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fe672989a9
Since the existing Promise class is designed with deferred tasks on the main thread only, we need a new class that will ensure we can handle promises that are resolved/rejected off the main thread. This new class ensures that the callbacks are only called on the same thread that the promise is fulfilled from. If the callbacks are not set before the thread tries to fulfill the promise, it will spin until they are so that they will run on that thread.
106 lines
4.2 KiB
C++
106 lines
4.2 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(Object& receiver, NonnullOwnPtr<Event>&&);
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void add_job(NonnullRefPtr<Promise<NonnullRefPtr<Object>>> job_promise);
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void deferred_invoke(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 int register_timer(Object&, int milliseconds, bool should_reload, TimerShouldFireWhenNotVisible);
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static bool unregister_timer(int 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, 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(Function<void()>);
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}
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