Reland "Throttle resource message requests during user interaction"

content/renderer/resource_dispatch_throttler.h

Index: content/renderer/resource_dispatch_throttler.h
diff --git a/content/renderer/resource_dispatch_throttler.h b/content/renderer/resource_dispatch_throttler.h
new file mode 100644
index 0000000000000000000000000000000000000000..44defbcc1e8dff0624003ad8caf69e543a271a20
--- /dev/null
+++ b/content/renderer/resource_dispatch_throttler.h
@@ -0,0 +1,74 @@
+// 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.
+
+#ifndef CONTENT_RENDERER_RESOURCE_DISPATCH_THROTTLER_H_
+#define CONTENT_RENDERER_RESOURCE_DISPATCH_THROTTLER_H_
+
+#include <map>
+
+#include "base/threading/thread_checker.h"
+#include "base/time/time.h"
+#include "base/timer/timer.h"
+#include "content/common/content_export.h"
+#include "ipc/ipc_sender.h"
+
+namespace content {
+
+class RendererScheduler;
+
+// Utility class for throttling a stream of resource requests targetted to a
+// specific IPC sender. The throttling itself is very basic:
+//  * When there is no high-priority work imminent to the main thread, as
+//    indicated by the RendererScheduler, throttling is disabled.
+//  * When >= N requests have been sent in a given time window, requests are
+//    throttled. A timer periodically flushes a portion of the queued requests
+//    until all such requests have been flushed.
+// TODO(jdduke): Remove this class after resource requests become sufficiently
+// cheap on the IO thread, crbug.com/440037.
+class CONTENT_EXPORT ResourceDispatchThrottler : public IPC::Sender {

[Sami, 2015/01/27 14:06:06]

Should this live in content/renderer/scheduler? It seems very schedulery. I'm
not opposed to leaving it where it is either.

[jdduke (slow), 2015/01/27 16:59:09]

Yeah, I had it there originally, and I'd be happy to move it back. It used to be
a lot more generic, i.e., you could throttle any IPC::Message stream. I've since
narrowed it down to resource requests, but yeah, putting it in
renderer/scheduler is probably best, particularly as we hope this is but a
temporary utility class.

+ public:
+  // |flush_period| and |max_requests_per_flush| must be strictly positive
+  // in duration/value.
+  ResourceDispatchThrottler(IPC::Sender* proxied_sender,
+                            RendererScheduler* scheduler,
+                            base::TimeDelta flush_period,
+                            uint32 max_requests_per_flush);
+  ~ResourceDispatchThrottler() override;
+
+  // IPC::Sender implementation:
+  bool Send(IPC::Message* msg) override;
+
+ private:
+  friend class ResourceDispatchThrottlerTest;
+
+  // Virtual for testing.
+  virtual base::TimeTicks Now() const;
+  virtual void ScheduleFlush();
+
+  void Flush();
+  bool ForwardRequest(IPC::Message* msg);
+  bool OnRequestResource(IPC::Message* msg);
+  bool OnDidChangePriority(IPC::Message* msg);
+  bool OnReleaseDownloadedFile(IPC::Message* msg);
+  bool OnCancelRequest(IPC::Message* msg);
+
+  base::ThreadChecker thread_checker_;
+
+  IPC::Sender* const proxied_sender_;
+  RendererScheduler* const scheduler_;
+  const base::TimeDelta flush_period_;
+  const uint32 max_requests_per_flush_;
+
+  base::Timer flush_timer_;
+  base::TimeTicks last_sent_request_time_;
+  uint32 sent_requests_since_last_flush_;
+  std::map<int, IPC::Message*> throttled_requests_;
+  bool is_forwarding_request_;
+
+  DISALLOW_COPY_AND_ASSIGN(ResourceDispatchThrottler);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_RESOURCE_DISPATCH_THROTTLER_H_