Shared Raster Worker Threads

cc/resources/worker_pool.cc

Index: cc/resources/worker_pool.cc
diff --git a/cc/resources/worker_pool.cc b/cc/resources/worker_pool.cc
index 602a8398f69fee9cf4ce6a00d14dcd6ca1ae9a3b..aa1a948ec0a2638e5d37a13e184eb4e80b549def 100644
--- a/cc/resources/worker_pool.cc
+++ b/cc/resources/worker_pool.cc
@@ -9,6 +9,8 @@
 #include "base/bind.h"
 #include "base/containers/hash_tables.h"
 #include "base/debug/trace_event.h"
+#include "base/lazy_instance.h"
+#include "base/memory/linked_ptr.h"
 #include "base/strings/stringprintf.h"
 #include "base/synchronization/condition_variable.h"
 #include "base/threading/simple_thread.h"
@@ -17,84 +19,34 @@
 
 namespace cc {
 
-namespace internal {
-
-WorkerPoolTask::WorkerPoolTask()
-    : did_schedule_(false),
-      did_run_(false),
-      did_complete_(false) {
-}
-
-WorkerPoolTask::~WorkerPoolTask() {
-  DCHECK_EQ(did_schedule_, did_complete_);
-  DCHECK(!did_run_ || did_schedule_);
-  DCHECK(!did_run_ || did_complete_);
-}
-
-void WorkerPoolTask::DidSchedule() {
-  DCHECK(!did_complete_);
-  did_schedule_ = true;
-}
-
-void WorkerPoolTask::WillRun() {
-  DCHECK(did_schedule_);
-  DCHECK(!did_complete_);
-  DCHECK(!did_run_);
-}
-
-void WorkerPoolTask::DidRun() {
-  did_run_ = true;
-}
-
-void WorkerPoolTask::WillComplete() {
-  DCHECK(!did_complete_);
-}
-
-void WorkerPoolTask::DidComplete() {
-  DCHECK(did_schedule_);
-  DCHECK(!did_complete_);
-  did_complete_ = true;
-}
-
-bool WorkerPoolTask::HasFinishedRunning() const {
-  return did_run_;
-}
+namespace {
 
-bool WorkerPoolTask::HasCompleted() const {
-  return did_complete_;
-}
-
-GraphNode::GraphNode(internal::WorkerPoolTask* task, unsigned priority)
-    : task_(task),
-      priority_(priority),
-      num_dependencies_(0) {
-}
-
-GraphNode::~GraphNode() {
-}
-
-}  // namespace internal
-
-// Internal to the worker pool. Any data or logic that needs to be
-// shared between threads lives in this class. All members are guarded
-// by |lock_|.
-class WorkerPool::Inner : public base::DelegateSimpleThread::Delegate {
+// TaskGraphRunners can process task graphs from multiple
+// workerpool instances. All members are guarded by |lock_|.
+class TaskGraphRunner : public base::DelegateSimpleThread::Delegate {
  public:
-  Inner(size_t num_threads, const std::string& thread_name_prefix);
-  virtual ~Inner();
+  typedef WorkerPool::TaskGraph TaskGraph;
+  typedef WorkerPool::TaskVector TaskVector;
 
-  void Shutdown();
+  TaskGraphRunner(size_t num_threads, const std::string& thread_name_prefix);
+  virtual ~TaskGraphRunner();
 
+  void Register(const WorkerPool* worker_pool);
+  void Unregister(const WorkerPool* worker_pool);
   // 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
+  // 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 they later get canceled by another
+  // |completed_tasks| queue even if it later get canceled by another
   // call to SetTaskGraph().
-  void SetTaskGraph(TaskGraph* graph);
+  void SetTaskGraph(const WorkerPool* worker_pool, TaskGraph* graph);
+
+  // Wait for all scheduled tasks to finish running.
+  void WaitForTasksToFinishRunning(const WorkerPool* worker_pool);
 
   // Collect all completed tasks in |completed_tasks|.
-  void CollectCompletedTasks(TaskVector* completed_tasks);
+  void CollectCompletedTasks(const WorkerPool* worker_pool,
+                             TaskVector* completed_tasks);
 
  private:
   static bool CompareTaskPriority(const internal::GraphNode* a,
@@ -107,9 +59,40 @@ class WorkerPool::Inner : public base::DelegateSimpleThread::Delegate {
     return a->dependents().size() < b->dependents().size();
   }
 
