content/browser/loader/resource_scheduler.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include <set>
   6
   7 #include "content/browser/loader/resource_scheduler.h"
   8
   9 #include "base/metrics/field_trial.h"
  10 #include "base/metrics/histogram.h"
  11 #include "base/stl_util.h"
  12 #include "base/time/time.h"
  13 #include "content/common/resource_messages.h"
  14 #include "content/browser/loader/resource_message_delegate.h"
  15 #include "content/public/browser/resource_controller.h"
  16 #include "content/public/browser/resource_request_info.h"
  17 #include "content/public/browser/resource_throttle.h"
  18 #include "ipc/ipc_message_macros.h"
  19 #include "net/base/host_port_pair.h"
  20 #include "net/base/load_flags.h"
  21 #include "net/base/request_priority.h"
  22 #include "net/http/http_server_properties.h"
  23 #include "net/url_request/url_request.h"
  24 #include "net/url_request/url_request_context.h"
  25
  26 namespace content {
  27
  28 namespace {
  29
  30 void PostHistogram(const char* base_name,
  31                    const char* suffix,
  32                    base::TimeDelta time) {
  33   std::string histogram_name =
  34       base::StringPrintf("ResourceScheduler.%s.%s", base_name, suffix);
  35   base::HistogramBase* histogram_counter = base::Histogram::FactoryTimeGet(
  36       histogram_name,
  37       base::TimeDelta::FromMilliseconds(1),
  38       base::TimeDelta::FromMinutes(5),
  39       50,
  40       base::Histogram::kUmaTargetedHistogramFlag);
  41   histogram_counter->AddTime(time);
  42 }
  43
  44 }  // namespace
  45
  46 static const size_t kCoalescedTimerPeriod = 5000;
  47 static const size_t kMaxNumDelayableRequestsPerClient = 10;
  48 static const size_t kMaxNumDelayableRequestsPerHost = 6;
  49 static const size_t kMaxNumThrottledRequestsPerClient = 1;
  50
  51 struct ResourceScheduler::RequestPriorityParams {
  52   RequestPriorityParams()
  53     : priority(net::DEFAULT_PRIORITY),
  54       intra_priority(0) {
  55   }
  56
  57   RequestPriorityParams(net::RequestPriority priority, int intra_priority)
  58     : priority(priority),
  59       intra_priority(intra_priority) {
  60   }
  61
  62   bool operator==(const RequestPriorityParams& other) const {
  63     return (priority == other.priority) &&
  64         (intra_priority == other.intra_priority);
  65   }
  66
  67   bool operator!=(const RequestPriorityParams& other) const {
  68     return !(*this == other);
  69   }
  70
  71   bool GreaterThan(const RequestPriorityParams& other) const {
  72     if (priority != other.priority)
  73       return priority > other.priority;
  74     return intra_priority > other.intra_priority;
  75   }
  76
  77   net::RequestPriority priority;
  78   int intra_priority;
  79 };
  80
  81 class ResourceScheduler::RequestQueue {
  82  public:
  83   typedef std::multiset<ScheduledResourceRequest*, ScheduledResourceSorter>
  84       NetQueue;
  85
  86   RequestQueue() : fifo_ordering_ids_(0) {}
  87   ~RequestQueue() {}
  88
  89   // Adds |request| to the queue with given |priority|.
  90   void Insert(ScheduledResourceRequest* request);
  91
  92   // Removes |request| from the queue.
  93   void Erase(ScheduledResourceRequest* request) {
  94     PointerMap::iterator it = pointers_.find(request);
  95     DCHECK(it != pointers_.end());
  96     if (it == pointers_.end())
  97       return;
  98     queue_.erase(it->second);
  99     pointers_.erase(it);
 100   }
 101
 102   NetQueue::iterator GetNextHighestIterator() {
 103     return queue_.begin();
 104   }
 105
 106   NetQueue::iterator End() {
 107     return queue_.end();
 108   }
 109
 110   // Returns true if |request| is queued.
 111   bool IsQueued(ScheduledResourceRequest* request) const {
 112     return ContainsKey(pointers_, request);
 113   }
 114
 115   // Returns true if no requests are queued.
 116   bool IsEmpty() const { return queue_.size() == 0; }
 117
 118  private:
 119   typedef std::map<ScheduledResourceRequest*, NetQueue::iterator> PointerMap;
 120
 121   uint32 MakeFifoOrderingId() {
 122     fifo_ordering_ids_ += 1;
 123     return fifo_ordering_ids_;
 124   }
 125
 126   // Used to create an ordering ID for scheduled resources so that resources
 127   // with same priority/intra_priority stay in fifo order.
 128   uint32 fifo_ordering_ids_;
 129
 130   NetQueue queue_;
 131   PointerMap pointers_;
 132 };
 133
 134 // This is the handle we return to the ResourceDispatcherHostImpl so it can
 135 // interact with the request.
