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// Copyright 2016 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 <stdint.h>
#include <vector>
#include "base/memory/ref_counted.h"
#include "cc/base/cc_export.h"
namespace cc {
class Task;
// This class provides states to manage life cycle of a task and given below is
// how it is used by TaskGraphWorkQueue to process life cycle of a task.
// Task is in NEW state when it is created. When task is added to
// |ready_to_run_tasks| then its state is changed to SCHEDULED. Task can be
// canceled from NEW state (not yet scheduled to run) or from SCHEDULED state,
// when new ScheduleTasks() is triggered and its state is changed to CANCELED.
// When task is about to run it is added |running_tasks| and its state is
// changed to RUNNING. Once task finishes running, its state is changed to
// FINISHED. Both CANCELED and FINISHED tasks are added to |completed_tasks|.
// ╔═════╗
// +------║ NEW ║------+
// | ╚═════╝ |
// v v
// ┌───────────┐ ╔══════════╗
// │ SCHEDULED │------> ║ CANCELED ║
// └───────────┘ ╚══════════╝
// |
// v
// ┌─────────┐ ╔══════════╗
// │ RUNNING │-------> ║ FINISHED ║
// └─────────┘ ╚══════════╝
class CC_EXPORT TaskState {
bool IsScheduled() const;
bool IsRunning() const;
bool IsFinished() const;
bool IsCanceled() const;
// Functions to change the state of task. These functions should be called
// only from TaskGraphWorkQueue where the life cycle of a task is decided or
// from tests. These functions are not thread-safe. Caller is responsible for
// thread safety.
void Reset(); // Sets state to NEW.
void DidSchedule();
void DidStart();
void DidFinish();
void DidCancel();
friend class Task;
// Let only Task class create the TaskState.
enum class Value : uint16_t { NEW, SCHEDULED, RUNNING, FINISHED, CANCELED };
Value value_;
// A task which can be run by a TaskGraphRunner. To run a Task, it should be
// inserted into a TaskGraph, which can then be scheduled on the
// TaskGraphRunner.
class CC_EXPORT Task : public base::RefCountedThreadSafe<Task> {
typedef std::vector<scoped_refptr<Task>> Vector;
TaskState& state() { return state_; }
// Subclasses should implement this method. RunOnWorkerThread may be called
// on any thread, and subclasses are responsible for locking and thread
// safety.
virtual void RunOnWorkerThread() = 0;
friend class base::RefCountedThreadSafe<Task>;
virtual ~Task();
TaskState state_;
// A task dependency graph describes the order in which to execute a set
// of tasks. Dependencies are represented as edges. Each node is assigned
// a category, a priority and a run count that matches the number of
// dependencies. Priority range from 0 (most favorable scheduling) to UINT16_MAX
// (least favorable). Categories range from 0 to UINT16_MAX. It is up to the
// implementation and its consumer to determine the meaning (if any) of a
// category. A TaskGraphRunner implementation may chose to prioritize certain
// categories over others, regardless of the individual priorities of tasks.
struct CC_EXPORT TaskGraph {
struct Node {
typedef std::vector<Node> Vector;
Node(Task* task,
uint16_t category,
uint16_t priority,
uint32_t dependencies)
: task(task),
dependencies(dependencies) {}
Task* task;
uint16_t category;
uint16_t priority;
uint32_t dependencies;
struct Edge {
typedef std::vector<Edge> Vector;
Edge(const Task* task, Task* dependent)
: task(task), dependent(dependent) {}
const Task* task;
Task* dependent;
TaskGraph(const TaskGraph& other);
void Swap(TaskGraph* other);
void Reset();
Node::Vector nodes;
Edge::Vector edges;
} // namespace cc
#endif // CC_RASTER_TASK_H_