[core] Add global settings object

include/mbgl/platform/settings.hpp

@@ -0,0 +1,48 @@
+#pragma once
+
+#include <mapbox/value.hpp>
+
+#include <memory>
+
+namespace mbgl {
+namespace platform {
+
+#define DECLARE_MAPBOX_SETTING(name, value) constexpr const char* name = "mapbox_" #value
+
+// The value for EXPERIMENTAL_THREAD_PRIORITY_* keys, must be a double.
+DECLARE_MAPBOX_SETTING(EXPERIMENTAL_THREAD_PRIORITY_WORKER, thread_priority_worker);
+DECLARE_MAPBOX_SETTING(EXPERIMENTAL_THREAD_PRIORITY_FILE, thread_priority_file);
+DECLARE_MAPBOX_SETTING(EXPERIMENTAL_THREAD_PRIORITY_NETWORK, thread_priority_network);
+DECLARE_MAPBOX_SETTING(EXPERIMENTAL_THREAD_PRIORITY_DATABASE, thread_priority_database);
+
+// Settings class provides non-persistent, in-process key-value storage.
+class Settings final {
+public:
+    // Returns singleton instance
+    static Settings& getInstance() noexcept;
+
+    // Sets setting value for a specified key.
+    void set(const std::string& key, mapbox::base::Value value) noexcept;
+
+    // Sets multiple setting values by merging current Settings object
+    // with provided `values` object.
+    void set(mapbox::base::ValueObject values) noexcept;
+
+    // Returns setting value for a specified key or NullValue if element
+    // for specified key is missing.
+    mapbox::base::Value get(const std::string& key) const noexcept;
+
+    // Returns values for settings whose keys are equal to the ones provided in `keys` argument.
+    // Null values would be provided for keys whose elements are missing in Settings.
+    mapbox::base::ValueObject get(const std::vector<std::string>& keys) const noexcept;
+
+private:
+    Settings();
+
+private:
+    class Impl;
+    std::unique_ptr<Impl> impl;
+};
+
+} // namespace platform
+} // namespace mbgl

next/CMakeLists.txt

@@ -121,6 +121,7 @@ add_library(
     ${MBGL_ROOT}/include/mbgl/math/log2.hpp
     ${MBGL_ROOT}/include/mbgl/math/minmax.hpp
     ${MBGL_ROOT}/include/mbgl/math/wrap.hpp
+    ${MBGL_ROOT}/include/mbgl/platform/settings.hpp
     ${MBGL_ROOT}/include/mbgl/platform/thread.hpp
     ${MBGL_ROOT}/include/mbgl/renderer/query.hpp
     ${MBGL_ROOT}/include/mbgl/renderer/renderer.hpp
@@ -353,6 +354,7 @@ add_library(
     ${MBGL_ROOT}/src/mbgl/map/transform_state.hpp
     ${MBGL_ROOT}/src/mbgl/map/zoom_history.hpp
     ${MBGL_ROOT}/src/mbgl/math/log2.cpp
+    ${MBGL_ROOT}/src/mbgl/platform/settings.cpp
     ${MBGL_ROOT}/src/mbgl/programs/attributes.hpp
     ${MBGL_ROOT}/src/mbgl/programs/background_pattern_program.hpp
     ${MBGL_ROOT}/src/mbgl/programs/background_program.cpp

src/mbgl/platform/settings.cpp

@@ -0,0 +1,58 @@
+#include <mbgl/platform/settings.hpp>
+
+#include <mutex>
+
+namespace mbgl {
+namespace platform {
+
+namespace {
+mapbox::base::Value getValue(const std::string& key, const mapbox::base::ValueObject& object) {
+    auto it = object.find(key);
+    if (it != object.end()) {
+        return it->second;
+    }
+    return {};
+}
+} // namespace
+
+class Settings::Impl {
+public:
+    mapbox::base::ValueObject settings;
+    std::mutex mutex;
+};
+
+Settings::Settings() : impl(std::make_unique<Impl>()) {}
+
+Settings& Settings::getInstance() noexcept {
+    static Settings instance;
+    return instance;
+}
+
+void Settings::set(const std::string& key, mapbox::base::Value value) noexcept {
+    std::lock_guard<std::mutex> lock(impl->mutex);
+    impl->settings[key] = std::move(value);
+}
+
+void Settings::set(mapbox::base::ValueObject values) noexcept {
+    std::lock_guard<std::mutex> lock(impl->mutex);
+    for (const auto& pair : values) {
+        impl->settings[pair.first] = pair.second;
+    }
+}
+
+mapbox::base::ValueObject Settings::get(const std::vector<std::string>& keys) const noexcept {
+    std::lock_guard<std::mutex> lock(impl->mutex);
+    mapbox::base::ValueObject result;
+    for (const auto& key : keys) {
+        result[key] = getValue(key, impl->settings);
+    }
+    return result;
+}
+
+mapbox::base::Value Settings::get(const std::string& key) const noexcept {
+    std::lock_guard<std::mutex> lock(impl->mutex);
+    return getValue(key, impl->settings);
+}
+
+} // namespace platform
+} // namespace mbgl