 136 class ResourceScheduler::ScheduledResourceRequest
 137     : public ResourceMessageDelegate,
 138       public ResourceThrottle {
 139  public:
 140   ScheduledResourceRequest(const ClientId& client_id,
 141                            net::URLRequest* request,
 142                            ResourceScheduler* scheduler,
 143                            const RequestPriorityParams& priority)
 144       : ResourceMessageDelegate(request),
 145         client_id_(client_id),
 146         client_state_on_creation_(scheduler->GetClientState(client_id_)),
 147         request_(request),
 148         ready_(false),
 149         deferred_(false),
 150         classification_(NORMAL_REQUEST),
 151         scheduler_(scheduler),
 152         priority_(priority),
 153         fifo_ordering_(0) {
 154     TRACE_EVENT_ASYNC_BEGIN1("net", "URLRequest", request_,
 155                              "url", request->url().spec());
 156   }
 157
 158   ~ScheduledResourceRequest() override { scheduler_->RemoveRequest(this); }
 159
 160   void Start() {
 161     TRACE_EVENT_ASYNC_STEP_PAST0("net", "URLRequest", request_, "Queued");
 162     ready_ = true;
 163     if (!request_->status().is_success())
 164       return;
 165     base::TimeTicks time = base::TimeTicks::Now();
 166     ClientState current_state = scheduler_->GetClientState(client_id_);
 167     // Note: the client state isn't perfectly accurate since it won't capture
 168     // tabs which have switched between active and background multiple times.
 169     // Ex: A tab with the following transitions Active -> Background -> Active
 170     // will be recorded as Active.
 171     const char* client_state = "Other";
 172     if (current_state == client_state_on_creation_ && current_state == ACTIVE) {
 173       client_state = "Active";
 174     } else if (current_state == client_state_on_creation_ &&
 175                current_state == BACKGROUND) {
 176       client_state = "Background";
 177     }
 178
 179     base::TimeDelta time_was_deferred = base::TimeDelta::FromMicroseconds(0);
 180     if (deferred_) {
 181       deferred_ = false;
 182       controller()->Resume();
 183       time_was_deferred = time - time_deferred_;
 184     }
 185     PostHistogram("RequestTimeDeferred", client_state, time_was_deferred);
 186     PostHistogram(
 187         "RequestTimeThrottled", client_state, time - request_->creation_time());
 188     // TODO(aiolos): Remove one of the above histograms after gaining an
 189     // understanding of the difference between them and which one is more
 190     // interesting.
 191   }
 192
 193   void set_request_priority_params(const RequestPriorityParams& priority) {
 194     priority_ = priority;
 195   }
 196   const RequestPriorityParams& get_request_priority_params() const {
 197     return priority_;
 198   }
 199   const ClientId& client_id() const { return client_id_; }
 200   net::URLRequest* url_request() { return request_; }
 201   const net::URLRequest* url_request() const { return request_; }
 202   uint32 fifo_ordering() const { return fifo_ordering_; }
 203   void set_fifo_ordering(uint32 fifo_ordering) {
 204     fifo_ordering_ = fifo_ordering;
 205   }
 206   RequestClassification classification() const {
 207     return classification_;
 208   }
 209   void set_classification(RequestClassification classification) {
 210     classification_ = classification;
 211   }
 212
 213  private:
 214   // ResourceMessageDelegate interface:
 215   bool OnMessageReceived(const IPC::Message& message) override {
 216     bool handled = true;
 217     IPC_BEGIN_MESSAGE_MAP(ScheduledResourceRequest, message)
 218       IPC_MESSAGE_HANDLER(ResourceHostMsg_DidChangePriority, DidChangePriority)
 219       IPC_MESSAGE_UNHANDLED(handled = false)
 220     IPC_END_MESSAGE_MAP()
 221     return handled;
 222   }
 223
 224   // ResourceThrottle interface:
 225   void WillStartRequest(bool* defer) override {
 226     deferred_ = *defer = !ready_;
 227     time_deferred_ = base::TimeTicks::Now();
 228   }
 229
 230   const char* GetNameForLogging() const override { return "ResourceScheduler"; }
 231
 232   void DidChangePriority(int request_id, net::RequestPriority new_priority,
 233                          int intra_priority_value) {
 234     scheduler_->ReprioritizeRequest(this, new_priority, intra_priority_value);
 235   }
 236
 237   const ClientId client_id_;
 238   const ResourceScheduler::ClientState client_state_on_creation_;
 239   net::URLRequest* request_;
 240   bool ready_;
 241   bool deferred_;
 242   RequestClassification classification_;
 243   ResourceScheduler* scheduler_;
 244   RequestPriorityParams priority_;
 245   uint32 fifo_ordering_;
 246   base::TimeTicks time_deferred_;
 247
 248   DISALLOW_COPY_AND_ASSIGN(ScheduledResourceRequest);
 249 };
 250
 251 bool ResourceScheduler::ScheduledResourceSorter::operator()(
 252     const ScheduledResourceRequest* a,
 253     const ScheduledResourceRequest* b) const {
 254   // Want the set to be ordered first by decreasing priority, then by
 255   // decreasing intra_priority.
 256   // ie. with (priority, intra_priority)
 257   // [(1, 0), (1, 0), (0, 100), (0, 0)]
 258   if (a->get_request_priority_params() != b->get_request_priority_params())
 259     return a->get_request_priority_params().GreaterThan(
 260         b->get_request_priority_params());
 261
 262   // If priority/intra_priority is the same, fall back to fifo ordering.
 263   // std::multiset doesn't guarantee this until c++11.
 264   return a->fifo_ordering() < b->fifo_ordering();
 265 }
 266
 267 void ResourceScheduler::RequestQueue::Insert(
 268     ScheduledResourceRequest* request) {
 269   DCHECK(!ContainsKey(pointers_, request));
 270   request->set_fifo_ordering(MakeFifoOrderingId());
 271   pointers_[request] = queue_.insert(request);
 272 }
 273
 274 // Each client represents a tab.
