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// 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> {
USING_FAST_MALLOC(EventLoop);
public:
// A pure virtual class implemented by the `environment settings object`.
// Callbacks exist for steps completed in the microtask completion
// algorithm.
class Delegate : public GarbageCollectedMixin {
public:
virtual void NotifyRejectedPromises() = 0;
};
EventLoop(const EventLoop&) = delete;
EventLoop& operator=(const EventLoop&) = delete;
// Queues |cb| to the backing v8::MicrotaskQueue.
void EnqueueMicrotask(base::OnceClosure cb);
// Runs |cb| at the end of microtask checkpoint.
// The tasks are run when control is returning to C++ from script, after
// executing a script task (e.g. callback, event) or microtasks
// (e.g. promise). This is explicitly needed for Indexed DB transactions
// per spec, but should in general be avoided.
void EnqueueEndOfMicrotaskCheckpointTask(base::OnceClosure cb);
// Run any pending tasks.
void RunEndOfMicrotaskCheckpointTasks();
// Runs pending microtasks until the queue is empty.
void PerformMicrotaskCheckpoint();
// Runs pending microtasks on the isolate's default MicrotaskQueue until it's
// empty.
static void PerformIsolateGlobalMicrotasksCheckpoint(v8::Isolate* isolate);
void AttachScheduler(FrameOrWorkerScheduler*);
void DetachScheduler(FrameOrWorkerScheduler*);
// Returns the MicrotaskQueue instance to be associated to v8::Context. Pass
// it to v8::Context::New().
v8::MicrotaskQueue* microtask_queue() const { return microtask_queue_.get(); }
bool IsSchedulerAttachedForTest(FrameOrWorkerScheduler*);
private:
friend class WTF::RefCounted<EventLoop>;
friend blink::Agent;
EventLoop(Delegate* delegate,
v8::Isolate* isolate,
std::unique_ptr<v8::MicrotaskQueue> microtask_queue);
~EventLoop();
static void RunPendingMicrotask(void* data);
static void RunEndOfCheckpointTasks(v8::Isolate* isolat, void* data);
WeakPersistent<Delegate> delegate_;
raw_ptr<v8::Isolate> isolate_;
bool loop_enabled_ = true;
Deque<base::OnceClosure> pending_microtasks_;
Vector<base::OnceClosure> end_of_checkpoint_tasks_;
std::unique_ptr<v8::MicrotaskQueue> microtask_queue_;
HashSet<FrameOrWorkerScheduler*> schedulers_;
};
} // namespace scheduler
} // namespace blink
#endif // THIRD_PARTY_BLINK_RENDERER_PLATFORM_SCHEDULER_PUBLIC_EVENT_LOOP_H_
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