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106 lines
4.3 KiB
C++
106 lines
4.3 KiB
C++
/*
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* Copyright (c) 2018-2023, Andreas Kling <kling@serenityos.org>
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* Copyright (c) 2022, kleines Filmröllchen <filmroellchen@serenityos.org>
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* Copyright (c) 2022, the SerenityOS developers.
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/Forward.h>
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#include <AK/Function.h>
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#include <AK/Noncopyable.h>
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#include <AK/NonnullOwnPtr.h>
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#include <AK/Time.h>
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#include <LibCore/Event.h>
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#include <LibCore/Forward.h>
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namespace Core {
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class EventLoopImplementation;
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class ThreadEventQueue;
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// The event loop enables asynchronous (not parallel or multi-threaded) computing by efficiently handling events from various sources.
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// Event loops are most important for GUI programs, where the various GUI updates and action callbacks run on the EventLoop,
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// as well as services, where asynchronous remote procedure calls of multiple clients are handled.
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// Event loops, through select(), allow programs to "go to sleep" for most of their runtime until some event happens.
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// EventLoop is too expensive to use in realtime scenarios (read: audio) where even the time required by a single select() system call is too large and unpredictable.
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//
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// There is at most one running event loop per thread.
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// Another event loop can be started while another event loop is already running; that new event loop will take over for the other event loop.
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// This is mainly used in LibGUI, where each modal window stacks another event loop until it is closed.
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// However, that means you need to be careful with storing the current event loop, as it might already be gone at the time of use.
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// Event loops currently handle these kinds of events:
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// - Deferred invocations caused by various objects. These are just a generic way of telling the EventLoop to run some function as soon as possible at a later point.
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// - Timers, which repeatedly (or once after a delay) run a function on the EventLoop. Note that timers are not super accurate.
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// - Filesystem notifications, i.e. whenever a file is read from, written to, etc.
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// - POSIX signals, which allow the event loop to act as a signal handler and dispatch those signals in a more user-friendly way.
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// - Fork events, because the child process event loop needs to clear its events and handlers.
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// - Quit events, i.e. the event loop should exit.
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// Any event that the event loop needs to wait on or needs to repeatedly handle is stored in a handle, e.g. s_timers.
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class EventLoop {
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friend struct EventLoopPusher;
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public:
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enum class WaitMode {
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WaitForEvents,
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PollForEvents,
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};
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EventLoop();
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~EventLoop();
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// Pump the event loop until its exit is requested.
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int exec();
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// Process events, generally called by exec() in a loop.
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// This should really only be used for integrating with other event loops.
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// The wait mode determines whether pump() uses select() to wait for the next event.
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size_t pump(WaitMode = WaitMode::WaitForEvents);
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// Pump the event loop until some condition is met.
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void spin_until(Function<bool()>);
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// Post an event to this event loop.
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void post_event(EventReceiver& receiver, NonnullOwnPtr<Event>&&);
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void add_job(NonnullRefPtr<Promise<NonnullRefPtr<EventReceiver>>> job_promise);
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void deferred_invoke(ESCAPING Function<void()>);
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void wake();
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void quit(int);
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void unquit();
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bool was_exit_requested() const;
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// The registration functions act upon the current loop of the current thread.
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static intptr_t register_timer(EventReceiver&, int milliseconds, bool should_reload, TimerShouldFireWhenNotVisible);
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static void unregister_timer(intptr_t timer_id);
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static void register_notifier(Badge<Notifier>, Notifier&);
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static void unregister_notifier(Badge<Notifier>, Notifier&);
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static int register_signal(int signo, ESCAPING Function<void(int)> handler);
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static void unregister_signal(int handler_id);
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// Note: Boost uses Parent/Child/Prepare, but we don't really have anything
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// interesting to do in the parent or before forking.
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enum class ForkEvent {
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Child,
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};
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static void notify_forked(ForkEvent);
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static bool is_running();
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static EventLoop& current();
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EventLoopImplementation& impl() { return *m_impl; }
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private:
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NonnullOwnPtr<EventLoopImplementation> m_impl;
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};
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void deferred_invoke(ESCAPING Function<void()>);
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}
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