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// Copyright 2014 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 "content/renderer/scheduler/renderer_task_queue_selector.h"
#include "base/debug/trace_event_argument.h"
#include "base/logging.h"
#include "base/pending_task.h"
namespace content {
RendererTaskQueueSelector::RendererTaskQueueSelector() : starvation_count_(0) {
}
RendererTaskQueueSelector::~RendererTaskQueueSelector() {
}
void RendererTaskQueueSelector::RegisterWorkQueues(
const std::vector<const base::TaskQueue*>& work_queues) {
main_thread_checker_.CalledOnValidThread();
work_queues_ = work_queues;
for (QueuePriority priority = FIRST_QUEUE_PRIORITY;
priority < QUEUE_PRIORITY_COUNT;
priority = NextPriority(priority)) {
queue_priorities_[priority].clear();
}
// By default, all work queues are set to normal priority.
for (size_t i = 0; i < work_queues.size(); i++) {
queue_priorities_[NORMAL_PRIORITY].insert(i);
}
}
void RendererTaskQueueSelector::SetQueuePriority(size_t queue_index,
QueuePriority priority) {
main_thread_checker_.CalledOnValidThread();
DCHECK_LT(queue_index, work_queues_.size());
DCHECK_LT(priority, QUEUE_PRIORITY_COUNT);
DisableQueue(queue_index);
queue_priorities_[priority].insert(queue_index);
}
void RendererTaskQueueSelector::EnableQueue(size_t queue_index,
QueuePriority priority) {
SetQueuePriority(queue_index, priority);
}
void RendererTaskQueueSelector::DisableQueue(size_t queue_index) {
main_thread_checker_.CalledOnValidThread();
DCHECK_LT(queue_index, work_queues_.size());
for (QueuePriority priority = FIRST_QUEUE_PRIORITY;
priority < QUEUE_PRIORITY_COUNT;
priority = NextPriority(priority)) {
queue_priorities_[priority].erase(queue_index);
}
}
bool RendererTaskQueueSelector::IsOlder(const base::TaskQueue* queueA,
const base::TaskQueue* queueB) {
// Note: the comparison is correct due to the fact that the PendingTask
// operator inverts its comparison operation in order to work well in a heap
// based priority queue.
return queueB->front() < queueA->front();
}
RendererTaskQueueSelector::QueuePriority
RendererTaskQueueSelector::NextPriority(QueuePriority priority) {
DCHECK(priority < QUEUE_PRIORITY_COUNT);
return static_cast<QueuePriority>(static_cast<int>(priority) + 1);
}
bool RendererTaskQueueSelector::ChooseOldestWithPriority(
QueuePriority priority,
size_t* out_queue_index) const {
bool found_non_empty_queue = false;
size_t chosen_queue = 0;
for (int queue_index : queue_priorities_[priority]) {
if (work_queues_[queue_index]->empty()) {
continue;
}
if (!found_non_empty_queue ||
IsOlder(work_queues_[queue_index], work_queues_[chosen_queue])) {
found_non_empty_queue = true;
chosen_queue = queue_index;
}
}
if (found_non_empty_queue) {
*out_queue_index = chosen_queue;
}
return found_non_empty_queue;
}
bool RendererTaskQueueSelector::SelectWorkQueueToService(
size_t* out_queue_index) {
main_thread_checker_.CalledOnValidThread();
DCHECK(work_queues_.size());
// Always service the control queue if it has any work.
if (ChooseOldestWithPriority(CONTROL_PRIORITY, out_queue_index)) {
DidSelectQueueWithPriority(CONTROL_PRIORITY);
return true;
}
// Select from the normal priority queue if we are starving it.
if (starvation_count_ >= kMaxStarvationTasks &&
ChooseOldestWithPriority(NORMAL_PRIORITY, out_queue_index)) {
DidSelectQueueWithPriority(NORMAL_PRIORITY);
return true;
}
// Otherwise choose in priority order.
for (QueuePriority priority = HIGH_PRIORITY; priority < QUEUE_PRIORITY_COUNT;
priority = NextPriority(priority)) {
if (ChooseOldestWithPriority(priority, out_queue_index)) {
DidSelectQueueWithPriority(priority);
return true;
}
}
return false;
}
void RendererTaskQueueSelector::DidSelectQueueWithPriority(
QueuePriority priority) {
switch (priority) {
case CONTROL_PRIORITY:
break;
case HIGH_PRIORITY:
starvation_count_++;
break;
case NORMAL_PRIORITY:
case BEST_EFFORT_PRIORITY:
starvation_count_ = 0;
break;
default:
NOTREACHED();
}
}
// static
const char* RendererTaskQueueSelector::PriorityToString(
QueuePriority priority) {
switch (priority) {
case CONTROL_PRIORITY:
return "control";
case HIGH_PRIORITY:
return "high";
case NORMAL_PRIORITY:
return "normal";
case BEST_EFFORT_PRIORITY:
return "best_effort";
default:
NOTREACHED();
return nullptr;
}
}
void RendererTaskQueueSelector::AsValueInto(
base::debug::TracedValue* state) const {
main_thread_checker_.CalledOnValidThread();
state->BeginDictionary("priorities");
for (QueuePriority priority = FIRST_QUEUE_PRIORITY;
priority < QUEUE_PRIORITY_COUNT; priority = NextPriority(priority)) {
state->BeginArray(PriorityToString(priority));
for (size_t queue_index : queue_priorities_[priority])
state->AppendInteger(queue_index);
state->EndArray();
}
state->EndDictionary();
state->SetInteger("starvation_count", starvation_count_);
}
} // namespace content
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