1 // Copyright 2015 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #ifndef BASE_TASK_SEQUENCE_MANAGER_WORK_QUEUE_H_
6 #define BASE_TASK_SEQUENCE_MANAGER_WORK_QUEUE_H_
7 
8 #include "base/base_export.h"
9 #include "base/task/sequence_manager/enqueue_order.h"
10 #include "base/task/sequence_manager/intrusive_heap.h"
11 #include "base/task/sequence_manager/sequenced_task_source.h"
12 #include "base/task/sequence_manager/task_queue_impl.h"
13 #include "base/trace_event/trace_event.h"
14 #include "base/trace_event/trace_event_argument.h"
15 
16 namespace base {
17 namespace sequence_manager {
18 namespace internal {
19 
20 class WorkQueueSets;
21 
22 // This class keeps track of immediate and delayed tasks which are due to run
23 // now. It interfaces deeply with WorkQueueSets which keeps track of which queue
24 // (with a given priority) contains the oldest task.
25 //
26 // If a fence is inserted, WorkQueue behaves normally up until
27 // TakeTaskFromWorkQueue reaches or exceeds the fence.  At that point it the
28 // API subset used by WorkQueueSets pretends the WorkQueue is empty until the
29 // fence is removed.  This functionality is a primitive intended for use by
30 // throttling mechanisms.
31 class BASE_EXPORT WorkQueue {
32  public:
33   using QueueType = internal::TaskQueueImpl::WorkQueueType;
34 
35   // Note |task_queue| can be null if queue_type is kNonNestable.
36   WorkQueue(TaskQueueImpl* task_queue, const char* name, QueueType queue_type);
37   ~WorkQueue();
38 
39   // Associates this work queue with the given work queue sets. This must be
40   // called before any tasks can be inserted into this work queue.
41   void AssignToWorkQueueSets(WorkQueueSets* work_queue_sets);
42 
43   // Assigns the current set index.
44   void AssignSetIndex(size_t work_queue_set_index);
45 
46   void AsValueInto(TimeTicks now, trace_event::TracedValue* state) const;
47 
48   // Returns true if the |tasks_| is empty. This method ignores any fences.
Empty()49   bool Empty() const { return tasks_.empty(); }
50 
51   // If the |tasks_| isn't empty and a fence hasn't been reached,
52   // |enqueue_order| gets set to the enqueue order of the front task and the
53   // function returns true. Otherwise the function returns false.
54   bool GetFrontTaskEnqueueOrder(EnqueueOrder* enqueue_order) const;
55 
56   // Returns the first task in this queue or null if the queue is empty. This
57   // method ignores any fences.
58   const TaskQueueImpl::Task* GetFrontTask() const;
59 
60   // Returns the last task in this queue or null if the queue is empty. This
61   // method ignores any fences.
62   const TaskQueueImpl::Task* GetBackTask() const;
63 
64   // Pushes the task onto the |tasks_| and if a fence hasn't been reached
65   // it informs the WorkQueueSets if the head changed.
66   void Push(TaskQueueImpl::Task task);
67 
68   // Pushes the task onto the front of the |tasks_| and if it's before any
69   // fence it informs the WorkQueueSets the head changed. Use with caution this
70   // API can easily lead to task starvation if misused.
71   void PushNonNestableTaskToFront(TaskQueueImpl::Task task);
72 
73   // Reloads the empty |tasks_| with
74   // |task_queue_->TakeImmediateIncomingQueue| and if a fence hasn't been
75   // reached it informs the WorkQueueSets if the head changed.
76   void ReloadEmptyImmediateQueue();
77 
Size()78   size_t Size() const { return tasks_.size(); }
79 
80   // Pulls a task off the |tasks_| and informs the WorkQueueSets.  If the
81   // task removed had an enqueue order >= the current fence then WorkQueue
82   // pretends to be empty as far as the WorkQueueSets is concerned.
83   TaskQueueImpl::Task TakeTaskFromWorkQueue();
84 
85   // Removes all canceled tasks from the head of the list. Returns true if any
86   // tasks were removed.
87   bool RemoveAllCanceledTasksFromFront();
88 
name()89   const char* name() const { return name_; }
90 
task_queue()91   TaskQueueImpl* task_queue() const { return task_queue_; }
92 
work_queue_sets()93   WorkQueueSets* work_queue_sets() const { return work_queue_sets_; }
94 
work_queue_set_index()95   size_t work_queue_set_index() const { return work_queue_set_index_; }
96 
heap_handle()97   HeapHandle heap_handle() const { return heap_handle_; }
98 
set_heap_handle(HeapHandle handle)99   void set_heap_handle(HeapHandle handle) { heap_handle_ = handle; }
100 
queue_type()101   QueueType queue_type() const { return queue_type_; }
102 
103   // Returns true if the front task in this queue has an older enqueue order
104   // than the front task of |other_queue|. Both queue are assumed to be
105   // non-empty. This method ignores any fences.
106   bool ShouldRunBefore(const WorkQueue* other_queue) const;
107 
108   // Submit a fence. When TakeTaskFromWorkQueue encounters a task whose
109   // enqueue_order is >= |fence| then the WorkQueue will start pretending to be.
110   // empty.
111   // Inserting a fence may supersede a previous one and unblock some tasks.
112   // Returns true if any tasks where unblocked, returns false otherwise.
113   bool InsertFence(EnqueueOrder fence);
114 
115   // Submit a fence without triggering a WorkQueueSets notification.
116   // Caller must ensure that WorkQueueSets are properly updated.
117   // This method should not be called when a fence is already present.
118   void InsertFenceSilently(EnqueueOrder fence);
119 
120   // Removes any fences that where added and if WorkQueue was pretending to be
121   // empty, then the real value is reported to WorkQueueSets. Returns true if
122   // any tasks where unblocked.
123   bool RemoveFence();
124 
125   // Returns true if any tasks are blocked by the fence. Returns true if the
126   // queue is empty and fence has been set (i.e. future tasks would be blocked).
127   // Otherwise returns false.
128   bool BlockedByFence() const;
129 
130   // Test support function. This should not be used in production code.
131   void PopTaskForTesting();
132 
133  private:
134   bool InsertFenceImpl(EnqueueOrder fence);
135 
136   TaskQueueImpl::TaskDeque tasks_;
137   WorkQueueSets* work_queue_sets_ = nullptr;  // NOT OWNED.
138   TaskQueueImpl* const task_queue_;           // NOT OWNED.
139   size_t work_queue_set_index_ = 0;
140   HeapHandle heap_handle_;
141   const char* const name_;
142   EnqueueOrder fence_;
143   const QueueType queue_type_;
144 
145   DISALLOW_COPY_AND_ASSIGN(WorkQueue);
146 };
147 
148 }  // namespace internal
149 }  // namespace sequence_manager
150 }  // namespace base
151 
152 #endif  // BASE_TASK_SEQUENCE_MANAGER_WORK_QUEUE_H_
153