 275 class ResourceScheduler::Client {
 276  public:
 277   explicit Client(ResourceScheduler* scheduler,
 278                   bool is_visible,
 279                   bool is_audible)
 280       : is_audible_(is_audible),
 281         is_visible_(is_visible),
 282         is_loaded_(false),
 283         is_paused_(false),
 284         has_body_(false),
 285         using_spdy_proxy_(false),
 286         in_flight_delayable_count_(0),
 287         total_layout_blocking_count_(0),
 288         throttle_state_(ResourceScheduler::THROTTLED) {
 289     scheduler_ = scheduler;
 290   }
 291
 292   ~Client() {
 293     // Update to default state and pause to ensure the scheduler has a
 294     // correct count of relevant types of clients.
 295     is_visible_ = false;
 296     is_audible_ = false;
 297     is_paused_ = true;
 298     UpdateThrottleState();
 299   }
 300
 301   void ScheduleRequest(
 302       net::URLRequest* url_request,
 303       ScheduledResourceRequest* request) {
 304     if (ShouldStartRequest(request) == START_REQUEST)
 305       StartRequest(request);
 306     else
 307       pending_requests_.Insert(request);
 308     SetRequestClassification(request, ClassifyRequest(request));
 309   }
 310
 311   void RemoveRequest(ScheduledResourceRequest* request) {
 312     if (pending_requests_.IsQueued(request)) {
 313       pending_requests_.Erase(request);
 314       DCHECK(!ContainsKey(in_flight_requests_, request));
 315     } else {
 316       EraseInFlightRequest(request);
 317
 318       // Removing this request may have freed up another to load.
 319       LoadAnyStartablePendingRequests();
 320     }
 321   }
 322
 323   RequestSet RemoveAllRequests() {
 324     RequestSet unowned_requests;
 325     for (RequestSet::iterator it = in_flight_requests_.begin();
 326          it != in_flight_requests_.end(); ++it) {
 327       unowned_requests.insert(*it);
 328       (*it)->set_classification(NORMAL_REQUEST);
 329     }
 330     ClearInFlightRequests();
 331     return unowned_requests;
 332   }
 333
 334   bool is_active() const { return is_visible_ || is_audible_; }
 335
 336   bool is_loaded() const { return is_loaded_; }
 337
 338   bool is_visible() const { return is_visible_; }
 339
 340   void OnAudibilityChanged(bool is_audible) {
 341     if (is_audible == is_audible_) {
 342       return;
 343     }
 344     is_audible_ = is_audible;
 345     UpdateThrottleState();
 346   }
 347
 348   void OnVisibilityChanged(bool is_visible) {
 349     if (is_visible == is_visible_) {
 350       return;
 351     }
 352     is_visible_ = is_visible;
 353     UpdateThrottleState();
 354   }
 355
 356   void OnLoadingStateChanged(bool is_loaded) {
 357     if (is_loaded == is_loaded_) {
 358       return;
 359     }
 360     is_loaded_ = is_loaded;
 361     UpdateThrottleState();
 362   }
 363
 364   void SetPaused() {
 365     is_paused_ = true;
 366     UpdateThrottleState();
 367   }
 368
 369   void UpdateThrottleState() {
 370     ClientThrottleState old_throttle_state = throttle_state_;
 371     if (!scheduler_->should_throttle()) {
 372       SetThrottleState(UNTHROTTLED);
 373     } else if (is_active() && !is_loaded_) {
 374       SetThrottleState(ACTIVE_AND_LOADING);
 375     } else if (is_active()) {
 376       SetThrottleState(UNTHROTTLED);
 377     } else if (is_paused_) {
 378       SetThrottleState(PAUSED);
 379     } else if (!scheduler_->active_clients_loaded()) {
 380       SetThrottleState(THROTTLED);
 381     } else if (is_loaded_ && scheduler_->should_coalesce()) {
 382       SetThrottleState(COALESCED);
 383     } else if (!is_active()) {
 384       SetThrottleState(UNTHROTTLED);
 385     }
 386
 387     if (throttle_state_ == old_throttle_state) {
 388       return;
 389     }
 390     if (throttle_state_ == ACTIVE_AND_LOADING) {
 391       scheduler_->IncrementActiveClientsLoading();
 392     } else if (old_throttle_state == ACTIVE_AND_LOADING) {
 393       scheduler_->DecrementActiveClientsLoading();
 394     }
 395     if (throttle_state_ == COALESCED) {
 396       scheduler_->IncrementCoalescedClients();
 397     } else if (old_throttle_state == COALESCED) {
 398       scheduler_->DecrementCoalescedClients();
 399     }
 400   }
 401
 402   void OnNavigate() {
 403     has_body_ = false;
 404     is_loaded_ = false;
 405   }
 406
 407   void OnWillInsertBody() {
 408     has_body_ = true;
 409     LoadAnyStartablePendingRequests();
 410   }
 411
 412   void OnReceivedSpdyProxiedHttpResponse() {
 413     if (!using_spdy_proxy_) {
 414       using_spdy_proxy_ = true;
 415       LoadAnyStartablePendingRequests();
 416     }
 417   }
 418
 419   void ReprioritizeRequest(ScheduledResourceRequest* request,
 420                            RequestPriorityParams old_priority_params,
 421                            RequestPriorityParams new_priority_params) {
 422     request->url_request()->SetPriority(new_priority_params.priority);
 423     request->set_request_priority_params(new_priority_params);
 424     if (!pending_requests_.IsQueued(request)) {
 425       DCHECK(ContainsKey(in_flight_requests_, request));
 426       // The priority and SPDY support may have changed, so update the
 427       // delayable count.
