Revert of cc: Remove WorkerPool class and instead use TaskGraphRunner directly.

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
new file mode 100644
index 0000000000000000000000000000000000000000..aa1a948ec0a2638e5d37a13e184eb4e80b549def
--- /dev/null
+++ b/cc/resources/worker_pool.cc
@@ -0,0 +1,601 @@
+// 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.
+
+#include "cc/resources/worker_pool.h"
+
+#include <algorithm>
+
+#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"
+#include "base/threading/thread_restrictions.h"
+#include "cc/base/scoped_ptr_deque.h"
+
+namespace cc {
+
+namespace {
+
+// TaskGraphRunners can process task graphs from multiple
+// workerpool instances. All members are guarded by |lock_|.
+class TaskGraphRunner : public base::DelegateSimpleThread::Delegate {
+ public:
+  typedef WorkerPool::TaskGraph TaskGraph;
+  typedef WorkerPool::TaskVector TaskVector;
+
+  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
+  // 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(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(const WorkerPool* worker_pool,
+                             TaskVector* completed_tasks);
+
+ private:
+  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();
+  }
+
+  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.
+  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 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_;
+
+  // This set contains all registered namespaces.
+  TaskNamespaceMap namespaces_;
+
+  // 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(TaskGraphRunner);
+};
+
+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_);
+
+  while (workers_.size() < num_threads) {
+    scoped_ptr<base::DelegateSimpleThread> worker = make_scoped_ptr(
+        new base::DelegateSimpleThread(
+            this,
+            thread_name_prefix +
+            base::StringPrintf(
+                "Worker%u",
+                static_cast<unsigned>(workers_.size() + 1)).c_str()));
+    worker->Start();
+#if defined(OS_ANDROID) || defined(OS_LINUX)
+    worker->SetThreadPriority(base::kThreadPriority_Background);
+#endif
+    workers_.push_back(worker.Pass());
+  }
+}
+
+TaskGraphRunner::~TaskGraphRunner() {
+  {
+    base::AutoLock lock(lock_);
+
+    DCHECK_EQ(0u, ready_to_run_namespaces_.size());
+    DCHECK_EQ(0u, namespaces_.size());
+
+    DCHECK(!shutdown_);
+    shutdown_ = true;
+
+    // Wake up a worker so it knows it should exit. This will cause all workers
+    // to exit as each will wake up another worker before exiting.
+    has_ready_to_run_tasks_cv_.Signal();
+  }
+
+  while (workers_.size()) {
+    scoped_ptr<base::DelegateSimpleThread> worker = workers_.take_front();
+    // http://crbug.com/240453 - Join() is considered IO and will block this
+    // thread. See also http://crbug.com/239423 for further ideas.
+    base::ThreadRestrictions::ScopedAllowIO allow_io;
+    worker->Join();
+  }
+}
+
+void TaskGraphRunner::Register(const WorkerPool* worker_pool) {
+  base::AutoLock lock(lock_);
+
+  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 = 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(
+          task);
+      if (node) {
+        for (internal::GraphNode::Vector::const_iterator it =
+                 node->dependents().begin();
+             it != node->dependents().end(); ++it) {
+          internal::GraphNode* dependent_node = *it;
+          dependent_node->remove_dependency();
+        }
+      }
+    }
+
+    // Build new running task set.
+    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
+      // NULL if |new_pending_tasks| doesn't contain task. This does
+      // the right in both cases.
+      new_running_tasks.set(task, new_pending_tasks.take_and_erase(task));
+    }
+
+    // Build new "ready to run" tasks queue.
+    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);
+      internal::GraphNode* node = it->second;
+
+      // Completed tasks should not exist in |new_pending_tasks|.
+      DCHECK(!task->HasFinishedRunning());
+
+      // Call DidSchedule() to indicate that this task has been scheduled.
+      // Note: This is only for debugging purposes.
+      task->DidSchedule();
+
+      if (!node->num_dependencies())
+        task_namespace->ready_to_run_tasks.push_back(node);
+
+      // Erase the task from old pending tasks.
