Don't start a second pre-render if one is in progress.

components/offline_pages/background/request_coordinator.cc

 // Copyright 2016 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 "components/offline_pages/background/request_coordinator.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/logging.h"
 #include "components/offline_pages/background/offliner_factory.h"
 #include "components/offline_pages/background/offliner_policy.h"
 #include "components/offline_pages/background/request_picker.h"
 #include "components/offline_pages/background/save_page_request.h"
 #include "components/offline_pages/background/scheduler.h"
 #include "components/offline_pages/offline_page_item.h"
 
 namespace offline_pages {
 
 RequestCoordinator::RequestCoordinator(std::unique_ptr<OfflinerPolicy> policy,
                                        std::unique_ptr<OfflinerFactory> factory,
                                        std::unique_ptr<RequestQueue> queue,
                                        std::unique_ptr<Scheduler> scheduler)
-    : policy_(std::move(policy)),
+    : is_busy_(false),
+      policy_(std::move(policy)),
       factory_(std::move(factory)),
       queue_(std::move(queue)),
       scheduler_(std::move(scheduler)),
       last_offlining_status_(Offliner::RequestStatus::UNKNOWN),
       weak_ptr_factory_(this) {
   DCHECK(policy_ != nullptr);
   picker_.reset(new RequestPicker(queue_.get()));
 }
 
 RequestCoordinator::~RequestCoordinator() {}
 
 bool RequestCoordinator::SavePageLater(
     const GURL& url, const ClientId& client_id) {
   DVLOG(2) << "URL is " << url << " " << __FUNCTION__;
 
   // TODO(petewil): We need a robust scheme for allocating new IDs.
   static int64_t id = 0;
 
   // Build a SavePageRequest.
   // TODO(petewil): Use something like base::Clock to help in testing.
   offline_pages::SavePageRequest request(
       id++, url, client_id, base::Time::Now());
 
   // Put the request on the request queue.
   queue_->AddRequest(request,
                      base::Bind(&RequestCoordinator::AddRequestResultCallback,
                                 weak_ptr_factory_.GetWeakPtr()));
-  // TODO(petewil): Do I need to persist the request in case the add fails?
-
-  // TODO(petewil): Make a new chromium command line switch to send the request
-  // immediately for testing.  It should call SendRequestToOffliner()
-
   return true;
 }
 
 void RequestCoordinator::AddRequestResultCallback(
     RequestQueue::AddRequestResult result,
     const SavePageRequest& request) {
 
   // Inform the scheduler that we have an outstanding task.
   // TODO(petewil): Define proper TriggerConditions and set them.
   Scheduler::TriggerCondition conditions;
@@ skipping 10 matching lines @@
   SendRequestToOffliner(request);
 }
 
 void RequestCoordinator::RequestQueueEmpty() {
   // Clear the outstanding "safety" task in the scheduler.
   scheduler_->Unschedule();
   // Return control to the scheduler when there is no more to do.
   scheduler_callback_.Run(true);
 }
 
+// Returns true if the caller should expect a callback, false otherwise. For
+// instance, this would return false if a request is already in progress.
 bool RequestCoordinator::StartProcessing(
     const DeviceConditions& device_conditions,
     const base::Callback<void(bool)>& callback) {
+  if (is_busy_) return false;
+
   scheduler_callback_ = callback;
   // TODO(petewil): Check existing conditions (should be passed down from
   // BackgroundTask)
 
   TryNextRequest();
 
-  // TODO(petewil): Should return true if the caller should expect a
-  // callback.  Return false if there is already a request running.
-  // Probably best to do this when I prevent multiple instances from
-  // running at the same time.
   return true;
 }
 
 void RequestCoordinator::TryNextRequest() {
   // Choose a request to process that meets the available conditions.
   // This is an async call, and returns right away.
   picker_->ChooseNextRequest(
       base::Bind(&RequestCoordinator::RequestPicked,
                  weak_ptr_factory_.GetWeakPtr()),
       base::Bind(&RequestCoordinator::RequestQueueEmpty,
                  weak_ptr_factory_.GetWeakPtr()));
 }
 
 void RequestCoordinator::StopProcessing() {
 }
 
 void RequestCoordinator::SendRequestToOffliner(const SavePageRequest& request) {
-  // TODO(petewil): Ensure only one offliner at a time is used.
   // TODO(petewil): When we have multiple offliners, we need to pick one.
   Offliner* offliner = factory_->GetOffliner(policy_.get());
   if (!offliner) {
     DVLOG(0) << "Unable to create Offliner. "
              << "Cannot background offline page.";
     return;
   }
 
+  DCHECK(!is_busy_);
+  is_busy_ = true;
+
   // Start the load and save process in the offliner (Async).
   offliner->LoadAndSave(request,
                         base::Bind(&RequestCoordinator::OfflinerDoneCallback,
                                    weak_ptr_factory_.GetWeakPtr()));
 }
 
 void RequestCoordinator::OfflinerDoneCallback(const SavePageRequest& request,
                                               Offliner::RequestStatus status) {
   DVLOG(2) << "offliner finished, saved: "
            << (status == Offliner::RequestStatus::SAVED) << ", "
            << __FUNCTION__;
   last_offlining_status_ = status;
 
+  is_busy_ = false;
+
   // If the request succeeded, remove it from the Queue and maybe schedule
   // another one.
   if (status == Offliner::RequestStatus::SAVED) {
     queue_->RemoveRequest(request.request_id(),
                           base::Bind(&RequestCoordinator::UpdateRequestCallback,
                                      weak_ptr_factory_.GetWeakPtr()));
 
     // TODO(petewil): Check time budget. Return to the scheduler if we are out.
 
     // Start another request if we have time.
     TryNextRequest();
   }
 }
 
 }  // namespace offline_pages