+  struct 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.
+    TaskVector completed_tasks;
+    // Ordered set of tasks that are ready to run.
+    internal::GraphNode::Vector ready_to_run_tasks;
+  };
+
+  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());
+  }
+
+  typedef std::map<const WorkerPool*, linked_ptr<TaskNamespace> >
+      TaskNamespaceMap;
+
   // Overridden from base::DelegateSimpleThread:
   virtual void Run() OVERRIDE;
 
+  inline bool has_finished_running_tasks(TaskNamespace* task_namespace) {
+    return (task_namespace->pending_tasks.empty() &&
+            task_namespace->running_tasks.empty());
+  }
+
   // This lock protects all members of this class except
   // |worker_pool_on_origin_thread_|. Do not read or modify anything
   // without holding this lock. Do not block while holding this lock.
@@ -119,6 +102,10 @@ class WorkerPool::Inner : public base::DelegateSimpleThread::Delegate {
   // 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 each running thread loop with a unique index. First thread
   // loop index is 0.
   unsigned next_thread_index_;
@@ -127,27 +114,22 @@ class WorkerPool::Inner : public base::DelegateSimpleThread::Delegate {
   // are pending.
   bool shutdown_;
 
-  // This set contains all pending tasks.
-  GraphNodeMap pending_tasks_;
-
-  // Priority queue containing tasks that are ready to run.
-  internal::GraphNode::Vector ready_to_run_tasks_;
-
-  // This set contains all currently running tasks.
-  GraphNodeMap running_tasks_;
+  // This set contains all registered namespaces.
+  TaskNamespaceMap namespaces_;
 
-  // Completed tasks not yet collected by origin thread.
-  TaskVector completed_tasks_;
+  // Ordered set of task namespaces that have ready to run tasks.
+  std::vector<TaskNamespace*> ready_to_run_namespaces_;
 
   ScopedPtrDeque<base::DelegateSimpleThread> workers_;
 
-  DISALLOW_COPY_AND_ASSIGN(Inner);
+  DISALLOW_COPY_AND_ASSIGN(TaskGraphRunner);
 };
 
-WorkerPool::Inner::Inner(
+TaskGraphRunner::TaskGraphRunner(
     size_t num_threads, const std::string& thread_name_prefix)
     : lock_(),
       has_ready_to_run_tasks_cv_(&lock_),
+      has_namespaces_with_finished_running_tasks_cv_(&lock_),
       next_thread_index_(0),
       shutdown_(false) {
   base::AutoLock lock(lock_);
@@ -168,21 +150,13 @@ WorkerPool::Inner::Inner(
   }
 }
 
-WorkerPool::Inner::~Inner() {
-  base::AutoLock lock(lock_);
-
-  DCHECK(shutdown_);
-
-  DCHECK_EQ(0u, pending_tasks_.size());
-  DCHECK_EQ(0u, ready_to_run_tasks_.size());
-  DCHECK_EQ(0u, running_tasks_.size());
-  DCHECK_EQ(0u, completed_tasks_.size());
-}
-
-void WorkerPool::Inner::Shutdown() {
+TaskGraphRunner::~TaskGraphRunner() {
   {
     base::AutoLock lock(lock_);
 
+    DCHECK_EQ(0u, ready_to_run_namespaces_.size());
+    DCHECK_EQ(0u, namespaces_.size());
+
     DCHECK(!shutdown_);
     shutdown_ = true;
 
@@ -200,22 +174,59 @@ void WorkerPool::Inner::Shutdown() {
   }
 }
 
-void WorkerPool::Inner::SetTaskGraph(TaskGraph* graph) {
-  // It is OK to call SetTaskGraph() after shutdown if |graph| is empty.
-  DCHECK(graph->empty() || !shutdown_);
+void TaskGraphRunner::Register(const WorkerPool* worker_pool) {
+  base::AutoLock lock(lock_);
 
