Introduce the ThreadContext

mbgl::Thread will keep a ThreadContext for each running instance
in a thread_local so we don't need to lookup a man in the Environment
every time we need some info about the current thread.

This patch is moving the ::currentlyOn check used on Debug build from
the Environment class to the ThreadContext.

9 files changed, 123 insertions, 31 deletions

diff --git a/src/mbgl/map/map.cpp b/src/mbgl/map/map.cpp
index 17bcd29893..c25d307c6e 100644
--- a/src/mbgl/map/map.cpp
+++ b/src/mbgl/map/map.cpp
@@ -12,7 +12,7 @@ namespace mbgl {
 
 Map::Map(View& view, FileSource& fileSource, MapMode mode)
     : data(std::make_unique<MapData>(view, mode)),
-      context(std::make_unique<util::Thread<MapContext>>("Map", util::ThreadPriority::Regular, view, fileSource, *data))
+      context(std::make_unique<util::Thread<MapContext>>(util::ThreadContext{"Map", util::ThreadType::Map, util::ThreadPriority::Regular}, view, fileSource, *data))
 {
     view.initialize(this);
 }
diff --git a/src/mbgl/map/map_context.cpp b/src/mbgl/map/map_context.cpp
index 69d3c7e215..ecb9d84639 100644
--- a/src/mbgl/map/map_context.cpp
+++ b/src/mbgl/map/map_context.cpp
@@ -33,7 +33,7 @@ MapContext::MapContext(uv_loop_t* loop, View& view_, FileSource& fileSource, Map
       updated(static_cast<UpdateType>(Update::Nothing)),
       asyncUpdate(std::make_unique<uv::async>(loop, [this] { update(); })),
       texturePool(std::make_unique<TexturePool>()) {
-    assert(Environment::currentlyOn(ThreadType::Map));
+    assert(util::ThreadContext::currentlyOn(util::ThreadType::Map));
 
     asyncUpdate->unref();
 
@@ -108,7 +108,7 @@ void MapContext::setStyleJSON(const std::string& json, const std::string& base)
 }
 
 void MapContext::loadStyleJSON(const std::string& json, const std::string& base) {
-    assert(Environment::currentlyOn(ThreadType::Map));
+    assert(util::ThreadContext::currentlyOn(util::ThreadType::Map));
 
     style.reset();
     style = std::make_unique<Style>(json, base, asyncUpdate->get()->loop, env);
@@ -125,13 +125,13 @@ void MapContext::loadStyleJSON(const std::string& json, const std::string& base)
 }
 
 void MapContext::updateTiles() {
-    assert(Environment::currentlyOn(ThreadType::Map));
+    assert(util::ThreadContext::currentlyOn(util::ThreadType::Map));
 
     style->update(data, transformState, *texturePool);
 }
 
 void MapContext::updateAnnotationTiles(const std::unordered_set<TileID, TileID::Hash>& ids) {
-    assert(Environment::currentlyOn(ThreadType::Map));
+    assert(util::ThreadContext::currentlyOn(util::ThreadType::Map));
 
     data.annotationManager.markStaleTiles(ids);
 
@@ -232,7 +232,7 @@ void MapContext::recalculateStyle(TimePoint now) {
 }
 
 void MapContext::update() {
-    assert(Environment::currentlyOn(ThreadType::Map));
+    assert(util::ThreadContext::currentlyOn(util::ThreadType::Map));
 
     const auto now = Clock::now();
     data.setAnimationTime(now);
@@ -303,7 +303,7 @@ void MapContext::renderStill(StillImageCallback fn) {
 }
 
 void MapContext::render() {
-    assert(Environment::currentlyOn(ThreadType::Map));
+    assert(util::ThreadContext::currentlyOn(util::ThreadType::Map));
 
     // Cleanup OpenGL objects that we abandoned since the last render call.
     env.performCleanup();
@@ -335,13 +335,13 @@ void MapContext::render() {
 }
 
 double MapContext::getTopOffsetPixelsForAnnotationSymbol(const std::string& symbol) {
-    assert(Environment::currentlyOn(ThreadType::Map));
+    assert(util::ThreadContext::currentlyOn(util::ThreadType::Map));
     const SpritePosition pos = style->sprite->getSpritePosition(symbol);
     return -pos.height / pos.pixelRatio / 2;
 }
 
 void MapContext::setSourceTileCacheSize(size_t size) {
-    assert(Environment::currentlyOn(ThreadType::Map));
+    assert(util::ThreadContext::currentlyOn(util::ThreadType::Map));
     if (size != sourceCacheSize) {
         sourceCacheSize = size;
         if (!style) return;
@@ -353,7 +353,7 @@ void MapContext::setSourceTileCacheSize(size_t size) {
 }
 
 void MapContext::onLowMemory() {
-    assert(Environment::currentlyOn(ThreadType::Map));
+    assert(util::ThreadContext::currentlyOn(util::ThreadType::Map));
     if (!style) return;
     for (const auto &source : style->sources) {
         source->onLowMemory();
@@ -362,12 +362,12 @@ void MapContext::onLowMemory() {
 }
 
