Re-land: cc: Remove WorkerPool class and instead use TaskGraphRunner directly.

cc/resources/task_graph_runner.h

Index: cc/resources/task_graph_runner.h
diff --git a/cc/resources/task_graph_runner.h b/cc/resources/task_graph_runner.h
new file mode 100755
index 0000000000000000000000000000000000000000..884a517ef721348bba09cc0f345b32c0fa1d8ae9
--- /dev/null
+++ b/cc/resources/task_graph_runner.h
@@ -0,0 +1,236 @@
+// 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 CC_RESOURCES_TASK_GRAPH_RUNNER_H_
+#define CC_RESOURCES_TASK_GRAPH_RUNNER_H_
+
+#include <queue>
+#include <string>
+#include <vector>
+
+#include "base/containers/scoped_ptr_hash_map.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/synchronization/condition_variable.h"
+#include "base/threading/simple_thread.h"
+#include "cc/base/cc_export.h"
+#include "cc/base/scoped_ptr_deque.h"
+
+namespace cc {
+namespace internal {
+
+class CC_EXPORT Task : public base::RefCountedThreadSafe<Task> {
+ public:
+  typedef std::vector<scoped_refptr<Task> > Vector;
+
+  virtual void RunOnWorkerThread(unsigned thread_index) = 0;
+
+  void DidSchedule();
+  void WillRun();
+  void DidRun();
+
+  bool HasFinishedRunning() const;
+
+ protected:
+  friend class base::RefCountedThreadSafe<Task>;
+
+  Task();
+  virtual ~Task();
+
+  bool did_schedule_;
+  bool did_run_;
+};
+
+}  // namespace internal
+}  // namespace cc
+
+#if defined(COMPILER_GCC)
+namespace BASE_HASH_NAMESPACE {
+template <> struct hash<cc::internal::Task*> {
+  size_t operator()(cc::internal::Task* ptr) const {
+    return hash<size_t>()(reinterpret_cast<size_t>(ptr));
+  }
+};
+}  // namespace BASE_HASH_NAMESPACE
+#endif  // COMPILER
+
+namespace cc {
+namespace internal {
+
+// Dependencies are represented by edges in a task graph. A graph node
+// store edges as a vector of dependents. Each graph node is assigned
+// a priority and a run count that matches the number of dependencies.
+class CC_EXPORT GraphNode {
+ public:
+  typedef std::vector<GraphNode*> Vector;
+  typedef base::ScopedPtrHashMap<Task*, GraphNode> Map;
+
+  GraphNode(Task* task, unsigned priority);
+  ~GraphNode();
+
+  Task* task() { return task_; }
+
+  void add_dependent(GraphNode* dependent) {
+    DCHECK(dependent);
+    dependents_.push_back(dependent);
+  }
+  const Vector& dependents() const { return dependents_; }
+
+  unsigned priority() const { return priority_; }
+
+  unsigned num_dependencies() const { return num_dependencies_; }
+  void add_dependency() { ++num_dependencies_; }
+  void remove_dependency() {
+    DCHECK(num_dependencies_);
+    --num_dependencies_;
+  }
+
+ private:
+  Task* task_;
+  Vector dependents_;
+  unsigned priority_;
+  unsigned num_dependencies_;
+
+  DISALLOW_COPY_AND_ASSIGN(GraphNode);
+};
+
+class TaskGraphRunner;
+
+// Opaque identifier that defines a namespace of tasks.
+class CC_EXPORT NamespaceToken {
+ public:
+  NamespaceToken() : id_(0) {}
+  ~NamespaceToken() {}
+
+  bool IsValid() const {
+    return id_ != 0;
+  }
+
+ private:
+  friend class TaskGraphRunner;
+
+  explicit NamespaceToken(int id) : id_(id) {}
+
+  int id_;
+};
+
+// A worker thread pool that runs tasks provided by task graph. Destructor
+// might block and should not be used on a thread that needs to be responsive.
+class CC_EXPORT TaskGraphRunner : public base::DelegateSimpleThread::Delegate {
+ public:
+  typedef GraphNode::Map TaskGraph;
+
+  TaskGraphRunner(size_t num_threads, const std::string& thread_name_prefix);
+  virtual ~TaskGraphRunner();
+
+  // Returns a unique token that can be used to pass a task graph to
+  // SetTaskGraph(). Valid tokens are always nonzero.
+  NamespaceToken GetNamespaceToken();
+
+  // Schedule running of tasks in |graph|. Tasks previously scheduled but
+  // no longer needed will be canceled unless already running. Canceled
+  // tasks are moved to |completed_tasks| without being run. The result
+  // is that once scheduled, a task is guaranteed to end up in the
+  // |completed_tasks| queue even if it later get canceled by another
+  // call to SetTaskGraph().
+  void SetTaskGraph(NamespaceToken token, TaskGraph* graph);
+
+  // Wait for all scheduled tasks to finish running.
+  void WaitForTasksToFinishRunning(NamespaceToken token);
+
+  // Collect all completed tasks in |completed_tasks|.
+  void CollectCompletedTasks(
+      NamespaceToken token, Task::Vector* completed_tasks);
+
+ private:
+  struct TaskNamespace {
+    typedef std::vector<TaskNamespace*> Vector;
+
+    TaskNamespace();
+    ~TaskNamespace();
+
+    // This set contains all pending tasks.
+    TaskGraph pending_tasks;
+    // This set contains all currently running tasks.
+    TaskGraph running_tasks;
+    // Completed tasks not yet collected by origin thread.
+    Task::Vector completed_tasks;
+    // Ordered set of tasks that are ready to run.
+    internal::GraphNode::Vector ready_to_run_tasks;
+  };
+
+  typedef base::ScopedPtrHashMap<int, TaskNamespace> TaskNamespaceMap;
+
+  static bool CompareTaskPriority(const internal::GraphNode* a,
+                                  const internal::GraphNode* b) {
+    // In this system, numerically lower priority is run first.
+    if (a->priority() != b->priority())
+      return a->priority() > b->priority();
+
+    // Run task with most dependents first when priority is the same.
+    return a->dependents().size() < b->dependents().size();
+  }
+
+  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());
+  }
+
+  static bool HasFinishedRunningTasksInNamespace(
+      TaskNamespace* task_namespace) {