-  GraphNodeMap new_pending_tasks;
-  GraphNodeMap new_running_tasks;
+  DCHECK(namespaces_.find(worker_pool) == namespaces_.end());
+  linked_ptr<TaskNamespace> task_set = make_linked_ptr(new TaskNamespace());
+  namespaces_[worker_pool] = task_set;
+}
+
+void TaskGraphRunner::Unregister(const WorkerPool* worker_pool) {
+  base::AutoLock lock(lock_);
+
+  DCHECK(namespaces_.find(worker_pool) != namespaces_.end());
+  DCHECK_EQ(0u, namespaces_[worker_pool]->pending_tasks.size());
+  DCHECK_EQ(0u, namespaces_[worker_pool]->ready_to_run_tasks.size());
+  DCHECK_EQ(0u, namespaces_[worker_pool]->running_tasks.size());
+  DCHECK_EQ(0u, namespaces_[worker_pool]->completed_tasks.size());
+
+  namespaces_.erase(worker_pool);
+}
+
+void TaskGraphRunner::WaitForTasksToFinishRunning(
+    const WorkerPool* worker_pool) {
+  base::AutoLock lock(lock_);
+
+  DCHECK(namespaces_.find(worker_pool) != namespaces_.end());
+  TaskNamespace* task_namespace = namespaces_[worker_pool].get();
+
+  while (!has_finished_running_tasks(task_namespace))
+    has_namespaces_with_finished_running_tasks_cv_.Wait();
+
+  // There may be other namespaces that have finished running
+  // tasks, so wake up another origin thread.
+  has_namespaces_with_finished_running_tasks_cv_.Signal();
+}
+
+void TaskGraphRunner::SetTaskGraph(const WorkerPool* worker_pool,
+                                   TaskGraph* graph) {
+  TaskGraph new_pending_tasks;
+  TaskGraph new_running_tasks;
 
   new_pending_tasks.swap(*graph);
 
   {
     base::AutoLock lock(lock_);
 
+    DCHECK(!shutdown_);
+    DCHECK(namespaces_.find(worker_pool) != namespaces_.end());
+    TaskNamespace* task_namespace = namespaces_[worker_pool].get();
+
     // First remove all completed tasks from |new_pending_tasks| and
     // adjust number of dependencies.
-    for (TaskVector::iterator it = completed_tasks_.begin();
-         it != completed_tasks_.end(); ++it) {
+    for (TaskVector::iterator it = task_namespace->completed_tasks.begin();
+         it != task_namespace->completed_tasks.end(); ++it) {
       internal::WorkerPoolTask* task = it->get();
 
       scoped_ptr<internal::GraphNode> node = new_pending_tasks.take_and_erase(
@@ -231,8 +242,8 @@ void WorkerPool::Inner::SetTaskGraph(TaskGraph* graph) {
     }
 
     // Build new running task set.
-    for (GraphNodeMap::iterator it = running_tasks_.begin();
-         it != running_tasks_.end(); ++it) {
+    for (TaskGraph::iterator it = task_namespace->running_tasks.begin();
+         it != task_namespace->running_tasks.end(); ++it) {
       internal::WorkerPoolTask* task = it->first;
       // Transfer scheduled task value from |new_pending_tasks| to
       // |new_running_tasks| if currently running. Value must be set to
@@ -242,8 +253,8 @@ void WorkerPool::Inner::SetTaskGraph(TaskGraph* graph) {
     }
 
     // Build new "ready to run" tasks queue.
-    ready_to_run_tasks_.clear();
-    for (GraphNodeMap::iterator it = new_pending_tasks.begin();
+    task_namespace->ready_to_run_tasks.clear();
+    for (TaskGraph::iterator it = new_pending_tasks.begin();
          it != new_pending_tasks.end(); ++it) {
       internal::WorkerPoolTask* task = it->first;
       DCHECK(task);
@@ -257,60 +268,78 @@ void WorkerPool::Inner::SetTaskGraph(TaskGraph* graph) {
       task->DidSchedule();
 
       if (!node->num_dependencies())
-        ready_to_run_tasks_.push_back(node);
+        task_namespace->ready_to_run_tasks.push_back(node);
 
       // Erase the task from old pending tasks.
-      pending_tasks_.erase(task);
+      task_namespace->pending_tasks.erase(task);
     }
 
-    // Rearrange the elements in |ready_to_run_tasks_| in such a way that
+    // Rearrange the elements in |ready_to_run_tasks| in such a way that
     // they form a heap.
-    std::make_heap(ready_to_run_tasks_.begin(),
-                   ready_to_run_tasks_.end(),
+    std::make_heap(task_namespace->ready_to_run_tasks.begin(),
+                   task_namespace->ready_to_run_tasks.end(),
                    CompareTaskPriority);
 
