Implement parallel pointer updates after evacuation.

src/heap/page-parallel-job.h

+// Copyright 2016 the V8 project 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 V8_HEAP_PAGE_PARALLEL_JOB_
+#define V8_HEAP_PAGE_PARALLEL_JOB_
+
+#include "src/allocation.h"
+#include "src/cancelable-task.h"
+#include "src/utils.h"
+#include "src/v8.h"
+
+namespace v8 {
+namespace internal {
+
+class Heap;
+class Isolate;
+
+// This class manages background tasks that process set of pages in parallel.
+// The JobTraits class needs to define:
+// - PerPageData type - state associated with each page.
+// - PerTaskData type - state associated with each task.
+// - static bool ProcessPageInParallel(Heap* heap,
+//                                     PerTaskData task_data,
+//                                     MemoryChunk* page,
+//                                     PerPageData page_data)
+//   The function should return true iff processing succeeded.
+// - static const bool NeedSequentialFinalization
+// - static void FinalizePageSequentially(Heap* heap,
+//                                        bool processing_succeeded,
+//                                        MemoryChunk* page,
+//                                        PerPageData page_data)
+template <typename JobTraits>
+class PageParallelJob {
+ public:
+  PageParallelJob(Heap* heap, CancelableTaskManager* cancelable_task_manager)
+      : heap_(heap),
+        cancelable_task_manager_(cancelable_task_manager),
+        items_(nullptr),
+        num_items_(0),
+        pending_tasks_(0) {}
+
+  ~PageParallelJob() {
+    Item* item = items_;
+    while (item != nullptr) {
+      Item* next = item->next;
+      delete item;
+      item = next;
+    }
+  }
+
+  void AddPage(MemoryChunk* chunk, typename JobTraits::PerPageData data) {
+    Item* item = new Item(chunk, data, items_);
+    items_ = item;
+    ++num_items_;
+  }
+
+  int NumberOfPages() { return num_items_; }
+
+  // Runs the given number of tasks in parallel and processes the previosly
+  // added pages. This function blocks until all tasks finish.
+  // The callback takes the index of a task and returns data for that task.
+  template <typename Callback>
+  void Run(int num_tasks, Callback per_task_data_callback) {
+    if (num_items_ == 0) return;

[Michael Lippautz, 2016/03/09 09:48:53]

Maybe add
  DCHECK_GE(num_tasks, 1)
after the bailout.

Currently we compute the number of tasks on the outside and they will be 0 iff
num_items == 0. It seems slightly fragile though.

[ulan, 2016/03/09 17:34:18]

Done.

+    uint32_t task_ids[kMaxNumberOfTasks];
+    const int max_num_tasks = Min(
+        kMaxNumberOfTasks,
+        static_cast<int>(
+            V8::GetCurrentPlatform()->NumberOfAvailableBackgroundThreads()));
+    num_tasks = Max(1, Min(num_tasks, max_num_tasks));
+    int items_per_task = (num_items_ + num_tasks - 1) / num_tasks;
+    int start_index = 0;
+    Task* main_task = nullptr;
+    for (int i = 0; i < num_tasks; i++, start_index += items_per_task) {
+      if (start_index >= num_items_) {
+        start_index -= num_items_;
+      }
+      Task* task = new Task(heap_, items_, num_items_, start_index,
+                            &pending_tasks_, per_task_data_callback(i));
+      task_ids[i] = task->id();
+      if (i > 0) {
+        V8::GetCurrentPlatform()->CallOnBackgroundThread(
+            task, v8::Platform::kShortRunningTask);
+      } else {
+        main_task = task;
+      }
+    }
+    // Contribute on main thread.
+    main_task->Run();
+    delete main_task;
+    // Wait for background tasks.
+    for (int i = 0; i < num_tasks; i++) {
+      if (!cancelable_task_manager_->TryAbort(task_ids[i])) {
+        pending_tasks_.Wait();
+      }
+    }
+    if (JobTraits::NeedSequentialFinalization) {
+      Item* item = items_;
+      while (item != nullptr) {
+        bool success = (item->state.Value() == kFinished);
+        JobTraits::FinalizePageSequentially(heap_, item->chunk, success,
+                                            item->data);
+        item = item->next;
+      }
+    }
+  }
+
+ private:
+  static const int kMaxNumberOfTasks = 10;
+
+  enum ProcessingState { kAvailable, kProcessing, kFinished, kFailed };
+
+  struct Item : public Malloced {
+    MemoryChunk* chunk;
+    AtomicValue<ProcessingState> state;
+    typename JobTraits::PerPageData data;
+    Item* next;
+    Item(MemoryChunk* chunk, typename JobTraits::PerPageData data, Item* next)

[Michael Lippautz, 2016/03/09 09:48:53]

nit: move constructor to top

[ulan, 2016/03/09 17:34:18]

Done.

+        : chunk(chunk), state(kAvailable), data(data), next(next) {}
+  };
+
+  class Task : public CancelableTask {
+   public:
+    Task(Heap* heap, Item* items, int num_items, int start_index,
+         base::Semaphore* on_finish, typename JobTraits::PerTaskData data)
+        : CancelableTask(heap->isolate()),
+          heap_(heap),
+          items_(items),
+          num_items_(num_items),
+          start_index_(start_index),
+          on_finish_(on_finish),
+          data_(data) {}
+
+    virtual ~Task() {}
+
+   private:
+    // v8::internal::CancelableTask overrides.
+    void RunInternal() override {
+      // Each task starts at a different index to improve parallelization.
+      Item* current = items_;
+      int skip = start_index_;
+      while (skip-- > 0) {
+        current = current->next;
+      }
+      for (int i = 0; i < num_items_; i++) {
+        if (current->state.TrySetValue(kAvailable, kProcessing)) {
+          bool success = JobTraits::ProcessPageInParallel(
+              heap_, data_, current->chunk, current->data);
+          current->state.SetValue(success ? kFinished : kFailed);
+        }
+        current = current->next;
+        // Wrap around if needed.
+        if (current == nullptr) {
+          current = items_;
+        }
+      }
+      on_finish_->Signal();
+    }
+
+    Heap* heap_;
+    Item* items_;
+    int num_items_;
+    int start_index_;
+    base::Semaphore* on_finish_;
+    typename JobTraits::PerTaskData data_;
+    DISALLOW_COPY_AND_ASSIGN(Task);
+  };
+
+  Heap* heap_;
+  CancelableTaskManager* cancelable_task_manager_;
+  Item* items_;
+  int num_items_;
+  base::Semaphore pending_tasks_;
+  DISALLOW_COPY_AND_ASSIGN(PageParallelJob);
+};
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_HEAP_PAGE_PARALLEL_JOB_