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