 void MapContext::onTileDataChanged() {
-    assert(Environment::currentlyOn(ThreadType::Map));
+    assert(util::ThreadContext::currentlyOn(util::ThreadType::Map));
     triggerUpdate();
 }
 
 void MapContext::onResourceLoadingFailed(std::exception_ptr error) {
-    assert(Environment::currentlyOn(ThreadType::Map));
+    assert(util::ThreadContext::currentlyOn(util::ThreadType::Map));
 
     if (data.mode == MapMode::Still && callback) {
         callback(error, nullptr);
diff --git a/src/mbgl/storage/default_file_source.cpp b/src/mbgl/storage/default_file_source.cpp
index b46696aaa3..dcd0090da1 100644
--- a/src/mbgl/storage/default_file_source.cpp
+++ b/src/mbgl/storage/default_file_source.cpp
@@ -28,7 +28,7 @@ namespace algo = boost::algorithm;
 namespace mbgl {
 
 DefaultFileSource::DefaultFileSource(FileCache* cache, const std::string& root)
-    : thread(std::make_unique<util::Thread<Impl>>("FileSource", util::ThreadPriority::Low, cache, root)) {
+    : thread(std::make_unique<util::Thread<Impl>>(util::ThreadContext{"FileSource", util::ThreadType::Unknown, util::ThreadPriority::Low}, cache, root)) {
 }
 
 DefaultFileSource::~DefaultFileSource() {
diff --git a/src/mbgl/style/style.cpp b/src/mbgl/style/style.cpp
index 0713bda0a2..24771e1859 100644
--- a/src/mbgl/style/style.cpp
+++ b/src/mbgl/style/style.cpp
@@ -159,7 +159,7 @@ bool Style::isLoaded() const {
 }
 
 void Style::setObserver(Observer* observer_) {
-    assert(Environment::currentlyOn(ThreadType::Map));
+    assert(util::ThreadContext::currentlyOn(util::ThreadType::Map));
     assert(!observer);
 
     observer = observer_;
@@ -206,7 +206,7 @@ void Style::onSpriteLoadingFailed(std::exception_ptr error) {
 }
 
 void Style::emitTileDataChanged() {
-    assert(Environment::currentlyOn(ThreadType::Map));
+    assert(util::ThreadContext::currentlyOn(util::ThreadType::Map));
 
     if (observer) {
         observer->onTileDataChanged();
@@ -214,7 +214,7 @@ void Style::emitTileDataChanged() {
 }
 
 void Style::emitResourceLoadingFailed(std::exception_ptr error) {
-    assert(Environment::currentlyOn(ThreadType::Map));
+    assert(util::ThreadContext::currentlyOn(util::ThreadType::Map));
 
     try {
         if (error) {
diff --git a/src/mbgl/util/thread.hpp b/src/mbgl/util/thread.hpp
index f3a9baa6f3..5bd856cbbc 100644
--- a/src/mbgl/util/thread.hpp
+++ b/src/mbgl/util/thread.hpp
@@ -8,6 +8,7 @@
 #include <functional>
 
 #include <mbgl/util/run_loop.hpp>
+#include <mbgl/util/thread_context.hpp>
 #include <mbgl/platform/platform.hpp>
 
 namespace mbgl {
@@ -21,16 +22,11 @@ namespace util {
 // Thread<> constructor blocks until the thread and the Object are fully created, so after the
 // object creation, it's safe to obtain the Object stored in this thread.
 
-enum class ThreadPriority : bool {
-    Regular,
-    Low,
-};
-
 template <class Object>
 class Thread {
 public:
     template <class... Args>
-    Thread(const std::string& name, ThreadPriority priority, Args&&... args);
+    Thread(const ThreadContext&, Args&&... args);
     ~Thread();
 
     // Invoke object->fn(args...) in the runloop thread.
@@ -81,7 +77,7 @@ private:
     }
 
     template <typename P, std::size_t... I>
-    void run(P&& params, std::index_sequence<I...>);
+    void run(ThreadContext, P&& params, std::index_sequence<I...>);
 
     std::promise<void> running;
     std::promise<void> joinable;
@@ -94,23 +90,21 @@ private:
 
 template <class Object>
 template <class... Args>
-Thread<Object>::Thread(const std::string& name, ThreadPriority priority, Args&&... args) {
+Thread<Object>::Thread(const ThreadContext& context, Args&&... args) {
     // Note: We're using std::tuple<> to store the arguments because GCC 4.9 has a bug
     // when expanding parameters packs captured in lambdas.
     std::tuple<Args...> params = std::forward_as_tuple(::std::forward<Args>(args)...);
 
     thread = std::thread([&] {
         #ifdef __APPLE__
-        pthread_setname_np(name.c_str());
-        #else
-        (void(name));
+        pthread_setname_np(context.name.c_str());
         #endif
 
-        if (priority == ThreadPriority::Low) {
+        if (context.priority == ThreadPriority::Low) {
             platform::makeThreadLowPriority();
         }
 