 428       SetRequestClassification(request, ClassifyRequest(request));
 429       // Request has already started.
 430       return;
 431     }
 432
 433     pending_requests_.Erase(request);
 434     pending_requests_.Insert(request);
 435
 436     if (new_priority_params.priority > old_priority_params.priority) {
 437       // Check if this request is now able to load at its new priority.
 438       LoadAnyStartablePendingRequests();
 439     }
 440   }
 441
 442   // Called on Client creation, when a Client changes user observability,
 443   // possibly when all observable Clients have finished loading, and
 444   // possibly when this Client has finished loading.
 445   // State changes:
 446   // Client became observable.
 447   //   any state -> UNTHROTTLED
 448   // Client is unobservable, but all observable clients finished loading.
 449   //   THROTTLED -> UNTHROTTLED
 450   // Non-observable client finished loading.
 451   //   THROTTLED || UNTHROTTLED -> COALESCED
 452   // Non-observable client, an observable client starts loading.
 453   //   COALESCED -> THROTTLED
 454   // A COALESCED client will transition into UNTHROTTLED when the network is
 455   // woken up by a heartbeat and then transition back into COALESCED.
 456   void SetThrottleState(ResourceScheduler::ClientThrottleState throttle_state) {
 457     if (throttle_state == throttle_state_) {
 458       return;
 459     }
 460     throttle_state_ = throttle_state;
 461     if (throttle_state_ != PAUSED) {
 462       is_paused_ = false;
 463     }
 464     LoadAnyStartablePendingRequests();
 465     // TODO(aiolos): Stop any started but not inflght requests when
 466     // switching to stricter throttle state?
 467   }
 468
 469   ResourceScheduler::ClientThrottleState throttle_state() const {
 470     return throttle_state_;
 471   }
 472
 473   void LoadCoalescedRequests() {
 474     if (throttle_state_ != COALESCED) {
 475       return;
 476     }
 477     if (scheduler_->active_clients_loaded()) {
 478       SetThrottleState(UNTHROTTLED);
 479     } else {
 480       SetThrottleState(THROTTLED);
 481     }
 482     LoadAnyStartablePendingRequests();
 483     SetThrottleState(COALESCED);
 484   }
 485
 486  private:
 487   enum ShouldStartReqResult {
 488     DO_NOT_START_REQUEST_AND_STOP_SEARCHING,
 489     DO_NOT_START_REQUEST_AND_KEEP_SEARCHING,
 490     START_REQUEST,
 491   };
 492
 493   void InsertInFlightRequest(ScheduledResourceRequest* request) {
 494     in_flight_requests_.insert(request);
 495     SetRequestClassification(request, ClassifyRequest(request));
 496   }
 497
 498   void EraseInFlightRequest(ScheduledResourceRequest* request) {
 499     size_t erased = in_flight_requests_.erase(request);
 500     DCHECK_EQ(1u, erased);
 501     // Clear any special state that we were tracking for this request.
 502     SetRequestClassification(request, NORMAL_REQUEST);
 503   }
 504
 505   void ClearInFlightRequests() {
 506     in_flight_requests_.clear();
 507     in_flight_delayable_count_ = 0;
 508     total_layout_blocking_count_ = 0;
 509   }
 510
 511   size_t CountRequestsWithClassification(
 512       const RequestClassification classification, const bool include_pending) {
 513     size_t classification_request_count = 0;
 514     for (RequestSet::const_iterator it = in_flight_requests_.begin();
 515          it != in_flight_requests_.end(); ++it) {
 516       if ((*it)->classification() == classification)
 517         classification_request_count++;
 518     }
 519     if (include_pending) {
 520       for (RequestQueue::NetQueue::const_iterator
 521            it = pending_requests_.GetNextHighestIterator();
 522            it != pending_requests_.End(); ++it) {
 523         if ((*it)->classification() == classification)
 524           classification_request_count++;
 525       }
 526     }
 527     return classification_request_count;
 528   }
 529
 530   void SetRequestClassification(ScheduledResourceRequest* request,
 531                                 RequestClassification classification) {
 532     RequestClassification old_classification = request->classification();
 533     if (old_classification == classification)
 534       return;
 535
 536     if (old_classification == IN_FLIGHT_DELAYABLE_REQUEST)
 537       in_flight_delayable_count_--;
 538     if (old_classification == LAYOUT_BLOCKING_REQUEST)
 539       total_layout_blocking_count_--;
 540
 541     if (classification == IN_FLIGHT_DELAYABLE_REQUEST)
 542       in_flight_delayable_count_++;
 543     if (classification == LAYOUT_BLOCKING_REQUEST)
 544       total_layout_blocking_count_++;
 545
 546     request->set_classification(classification);
 547     DCHECK_EQ(
 548         CountRequestsWithClassification(IN_FLIGHT_DELAYABLE_REQUEST, false),
 549         in_flight_delayable_count_);
 550     DCHECK_EQ(CountRequestsWithClassification(LAYOUT_BLOCKING_REQUEST, true),
 551               total_layout_blocking_count_);
 552   }
 553
 554   RequestClassification ClassifyRequest(ScheduledResourceRequest* request) {
 555     // If a request is already marked as layout-blocking make sure to keep the
 556     // classification across redirects unless the priority was lowered.
