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// Copyright 2018 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/callback.h"
#include "base/pending_task.h"
#include "base/time/time.h"
namespace base {
// A source of tasks to be executed sequentially. Unless specified otherwise,
// methods below are not thread-safe (must be called from the executing
// sequence).
// TODO(scheduler-dev): Coalesce with
// base::sequence_manager::SequencedTaskSource.
class SequencedTaskSource {
class Observer {
virtual ~Observer() = default;
// Notifies this Observer that |task| is about to be enqueued in the
// SequencedTaskSource it observes.
// WillQueueTask() may be invoked from any thread.
virtual void WillQueueTask(PendingTask* task) = 0;
// Notifies this Observer that a task was enqueued in the
// SequencedTaskSource it observes. |was_empty| is true if the task source
// was empty (i.e. |!HasTasks()|) before this task was posted.
// DidQueueTask() may be invoked from any thread.
virtual void DidQueueTask(bool was_empty) = 0;
virtual ~SequencedTaskSource() = default;
// Take a next task to run from a sequence. Must only be called if
// HasTasks() returns true.
virtual PendingTask TakeTask() = 0;
// Returns true if this SequencedTaskSource will return a task from the next
// TakeTask() call.
virtual bool HasTasks() = 0;
// Injects |task| at the end of this SequencedTaskSource (such that it will be
// the last task returned by TakeTask() if no other task are posted after this
// point). TODO(gab): This is only required to support clearing tasks on
// shutdown, maybe leaking tasks on shutdown is a better alternative.
virtual void InjectTask(OnceClosure task) = 0;
} // namespace base