service/sockets: Add worker abstraction to execute blocking calls asynchronously

This abstraction allows executing blocking functions (like recvfrom on a
socket configured for blocking) without blocking the service thread.
It is intended to be used with SleepClientThread.

src/core/CMakeLists.txt

@@ -491,6 +491,7 @@ add_library(core STATIC
     hle/service/sm/controller.h
     hle/service/sm/sm.cpp
     hle/service/sm/sm.h
+    hle/service/sockets/blocking_worker.h
     hle/service/sockets/bsd.cpp
     hle/service/sockets/bsd.h
     hle/service/sockets/ethc.cpp

src/core/hle/service/sockets/blocking_worker.h

@@ -0,0 +1,132 @@
+// Copyright 2020 yuzu emulator team
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <atomic>
+#include <memory>
+#include <string>
+#include <string_view>
+#include <thread>
+#include <variant>
+
+#include <fmt/format.h>
+
+#include "common/assert.h"
+#include "common/microprofile.h"
+#include "common/thread.h"
+#include "core/core.h"
+#include "core/hle/kernel/hle_ipc.h"
+#include "core/hle/kernel/kernel.h"
+#include "core/hle/kernel/thread.h"
+#include "core/hle/kernel/writable_event.h"
+
+namespace Service::Sockets {
+
+/**
+ * Worker abstraction to execute blocking calls on host without blocking the guest thread
+ *
+ * @tparam Service  Service where the work is executed
+ * @tparam ...Types Types of work to execute
+ */
+template <class Service, class... Types>
+class BlockingWorker {
+    using This = BlockingWorker<Service, Types...>;
+    using WorkVariant = std::variant<std::monostate, Types...>;
+
+public:
+    /// Create a new worker
+    static std::unique_ptr<This> Create(Core::System& system, Service* service,
+                                        std::string_view name) {
+        return std::unique_ptr<This>(new This(system, service, name));
+    }
+
+    ~BlockingWorker() {
+        while (!is_available.load(std::memory_order_relaxed)) {
+            // Busy wait until work is finished
+            std::this_thread::yield();
+        }
+        // Monostate means to exit the thread
+        work = std::monostate{};
+        work_event.Set();
+        thread.join();
+    }
+
+    /**
+     * Try to capture the worker to send work after a success
+     * @returns True when the worker has been successfully captured
+     */
+    bool TryCapture() {
+        bool expected = true;
+        return is_available.compare_exchange_weak(expected, false, std::memory_order_relaxed,
+                                                  std::memory_order_relaxed);
+    }
+
+    /**
+     * Send work to this worker abstraction
+     * @see TryCapture must be called before attempting to call this function
+     */
+    template <class Work>
+    void SendWork(Work new_work) {
+        ASSERT_MSG(!is_available, "Trying to send work on a worker that's not captured");
+        work = std::move(new_work);
+        work_event.Set();
+    }
+
+    /// Generate a callback for @see SleepClientThread
+    template <class Work>
+    auto Callback() {
+        return [this](std::shared_ptr<Kernel::Thread>, Kernel::HLERequestContext& ctx,
+                      Kernel::ThreadWakeupReason reason) {
+            ASSERT(reason == Kernel::ThreadWakeupReason::Signal);
+            std::get<Work>(work).Response(ctx);
+            is_available.store(true);
+        };
+    }
+
+    /// Get kernel event that will be signalled by the worker when the host operation finishes
+    std::shared_ptr<Kernel::WritableEvent> KernelEvent() const {
+        return kernel_event;
+    }
+
+private:
+    explicit BlockingWorker(Core::System& system, Service* service, std::string_view name) {
+        auto pair = Kernel::WritableEvent::CreateEventPair(system.Kernel(), std::string(name));
+        kernel_event = std::move(pair.writable);
+        thread = std::thread([this, &system, service, name] { Run(system, service, name); });
+    }
+
+    void Run(Core::System& system, Service* service, std::string_view name) {
+        system.RegisterHostThread();
+
+        const std::string thread_name = fmt::format("yuzu:{}", name);
+        MicroProfileOnThreadCreate(thread_name.c_str());
+        Common::SetCurrentThreadName(thread_name.c_str());
+
+        bool keep_running = true;
+        while (keep_running) {
+            work_event.Wait();
+
+            const auto visit_fn = [service, &keep_running](auto&& w) {
+                using T = std::decay_t<decltype(w)>;
+                if constexpr (std::is_same_v<T, std::monostate>) {
+                    keep_running = false;
+                } else {
+                    w.Execute(service);
+                }
+            };
+            std::visit(visit_fn, work);
+
+            kernel_event->Signal();
+        }
+    }
+
+    std::thread thread;
+    WorkVariant work;
+    Common::Event work_event;
+    std::shared_ptr<Kernel::WritableEvent> kernel_event;
+    std::atomic_bool is_available{true};
+};
+
+} // namespace Service::Sockets