+      task_namespace->pending_tasks.erase(task);
+    }
+
+    // Rearrange the elements in |ready_to_run_tasks| in such a way that
+    // they form a heap.
+    std::make_heap(task_namespace->ready_to_run_tasks.begin(),
+                   task_namespace->ready_to_run_tasks.end(),
+                   CompareTaskPriority);
+
+    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 (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_|.
+    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
+    // running tasks, or we have no pending tasks.
+    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_namespaces_.empty())
+      has_ready_to_run_tasks_cv_.Signal();
+  }
+}
+
+void TaskGraphRunner::CollectCompletedTasks(
+    const WorkerPool* worker_pool, TaskVector* completed_tasks) {
+  base::AutoLock lock(lock_);
+
+  DCHECK_EQ(0u, completed_tasks->size());
+  DCHECK(namespaces_.find(worker_pool) != namespaces_.end());
+  completed_tasks->swap(namespaces_[worker_pool]->completed_tasks);
+}
+
+void TaskGraphRunner::Run() {
+  base::AutoLock lock(lock_);
+
+  // Get a unique thread index.
+  int thread_index = next_thread_index_++;
+
+  while (true) {
+    if (ready_to_run_namespaces_.empty()) {
+      // Exit when shutdown is set and no more tasks are pending.
+      if (shutdown_)
+        break;
+
+      // Wait for more tasks.
+      has_ready_to_run_tasks_cv_.Wait();
+      continue;
+    }
+
+    // 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(
+        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(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();
+
+    // Call WillRun() before releasing |lock_| and running task.
+    task->WillRun();
+
+    {
+      base::AutoUnlock unlock(lock_);
+
+      task->RunOnWorkerThread(thread_index);
+    }
+
+    // This will mark task as finished running.
+    task->DidRun();
+
+    // Now iterate over all dependents to remove dependency and check
+    // if they are ready to run.
+    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) {
+        internal::GraphNode* dependent_node = *it;
+
+        dependent_node->remove_dependency();
+        // Task is ready if it has no dependencies. Add it to
+        // |ready_to_run_tasks_|.
+        if (!dependent_node->num_dependencies()) {
+          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_|.
+    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
+  // exit as well (because the Shutdown() code only signals once).
+  has_ready_to_run_tasks_cv_.Signal();
+}
+
+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() {
+  TRACE_EVENT0("cc", "WorkerPool::Shutdown");
+
+  DCHECK(!in_dispatch_completion_callbacks_);
+
+  g_task_graph_runner.Pointer()->WaitForTasksToFinishRunning(this);
+}
+
+void WorkerPool::SetTaskGraph(TaskGraph* graph) {
+  TRACE_EVENT1("cc", "WorkerPool::SetTaskGraph",
+               "num_tasks", graph->size());
+
+  DCHECK(!in_dispatch_completion_callbacks_);
+
+  g_task_graph_runner.Pointer()->SetTaskGraph(this, graph);
+}
+
+void WorkerPool::CheckForCompletedWorkerTasks() {
+  TRACE_EVENT0("cc", "WorkerPool::CheckForCompletedWorkerTasks");
+
+  DCHECK(!in_dispatch_completion_callbacks_);
+
+  TaskVector completed_tasks;
+  g_task_graph_runner.Pointer()->CollectCompletedTasks(this, &completed_tasks);
+  ProcessCompletedTasks(completed_tasks);
+}
+
+void WorkerPool::ProcessCompletedTasks(
+    const TaskVector& completed_tasks) {
+  TRACE_EVENT1("cc", "WorkerPool::ProcessCompletedTasks",
+               "completed_task_count", completed_tasks.size());
+
+  // Worker pool instance is not reentrant while processing completed tasks.
+  in_dispatch_completion_callbacks_ = true;
+
+  for (TaskVector::const_iterator it = completed_tasks.begin();
+       it != completed_tasks.end();
+       ++it) {
+    internal::WorkerPoolTask* task = it->get();
+
+    task->WillComplete();
+    task->CompleteOnOriginThread();
+    task->DidComplete();
+  }
+
+  in_dispatch_completion_callbacks_ = false;
+}
+
+}  // namespace cc