Kernel/Threads: Implement an SleepClientThread function for HLERequestContext-based services to make performing async tasks on the host while in an HLE service function easier.

An HLE service function that wants to perform an async operation should put the caller guest thread to sleep using SleepClientThread, passing in a callback to execute when the thread is resumed.
SleepClientThread returns a Kernel::Event that should be signaled to resume the guest thread when the host async operation completes.

src/core/hle/kernel/hle_ipc.cpp

@@ -6,6 +6,7 @@
 #include <boost/range/algorithm_ext/erase.hpp>
 #include "common/assert.h"
 #include "common/common_types.h"
+#include "core/hle/kernel/event.h"
 #include "core/hle/kernel/handle_table.h"
 #include "core/hle/kernel/hle_ipc.h"
 #include "core/hle/kernel/kernel.h"
@@ -24,6 +25,40 @@ void SessionRequestHandler::ClientDisconnected(SharedPtr<ServerSession> server_s
     boost::range::remove_erase(connected_sessions, server_session);
 }
 
+SharedPtr<Event> HLERequestContext::SleepClientThread(SharedPtr<Thread> thread,
+                                                      const std::string& reason, u64 timeout,
+                                                      WakeupCallback&& callback) {
+    // Put the client thread to sleep until the wait event is signaled or the timeout expires.
+    thread->wakeup_callback = [context = *this, callback](ThreadWakeupReason reason,
+                                                          SharedPtr<Thread> thread,
+                                                          SharedPtr<WaitObject> object) mutable {
+        ASSERT(thread->status == THREADSTATUS_WAIT_HLE_EVENT);
+        callback(thread, context, reason);
+
+        auto& process = thread->owner_process;
+        // We must copy the entire command buffer *plus* the entire static buffers area, since
+        // the translation might need to read from it in order to retrieve the StaticBuffer
+        // target addresses.
+        std::array<u32, IPC::COMMAND_BUFFER_LENGTH + 2 * IPC::MAX_STATIC_BUFFERS> cmd_buff;
+        Memory::ReadBlock(*process, thread->GetCommandBufferAddress(), cmd_buff.data(),
+                          cmd_buff.size() * sizeof(u32));
+        context.WriteToOutgoingCommandBuffer(cmd_buff.data(), *process, Kernel::g_handle_table);
+        // Copy the translated command buffer back into the thread's command buffer area.
+        Memory::WriteBlock(*process, thread->GetCommandBufferAddress(), cmd_buff.data(),
+                           cmd_buff.size() * sizeof(u32));
+    };
+
+    auto event = Kernel::Event::Create(Kernel::ResetType::OneShot, "HLE Pause Event: " + reason);
+    thread->status = THREADSTATUS_WAIT_HLE_EVENT;
+    thread->wait_objects = {event};
+    event->AddWaitingThread(thread);
+
+    if (timeout > 0)
+        thread->WakeAfterDelay(timeout);
+
+    return event;
+}
+
 HLERequestContext::HLERequestContext(SharedPtr<ServerSession> session)
     : session(std::move(session)) {
     cmd_buf[0] = 0;