TaskGraphRunner refactor

cc/raster/task_graph_work_queue.h

+// Copyright 2014 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 CC_RASTER_TASK_GRAPH_WORK_QUEUE_H_
+#define CC_RASTER_TASK_GRAPH_WORK_QUEUE_H_
+
+#include <map>
+#include <vector>
+
+#include "cc/base/cc_export.h"
+#include "cc/raster/task_graph_runner.h"
+
+namespace cc {
+
+// Implements a queue of incoming TaskGraph work. Designed for use by
+// implementations of TaskGraphRunner. Not thread safe, so the caller is
+// responsible for all necessary locking.
+class CC_EXPORT TaskGraphWorkQueue {
+ public:
+  struct TaskNamespace;
+
+  struct PrioritizedTask {
+    typedef std::vector<PrioritizedTask> Vector;
+
+    PrioritizedTask(Task* task, TaskNamespace* task_namespace, size_t priority)
+        : task(task), task_namespace(task_namespace), priority(priority) {}
+
+    Task* task;
+    TaskNamespace* task_namespace;
+    size_t priority;
+  };
+
+  // Helper classes and static methods used by dependent classes.
+  struct TaskNamespace {
+    typedef std::vector<TaskNamespace*> Vector;
+
+    TaskNamespace();
+    ~TaskNamespace();
+
+    // Current task graph.
+    TaskGraph graph;
+
+    // Ordered set of tasks that are ready to run.
+    PrioritizedTask::Vector ready_to_run_tasks;
+
+    // Completed tasks not yet collected by origin thread.
+    Task::Vector completed_tasks;
+
+    // This set contains all currently running tasks.
+    Task::Vector running_tasks;
+  };
+
+  TaskGraphWorkQueue();
+  virtual ~TaskGraphWorkQueue();
+
+  // Gets a NamespaceToken which is guaranteed to be unique within this
+  // TaskGraphWorkQueue.
+  NamespaceToken GetNamespaceToken();
+
+  // Updates a TaskNamespace with a new TaskGraph to run. This cancels any
+  // previous tasks in the graph being replaced.
+  void ScheduleTasks(NamespaceToken token, TaskGraph* graph);
+
+  // Returns the next task to run paired with its namespace.
+  PrioritizedTask GetNextTaskToRun();
+
+  // Marks a task as completed, adding it to its namespace's list of completed
+  // tasks and updating the list of |ready_to_run_namespaces|.
+  void CompleteTask(const PrioritizedTask& completed_task);
+
+  // Helper which populates a vector of completed tasks from the provided
+  // namespace.
+  void CollectCompletedTasks(NamespaceToken token,
+                             Task::Vector* completed_tasks);
+
+  // Helper which returns the raw TaskNamespace* for the given token. Used to
+  // allow callers to re-use a TaskNamespace*, reducing the number of lookups
+  // needed.
+  TaskNamespace* GetNamespaceForToken(NamespaceToken token) {
+    auto it = namespaces_.find(token);
+    if (it == namespaces_.end())
+      return nullptr;
+    return &it->second;
+  }
+
+  static bool HasFinishedRunningTasksInNamespace(
+      const TaskNamespace* task_namespace) {
+    return task_namespace->running_tasks.empty() &&
+           task_namespace->ready_to_run_tasks.empty();
+  }
+
+  bool HasReadyToRunTasks() const { return !ready_to_run_namespaces_.empty(); }
+
+  bool HasAnyNamespaces() const { return !namespaces_.empty(); }
+
+  bool HasFinishedRunningTasksInAllNamespaces() {
+    return std::find_if(
+               namespaces_.begin(), namespaces_.end(),
+               [](const TaskNamespaceMap::value_type& entry) {
+                 return !HasFinishedRunningTasksInNamespace(&entry.second);
+               }) == namespaces_.end();
+  }
+
+  // Helper function which ensures that graph dependencies were correctly
+  // configured.
+  static bool DependencyMismatch(const TaskGraph* graph);
+
+ private:
+  // Helper class used to provide NamespaceToken comparison to TaskNamespaceMap.
+  class CompareToken {
+   public:
+    bool operator()(const NamespaceToken& lhs,
+                    const NamespaceToken& rhs) const {
+      return lhs.id_ < rhs.id_;
+    }
+  };
+
+  static bool CompareTaskPriority(const PrioritizedTask& a,
+                                  const PrioritizedTask& b) {
+    // In this system, numerically lower priority is run first.
+    return a.priority > b.priority;
+  }
+
+  static bool CompareTaskNamespacePriority(const TaskNamespace* a,
+                                           const TaskNamespace* b) {
+    DCHECK(!a->ready_to_run_tasks.empty());
+    DCHECK(!b->ready_to_run_tasks.empty());
+
+    // Compare based on task priority of the ready_to_run_tasks heap .front()
+    // will hold the max element of the heap, except after pop_heap, when max
+    // element is moved to .back().
+    return CompareTaskPriority(a->ready_to_run_tasks.front(),
+                               b->ready_to_run_tasks.front());
+  }
+
+  using TaskNamespaceMap =
+      std::map<NamespaceToken, TaskNamespace, CompareToken>;
+
+  TaskNamespaceMap namespaces_;
+  TaskNamespace::Vector ready_to_run_namespaces_;
+
+  // Provides a unique id to each NamespaceToken.
+  int next_namespace_id_;
+};
+
+}  // namespace cc
+
+#endif  // CC_RASTER_TASK_GRAPH_WORK_QUEUE_H_