 557     if (request->classification() == LAYOUT_BLOCKING_REQUEST &&
 558         request->url_request()->priority() > net::LOW) {
 559       return LAYOUT_BLOCKING_REQUEST;
 560     }
 561
 562     if (!has_body_ && request->url_request()->priority() > net::LOW)
 563       return LAYOUT_BLOCKING_REQUEST;
 564
 565     if (request->url_request()->priority() < net::LOW) {
 566       net::HostPortPair host_port_pair =
 567           net::HostPortPair::FromURL(request->url_request()->url());
 568       net::HttpServerProperties& http_server_properties =
 569           *request->url_request()->context()->http_server_properties();
 570       if (!http_server_properties.SupportsSpdy(host_port_pair) &&
 571           ContainsKey(in_flight_requests_, request)) {
 572         return IN_FLIGHT_DELAYABLE_REQUEST;
 573       }
 574     }
 575     return NORMAL_REQUEST;
 576   }
 577
 578   bool ShouldKeepSearching(
 579       const net::HostPortPair& active_request_host) const {
 580     size_t same_host_count = 0;
 581     for (RequestSet::const_iterator it = in_flight_requests_.begin();
 582          it != in_flight_requests_.end(); ++it) {
 583       net::HostPortPair host_port_pair =
 584           net::HostPortPair::FromURL((*it)->url_request()->url());
 585       if (active_request_host.Equals(host_port_pair)) {
 586         same_host_count++;
 587         if (same_host_count >= kMaxNumDelayableRequestsPerHost)
 588           return true;
 589       }
 590     }
 591     return false;
 592   }
 593
 594   void StartRequest(ScheduledResourceRequest* request) {
 595     InsertInFlightRequest(request);
 596     request->Start();
 597   }
 598
 599   // ShouldStartRequest is the main scheduling algorithm.
 600   //
 601   // Requests are evaluated on five attributes:
 602   //
 603   // 1. Non-delayable requests:
 604   //   * Synchronous requests.
 605   //   * Non-HTTP[S] requests.
 606   //
 607   // 2. Requests to SPDY-capable origin servers.
 608   //
 609   // 3. High-priority requests:
 610   //   * Higher priority requests (>= net::LOW).
 611   //
 612   // 4. Layout-blocking requests:
 613   //   * High-priority requests (> net::LOW) initiated before the renderer has
 614   //     a <body>.
 615   //
 616   // 5. Low priority requests
 617   //
 618   //  The following rules are followed:
 619   //
 620   //  ACTIVE_AND_LOADING and UNTHROTTLED Clients follow these rules:
 621   //   * Non-delayable, High-priority and SPDY capable requests are issued
 622   //     immediately.
 623   //   * Low priority requests are delayable.
 624   //   * Allow one delayable request to load at a time while layout-blocking
 625   //     requests are loading or the body tag has not yet been parsed.
 626   //   * If no high priority or layout-blocking requests are in flight, start
 627   //     loading delayable requests.
 628   //   * Never exceed 10 delayable requests in flight per client.
 629   //   * Never exceed 6 delayable requests for a given host.
 630   //
 631   //  THROTTLED Clients follow these rules:
 632   //   * Non-delayable and SPDY-capable requests are issued immediately.
 633   //   * At most one non-SPDY request will be issued per THROTTLED Client
 634   //   * If no high priority requests are in flight, start loading low priority
 635   //     requests.
 636   //
 637   //  COALESCED Clients never load requests, with the following exceptions:
 638   //   * Non-delayable requests are issued imediately.
 639   //   * On a (currently 5 second) heart beat, they load all requests as an
 640   //     UNTHROTTLED Client, and then return to the COALESCED state.
 641   //   * When an active Client makes a request, they are THROTTLED until the
 642   //     active Client finishes loading.
 643   ShouldStartReqResult ShouldStartRequest(
 644       ScheduledResourceRequest* request) const {
 645     const net::URLRequest& url_request = *request->url_request();
 646     // Syncronous requests could block the entire render, which could impact
 647     // user-observable Clients.
 648     if (!ResourceRequestInfo::ForRequest(&url_request)->IsAsync()) {
 649       return START_REQUEST;
 650     }
 651
 652     // TODO(simonjam): This may end up causing disk contention. We should
 653     // experiment with throttling if that happens.
 654     // TODO(aiolos): We probably want to Coalesce these as well to avoid
 655     // waking the disk.
 656     if (!url_request.url().SchemeIsHTTPOrHTTPS()) {
 657       return START_REQUEST;
 658     }
 659
 660     if (throttle_state_ == COALESCED) {
 661       return DO_NOT_START_REQUEST_AND_STOP_SEARCHING;
 662     }
 663
 664     if (using_spdy_proxy_ && url_request.url().SchemeIs(url::kHttpScheme)) {
 665       return START_REQUEST;
 666     }
 667
 668     net::HostPortPair host_port_pair =
 669         net::HostPortPair::FromURL(url_request.url());
 670     net::HttpServerProperties& http_server_properties =
 671         *url_request.context()->http_server_properties();
 672
 673     // TODO(willchan): We should really improve this algorithm as described in
 674     // crbug.com/164101. Also, theoretically we should not count a SPDY request
 675     // against the delayable requests limit.
 676     if (http_server_properties.SupportsSpdy(host_port_pair)) {
 677       return START_REQUEST;
 678     }
 679
 680     if (throttle_state_ == THROTTLED &&
 681         in_flight_requests_.size() >= kMaxNumThrottledRequestsPerClient) {
 682       // There may still be SPDY-capable requests that should be issued.
 683       return DO_NOT_START_REQUEST_AND_KEEP_SEARCHING;
 684     }
 685
 686     // High-priority and layout-blocking requests.