-    completed_tasks_.reserve(completed_tasks_.size() + pending_tasks_.size());
+    task_namespace->completed_tasks.reserve(
+        task_namespace->completed_tasks.size() +
+        task_namespace->pending_tasks.size());
 
-    // The items left in |pending_tasks_| need to be canceled.
-    for (GraphNodeMap::const_iterator it = pending_tasks_.begin();
-         it != pending_tasks_.end();
-         ++it) {
-      completed_tasks_.push_back(it->first);
+    // The items left in |pending_tasks| need to be canceled.
+    for (TaskGraph::const_iterator it = task_namespace->pending_tasks.begin();
+         it != task_namespace->pending_tasks.end(); ++it) {
+      task_namespace->completed_tasks.push_back(it->first);
     }
 
     // Swap task sets.
     // Note: old tasks are intentionally destroyed after releasing |lock_|.
-    pending_tasks_.swap(new_pending_tasks);
-    running_tasks_.swap(new_running_tasks);
+    task_namespace->pending_tasks.swap(new_pending_tasks);
+    task_namespace->running_tasks.swap(new_running_tasks);
 
-    // If |ready_to_run_tasks_| is empty, it means we either have
+    // If |ready_to_run_tasks| is empty, it means we either have
     // running tasks, or we have no pending tasks.
-    DCHECK(!ready_to_run_tasks_.empty() ||
-           (pending_tasks_.empty() || !running_tasks_.empty()));
+    DCHECK(!task_namespace->ready_to_run_tasks.empty() ||
+           (task_namespace->pending_tasks.empty() ||
+            !task_namespace->running_tasks.empty()));
+
+    // Build new "ready to run" task namespaces queue.
+    ready_to_run_namespaces_.clear();
+    for (TaskNamespaceMap::iterator it = namespaces_.begin();
+         it != namespaces_.end(); ++it) {
+      if (!it->second->ready_to_run_tasks.empty())
+        ready_to_run_namespaces_.push_back(it->second.get());
+    }
+
+    // Rearrange the task namespaces in |ready_to_run_namespaces_|
+    // in such a way that they form a heap.
+    std::make_heap(ready_to_run_namespaces_.begin(),
+                   ready_to_run_namespaces_.end(),
+                   CompareTaskNamespacePriority);
 
     // If there is more work available, wake up worker thread.
-    if (!ready_to_run_tasks_.empty())
+    if (!ready_to_run_namespaces_.empty())
       has_ready_to_run_tasks_cv_.Signal();
   }
 }
 
-void WorkerPool::Inner::CollectCompletedTasks(TaskVector* completed_tasks) {
+void TaskGraphRunner::CollectCompletedTasks(
+    const WorkerPool* worker_pool, TaskVector* completed_tasks) {
   base::AutoLock lock(lock_);
 
   DCHECK_EQ(0u, completed_tasks->size());
-  completed_tasks->swap(completed_tasks_);
+  DCHECK(namespaces_.find(worker_pool) != namespaces_.end());
+  completed_tasks->swap(namespaces_[worker_pool]->completed_tasks);
 }
 
-void WorkerPool::Inner::Run() {
+void TaskGraphRunner::Run() {
   base::AutoLock lock(lock_);
 
   // Get a unique thread index.
   int thread_index = next_thread_index_++;
 
   while (true) {
-    if (ready_to_run_tasks_.empty()) {
+    if (ready_to_run_namespaces_.empty()) {
       // Exit when shutdown is set and no more tasks are pending.
-      if (shutdown_ && pending_tasks_.empty())
+      if (shutdown_)
         break;
 
       // Wait for more tasks.
@@ -318,18 +347,37 @@ void WorkerPool::Inner::Run() {
       continue;
     }
 
