// 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_CORE_SCHEDULER_DOM_SCHEDULER_H_
#define THIRD_PARTY_BLINK_RENDERER_CORE_SCHEDULER_DOM_SCHEDULER_H_

#include <atomic>

#include "base/memory/scoped_refptr.h"
#include "third_party/blink/public/common/scheduler/task_attribution_id.h"
#include "third_party/blink/renderer/bindings/core/v8/script_promise.h"
#include "third_party/blink/renderer/core/core_export.h"
#include "third_party/blink/renderer/core/execution_context/execution_context.h"
#include "third_party/blink/renderer/core/execution_context/execution_context_lifecycle_observer.h"
#include "third_party/blink/renderer/core/scheduler/dom_task_signal.h"
#include "third_party/blink/renderer/platform/bindings/script_wrappable.h"
#include "third_party/blink/renderer/platform/heap/collection_support/heap_hash_map.h"
#include "third_party/blink/renderer/platform/heap/garbage_collected.h"
#include "third_party/blink/renderer/platform/scheduler/public/web_scheduling_priority.h"
#include "third_party/blink/renderer/platform/scheduler/public/web_scheduling_queue_type.h"
#include "third_party/blink/renderer/platform/supplementable.h"
#include "third_party/blink/renderer/platform/wtf/allocator/allocator.h"
#include "third_party/blink/renderer/platform/wtf/text/atomic_string.h"

namespace base {
class SingleThreadTaskRunner;
}  // namespace base

namespace v8 {
class Isolate;
}  // namespace v8

namespace blink {
class AbortSignal;
class DOMTaskSignal;
class ExceptionState;
class SchedulerPostTaskOptions;
class SchedulerTaskContext;
class DOMSchedulerTest;
class V8SchedulerPostTaskCallback;
class WebSchedulingTaskQueue;

/*
 * DOMScheduler maintains a set of DOMTaskQueues (wrappers around
 * WebSchedulingTaskQueues) which are used to schedule tasks.
 *
 * There are two types of task queues that the scheduler maintains:
 *  1. Fixed-priority, shared task queues. The priority of these task queues
 *  never changes, which allows them to be shared by any tasks that don't
 *  require variable priority. These are postTask tasks created where one of the
 *  following are passed to postTask:
 *    a) A fixed priority
 *    b) Undefined priority and an AbortSignal or undefined signal
 *  These task queues are created when the DOMScheduler is created and destroyed
 *  when the underlying context is destroyed.
 *
 *  2. Variable-priority, per-signal task queues. The priority of these task
 *  queues can change, and is controlled by the associated TaskController. These
 *  task queues are created the first time a TaskSignal is passed to postTask,
 *  and their lifetime matches that of the associated TaskSignal.
 */
class CORE_EXPORT DOMScheduler : public ScriptWrappable,
                                 public ExecutionContextLifecycleObserver,
                                 public Supplement<ExecutionContext> {
  DEFINE_WRAPPERTYPEINFO();

 public:
  static const char kSupplementName[];

  static DOMScheduler* scheduler(ExecutionContext&);

  explicit DOMScheduler(ExecutionContext*);

  // postTask creates and queues a DOMTask and returns a Promise that will
  // resolve when it completes. The task will be scheduled in the queue
  // corresponding to the priority in the SchedulerPostTaskOptions, or in a
  // queue associated with the given DOMTaskSignal if one is provided. If the
  // underlying context is destroyed, e.g. for detached windows, this will
  // return a rejected promise.
  ScriptPromise<IDLAny> postTask(ScriptState*,
                                 V8SchedulerPostTaskCallback*,
                                 SchedulerPostTaskOptions*,
                                 ExceptionState&);

  ScriptPromise<IDLUndefined> yield(ScriptState*,
                                    ExceptionState&);

  uint32_t asyncData(v8::Isolate*);
  void setAsyncData(v8::Isolate*, uint32_t);

  void ContextDestroyed() override;

  void Trace(Visitor*) const override;

  // Gets the fixed priority TaskSignal for `priority`, creating it if needed.
  DOMTaskSignal* GetFixedPriorityTaskSignal(ScriptState*,
                                            WebSchedulingPriority);

 private:
  // TODO(crbug.com/c/979020): Move DOMTaskQueue out of DOMScheduler.
  friend class DOMTask;              // For DOMTaskQueue
  friend class DOMTaskContinuation;  // For DOMTaskQueue
  friend class DOMSchedulerTest;

  static constexpr size_t kWebSchedulingPriorityCount =
      static_cast<size_t>(WebSchedulingPriority::kLastPriority) + 1;

  static constexpr WebSchedulingPriority kDefaultPriority =
      WebSchedulingPriority::kUserVisiblePriority;

