[core] Use an actor model for tile worker concurrency

test/actor/actor.cpp

@@ -0,0 +1,139 @@
+#include <mbgl/actor/actor.hpp>
+#include <mbgl/actor/thread_pool.hpp>
+
+#include <mbgl/test/util.hpp>
+
+#include <chrono>
+#include <functional>
+#include <future>
+
+using namespace mbgl;
+using namespace std::chrono_literals;
+
+TEST(Actor, Construction) {
+    // Construction is currently synchronous. It may become asynchronous in the future.
+
+    struct Test {
+        Test(ActorRef<Test>, bool& constructed) {
+            constructed = true;
+        };
+    };
+
+    ThreadPool pool { 1 };
+    bool constructed = false;
+    Actor<Test> test(pool, std::ref(constructed));
+
+    EXPECT_TRUE(constructed);
+}
+
+TEST(Actor, DestructionClosesMailbox) {
+    // Destruction blocks until the actor is not receiving.
+
+    struct Test {
+        std::promise<void> promise;
+        std::future<void> future;
+        std::atomic<bool> waited;
+
+        Test(ActorRef<Test>, std::promise<void> promise_, std::future<void> future_)
+            : promise(std::move(promise_)),
+              future(std::move(future_)),
+              waited(false) {
+        }
+
+        ~Test() {
+            EXPECT_TRUE(waited.load());
+        }
+
+        void wait() {
+            promise.set_value();
+            future.wait();
+            std::this_thread::sleep_for(1ms);
+            waited = true;
+        }
+    };
+
+    ThreadPool pool { 1 };
+
+    std::promise<void> enteredPromise;
+    std::future<void> enteredFuture = enteredPromise.get_future();
+
+    std::promise<void> exitingPromise;
+    std::future<void> exitingFuture = exitingPromise.get_future();
+
+    Actor<Test> test(pool, std::move(enteredPromise), std::move(exitingFuture));
+
+    test.invoke(&Test::wait);
+    enteredFuture.wait();
+    exitingPromise.set_value();
+}
+
+TEST(Actor, OrderedMailbox) {
+    // Messages are processed in order.
+
+    struct Test {
+        int last = 0;
+        std::promise<void> promise;
+
+        Test(ActorRef<Test>, std::promise<void> promise_)
+            : promise(std::move(promise_))  {
+        }
+
+        void receive(int i) {
+            EXPECT_EQ(i, last + 1);
+            last = i;
+        }
+
+        void end() {
+            promise.set_value();
+        }
+    };
+
+    ThreadPool pool { 1 };
+
+    std::promise<void> endedPromise;
+    std::future<void> endedFuture = endedPromise.get_future();
+    Actor<Test> test(pool, std::move(endedPromise));
+
+    for (auto i = 1; i <= 10; ++i) {
+        test.invoke(&Test::receive, i);
+    }
+
+    test.invoke(&Test::end);
+    endedFuture.wait();
+}
+
+TEST(Actor, NonConcurrentMailbox) {
+    // An individual actor is never itself concurrent.
+
+    struct Test {
+        int last = 0;
+        std::promise<void> promise;
+
+        Test(ActorRef<Test>, std::promise<void> promise_)
+            : promise(std::move(promise_))  {
+        }
+
+        void receive(int i) {
+            EXPECT_EQ(i, last + 1);
+            last = i;
+            std::this_thread::sleep_for(1ms);
+        }
+
+        void end() {
+            promise.set_value();
+        }
+    };
+
+    ThreadPool pool { 10 };
+
+    std::promise<void> endedPromise;
+    std::future<void> endedFuture = endedPromise.get_future();
+    Actor<Test> test(pool, std::move(endedPromise));
+
+    for (auto i = 1; i <= 10; ++i) {
+        test.invoke(&Test::receive, i);
+    }
+
+    test.invoke(&Test::end);
+    endedFuture.wait();
+}