-    // Take top priority task from |ready_to_run_tasks_|.
-    std::pop_heap(ready_to_run_tasks_.begin(),
-                  ready_to_run_tasks_.end(),
+    // Take top priority TaskNamespace from |ready_to_run_namespaces_|.
+    std::pop_heap(ready_to_run_namespaces_.begin(),
+                  ready_to_run_namespaces_.end(),
+                  CompareTaskNamespacePriority);
+    TaskNamespace* task_namespace = ready_to_run_namespaces_.back();
+    ready_to_run_namespaces_.pop_back();
+    DCHECK(!task_namespace->ready_to_run_tasks.empty());
+
+    // Take top priority task from |ready_to_run_tasks|.
+    std::pop_heap(task_namespace->ready_to_run_tasks.begin(),
+                  task_namespace->ready_to_run_tasks.end(),
                   CompareTaskPriority);
     scoped_refptr<internal::WorkerPoolTask> task(
-        ready_to_run_tasks_.back()->task());
-    ready_to_run_tasks_.pop_back();
+        task_namespace->ready_to_run_tasks.back()->task());
+    task_namespace->ready_to_run_tasks.pop_back();
+
+    // Add task namespace back to |ready_to_run_namespaces_| if not
+    // empty after taking top priority task.
+    if (!task_namespace->ready_to_run_tasks.empty()) {
+      ready_to_run_namespaces_.push_back(task_namespace);
+      std::push_heap(ready_to_run_namespaces_.begin(),
+                     ready_to_run_namespaces_.end(),
+                     CompareTaskNamespacePriority);
+    }
 
-    // Move task from |pending_tasks_| to |running_tasks_|.
-    DCHECK(pending_tasks_.contains(task.get()));
-    DCHECK(!running_tasks_.contains(task.get()));
-    running_tasks_.set(task.get(), pending_tasks_.take_and_erase(task.get()));
+    // Move task from |pending_tasks| to |running_tasks|.
+    DCHECK(task_namespace->pending_tasks.contains(task.get()));
+    DCHECK(!task_namespace->running_tasks.contains(task.get()));
+    task_namespace->running_tasks.set(
+        task.get(),
+        task_namespace->pending_tasks.take_and_erase(task.get()));
 
     // There may be more work available, so wake up another worker thread.
     has_ready_to_run_tasks_cv_.Signal();
@@ -348,9 +396,11 @@ void WorkerPool::Inner::Run() {
 
     // Now iterate over all dependents to remove dependency and check
     // if they are ready to run.
-    scoped_ptr<internal::GraphNode> node = running_tasks_.take_and_erase(
-        task.get());
+    scoped_ptr<internal::GraphNode> node =
+        task_namespace->running_tasks.take_and_erase(task.get());
     if (node) {
+      bool ready_to_run_namespaces_has_heap_properties = true;
+
       for (internal::GraphNode::Vector::const_iterator it =
                node->dependents().begin();
            it != node->dependents().end(); ++it) {
@@ -360,16 +410,40 @@ void WorkerPool::Inner::Run() {
         // Task is ready if it has no dependencies. Add it to
         // |ready_to_run_tasks_|.
         if (!dependent_node->num_dependencies()) {
-          ready_to_run_tasks_.push_back(dependent_node);
-          std::push_heap(ready_to_run_tasks_.begin(),
-                         ready_to_run_tasks_.end(),
+          bool was_empty = task_namespace->ready_to_run_tasks.empty();
+          task_namespace->ready_to_run_tasks.push_back(dependent_node);
+          std::push_heap(task_namespace->ready_to_run_tasks.begin(),
+                         task_namespace->ready_to_run_tasks.end(),
                          CompareTaskPriority);
+          // Task namespace is ready if it has at least one ready
+          // to run task. Add it to |ready_to_run_namespaces_| if
+          // it just become ready.
+          if (was_empty) {
+            DCHECK(std::find(ready_to_run_namespaces_.begin(),
+                             ready_to_run_namespaces_.end(),
+                             task_namespace) ==
+                   ready_to_run_namespaces_.end());
+            ready_to_run_namespaces_.push_back(task_namespace);
+          }
+          ready_to_run_namespaces_has_heap_properties = false;
         }
       }
+
+      // Rearrange the task namespaces in |ready_to_run_namespaces_|
+      // in such a way that they yet again form a heap.
+      if (!ready_to_run_namespaces_has_heap_properties) {
+        std::make_heap(ready_to_run_namespaces_.begin(),
+                       ready_to_run_namespaces_.end(),
+                       CompareTaskNamespacePriority);
+      }
     }
 
     // Finally add task to |completed_tasks_|.
-    completed_tasks_.push_back(task);
+    task_namespace->completed_tasks.push_back(task);
+
+    // If namespace has finished running all tasks, wake up origin thread.
+    if (has_finished_running_tasks(task_namespace))
+      has_namespaces_with_finished_running_tasks_cv_.Signal();
   }
 
   // We noticed we should exit. Wake up the next worker so it knows it should
@@ -377,13 +451,103 @@ void WorkerPool::Inner::Run() {
   has_ready_to_run_tasks_cv_.Signal();
 }
 
