registry get cannot create instance by default

Author: lia-viam

src/viam/sdk/common/instance.cpp

@@ -34,10 +34,14 @@ Instance::~Instance() {
     impl_.reset();
 }
 
-Instance& Instance::current() {
+Instance& Instance::current(Instance::Creation creation) {
     if (!current_instance.load()) {
-        // This variable declaration calls the default ctor, storing a current instance.
-        static Instance inst;  // NOLINT (misc-const-correctness)
+        if (creation == Creation::if_needed) {
+            // This variable declaration calls the default ctor, storing a current instance.
+            static Instance inst;  // NOLINT (misc-const-correctness)
+        } else {
+            throw Exception("Instance has not yet been created");
+        }
     }
 
     Instance* current = current_instance.load();

src/viam/sdk/common/instance.hpp

@@ -12,10 +12,19 @@ namespace sdk {
 /// objects in the same program is an error.
 class Instance {
    public:
+    /// @brief Enumeration for creation behavior of @ref current
+    enum class Creation {
+        open_existing,  ///< Instance must already exist
+        if_needed       ///< Use existing instance if present, else create one.
+    };
+
     Instance();
     ~Instance();
 
-    static Instance& current();
+    /// @brief Get the current Instance according to the Creation behavior.
+    /// Calling current(Creation::open_existing) when an instance has not yet been constructed is an
+    /// error.
+    static Instance& current(Creation);
 
    private:
     friend class Registry;

src/viam/sdk/registry/registry.cpp

@@ -92,7 +92,7 @@ const Model& ModelRegistration::model() const {
 };
 
 Registry& Registry::get() {
-    static Registry& result = Instance::current().impl_->registry;
+    static Registry& result = Instance::current(Instance::Creation::open_existing).impl_->registry;
 
     return result;
 }

src/viam/sdk/tests/test_utils.cpp

@@ -10,8 +10,8 @@
 #include <viam/sdk/spatialmath/orientation_types.hpp>
 
 namespace viam {
-namespace sdktests {
 
+namespace sdktests {
 using namespace viam::sdk;
 
 ProtoStruct fake_map() {

src/viam/sdk/tests/test_utils.hpp

@@ -2,6 +2,9 @@
 
 #include <grpcpp/grpcpp.h>
 
+#include <boost/test/unit_test.hpp>
+
+#include <viam/sdk/common/instance.hpp>
 #include <viam/sdk/config/resource.hpp>
 #include <viam/sdk/registry/registry.hpp>
 #include <viam/sdk/resource/resource.hpp>
@@ -10,6 +13,15 @@
 namespace viam {
 namespace sdktests {
 
+struct GlobalFixture {
+    GlobalFixture() {
+        BOOST_TEST_MESSAGE("Creating instance");
+        (void)sdk::Instance::current(sdk::Instance::Creation::if_needed);
+    }
+};
+
+BOOST_TEST_GLOBAL_FIXTURE(GlobalFixture);
+
 using namespace viam::sdk;
 
 ProtoStruct fake_map();