compat/util: split out run-in-thread{,-async}

1 files changed, 85 insertions, 0 deletions

diff --git a/compat/run-in-thread.hpp b/compat/run-in-thread.hpp
new file mode 100644
index 00000000..d377f625
--- /dev/null
+++ b/compat/run-in-thread.hpp
@@ -0,0 +1,85 @@
+#pragma once
+
+#include <QObject>
+
+#include <thread>
+#include <condition_variable>
+#include <utility>
+
+namespace detail {
+
+template<typename t>
+struct run_in_thread_traits
+{
+    using type = t;
+    using ret_type = t&&;
+    static inline void assign(t& lvalue, t&& rvalue) { lvalue = rvalue; }
+    static inline ret_type&& pass(ret_type&& val) { return std::move(val); }
+    template<typename F> static ret_type call(F& fun) { return std::move(fun()); }
+};
+
+template<>
+struct run_in_thread_traits<void>
+{
+    using type = unsigned char;
+    using ret_type = void;
+    static inline void assign(unsigned char&, unsigned char&&) {}
+    static inline void pass(type&&) {}
+    template<typename F> static type&& call(F& fun) { fun(); return std::move(type(0)); }
+};
+
+}
+
+template<typename F>
+auto run_in_thread_sync(QObject* obj, F&& fun)
+    -> typename detail::run_in_thread_traits<decltype(std::forward<F>(fun)())>::ret_type
+{
+    using lock_guard = std::unique_lock<std::mutex>;
+
+    std::mutex mtx;
+    lock_guard guard(mtx);
+    std::condition_variable cvar;
+
+    std::thread::id waiting_thread = std::this_thread::get_id();
+
+    using traits = detail::run_in_thread_traits<decltype(std::forward<F>(fun)())>;
+
+    typename traits::type ret;
+
+    bool skip_wait = false;
+
+    {
+        QObject src;
+        src.moveToThread(obj->thread());
+        QObject::connect(&src,
+                         &QObject::destroyed,
+                         obj,
+                         [&]() {
+            std::thread::id calling_thread = std::this_thread::get_id();
+            if (waiting_thread == calling_thread)
+            {
+                skip_wait = true;
+                traits::assign(ret, traits::call(fun));
+            }
+            else
+            {
+                lock_guard guard(mtx);
+                traits::assign(ret, traits::call(fun));
+                cvar.notify_one();
+            }
+        },
+        Qt::AutoConnection);
+    }
+
+    if (!skip_wait)
+        cvar.wait(guard);
+    return traits::pass(std::move(ret));
+}
+
+template<typename F>
+void run_in_thread_async(QObject* obj, F&& fun)
+{
+    QObject src;
+    src.moveToThread(obj->thread());
+    QObject::connect(&src, &QObject::destroyed, obj, std::move(fun), Qt::AutoConnection);
+}