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      1 // Copyright 2017 the V8 project 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 V8_LIBPLATFORM_DEFAULT_FOREGROUND_TASK_RUNNER_H_
      6 #define V8_LIBPLATFORM_DEFAULT_FOREGROUND_TASK_RUNNER_H_
      7 
      8 #include <queue>
      9 
     10 #include "include/libplatform/libplatform.h"
     11 #include "include/v8-platform.h"
     12 #include "src/base/platform/condition-variable.h"
     13 #include "src/base/platform/mutex.h"
     14 
     15 namespace v8 {
     16 namespace platform {
     17 
     18 class V8_PLATFORM_EXPORT DefaultForegroundTaskRunner
     19     : public NON_EXPORTED_BASE(TaskRunner) {
     20  public:
     21   using TimeFunction = double (*)();
     22 
     23   DefaultForegroundTaskRunner(IdleTaskSupport idle_task_support,
     24                               TimeFunction time_function);
     25 
     26   void Terminate();
     27 
     28   std::unique_ptr<Task> PopTaskFromQueue(MessageLoopBehavior wait_for_work);
     29 
     30   std::unique_ptr<IdleTask> PopTaskFromIdleQueue();
     31 
     32   void WaitForTaskLocked(const base::LockGuard<base::Mutex>&);
     33 
     34   double MonotonicallyIncreasingTime();
     35 
     36   // v8::TaskRunner implementation.
     37   void PostTask(std::unique_ptr<Task> task) override;
     38 
     39   void PostDelayedTask(std::unique_ptr<Task> task,
     40                        double delay_in_seconds) override;
     41 
     42   void PostIdleTask(std::unique_ptr<IdleTask> task) override;
     43 
     44   bool IdleTasksEnabled() override;
     45 
     46  private:
     47   // The same as PostTask, but the lock is already held by the caller. The
     48   // {guard} parameter should make sure that the caller is holding the lock.
     49   void PostTaskLocked(std::unique_ptr<Task> task,
     50                       const base::LockGuard<base::Mutex>&);
     51 
     52   // A caller of this function has to hold {lock_}. The {guard} parameter should
     53   // make sure that the caller is holding the lock.
     54   std::unique_ptr<Task> PopTaskFromDelayedQueueLocked(
     55       const base::LockGuard<base::Mutex>&);
     56 
     57   bool terminated_ = false;
     58   base::Mutex lock_;
     59   base::ConditionVariable event_loop_control_;
     60   std::queue<std::unique_ptr<Task>> task_queue_;
     61   IdleTaskSupport idle_task_support_;
     62   std::queue<std::unique_ptr<IdleTask>> idle_task_queue_;
     63 
     64   // Some helper constructs for the {delayed_task_queue_}.
     65   using DelayedEntry = std::pair<double, std::unique_ptr<Task>>;
     66   // Define a comparison operator for the delayed_task_queue_ to make sure
     67   // that the unique_ptr in the DelayedEntry is not accessed in the priority
     68   // queue. This is necessary because we have to reset the unique_ptr when we
     69   // remove a DelayedEntry from the priority queue.
     70   struct DelayedEntryCompare {
     71     bool operator()(DelayedEntry& left, DelayedEntry& right) {
     72       return left.first > right.first;
     73     }
     74   };
     75   std::priority_queue<DelayedEntry, std::vector<DelayedEntry>,
     76                       DelayedEntryCompare>
     77       delayed_task_queue_;
     78 
     79   TimeFunction time_function_;
     80 };
     81 
     82 }  // namespace platform
     83 }  // namespace v8
     84 #endif  // V8_LIBPLATFORM_DEFAULT_FOREGROUND_TASK_RUNNER_H_
     85