From 694159c49ebc15e0d6e92addc31f65b623dbe1f9 Mon Sep 17 00:00:00 2001
From: John Firebaugh <john.firebaugh@gmail.com>
Date: Fri, 17 Feb 2017 10:57:21 -0800
Subject: [core] Nestable BackendScope

---
 cmake/core-files.cmake                   |  2 ++
 include/mbgl/map/backend.hpp             | 14 --------------
 include/mbgl/map/backend_scope.hpp       | 17 +++++++++++++++++
 platform/android/src/native_map_view.cpp |  1 +
 src/mbgl/map/backend_scope.cpp           | 26 ++++++++++++++++++++++++++
 src/mbgl/map/map.cpp                     |  1 +
 6 files changed, 47 insertions(+), 14 deletions(-)
 create mode 100644 include/mbgl/map/backend_scope.hpp
 create mode 100644 src/mbgl/map/backend_scope.cpp

diff --git a/cmake/core-files.cmake b/cmake/core-files.cmake
index 2696d2bf3e..5173b92c05 100644
--- a/cmake/core-files.cmake
+++ b/cmake/core-files.cmake
@@ -104,11 +104,13 @@ set(MBGL_CORE_FILES
 
     # map
     include/mbgl/map/backend.hpp
+    include/mbgl/map/backend_scope.hpp
     include/mbgl/map/camera.hpp
     include/mbgl/map/map.hpp
     include/mbgl/map/mode.hpp
     include/mbgl/map/view.hpp
     src/mbgl/map/backend.cpp
+    src/mbgl/map/backend_scope.cpp
     src/mbgl/map/change.hpp
     src/mbgl/map/map.cpp
     src/mbgl/map/transform.cpp
diff --git a/include/mbgl/map/backend.hpp b/include/mbgl/map/backend.hpp
index 0468449155..a7c78cf03d 100644
--- a/include/mbgl/map/backend.hpp
+++ b/include/mbgl/map/backend.hpp
@@ -47,18 +47,4 @@ private:
     friend class BackendScope;
 };
 
-class BackendScope {
-public:
-    BackendScope(Backend& backend_) : backend(backend_) {
-        backend.activate();
-    }
-
-    ~BackendScope() {
-        backend.deactivate();
-    }
-
-private:
-    Backend& backend;
-};
-
 } // namespace mbgl
diff --git a/include/mbgl/map/backend_scope.hpp b/include/mbgl/map/backend_scope.hpp
new file mode 100644
index 0000000000..c13fb88ded
--- /dev/null
+++ b/include/mbgl/map/backend_scope.hpp
@@ -0,0 +1,17 @@
+#pragma once
+
+namespace mbgl {
+
+class Backend;
+
+class BackendScope {
+public:
+    BackendScope(Backend&);
+    ~BackendScope();
+
+private:
+    Backend* priorBackend;
+    Backend& backend;
+};
+
+} // namespace mbgl
diff --git a/platform/android/src/native_map_view.cpp b/platform/android/src/native_map_view.cpp
index 22711f1547..b36b477f2f 100755
--- a/platform/android/src/native_map_view.cpp
+++ b/platform/android/src/native_map_view.cpp
@@ -16,6 +16,7 @@
 #include <mbgl/util/logging.hpp>
 #include <mbgl/gl/extension.hpp>
 #include <mbgl/gl/context.hpp>
+#include <mbgl/map/backend_scope.hpp>
 #include <mbgl/util/constants.hpp>
 #include <mbgl/util/image.hpp>
 #include <mbgl/util/shared_thread_pool.hpp>
diff --git a/src/mbgl/map/backend_scope.cpp b/src/mbgl/map/backend_scope.cpp
new file mode 100644
index 0000000000..302dfd70cf
--- /dev/null
+++ b/src/mbgl/map/backend_scope.cpp
@@ -0,0 +1,26 @@
+#include <mbgl/map/backend_scope.hpp>
+#include <mbgl/map/backend.hpp>
+#include <mbgl/util/thread_local.hpp>
+
+namespace mbgl {
+
+static util::ThreadLocal<Backend> currentBackend;
+
+BackendScope::BackendScope(Backend& backend_)
+    : priorBackend(currentBackend.get()),
+      backend(backend_) {
+    backend.activate();
+    currentBackend.set(&backend);
+}
+
+BackendScope::~BackendScope() {
+    if (priorBackend) {
+        priorBackend->activate();
+        currentBackend.set(priorBackend);
+    } else {
+        backend.deactivate();
+        currentBackend.set(nullptr);
+    }
+}
+
+} // namespace mbgl
diff --git a/src/mbgl/map/map.cpp b/src/mbgl/map/map.cpp
index 2837a95bc5..82c0a5f901 100644
--- a/src/mbgl/map/map.cpp
+++ b/src/mbgl/map/map.cpp
@@ -2,6 +2,7 @@
 #include <mbgl/map/camera.hpp>
 #include <mbgl/map/view.hpp>
 #include <mbgl/map/backend.hpp>
+#include <mbgl/map/backend_scope.hpp>
 #include <mbgl/map/transform.hpp>
 #include <mbgl/map/transform_state.hpp>
 #include <mbgl/annotation/annotation_manager.hpp>
-- 
cgit v1.2.1