  // DOMTaskQueue is a thin wrapper around WebSchedulingTaskQueue to make it
  // pseudo garbage collected. This allows us to store WebSchedulingTaskQueues
  // in on-heap collections.
  class DOMTaskQueue final : public GarbageCollected<DOMTaskQueue> {
   public:
    DOMTaskQueue(std::unique_ptr<WebSchedulingTaskQueue> task_queue,
                 WebSchedulingPriority priority);
    ~DOMTaskQueue();

    void Trace(Visitor* visitor) const;

    base::SingleThreadTaskRunner& GetTaskRunner() { return *task_runner_; }

    WebSchedulingPriority GetPriority() const { return priority_; }

    void SetPriorityChangeHandle(DOMTaskSignal::AlgorithmHandle* handle) {
      priority_change_handle_ = handle;
    }

    void SetPriority(WebSchedulingPriority);

   private:
    std::unique_ptr<WebSchedulingTaskQueue> web_scheduling_task_queue_;
    scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
    WebSchedulingPriority priority_;
    Member<DOMTaskSignal::AlgorithmHandle> priority_change_handle_;
  };

  using FixedPriorityTaskQueueVector =
      HeapVector<Member<DOMTaskQueue>, kWebSchedulingPriorityCount>;
  using SignalToTaskQueueMap =
      HeapHashMap<WeakMember<DOMTaskSignal>, WeakMember<DOMTaskQueue>>;

  static uint64_t NextIdForTracing() {
    static std::atomic<uint64_t> next_id(0);
    return next_id.fetch_add(1, std::memory_order_relaxed);
  }

  // Creates and enqueues one fixed priority task queue for each priority with
  // the given queue type in the given vector.
  void CreateFixedPriorityTaskQueues(ExecutionContext*,
                                     WebSchedulingQueueType,
                                     FixedPriorityTaskQueueVector&);

  // Creates and initializes a new dynamic priority WebSchedulingTaskQueue for
  // the given task signal and `WebSchedulingQueueType`.
  DOMTaskQueue* CreateDynamicPriorityTaskQueue(DOMTaskSignal*,
                                               WebSchedulingQueueType);

  // Callback for when the signal signals priority change.
  void OnPriorityChange(DOMTaskSignal*, DOMTaskQueue*);

  // Gets the task queue used to schedule tasks or continuations with the given
  // signal and type, creating it if needed.
  DOMTaskQueue* GetTaskQueue(DOMTaskSignal*, WebSchedulingQueueType);

  // Returns the `SchedulerTaskContext` to use for scheduler.yield(). Records
  // UseCounters for non-trivial inheritance, both for the case where the
  // context is used, and the cross-frame case where it's ignored.
  SchedulerTaskContext* GetSchedulerTaskContextForYield();

  // `fixed_priority_task_queues_` is initialized with one entry per priority,
  // indexed by priority. This will be empty when the window is detached.
  FixedPriorityTaskQueueVector fixed_priority_task_queues_;

  // Same as `fixed_priority_task_queues_` but for continuation queues.
  FixedPriorityTaskQueueVector fixed_priority_continuation_queues_;

  // Fixed priority task signals, indexed by priority, used for inheriting a
  // fixed priority.
  HeapVector<Member<DOMTaskSignal>, kWebSchedulingPriorityCount>
      fixed_priority_task_signals_;

  // `signal_to_task_queue_map_` tracks the associated task queue for task
  // signals the scheduler knows about that are still alive, with each signal
  // mapping to the corresponding dynamic priority DOMTaskQueue. Mappings are
  // removed automatically when either the corresponding signal or DOMTaskQueue
  // is garbage collected. This will be empty when the window is detached.
  SignalToTaskQueueMap signal_to_task_queue_map_;

  // Same as `signal_to_task_queue_map_` but for continuation queues.
  SignalToTaskQueueMap signal_to_continuation_queue_map_;
};

}  // namespace blink

#endif  // THIRD_PARTY_BLINK_RENDERER_CORE_SCHEDULER_DOM_SCHEDULER_H_