Kernel/IPC: Use Ports and Sessions as the fundamental building block of Inter Process Communication.

All handles obtained via srv::GetServiceHandle or svcConnectToPort are references to ClientSessions.
Service modules will wait on the counterpart of those ClientSessions (Called ServerSessions) using svcReplyAndReceive or svcWaitSynchronization[1|N], and will be awoken when a SyncRequest is performed.

HLE Interfaces are now ClientPorts which override the HandleSyncRequest virtual member function to perform command handling immediately.

src/core/hle/kernel/server_session.cpp

@@ -0,0 +1,58 @@
+// Copyright 2016 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include <tuple>
+
+#include "core/hle/kernel/client_port.h"
+#include "core/hle/kernel/client_session.h"
+#include "core/hle/kernel/server_session.h"
+#include "core/hle/kernel/thread.h"
+
+namespace Kernel {
+
+ServerSession::ServerSession() {}
+ServerSession::~ServerSession() {}
+
+ResultVal<SharedPtr<ServerSession>> ServerSession::Create(std::string name) {
+    SharedPtr<ServerSession> server_session(new ServerSession);
+
+    server_session->name = std::move(name);
+    server_session->signaled = false;
+
+    return MakeResult<SharedPtr<ServerSession>>(std::move(server_session));
+}
+
+bool ServerSession::ShouldWait() {
+    return !signaled;
+}
+
+void ServerSession::Acquire() {
+    ASSERT_MSG(!ShouldWait(), "object unavailable!");
+    signaled = false;
+}
+
+ResultCode ServerSession::HandleSyncRequest() {
+    // The ServerSession received a sync request, this means that there's new data available
+    // from one of its ClientSessions, so wake up any threads that may be waiting on a svcReplyAndReceive or similar.
+    signaled = true;
+    WakeupAllWaitingThreads();
+    return RESULT_SUCCESS;
+}
+
+SharedPtr<ClientSession> ServerSession::CreateClientSession() {
+    // In Citra, some types of ServerSessions (File and Directory sessions) are not created as a pair of Server-Client sessions,
+    // but are instead created as a single ServerSession, which then hands over a ClientSession on demand (When opening the File or Directory).
+    // The real kernel (Or more specifically, the real FS service) does create the pair of Sessions at the same time (via svcCreateSession), and simply
+    // stores the ClientSession until it is needed.
+    return ClientSession::Create(SharedPtr<ServerSession>(this), nullptr, name + "Client").MoveFrom();
+}
+
+std::tuple<SharedPtr<ServerSession>, SharedPtr<ClientSession>> ServerSession::CreateSessionPair(SharedPtr<ClientPort> client_port, std::string name) {
+    auto server_session = ServerSession::Create(name + "Server").MoveFrom();
+    auto client_session = ClientSession::Create(server_session, client_port, name + "Client").MoveFrom();
+
+    return std::make_tuple(server_session, client_session);
+}
+
+}