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// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/base_export.h"
#include "base/task/sequence_manager/enqueue_order.h"
#include "base/task/sequence_manager/intrusive_heap.h"
#include "base/task/sequence_manager/sequenced_task_source.h"
#include "base/task/sequence_manager/task_queue_impl.h"
#include "base/trace_event/trace_event.h"
#include "base/trace_event/trace_event_argument.h"
namespace base {
namespace sequence_manager {
namespace internal {
class WorkQueueSets;
// This class keeps track of immediate and delayed tasks which are due to run
// now. It interfaces deeply with WorkQueueSets which keeps track of which queue
// (with a given priority) contains the oldest task.
// If a fence is inserted, WorkQueue behaves normally up until
// TakeTaskFromWorkQueue reaches or exceeds the fence. At that point it the
// API subset used by WorkQueueSets pretends the WorkQueue is empty until the
// fence is removed. This functionality is a primitive intended for use by
// throttling mechanisms.
class BASE_EXPORT WorkQueue {
using QueueType = internal::TaskQueueImpl::WorkQueueType;
// Note |task_queue| can be null if queue_type is kNonNestable.
WorkQueue(TaskQueueImpl* task_queue, const char* name, QueueType queue_type);
// Associates this work queue with the given work queue sets. This must be
// called before any tasks can be inserted into this work queue.
void AssignToWorkQueueSets(WorkQueueSets* work_queue_sets);
// Assigns the current set index.
void AssignSetIndex(size_t work_queue_set_index);
void AsValueInto(TimeTicks now, trace_event::TracedValue* state) const;
// Returns true if the |tasks_| is empty. This method ignores any fences.
bool Empty() const { return tasks_.empty(); }
// If the |tasks_| isn't empty and a fence hasn't been reached,
// |enqueue_order| gets set to the enqueue order of the front task and the
// function returns true. Otherwise the function returns false.
bool GetFrontTaskEnqueueOrder(EnqueueOrder* enqueue_order) const;
// Returns the first task in this queue or null if the queue is empty. This
// method ignores any fences.
const Task* GetFrontTask() const;
// Returns the last task in this queue or null if the queue is empty. This
// method ignores any fences.
const Task* GetBackTask() const;
// Pushes the task onto the |tasks_| and if a fence hasn't been reached
// it informs the WorkQueueSets if the head changed.
void Push(Task task);
// Pushes the task onto the front of the |tasks_| and if it's before any
// fence it informs the WorkQueueSets the head changed. Use with caution this
// API can easily lead to task starvation if misused.
void PushNonNestableTaskToFront(Task task);
// Reloads the empty |tasks_| with
// |task_queue_->TakeImmediateIncomingQueue| and if a fence hasn't been
// reached it informs the WorkQueueSets if the head changed.
void ReloadEmptyImmediateQueue();
size_t Size() const { return tasks_.size(); }
size_t Capacity() const { return tasks_.capacity(); }
// Pulls a task off the |tasks_| and informs the WorkQueueSets. If the
// task removed had an enqueue order >= the current fence then WorkQueue
// pretends to be empty as far as the WorkQueueSets is concerned.
Task TakeTaskFromWorkQueue();
// Removes all canceled tasks from the head of the list. Returns true if any
// tasks were removed.
bool RemoveAllCanceledTasksFromFront();
const char* name() const { return name_; }
TaskQueueImpl* task_queue() const { return task_queue_; }
WorkQueueSets* work_queue_sets() const { return work_queue_sets_; }
size_t work_queue_set_index() const { return work_queue_set_index_; }
HeapHandle heap_handle() const { return heap_handle_; }
void set_heap_handle(HeapHandle handle) { heap_handle_ = handle; }
QueueType queue_type() const { return queue_type_; }
// Returns true if the front task in this queue has an older enqueue order
// than the front task of |other_queue|. Both queue are assumed to be
// non-empty. This method ignores any fences.
bool ShouldRunBefore(const WorkQueue* other_queue) const;
// Submit a fence. When TakeTaskFromWorkQueue encounters a task whose
// enqueue_order is >= |fence| then the WorkQueue will start pretending to be.
// empty.
// Inserting a fence may supersede a previous one and unblock some tasks.
// Returns true if any tasks where unblocked, returns false otherwise.
bool InsertFence(EnqueueOrder fence);
// Submit a fence without triggering a WorkQueueSets notification.
// Caller must ensure that WorkQueueSets are properly updated.
// This method should not be called when a fence is already present.
void InsertFenceSilently(EnqueueOrder fence);
// Removes any fences that where added and if WorkQueue was pretending to be
// empty, then the real value is reported to WorkQueueSets. Returns true if
// any tasks where unblocked.
bool RemoveFence();
// Returns true if any tasks are blocked by the fence. Returns true if the
// queue is empty and fence has been set (i.e. future tasks would be blocked).
// Otherwise returns false.
bool BlockedByFence() const;
// Test support function. This should not be used in production code.
void PopTaskForTesting();
// Shrinks |tasks_| if it's wasting memory.
void MaybeShrinkQueue();
bool InsertFenceImpl(EnqueueOrder fence);
TaskQueueImpl::TaskDeque tasks_;
WorkQueueSets* work_queue_sets_ = nullptr; // NOT OWNED.
TaskQueueImpl* const task_queue_; // NOT OWNED.
size_t work_queue_set_index_ = 0;
HeapHandle heap_handle_;
const char* const name_;
EnqueueOrder fence_;
const QueueType queue_type_;
} // namespace internal
} // namespace sequence_manager
} // namespace base