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// Copyright 2018 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.
#include "src/heap/item-parallel-job.h"
#include "src/base/platform/semaphore.h"
#include "src/v8.h"
namespace v8 {
namespace internal {
ItemParallelJob::Task::Task(Isolate* isolate) : CancelableTask(isolate) {}
ItemParallelJob::Task::~Task() {
// The histogram is reset in RunInternal(). If it's still around it means
// this task was cancelled before being scheduled.
if (gc_parallel_task_latency_histogram_)
gc_parallel_task_latency_histogram_->RecordAbandon();
}
void ItemParallelJob::Task::SetupInternal(
base::Semaphore* on_finish, std::vector<Item*>* items, size_t start_index,
base::Optional<AsyncTimedHistogram> gc_parallel_task_latency_histogram) {
on_finish_ = on_finish;
items_ = items;
if (start_index < items->size()) {
cur_index_ = start_index;
} else {
items_considered_ = items_->size();
}
gc_parallel_task_latency_histogram_ =
std::move(gc_parallel_task_latency_histogram);
}
void ItemParallelJob::Task::RunInternal() {
if (gc_parallel_task_latency_histogram_) {
gc_parallel_task_latency_histogram_->RecordDone();
gc_parallel_task_latency_histogram_.reset();
}
RunInParallel();
on_finish_->Signal();
}
ItemParallelJob::ItemParallelJob(CancelableTaskManager* cancelable_task_manager,
base::Semaphore* pending_tasks)
: cancelable_task_manager_(cancelable_task_manager),
pending_tasks_(pending_tasks) {}
ItemParallelJob::~ItemParallelJob() {
for (size_t i = 0; i < items_.size(); i++) {
Item* item = items_[i];
CHECK(item->IsFinished());
delete item;
}
}
void ItemParallelJob::Run(const std::shared_ptr<Counters>& async_counters) {
DCHECK_GT(tasks_.size(), 0);
const size_t num_items = items_.size();
const size_t num_tasks = tasks_.size();
TRACE_EVENT_INSTANT2(TRACE_DISABLED_BY_DEFAULT("v8.gc"),
"ItemParallelJob::Run", TRACE_EVENT_SCOPE_THREAD,
"num_tasks", static_cast<int>(num_tasks), "num_items",
static_cast<int>(num_items));
AsyncTimedHistogram gc_parallel_task_latency_histogram(
async_counters->gc_parallel_task_latency(), async_counters);
// Some jobs have more tasks than items (when the items are mere coarse
// grain tasks that generate work dynamically for a second phase which all
// tasks participate in). Some jobs even have 0 items to preprocess but
// still have multiple tasks.
// TODO(gab): Figure out a cleaner scheme for this.
const size_t num_tasks_processing_items = Min(num_items, tasks_.size());
// In the event of an uneven workload, distribute an extra item to the first
// |items_remainder| tasks.
const size_t items_remainder = num_tasks_processing_items > 0
? num_items % num_tasks_processing_items
: 0;
// Base |items_per_task|, will be bumped by 1 for the first
// |items_remainder| tasks.
const size_t items_per_task = num_tasks_processing_items > 0
? num_items / num_tasks_processing_items
: 0;
CancelableTaskManager::Id* task_ids =
new CancelableTaskManager::Id[num_tasks];
std::unique_ptr<Task> main_task;
for (size_t i = 0, start_index = 0; i < num_tasks;
i++, start_index += items_per_task + (i < items_remainder ? 1 : 0)) {
auto task = std::move(tasks_[i]);
DCHECK(task);
// By definition there are less |items_remainder| to distribute then
// there are tasks processing items so this cannot overflow while we are
// assigning work items.
DCHECK_IMPLIES(start_index >= num_items, i >= num_tasks_processing_items);
task->SetupInternal(pending_tasks_, &items_, start_index,
i > 0 ? gc_parallel_task_latency_histogram
: base::Optional<AsyncTimedHistogram>());
task_ids[i] = task->id();
if (i > 0) {
V8::GetCurrentPlatform()->CallBlockingTaskOnWorkerThread(std::move(task));
} else {
main_task = std::move(task);
}
}
// Contribute on main thread.
DCHECK(main_task);
main_task->Run();
// Wait for background tasks.
for (size_t i = 0; i < num_tasks; i++) {
if (cancelable_task_manager_->TryAbort(task_ids[i]) !=
CancelableTaskManager::kTaskAborted) {
pending_tasks_->Wait();
}
}
delete[] task_ids;
}
} // namespace internal
} // namespace v8
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