique<CompositeKVRJsonAdapter>(*myPropertyRepositoryHost);
   }
   catch (const SqliteError& err) {
     Logger::error("sqlite DB " + databaseFileName() + " failed to initialize: " + err.what());

src/common/repository/sqlite/SettingsDb.hxx

@@ -21,7 +21,7 @@
 #include "bspf.hxx"
 #include "SqliteDatabase.hxx"
 #include "KeyValueRepositorySqlite.hxx"
-#include "CompositeKeyValueRepositorySqlite.hxx"
+#include "repository/CompositeKVRJsonAdapter.hxx"
 
 class SettingsDb
 {
@@ -44,7 +44,8 @@ class SettingsDb
 
     shared_ptr<SqliteDatabase> myDb;
     unique_ptr<KeyValueRepositorySqlite> mySettingsRepository;
-    unique_ptr<CompositeKeyValueRepositorySqlite> myPropertyRepository;
+    unique_ptr<KeyValueRepositorySqlite> myPropertyRepositoryHost;
+    unique_ptr<CompositeKVRJsonAdapter> myPropertyRepository;
 };
 
 #endif // SETTINGS_DB_HXX

src/emucore/Props.cxx

@@ -50,11 +50,12 @@ bool Properties::save(KeyValueRepository& repo) const
   std::map<string, Variant> props;
 
   for (size_t i = 0; i < static_cast<size_t>(PropType::NumTypes); i++) {
-    if (myProperties[i] == ourDefaultProperties[i])
+    if (myProperties[i] == ourDefaultProperties[i]) {
-      repo.remove(ourPropertyNames[i]);
+      if (repo.atomic()) repo.atomic()->remove(ourPropertyNames[i]);
-    else
+    } else {
       props[ourPropertyNames[i]] = myProperties[i];
     }
+  }
 
   return repo.save(props);
 }

src/emucore/Settings.cxx

@@ -717,7 +717,7 @@ void Settings::setValue(const string& key, const Variant& value, bool persist)
 {
   auto it = myPermanentSettings.find(key);
   if(it != myPermanentSettings.end()) {
-    if (persist && it->second != value) myRespository->save(key, value);
+    if (persist && it->second != value && myRespository->atomic()) myRespository->atomic()->save(key, value);
     it->second = value;
   }
   else
@@ -760,5 +760,6 @@ void Settings::migrate()
 {
   while (getInt(SETTINGS_VERSION_KEY) < SETTINGS_VERSION) migrateOne();
 
-  myRespository->save(SETTINGS_VERSION_KEY, SETTINGS_VERSION);
+  if (myRespository->atomic())
+    myRespository->atomic()->save(SETTINGS_VERSION_KEY, SETTINGS_VERSION);
 }