 687     if (url_request.priority() >= net::LOW) {
 688       return START_REQUEST;
 689     }
 690
 691     if (in_flight_delayable_count_ >= kMaxNumDelayableRequestsPerClient) {
 692       return DO_NOT_START_REQUEST_AND_STOP_SEARCHING;
 693     }
 694
 695     if (ShouldKeepSearching(host_port_pair)) {
 696       // There may be other requests for other hosts we'd allow,
 697       // so keep checking.
 698       return DO_NOT_START_REQUEST_AND_KEEP_SEARCHING;
 699     }
 700
 701     bool have_immediate_requests_in_flight =
 702         in_flight_requests_.size() > in_flight_delayable_count_;
 703     if (have_immediate_requests_in_flight &&
 704         (!has_body_ || total_layout_blocking_count_ != 0) &&
 705         in_flight_delayable_count_ != 0) {
 706       return DO_NOT_START_REQUEST_AND_STOP_SEARCHING;
 707     }
 708
 709     return START_REQUEST;
 710   }
 711
 712   void LoadAnyStartablePendingRequests() {
 713     // We iterate through all the pending requests, starting with the highest
 714     // priority one. For each entry, one of three things can happen:
 715     // 1) We start the request, remove it from the list, and keep checking.
 716     // 2) We do NOT start the request, but ShouldStartRequest() signals us that
 717     //     there may be room for other requests, so we keep checking and leave
 718     //     the previous request still in the list.
 719     // 3) We do not start the request, same as above, but StartRequest() tells
 720     //     us there's no point in checking any further requests.
 721     RequestQueue::NetQueue::iterator request_iter =
 722         pending_requests_.GetNextHighestIterator();
 723
 724     while (request_iter != pending_requests_.End()) {
 725       ScheduledResourceRequest* request = *request_iter;
 726       ShouldStartReqResult query_result = ShouldStartRequest(request);
 727
 728       if (query_result == START_REQUEST) {
 729         pending_requests_.Erase(request);
 730         StartRequest(request);
 731
 732         // StartRequest can modify the pending list, so we (re)start evaluation
 733         // from the currently highest priority request. Avoid copying a singular
 734         // iterator, which would trigger undefined behavior.
 735         if (pending_requests_.GetNextHighestIterator() ==
 736             pending_requests_.End())
 737           break;
 738         request_iter = pending_requests_.GetNextHighestIterator();
 739       } else if (query_result == DO_NOT_START_REQUEST_AND_KEEP_SEARCHING) {
 740         ++request_iter;
 741         continue;
 742       } else {
 743         DCHECK(query_result == DO_NOT_START_REQUEST_AND_STOP_SEARCHING);
 744         break;
 745       }
 746     }
 747   }
 748
 749   bool is_audible_;
 750   bool is_visible_;
 751   bool is_loaded_;
 752   bool is_paused_;
 753   bool has_body_;
 754   bool using_spdy_proxy_;
 755   RequestQueue pending_requests_;
 756   RequestSet in_flight_requests_;
 757   ResourceScheduler* scheduler_;
 758   // The number of delayable in-flight requests.
 759   size_t in_flight_delayable_count_;
 760   // The number of layout-blocking in-flight requests.
 761   size_t total_layout_blocking_count_;
 762   ResourceScheduler::ClientThrottleState throttle_state_;
 763 };
 764
 765 ResourceScheduler::ResourceScheduler()
 766     : should_coalesce_(false),
 767       should_throttle_(false),
 768       active_clients_loading_(0),
 769       coalesced_clients_(0),
 770       coalescing_timer_(new base::Timer(true /* retain_user_task */,
 771                                         true /* is_repeating */)) {
 772   std::string throttling_trial_group =
 773       base::FieldTrialList::FindFullName("RequestThrottlingAndCoalescing");
 774   if (throttling_trial_group == "Throttle") {
 775     should_throttle_ = true;
 776   } else if (throttling_trial_group == "Coalesce") {
 777     should_coalesce_ = true;
 778     should_throttle_ = true;
 779   }
 780 }
 781
 782 ResourceScheduler::~ResourceScheduler() {
 783   DCHECK(unowned_requests_.empty());
 784   DCHECK(client_map_.empty());
 785 }
 786
 787 void ResourceScheduler::SetThrottleOptionsForTesting(bool should_throttle,
 788                                                      bool should_coalesce) {
 789   should_coalesce_ = should_coalesce;
 790   should_throttle_ = should_throttle;
 791   OnLoadingActiveClientsStateChangedForAllClients();
 792 }
 793
 794 ResourceScheduler::ClientThrottleState
 795 ResourceScheduler::GetClientStateForTesting(int child_id, int route_id) {
 796   Client* client = GetClient(child_id, route_id);
 797   DCHECK(client);
 798   return client->throttle_state();
 799 }
 800
 801 scoped_ptr<ResourceThrottle> ResourceScheduler::ScheduleRequest(
 802     int child_id,
 803     int route_id,
 804     net::URLRequest* url_request) {
 805   DCHECK(CalledOnValidThread());
 806   ClientId client_id = MakeClientId(child_id, route_id);
 807   scoped_ptr<ScheduledResourceRequest> request(new ScheduledResourceRequest(
 808       client_id,
 809       url_request,
 810       this,
 811       RequestPriorityParams(url_request->priority(), 0)));
 812
 813   ClientMap::iterator it = client_map_.find(client_id);
 814   if (it == client_map_.end()) {
 815     // There are several ways this could happen:
 816     // 1. <a ping> requests don't have a route_id.
