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// Copyright 2013 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.
#ifndef BASE_MESSAGE_LOOP_INCOMING_TASK_QUEUE_H_
#define BASE_MESSAGE_LOOP_INCOMING_TASK_QUEUE_H_
#include "base/base_export.h"
#include "base/callback.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/pending_task.h"
#include "base/synchronization/lock.h"
#include "base/synchronization/read_write_lock.h"
#include "base/time/time.h"
namespace base {
class MessageLoop;
namespace internal {
// Implements a queue of tasks posted to the message loop running on the current
// thread. This class takes care of synchronizing posting tasks from different
// threads and together with MessageLoop ensures clean shutdown.
class BASE_EXPORT IncomingTaskQueue
: public RefCountedThreadSafe<IncomingTaskQueue> {
public:
explicit IncomingTaskQueue(MessageLoop* message_loop);
// Appends a task to the incoming queue. Posting of all tasks is routed though
// AddToIncomingQueue() or TryAddToIncomingQueue() to make sure that posting
// task is properly synchronized between different threads.
//
// Returns true if the task was successfully added to the queue, otherwise
// returns false. In all cases, the ownership of |task| is transferred to the
// called method.
bool AddToIncomingQueue(const tracked_objects::Location& from_here,
OnceClosure task,
TimeDelta delay,
bool nestable);
// Returns true if the queue contains tasks that require higher than default
// timer resolution. Currently only needed for Windows.
bool HasHighResolutionTasks();
// Returns true if the message loop is "idle". Provided for testing.
bool IsIdleForTesting();
// Loads tasks from the |incoming_queue_| into |*work_queue|. Must be called
// from the thread that is running the loop. Returns the number of tasks that
// require high resolution timers.
int ReloadWorkQueue(TaskQueue* work_queue);
// Disconnects |this| from the parent message loop.
void WillDestroyCurrentMessageLoop();
// This should be called when the message loop becomes ready for
// scheduling work.
void StartScheduling();
private:
friend class RefCountedThreadSafe<IncomingTaskQueue>;
virtual ~IncomingTaskQueue();
// Adds a task to |incoming_queue_|. The caller retains ownership of
// |pending_task|, but this function will reset the value of
// |pending_task->task|. This is needed to ensure that the posting call stack
// does not retain |pending_task->task| beyond this function call.
bool PostPendingTask(PendingTask* pending_task);
// Wakes up the message loop and schedules work.
void ScheduleWork();
// Number of tasks that require high resolution timing. This value is kept
// so that ReloadWorkQueue() completes in constant time.
int high_res_task_count_;
// The lock that protects access to the members of this class, except
// |message_loop_|.
base::Lock incoming_queue_lock_;
// Lock that protects |message_loop_| to prevent it from being deleted while a
// task is being posted.
base::subtle::ReadWriteLock message_loop_lock_;
// An incoming queue of tasks that are acquired under a mutex for processing
// on this instance's thread. These tasks have not yet been been pushed to
// |message_loop_|.
TaskQueue incoming_queue_;
// Points to the message loop that owns |this|.
MessageLoop* message_loop_;
// The next sequence number to use for delayed tasks.
int next_sequence_num_;
// True if our message loop has already been scheduled and does not need to be
// scheduled again until an empty reload occurs.
bool message_loop_scheduled_;
// True if we always need to call ScheduleWork when receiving a new task, even
// if the incoming queue was not empty.
const bool always_schedule_work_;
// False until StartScheduling() is called.
bool is_ready_for_scheduling_;
DISALLOW_COPY_AND_ASSIGN(IncomingTaskQueue);
};
} // namespace internal
} // namespace base
#endif // BASE_MESSAGE_LOOP_INCOMING_TASK_QUEUE_H_
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