[alokp, 2014/01/21 18:42:50]

nit: this may fit in 80 chars.

[reveman, 2014/01/21 19:51:32]

It does seem like that would fit but clang-format doesn't like it that way so
I'll keep it like this as I'm planning to clang-format all these files in a
follow up.

+    return
+        task_namespace->pending_tasks.empty() &&
+        task_namespace->running_tasks.empty();
+  }
+
+  // Overridden from base::DelegateSimpleThread:
+  virtual void Run() OVERRIDE;
+
+  // This lock protects all members of this class. Do not read or modify
+  // anything without holding this lock. Do not block while holding this
+  // lock.
+  mutable base::Lock lock_;
+
+  // Condition variable that is waited on by worker threads until new
+  // tasks are ready to run or shutdown starts.
+  base::ConditionVariable has_ready_to_run_tasks_cv_;
+
+  // Condition variable that is waited on by origin threads until a
+  // namespace has finished running all associated tasks.
+  base::ConditionVariable has_namespaces_with_finished_running_tasks_cv_;
+
+  // Provides a unique id to each NamespaceToken.
+  int next_namespace_id_;
+
+  // This set contains all namespaces with pending, running or completed
+  // tasks not yet collected.
+  TaskNamespaceMap namespaces_;
+
+  // Ordered set of task namespaces that have ready to run tasks.
+  TaskNamespace::Vector ready_to_run_namespaces_;
+
+  // Provides each running thread loop with a unique index. First thread
+  // loop index is 0.
+  unsigned next_thread_index_;
+
+  // Set during shutdown. Tells workers to exit when no more tasks
+  // are pending.
+  bool shutdown_;
+
+  ScopedPtrDeque<base::DelegateSimpleThread> workers_;
+
+  DISALLOW_COPY_AND_ASSIGN(TaskGraphRunner);
+};
+
+}  // namespace internal
+}  // namespace cc
+
+#endif  // CC_RESOURCES_TASK_GRAPH_RUNNER_H_