 817     // 2. Most unittests don't send the IPCs needed to register Clients.
 818     // 3. The tab is closed while a RequestResource IPC is in flight.
 819     unowned_requests_.insert(request.get());
 820     request->Start();
 821     return request.Pass();
 822   }
 823
 824   Client* client = it->second;
 825   client->ScheduleRequest(url_request, request.get());
 826   return request.Pass();
 827 }
 828
 829 void ResourceScheduler::RemoveRequest(ScheduledResourceRequest* request) {
 830   DCHECK(CalledOnValidThread());
 831   if (ContainsKey(unowned_requests_, request)) {
 832     unowned_requests_.erase(request);
 833     return;
 834   }
 835
 836   ClientMap::iterator client_it = client_map_.find(request->client_id());
 837   if (client_it == client_map_.end()) {
 838     return;
 839   }
 840
 841   Client* client = client_it->second;
 842   client->RemoveRequest(request);
 843 }
 844
 845 void ResourceScheduler::OnClientCreated(int child_id,
 846                                         int route_id,
 847                                         bool is_visible,
 848                                         bool is_audible) {
 849   DCHECK(CalledOnValidThread());
 850   ClientId client_id = MakeClientId(child_id, route_id);
 851   DCHECK(!ContainsKey(client_map_, client_id));
 852
 853   Client* client = new Client(this, is_visible, is_audible);
 854   client_map_[client_id] = client;
 855
 856   // TODO(aiolos): set Client visibility/audibility when signals are added
 857   // this will UNTHROTTLE Clients as needed
 858   client->UpdateThrottleState();
 859 }
 860
 861 void ResourceScheduler::OnClientDeleted(int child_id, int route_id) {
 862   DCHECK(CalledOnValidThread());
 863   ClientId client_id = MakeClientId(child_id, route_id);
 864   DCHECK(ContainsKey(client_map_, client_id));
 865   ClientMap::iterator it = client_map_.find(client_id);
 866   if (it == client_map_.end())
 867     return;
 868
 869   Client* client = it->second;
 870   // FYI, ResourceDispatcherHost cancels all of the requests after this function
 871   // is called. It should end up canceling all of the requests except for a
 872   // cross-renderer navigation.
 873   RequestSet client_unowned_requests = client->RemoveAllRequests();
 874   for (RequestSet::iterator it = client_unowned_requests.begin();
 875        it != client_unowned_requests.end(); ++it) {
 876     unowned_requests_.insert(*it);
 877   }
 878
 879   delete client;
 880   client_map_.erase(it);
 881 }
 882
 883 void ResourceScheduler::OnLoadingStateChanged(int child_id,
 884                                               int route_id,
 885                                               bool is_loaded) {
 886   Client* client = GetClient(child_id, route_id);
 887   DCHECK(client);
 888   client->OnLoadingStateChanged(is_loaded);
 889 }
 890
 891 void ResourceScheduler::OnVisibilityChanged(int child_id,
 892                                             int route_id,
 893                                             bool is_visible) {
 894   Client* client = GetClient(child_id, route_id);
 895   DCHECK(client);
 896   client->OnVisibilityChanged(is_visible);
 897 }
 898
 899 void ResourceScheduler::OnAudibilityChanged(int child_id,
 900                                             int route_id,
 901                                             bool is_audible) {
 902   Client* client = GetClient(child_id, route_id);
 903   // We might get this call after the client has been deleted.
 904   if (client)
 905     client->OnAudibilityChanged(is_audible);
 906 }
 907
 908 void ResourceScheduler::OnNavigate(int child_id, int route_id) {
 909   DCHECK(CalledOnValidThread());
 910   ClientId client_id = MakeClientId(child_id, route_id);
 911
 912   ClientMap::iterator it = client_map_.find(client_id);
 913   if (it == client_map_.end()) {
 914     // The client was likely deleted shortly before we received this IPC.
 915     return;
 916   }
 917
 918   Client* client = it->second;
 919   client->OnNavigate();
 920 }
 921
 922 void ResourceScheduler::OnWillInsertBody(int child_id, int route_id) {
 923   DCHECK(CalledOnValidThread());
 924   ClientId client_id = MakeClientId(child_id, route_id);
 925
 926   ClientMap::iterator it = client_map_.find(client_id);
 927   if (it == client_map_.end()) {
 928     // The client was likely deleted shortly before we received this IPC.
