Introduce uv::async

include/mbgl/util/uv.hpp

@@ -15,6 +15,7 @@ std::string cwd();
 class thread;
 class rwlock;
 class loop;
+class async;
 class worker;
 
 }

include/mbgl/util/uv_detail.hpp

@@ -13,6 +13,11 @@
 
 namespace uv {
 
+template <class T>
+void close(T* handle) {
+    uv_close(reinterpret_cast<uv_handle_t*>(handle), nullptr);
+}
+
 class thread : public mbgl::util::noncopyable {
 public:
     inline operator uv_thread_t *() { return &t; }
@@ -51,6 +56,39 @@ private:
     uv_loop_t *l = nullptr;
 };
 
+class async : public mbgl::util::noncopyable {
+public:
+    inline async(uv_loop_t* loop, std::function<void ()> fn_)
+        : fn(fn_) {
+        a.data = this;
+        if (uv_async_init(loop, &a, async_cb) != 0) {
+            throw std::runtime_error("failed to initialize async");
+        }
+    }
+
+    inline ~async() {
+        close(&a);
+    }
+
+    inline void send() {
+        if (uv_async_send(&a) != 0) {
+            throw std::runtime_error("failed to async send");
+        }
+    }
+
+private:
+#if UV_VERSION_MAJOR == 0 && UV_VERSION_MINOR <= 10
+    static void async_cb(uv_async_t* a, int) {
+#else
+    static void async_cb(uv_async_t* a) {
+#endif
+        reinterpret_cast<async*>(a->data)->fn();
+    }
+
+    uv_async_t a;
+    std::function<void ()> fn;
+};
+
 class mutex : public mbgl::util::noncopyable {
 public:
     inline mutex() {