-WorkerPool::WorkerPool(size_t num_threads,
-                       const std::string& thread_name_prefix)
-    : in_dispatch_completion_callbacks_(false),
-      inner_(make_scoped_ptr(new Inner(num_threads, thread_name_prefix))) {
+class CompositorRasterTaskGraphRunner
+    : public TaskGraphRunner {
+ public:
+  CompositorRasterTaskGraphRunner() : TaskGraphRunner(
+      WorkerPool::GetNumRasterThreads(), "CompositorRaster") {
+  }
+};
+
+base::LazyInstance<CompositorRasterTaskGraphRunner>
+    g_task_graph_runner = LAZY_INSTANCE_INITIALIZER;
+
+const int kDefaultNumRasterThreads = 1;
+
+int g_num_raster_threads = 0;
+
+}  // namespace
+
+namespace internal {
+
+WorkerPoolTask::WorkerPoolTask()
+    : did_schedule_(false),
+      did_run_(false),
+      did_complete_(false) {
+}
+
+WorkerPoolTask::~WorkerPoolTask() {
+  DCHECK_EQ(did_schedule_, did_complete_);
+  DCHECK(!did_run_ || did_schedule_);
+  DCHECK(!did_run_ || did_complete_);
+}
+
+void WorkerPoolTask::DidSchedule() {
+  DCHECK(!did_complete_);
+  did_schedule_ = true;
+}
+
+void WorkerPoolTask::WillRun() {
+  DCHECK(did_schedule_);
+  DCHECK(!did_complete_);
+  DCHECK(!did_run_);
+}
+
+void WorkerPoolTask::DidRun() {
+  did_run_ = true;
+}
+
+void WorkerPoolTask::WillComplete() {
+  DCHECK(!did_complete_);
+}
+
+void WorkerPoolTask::DidComplete() {
+  DCHECK(did_schedule_);
+  DCHECK(!did_complete_);
+  did_complete_ = true;
+}
+
+bool WorkerPoolTask::HasFinishedRunning() const {
+  return did_run_;
+}
+
+bool WorkerPoolTask::HasCompleted() const {
+  return did_complete_;
+}
+
+GraphNode::GraphNode(internal::WorkerPoolTask* task, unsigned priority)
+    : task_(task),
+      priority_(priority),
+      num_dependencies_(0) {
+}
+
+GraphNode::~GraphNode() {
+}
+
+}  // namespace internal
+
+// static
+void WorkerPool::SetNumRasterThreads(int num_threads) {
+  DCHECK_LT(0, num_threads);
+  DCHECK_EQ(0, g_num_raster_threads);
+
+  g_num_raster_threads = num_threads;
+}
+
+// static
+int WorkerPool::GetNumRasterThreads() {
+  if (!g_num_raster_threads)
+    g_num_raster_threads = kDefaultNumRasterThreads;
+
+  return g_num_raster_threads;
+}
+
+WorkerPool::WorkerPool() : in_dispatch_completion_callbacks_(false) {
+  g_task_graph_runner.Pointer()->Register(this);
 }
 
 WorkerPool::~WorkerPool() {
+  g_task_graph_runner.Pointer()->Unregister(this);
 }
 
 void WorkerPool::Shutdown() {
@@ -391,7 +555,7 @@ void WorkerPool::Shutdown() {
 
   DCHECK(!in_dispatch_completion_callbacks_);
 
-  inner_->Shutdown();
+  g_task_graph_runner.Pointer()->WaitForTasksToFinishRunning(this);
 }
 
 void WorkerPool::SetTaskGraph(TaskGraph* graph) {
@@ -400,7 +564,7 @@ void WorkerPool::SetTaskGraph(TaskGraph* graph) {
 
   DCHECK(!in_dispatch_completion_callbacks_);
 
-  inner_->SetTaskGraph(graph);
+  g_task_graph_runner.Pointer()->SetTaskGraph(this, graph);
 }
 
 void WorkerPool::CheckForCompletedWorkerTasks() {
@@ -409,7 +573,7 @@ void WorkerPool::CheckForCompletedWorkerTasks() {
   DCHECK(!in_dispatch_completion_callbacks_);
 
   TaskVector completed_tasks;
-  inner_->CollectCompletedTasks(&completed_tasks);
+  g_task_graph_runner.Pointer()->CollectCompletedTasks(this, &completed_tasks);
   ProcessCompletedTasks(completed_tasks);
 }