chromium/third_party/blink/renderer/platform/scheduler/public/event_loop.h

// Copyright 2019 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_SCHEDULER_PUBLIC_EVENT_LOOP_H_
#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_SCHEDULER_PUBLIC_EVENT_LOOP_H_

#include <memory>

#include "base/functional/callback.h"
#include "base/memory/raw_ptr.h"
#include "base/memory/scoped_refptr.h"
#include "third_party/blink/renderer/platform/heap/garbage_collected.h"
#include "third_party/blink/renderer/platform/heap/persistent.h"
#include "third_party/blink/renderer/platform/platform_export.h"
#include "third_party/blink/renderer/platform/wtf/deque.h"
#include "third_party/blink/renderer/platform/wtf/hash_set.h"
#include "third_party/blink/renderer/platform/wtf/ref_counted.h"

namespace v8 {
class Isolate;
class MicrotaskQueue;
}  // namespace v8

namespace blink {

class Agent;
class FrameOrWorkerScheduler;

namespace scheduler {

// Represents an event loop. The instance is held by ExecutionContexts.
// https://html.spec.whatwg.org/C#event-loop
//
// Browsing contexts must share the same EventLoop if they have a chance to
// access each other synchronously.
// That is:
//  - Two Documents must share the same EventLoop if they are scriptable with
//    each other.
//  - Workers and Worklets can have its own EventLoop, as no other browsing
//    context can access it synchronously.
//
// The specification says an event loop has (non-micro) task queues. However,
// we process regular tasks in a different granularity; in our implementation,
// a frame has task queues. This is an intentional violation of the
// specification.
//
// Therefore, currently, EventLoop is a unit that just manages a microtask
// queue: <https://html.spec.whatwg.org/C#microtask-queue>
//
// Microtasks queued during a task are executed at the end of the task or
// after a user script is executed (for the exact timings, refer to the
// specification). Some web platform features require this functionality.
//
// Implementation notes: Originally, microtask queues were created in V8
// for JavaScript promises. V8 allocates a default microtask queue per isolate,
// and it still uses the default queue, not the one in this EventLoop class.
// This is not correct in terms of the standards conformance, and we'll
// eventually merge the queues so both Blink and V8 can use the microtask queue
// allocated in the correct granularity.
class PLATFORM_EXPORT EventLoop final : public WTF::RefCounted<EventLoop> { … };

}  // namespace scheduler
}  // namespace blink

#endif  // THIRD_PARTY_BLINK_RENDERER_PLATFORM_SCHEDULER_PUBLIC_EVENT_LOOP_H_