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// Copyright 2017 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_ITEM_PARALLEL_JOB_H_
#define V8_HEAP_ITEM_PARALLEL_JOB_H_
#include <memory>
#include <vector>
#include "src/base/atomic-utils.h"
#include "src/base/logging.h"
#include "src/base/macros.h"
#include "src/base/optional.h"
#include "src/cancelable-task.h"
#include "src/counters.h"
#include "src/globals.h"
namespace v8 {
namespace base {
class Semaphore;
}
namespace internal {
class Counters;
class Isolate;
// This class manages background tasks that process a set of items in parallel.
// The first task added is executed on the same thread as |job.Run()| is called.
// All other tasks are scheduled in the background.
//
// - Items need to inherit from ItemParallelJob::Item.
// - Tasks need to inherit from ItemParallelJob::Task.
//
// Items need to be marked as finished after processing them. Task and Item
// ownership is transferred to the job.
//
// Each parallel (non-main thread) task will report the time between the job
// being created and it being scheduled to |gc_parallel_task_latency_histogram|.
class V8_EXPORT_PRIVATE ItemParallelJob {
public:
class Task;
class V8_EXPORT_PRIVATE Item {
public:
Item() = default;
virtual ~Item() = default;
// Marks an item as being finished.
void MarkFinished() { CHECK_EQ(kProcessing, state_.exchange(kFinished)); }
private:
enum ProcessingState : uintptr_t { kAvailable, kProcessing, kFinished };
bool TryMarkingAsProcessing() {
ProcessingState available = kAvailable;
return state_.compare_exchange_strong(available, kProcessing);
}
bool IsFinished() { return state_ == kFinished; }
std::atomic<ProcessingState> state_{kAvailable};
friend class ItemParallelJob;
friend class ItemParallelJob::Task;
DISALLOW_COPY_AND_ASSIGN(Item);
};
class V8_EXPORT_PRIVATE Task : public CancelableTask {
public:
explicit Task(Isolate* isolate);
virtual ~Task();
virtual void RunInParallel() = 0;
protected:
// Retrieves a new item that needs to be processed. Returns |nullptr| if
// all items are processed. Upon returning an item, the task is required
// to process the item and mark the item as finished after doing so.
template <class ItemType>
ItemType* GetItem() {
while (items_considered_++ != items_->size()) {
// Wrap around.
if (cur_index_ == items_->size()) {
cur_index_ = 0;
}
Item* item = (*items_)[cur_index_++];
if (item->TryMarkingAsProcessing()) {
return static_cast<ItemType*>(item);
}
}
return nullptr;
}
private:
friend class ItemParallelJob;
friend class Item;
// Sets up state required before invoking Run(). If
// |start_index is >= items_.size()|, this task will not process work items
// (some jobs have more tasks than work items in order to parallelize post-
// processing, e.g. scavenging). If |gc_parallel_task_latency_histogram| is
// provided, it will be used to report histograms on the latency between
// posting the task and it being scheduled.
void SetupInternal(
base::Semaphore* on_finish, std::vector<Item*>* items,
size_t start_index,
base::Optional<AsyncTimedHistogram> gc_parallel_task_latency_histogram);
// We don't allow overriding this method any further.
void RunInternal() final;
std::vector<Item*>* items_ = nullptr;
size_t cur_index_ = 0;
size_t items_considered_ = 0;
base::Semaphore* on_finish_ = nullptr;
base::Optional<AsyncTimedHistogram> gc_parallel_task_latency_histogram_;
DISALLOW_COPY_AND_ASSIGN(Task);
};
ItemParallelJob(CancelableTaskManager* cancelable_task_manager,
base::Semaphore* pending_tasks);
~ItemParallelJob();
// Adds a task to the job. Transfers ownership to the job.
void AddTask(Task* task) { tasks_.push_back(std::unique_ptr<Task>(task)); }
// Adds an item to the job. Transfers ownership to the job.
void AddItem(Item* item) { items_.push_back(item); }
int NumberOfItems() const { return static_cast<int>(items_.size()); }
int NumberOfTasks() const { return static_cast<int>(tasks_.size()); }
// Runs this job. Reporting metrics in a thread-safe manner to
// |async_counters|.
void Run(std::shared_ptr<Counters> async_counters);
private:
std::vector<Item*> items_;
std::vector<std::unique_ptr<Task>> tasks_;
CancelableTaskManager* cancelable_task_manager_;
base::Semaphore* pending_tasks_;
DISALLOW_COPY_AND_ASSIGN(ItemParallelJob);
};
} // namespace internal
} // namespace v8
#endif // V8_HEAP_ITEM_PARALLEL_JOB_H_
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