-        run(std::move(params), std::index_sequence_for<Args...>{});
+        run(context, std::move(params), std::index_sequence_for<Args...>{});
     });
 
     running.get_future().get();
@@ -118,10 +112,12 @@ Thread<Object>::Thread(const std::string& name, ThreadPriority priority, Args&&.
 
 template <class Object>
 template <typename P, std::size_t... I>
-void Thread<Object>::run(P&& params, std::index_sequence<I...>) {
+void Thread<Object>::run(ThreadContext context, P&& params, std::index_sequence<I...>) {
     uv::loop l;
 
     {
+        ThreadContext::current.set(&context);
+
         RunLoop loop_(l.get());
         loop = &loop_;
 
@@ -133,6 +129,8 @@ void Thread<Object>::run(P&& params, std::index_sequence<I...>) {
 
         loop = nullptr;
         object = nullptr;
+
+        ThreadContext::current.set(nullptr);
     }
 
     // Run the loop again to ensure that async close callbacks have been called.
diff --git a/src/mbgl/util/thread_context.cpp b/src/mbgl/util/thread_context.cpp
new file mode 100644
index 0000000000..6742d5e75e
--- /dev/null
+++ b/src/mbgl/util/thread_context.cpp
@@ -0,0 +1,34 @@
+#include <mbgl/util/thread_context.hpp>
+
+namespace mbgl {
+namespace util {
+
+class MainThreadContextRegistrar {
+public:
+    MainThreadContextRegistrar() : context("Main", ThreadType::Main, ThreadPriority::Regular) {
+        ThreadContext::current.set(&context);
+    }
+
+    ~MainThreadContextRegistrar() {
+        ThreadContext::current.set(nullptr);
+    }
+
+private:
+    ThreadContext context;
+};
+
+ThreadContext::ThreadContext(const std::string& name_, ThreadType type_, ThreadPriority priority_)
+    : name(name_),
+      type(type_),
+      priority(priority_) {
+}
+
+uv::tls<ThreadContext> ThreadContext::current;
+
+// Will auto register the main thread context
+// at startup. Must be instantiated after the
+// ThreadContext::current object.
+MainThreadContextRegistrar registrar;
+
+}
+}
diff --git a/src/mbgl/util/thread_context.hpp b/src/mbgl/util/thread_context.hpp
new file mode 100644
index 0000000000..d4b56cafa8
--- /dev/null
+++ b/src/mbgl/util/thread_context.hpp
@@ -0,0 +1,55 @@
+#ifndef MBGL_UTIL_THREAD_CONTEXT
+#define MBGL_UTIL_THREAD_CONTEXT
+
+#include <mbgl/util/uv_detail.hpp>
+
+#include <cstdint>
+#include <string>
+#include <thread>
+
+namespace mbgl {
+namespace util {
+
+enum class ThreadPriority : bool {
+    Regular,
+    Low,
+};
+
+enum class ThreadType : uint8_t {
+    Main,
+    Map,
+    Worker,
+    Unknown,
+};
+
+struct ThreadContext {
+public:
+    ThreadContext(const std::string& name, ThreadType type, ThreadPriority priority);
+
+    static bool currentlyOn(ThreadType type) {
+        return current.get()->type == type;
+    }
+
+    static std::string getName() {
+        return current.get()->name;
+    }
+
+    static ThreadPriority getPriority() {
+        return current.get()->priority;
+    }
+
+private:
+    std::string name;
+    ThreadType type;
+    ThreadPriority priority;
+
+    static uv::tls<ThreadContext> current;
+
+    friend class MainThreadContextRegistrar;
+    template <class Object> friend class Thread;
+};
+
+}
+}
+
+#endif
diff --git a/src/mbgl/util/uv_detail.hpp b/src/mbgl/util/uv_detail.hpp
index 7e2c16a2a3..fc72ab6401 100644
--- a/src/mbgl/util/uv_detail.hpp
+++ b/src/mbgl/util/uv_detail.hpp
@@ -191,6 +191,10 @@ private:
 template <class T>
 class tls : public mbgl::util::noncopyable {
 public:
+    inline tls(T* val) {
+        tls();
+        set(val);
+    }
     inline tls() {
         if (uv_key_create(&key) != 0) {
             throw std::runtime_error("failed to initialize thread local storage key");
diff --git a/src/mbgl/util/worker.cpp b/src/mbgl/util/worker.cpp
index 3022d30277..1806ba78ce 100644
--- a/src/mbgl/util/worker.cpp
+++ b/src/mbgl/util/worker.cpp
@@ -18,8 +18,9 @@ public:
 };
 
 Worker::Worker(std::size_t count) {
+    util::ThreadContext context = {"Worker", util::ThreadType::Worker, util::ThreadPriority::Low};
     for (std::size_t i = 0; i < count; i++) {
-        threads.emplace_back(std::make_unique<util::Thread<Impl>>("Worker", util::ThreadPriority::Low));
+        threads.emplace_back(std::make_unique<util::Thread<Impl>>(context));
     }
 }