Reland "Throttle resource message requests during user interaction"

content/renderer/scheduler/resource_dispatch_throttler.cc

Index: content/renderer/scheduler/resource_dispatch_throttler.cc
diff --git a/content/renderer/scheduler/resource_dispatch_throttler.cc b/content/renderer/scheduler/resource_dispatch_throttler.cc
new file mode 100644
index 0000000000000000000000000000000000000000..927db73d9ed73f6cb5e63abc415fe15b69ac0736
--- /dev/null
+++ b/content/renderer/scheduler/resource_dispatch_throttler.cc
@@ -0,0 +1,146 @@
+// Copyright 2015 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/resource_dispatch_throttler.h"
+
+#include "base/auto_reset.h"
+#include "base/trace_event/trace_event.h"
+#include "content/common/resource_messages.h"
+#include "content/renderer/scheduler/renderer_scheduler.h"
+#include "ipc/ipc_message_macros.h"
+
+namespace content {
+namespace {
+
+bool IsResourceRequest(const IPC::Message& msg) {
+  return msg.type() == ResourceHostMsg_RequestResource::ID;
+}
+
+}  // namespace
+
+ResourceDispatchThrottler::ResourceDispatchThrottler(
+    IPC::Sender* proxied_sender,
+    RendererScheduler* scheduler,
+    base::TimeDelta flush_period,
+    uint32 max_requests_per_flush)
+    : proxied_sender_(proxied_sender),
+      scheduler_(scheduler),
+      flush_period_(flush_period),
+      max_requests_per_flush_(max_requests_per_flush),
+      flush_timer_(
+          FROM_HERE,
+          flush_period_,
+          base::Bind(&ResourceDispatchThrottler::Flush, base::Unretained(this)),
+          false /* is_repeating */),
+      sent_requests_since_last_flush_(0) {
+  DCHECK(proxied_sender);
+  DCHECK(scheduler);
+  DCHECK_NE(flush_period_, base::TimeDelta());
+  DCHECK(max_requests_per_flush_);
+  flush_timer_.SetTaskRunner(scheduler->LoadingTaskRunner());
+}
+
+ResourceDispatchThrottler::~ResourceDispatchThrottler() {
+  FlushAll();
+}
+
+bool ResourceDispatchThrottler::Send(IPC::Message* msg) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  if (msg->is_sync()) {
+    // Flush any pending requests, preserving dispatch order between async and
+    // sync requests.
+    FlushAll();
+    return ForwardMessage(msg);
+  }
+
+  // Always defer message forwarding if there are pending messages, ensuring
+  // message dispatch ordering consistency.
+  if (!throttled_messages_.empty()) {
+    TRACE_EVENT_INSTANT0("loader", "ResourceDispatchThrottler::ThrottleMessage",
+                         TRACE_EVENT_SCOPE_THREAD);
+    throttled_messages_.push_back(msg);
+    return true;
+  }
+
+  if (!IsResourceRequest(*msg))
+    return ForwardMessage(msg);
+
+  if (!scheduler_->IsHighPriorityWorkAnticipated())
+    return ForwardMessage(msg);
+
+  if (Now() > (last_sent_request_time_ + flush_period_)) {
+    // If sufficient time has passed since the previous send, we can effectively
+    // mark the pipeline as flushed.
+    sent_requests_since_last_flush_ = 0;
+    return ForwardMessage(msg);
+  }
+
+  if (sent_requests_since_last_flush_ < max_requests_per_flush_)
+    return ForwardMessage(msg);
+
+  TRACE_EVENT_INSTANT0("loader", "ResourceDispatchThrottler::ThrottleRequest",
+                       TRACE_EVENT_SCOPE_THREAD);
+  throttled_messages_.push_back(msg);
+  ScheduleFlush();
+  return true;
+}
+
+base::TimeTicks ResourceDispatchThrottler::Now() const {
+  return base::TimeTicks::Now();
+}
+
+void ResourceDispatchThrottler::ScheduleFlush() {
+  DCHECK(!flush_timer_.IsRunning());
+  flush_timer_.Reset();
+}
+
+void ResourceDispatchThrottler::Flush() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  TRACE_EVENT1("loader", "ResourceDispatchThrottler::Flush",
+               "total_throttled_messages", throttled_messages_.size());
+  sent_requests_since_last_flush_ = 0;
+
+  // If high-priority work is no longer anticipated, dispatch can be safely
+  // accelerated. Avoid completely flushing in such case in the event that
+  // a large number of requests have been throttled.
+  uint32 max_requests = scheduler_->IsHighPriorityWorkAnticipated()
+                            ? max_requests_per_flush_
+                            : max_requests_per_flush_ * 2;
+
+  while (!throttled_messages_.empty() &&
+         (sent_requests_since_last_flush_ < max_requests ||
+          !IsResourceRequest(*throttled_messages_.front()))) {
+    IPC::Message* msg = throttled_messages_.front();
+    throttled_messages_.pop_front();
+    ForwardMessage(msg);
+  }
+
+  if (!throttled_messages_.empty())
+    ScheduleFlush();
+}
+
+void ResourceDispatchThrottler::FlushAll() {
+  if (throttled_messages_.empty())
+    return;
+
+  TRACE_EVENT1("loader", "ResourceDispatchThrottler::FlushAll",
+               "total_throttled_messages", throttled_messages_.size());
+  std::deque<IPC::Message*> throttled_messages;
+  throttled_messages.swap(throttled_messages_);
+  for (auto& message : throttled_messages)
+    ForwardMessage(message);
+  // There shouldn't be re-entrancy issues when forwarding an IPC, but validate
+  // as a safeguard.
+  DCHECK(throttled_messages_.empty());
+}
+
+bool ResourceDispatchThrottler::ForwardMessage(IPC::Message* msg) {
+  if (IsResourceRequest(*msg)) {
+    last_sent_request_time_ = Now();
+    ++sent_requests_since_last_flush_;
+  }
+  return proxied_sender_->Send(msg);
+}
+
+}  // namespace content