[build] rework platform/default directory and add -files.txt for vendored libs

platform/default/src/mbgl/util/async_task.cpp

@@ -0,0 +1,66 @@
+#include <mbgl/util/async_task.hpp>
+
+#include <mbgl/util/run_loop.hpp>
+
+#include <atomic>
+#include <functional>
+
+#include <uv.h>
+
+namespace mbgl {
+namespace util {
+
+class AsyncTask::Impl {
+public:
+    Impl(std::function<void()>&& fn)
+        : async(new uv_async_t),
+          task(std::move(fn)) {
+
+        auto* loop = reinterpret_cast<uv_loop_t*>(RunLoop::getLoopHandle());
+        if (uv_async_init(loop, async, asyncCallback) != 0) {
+            throw std::runtime_error("Failed to initialize async.");
+        }
+
+        handle()->data = this;
+        uv_unref(handle());
+    }
+
+    ~Impl() {
+        uv_close(handle(), [](uv_handle_t* h) {
+            delete reinterpret_cast<uv_async_t*>(h);
+        });
+    }
+
+    void maySend() {
+        // uv_async_send will do the call coalescing for us.
+        if (uv_async_send(async) != 0) {
+            throw std::runtime_error("Failed to async send.");
+        }
+    }
+
+private:
+    static void asyncCallback(uv_async_t* handle) {
+        reinterpret_cast<Impl*>(handle->data)->task();
+    }
+
+    uv_handle_t* handle() {
+        return reinterpret_cast<uv_handle_t*>(async);
+    }
+
+    uv_async_t* async;
+
+    std::function<void()> task;
+};
+
+AsyncTask::AsyncTask(std::function<void()>&& fn)
+    : impl(std::make_unique<Impl>(std::move(fn))) {
+}
+
+AsyncTask::~AsyncTask() = default;
+
+void AsyncTask::send() {
+    impl->maySend();
+}
+
+} // namespace util
+} // namespace mbgl