 929     return;
 930   }
 931
 932   Client* client = it->second;
 933   client->OnWillInsertBody();
 934 }
 935
 936 void ResourceScheduler::OnReceivedSpdyProxiedHttpResponse(
 937     int child_id,
 938     int route_id) {
 939   DCHECK(CalledOnValidThread());
 940   ClientId client_id = MakeClientId(child_id, route_id);
 941
 942   ClientMap::iterator client_it = client_map_.find(client_id);
 943   if (client_it == client_map_.end()) {
 944     return;
 945   }
 946
 947   Client* client = client_it->second;
 948   client->OnReceivedSpdyProxiedHttpResponse();
 949 }
 950
 951 bool ResourceScheduler::IsClientVisibleForTesting(int child_id, int route_id) {
 952   Client* client = GetClient(child_id, route_id);
 953   DCHECK(client);
 954   return client->is_visible();
 955 }
 956
 957 ResourceScheduler::Client* ResourceScheduler::GetClient(int child_id,
 958                                                         int route_id) {
 959   ClientId client_id = MakeClientId(child_id, route_id);
 960   ClientMap::iterator client_it = client_map_.find(client_id);
 961   if (client_it == client_map_.end()) {
 962     return NULL;
 963   }
 964   return client_it->second;
 965 }
 966
 967 void ResourceScheduler::DecrementActiveClientsLoading() {
 968   DCHECK_NE(0u, active_clients_loading_);
 969   --active_clients_loading_;
 970   DCHECK_EQ(active_clients_loading_, CountActiveClientsLoading());
 971   if (active_clients_loading_ == 0) {
 972     OnLoadingActiveClientsStateChangedForAllClients();
 973   }
 974 }
 975
 976 void ResourceScheduler::IncrementActiveClientsLoading() {
 977   ++active_clients_loading_;
 978   DCHECK_EQ(active_clients_loading_, CountActiveClientsLoading());
 979   if (active_clients_loading_ == 1) {
 980     OnLoadingActiveClientsStateChangedForAllClients();
 981   }
 982 }
 983
 984 void ResourceScheduler::OnLoadingActiveClientsStateChangedForAllClients() {
 985   ClientMap::iterator client_it = client_map_.begin();
 986   while (client_it != client_map_.end()) {
 987     Client* client = client_it->second;
 988     client->UpdateThrottleState();
 989     ++client_it;
 990   }
 991 }
 992
 993 size_t ResourceScheduler::CountActiveClientsLoading() const {
 994   size_t active_and_loading = 0;
 995   ClientMap::const_iterator client_it = client_map_.begin();
 996   while (client_it != client_map_.end()) {
 997     Client* client = client_it->second;
 998     if (client->throttle_state() == ACTIVE_AND_LOADING) {
 999       ++active_and_loading;
1000     }
1001     ++client_it;
1002   }
1003   return active_and_loading;
1004 }
1005
1006 void ResourceScheduler::IncrementCoalescedClients() {
1007   ++coalesced_clients_;
1008   DCHECK(should_coalesce_);
1009   DCHECK_EQ(coalesced_clients_, CountCoalescedClients());
1010   if (coalesced_clients_ == 1) {
1011     coalescing_timer_->Start(
1012         FROM_HERE,
1013         base::TimeDelta::FromMilliseconds(kCoalescedTimerPeriod),
1014         base::Bind(&ResourceScheduler::LoadCoalescedRequests,
1015                    base::Unretained(this)));
1016   }
1017 }
1018
1019 void ResourceScheduler::DecrementCoalescedClients() {
1020   DCHECK(should_coalesce_);
1021   DCHECK_NE(0U, coalesced_clients_);
1022   --coalesced_clients_;
1023   DCHECK_EQ(coalesced_clients_, CountCoalescedClients());
1024   if (coalesced_clients_ == 0) {
1025     coalescing_timer_->Stop();
1026   }
1027 }
1028
1029 size_t ResourceScheduler::CountCoalescedClients() const {
1030   DCHECK(should_coalesce_);
1031   size_t coalesced_clients = 0;
1032   ClientMap::const_iterator client_it = client_map_.begin();
1033   while (client_it != client_map_.end()) {
1034     Client* client = client_it->second;
1035     if (client->throttle_state() == COALESCED) {
1036       ++coalesced_clients;
1037     }
1038     ++client_it;
1039   }
1040   return coalesced_clients_;
1041 }
1042
1043 void ResourceScheduler::LoadCoalescedRequests() {
1044   DCHECK(should_coalesce_);
1045   ClientMap::iterator client_it = client_map_.begin();
1046   while (client_it != client_map_.end()) {
1047     Client* client = client_it->second;
1048     client->LoadCoalescedRequests();
1049     ++client_it;
1050   }
1051 }
1052
1053 ResourceScheduler::ClientState ResourceScheduler::GetClientState(
1054     ClientId client_id) const {
1055   ClientMap::const_iterator client_it = client_map_.find(client_id);
1056   if (client_it == client_map_.end())
1057     return UNKNOWN;
1058   return client_it->second->is_active() ? ACTIVE : BACKGROUND;
1059 }
1060
1061 void ResourceScheduler::ReprioritizeRequest(ScheduledResourceRequest* request,
1062                                             net::RequestPriority new_priority,
1063                                             int new_intra_priority_value) {
1064   if (request->url_request()->load_flags() & net::LOAD_IGNORE_LIMITS) {
1065     // We should not be re-prioritizing requests with the
1066     // IGNORE_LIMITS flag.
1067     NOTREACHED();
1068     return;
1069   }
1070   RequestPriorityParams new_priority_params(new_priority,
1071       new_intra_priority_value);
1072   RequestPriorityParams old_priority_params =
1073       request->get_request_priority_params();
1074
1075   DCHECK(old_priority_params != new_priority_params);
1076
1077   ClientMap::iterator client_it = client_map_.find(request->client_id());
1078   if (client_it == client_map_.end()) {
1079     // The client was likely deleted shortly before we received this IPC.
1080     request->url_request()->SetPriority(new_priority_params.priority);
1081     request->set_request_priority_params(new_priority_params);
1082     return;
1083   }
1084
1085   if (old_priority_params == new_priority_params)
1086     return;
1087
1088   Client *client = client_it->second;
1089   client->ReprioritizeRequest(
1090       request, old_priority_params, new_priority_params);
1091 }
1092
1093 ResourceScheduler::ClientId ResourceScheduler::MakeClientId(
1094     int child_id, int route_id) {
1095   return (static_cast<ResourceScheduler::ClientId>(child_id) << 32) | route_id;
1096 }
1097
1098 }  // namespace content