LibIPC: Allow overriding the use of deferred_invoke()

This will allow Ladybird to use IPC::Connection without having an
actively running Core::EventLoop.

The abstraction here is not great, and we should think of something
nicer, but we have to start somewhere.

Userland/Libraries/LibIPC/Connection.cpp

@@ -12,14 +12,29 @@
 
 namespace IPC {
 
+struct CoreEventLoopDeferredInvoker final : public DeferredInvoker {
+    virtual ~CoreEventLoopDeferredInvoker() = default;
+
+    virtual void schedule(Function<void()> callback) override
+    {
+        Core::deferred_invoke(move(callback));
+    }
+};
+
 ConnectionBase::ConnectionBase(IPC::Stub& local_stub, NonnullOwnPtr<Core::Stream::LocalSocket> socket, u32 local_endpoint_magic)
     : m_local_stub(local_stub)
     , m_socket(move(socket))
     , m_local_endpoint_magic(local_endpoint_magic)
+    , m_deferred_invoker(make<CoreEventLoopDeferredInvoker>())
 {
     m_responsiveness_timer = Core::Timer::create_single_shot(3000, [this] { may_have_become_unresponsive(); });
 }
 
+void ConnectionBase::set_deferred_invoker(NonnullOwnPtr<DeferredInvoker> deferred_invoker)
+{
+    m_deferred_invoker = move(deferred_invoker);
+}
+
 void ConnectionBase::set_fd_passing_socket(NonnullOwnPtr<Core::Stream::LocalSocket> socket)
 {
     m_fd_passing_socket = move(socket);
@@ -157,7 +172,9 @@ ErrorOr<Vector<u8>> ConnectionBase::read_as_much_as_possible_from_socket_without
 
         auto bytes_read = maybe_bytes_read.release_value();
         if (bytes_read.is_empty()) {
-            deferred_invoke([this] { shutdown(); });
+            m_deferred_invoker->schedule([strong_this = NonnullRefPtr(*this)]() mutable {
+                strong_this->shutdown();
+            });
             if (!bytes.is_empty())
                 break;
             return Error::from_string_literal("IPC connection EOF");
@@ -194,8 +211,8 @@ ErrorOr<void> ConnectionBase::drain_messages_from_peer()
     }
 
     if (!m_unprocessed_messages.is_empty()) {
-        deferred_invoke([this] {
+        m_deferred_invoker->schedule([strong_this = NonnullRefPtr(*this)]() mutable {
-            handle_messages();
+            strong_this->handle_messages();
         });
     }
     return {};

Userland/Libraries/LibIPC/Connection.h

@@ -27,6 +27,13 @@
 
 namespace IPC {
 
+// NOTE: This is an abstraction to allow using IPC::Connection without a Core::EventLoop.
+// FIXME: It's not particularly nice, think of something nicer.
+struct DeferredInvoker {
+    virtual ~DeferredInvoker() = default;
+    virtual void schedule(Function<void()>) = 0;
+};
+
 class ConnectionBase : public Core::Object {
     C_OBJECT_ABSTRACT(ConnectionBase);
 
@@ -34,6 +41,7 @@ public:
     virtual ~ConnectionBase() override = default;
 
     void set_fd_passing_socket(NonnullOwnPtr<Core::Stream::LocalSocket>);
+    void set_deferred_invoker(NonnullOwnPtr<DeferredInvoker>);
 
     bool is_open() const { return m_socket->is_open(); }
     ErrorOr<void> post_message(Message const&);
@@ -41,12 +49,12 @@ public:
     void shutdown();
     virtual void die() { }
 
-protected:
-    explicit ConnectionBase(IPC::Stub&, NonnullOwnPtr<Core::Stream::LocalSocket>, u32 local_endpoint_magic);
-
     Core::Stream::LocalSocket& socket() { return *m_socket; }
     Core::Stream::LocalSocket& fd_passing_socket();
 
+protected:
+    explicit ConnectionBase(IPC::Stub&, NonnullOwnPtr<Core::Stream::LocalSocket>, u32 local_endpoint_magic);
+
     virtual void may_have_become_unresponsive() { }
     virtual void did_become_responsive() { }
     virtual void try_parse_messages(Vector<u8> const& bytes, size_t& index) = 0;
@@ -71,6 +79,8 @@ protected:
     ByteBuffer m_unprocessed_bytes;
 
     u32 m_local_endpoint_magic { 0 };
+
+    NonnullOwnPtr<DeferredInvoker> m_deferred_invoker;
 };
 
 template<typename LocalEndpoint, typename PeerEndpoint>