From bfac9b6292fdb4fe167a69e652be5751b2e2f4b8 Mon Sep 17 00:00:00 2001
From: Ivo van Dongen <info@ivovandongen.nl>
Date: Fri, 21 Jul 2017 15:54:26 +0300
Subject: [core] allow safe direct access to actor on single threaded scheduler

---
 include/mbgl/actor/actor.hpp |  8 ++++++++
 include/mbgl/util/thread.hpp | 29 +++++++++++++++++++++++++++++
 test/util/thread.test.cpp    | 28 ++++++++++++++++++++++++++++
 3 files changed, 65 insertions(+)

diff --git a/include/mbgl/actor/actor.hpp b/include/mbgl/actor/actor.hpp
index a0df19208e..93de4a948f 100644
--- a/include/mbgl/actor/actor.hpp
+++ b/include/mbgl/actor/actor.hpp
@@ -45,6 +45,11 @@ namespace mbgl {
     purpose of the actor model: prohibiting direct concurrent access to shared state.
 */
 
+
+namespace util {
+template <class> class Thread;
+} // namespace util
+
 template <class Object>
 class Actor : public util::noncopyable {
 public:
@@ -91,6 +96,9 @@ public:
     }
 
 private:
+    template<typename U>
+    friend class util::Thread;
+
     std::shared_ptr<Mailbox> mailbox;
     Object object;
 };
diff --git a/include/mbgl/util/thread.hpp b/include/mbgl/util/thread.hpp
index 06254569a9..c0cbc532ce 100644
--- a/include/mbgl/util/thread.hpp
+++ b/include/mbgl/util/thread.hpp
@@ -131,6 +131,13 @@ public:
     }
 
 private:
+    template <class U>
+    friend class BlockingThreadGuard;
+
+    Object& getObject() {
+        return object->object;
+    }
+
     MBGL_STORE_THREAD(tid);
 
     void schedule(std::weak_ptr<Mailbox> mailbox) override {
@@ -157,11 +164,33 @@ private:
     std::thread thread;
     std::unique_ptr<Actor<Object>> object;
 
+    std::mutex pauseMutex;
     std::unique_ptr<std::promise<void>> paused;
     std::unique_ptr<std::promise<void>> resumed;
 
     util::RunLoop* loop = nullptr;
 };
 
+
+template <class Object>
+class BlockingThreadGuard {
+public:
+    BlockingThreadGuard(Thread<Object>& thread_)
+        : thread(thread_) {
+        thread.pause();
+    }
+
+    ~BlockingThreadGuard() {
+        thread.resume();
+    }
+
+    Object& object() {
+        return thread.getObject();
+    }
+
+private:
+    Thread<Object>& thread;
+};
+
 } // namespace util
 } // namespace mbgl
diff --git a/test/util/thread.test.cpp b/test/util/thread.test.cpp
index 228e463d9e..1bc55eadda 100644
--- a/test/util/thread.test.cpp
+++ b/test/util/thread.test.cpp
@@ -6,6 +6,7 @@
 #include <mbgl/util/timer.hpp>
 
 #include <atomic>
+#include <chrono>
 #include <memory>
 #include <thread>
 
@@ -308,3 +309,30 @@ TEST(Thread, PauseResumeMultiThreaded) {
     thread1.join();
     thread2.join();
 }
+
+TEST(Thread, DirectAccess) {
+    
+    Thread<TestWorker> test("Test");
+    
+    // Use the thread's object directly
+    std::atomic<bool> flag { false };
+    auto guard = std::make_unique<BlockingThreadGuard<TestWorker>>( test );
+    guard->object().send([&] { flag = true; });
+    ASSERT_TRUE(flag);
+    
+    // Ensure messages queued up are processed
+    std::atomic<bool> message1Consumed { false };
+    test.actor().invoke(&TestWorker::send, [&]() { message1Consumed = true; });
+    
+    // Release the guard
+    guard.reset();
+    
+    // Ensure messages send after releasing the guard are processed
+    std::atomic<bool> message2Consumed { false };
+    test.actor().invoke(&TestWorker::send, [&]() { message2Consumed = true; });
+    
+    while (!message1Consumed && !message2Consumed) {
+        using namespace std::chrono_literals;
+        std::this_thread::sleep_for(10ms);
+    };
+}
-- 
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