Protected Audience: prepare contexts only if we received promises

We're currently preparing more bidder contexts than we need. Aborted
auctions are likely a major cause of unused contexts. Only prepare
contexts if we've received promises (using promises as an indicator that
an auction is likely to proceed).

Bug: 405175230
Change-Id: I5a0c64d39cfe90029ea4384cd16e4ed025b24baa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6377184
Reviewed-by: Russ Hamilton <behamilton@google.com>
Commit-Queue: Abigail Katcoff <abigailkatcoff@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1436100}

content/services/auction_worklet/bidder_worklet.cc

@@ -788,6 +788,12 @@ void BidderWorklet::FinishGenerateBid(
   task->finalize_generate_bid_receiver_id = std::nullopt;
   task->wait_promises = base::TimeTicks::Now() - task->trace_wait_deps_start;
   GenerateBidIfReady(task);
+  if (!finalized_any_bid_) {
+    finalized_any_bid_ = true;
+    if (features::kFledgeWaitForPromisesToPrepareContexts.Get()) {
+      MaybePrepareContexts();
+    }
+  }
 }
 
 BidderWorklet::GenerateBidTask::GenerateBidTask() = default;
@@ -2499,6 +2505,8 @@ void BidderWorklet::MaybePrepareContexts() {
   if (!base::FeatureList::IsEnabled(
           features::kFledgePrepareBidderContextsInAdvance) ||
       generate_bid_tasks_.empty() || !IsCodeReady() ||
+      (!finalized_any_bid_ &&
+       features::kFledgeWaitForPromisesToPrepareContexts.Get()) ||
       base::FeatureList::IsEnabled(features::kFledgeAlwaysReuseBidderContext)) {
     return;
   }

content/services/auction_worklet/bidder_worklet.h

@@ -947,6 +947,11 @@ class CONTENT_EXPORT BidderWorklet : public mojom::BidderWorklet,
                               GenerateBidTaskList::iterator>
       finalize_receiver_set_;
 
+  // Whether any bid was finalized. We use this as a heuristic to indicate that
+  // at least one auction is going to proceed without being aborted. In
+  // particular, we use it to determine whether we should prepare contexts.
+  bool finalized_any_bid_ = false;
+
   ClosePipeCallback close_pipe_callback_;
 
   // Errors that occurred while loading the code, if any.

content/services/auction_worklet/bidder_worklet_unittest.cc

@@ -884,6 +884,22 @@ class BidderWorkletTest : public testing::Test {
         direct_from_seller_auction_signals_header_ad_slot_);
   }
 
+  void FinishGenerateBid(
+      mojo::AssociatedRemote<auction_worklet::mojom::GenerateBidFinalizer>&
+          bid_finalizer) {
+    bid_finalizer->FinishGenerateBid(
+        auction_signals_, per_buyer_signals_, per_buyer_timeout_,
+        per_buyer_currency_,
+        provide_direct_from_seller_signals_late_
+            ? direct_from_seller_per_buyer_signals_
+            : std::nullopt,
+        direct_from_seller_per_buyer_signals_header_ad_slot_,
+        provide_direct_from_seller_signals_late_
+            ? direct_from_seller_auction_signals_
+            : std::nullopt,
+        direct_from_seller_auction_signals_header_ad_slot_);
+  }
+
   // Calls BeginGenerateBid()/FinishGenerateBid(), expecting the
   // GenerateBidClient's OnGenerateBidComplete() method never to be invoked.
   void GenerateBidExpectingNeverCompletes(
@@ -9138,6 +9154,116 @@ TEST_P(BidderWorkletMultiThreadingTest,
       "Ads.InterestGroup.Auction.PremadeContextsScheduledPerThread", 0);
 }
 
+TEST_P(BidderWorkletMultiThreadingTest,
+       PreparesContextsIfFinishGenerateBidBeforeOrAfterJavascriptDownload) {
+  base::test::ScopedFeatureList scoped_feature_list;
+  scoped_feature_list.InitAndEnableFeatureWithParameters(
+      features::kFledgePrepareBidderContextsInAdvance,
+      {{"WaitForPromisesToPrepareContexts", "true"}});
+  interest_group_trusted_bidding_signals_url_ = GURL("https://signals.test/");
+  const GURL kFullSignalsUrl(
+      "https://signals.test/?hostname=top.window.test&interestGroupNames=Fred");
+
+  const char kJson[] = R"({"perInterestGroupData":
+                         {"Fred": {"priorityVector": {"foo": 1.0}}}
+                       })";
+
+  for (bool finalize_before_js_download : {true, false}) {
+    SCOPED_TRACE(finalize_before_js_download);
+    url_loader_factory_.ClearResponses();
+    auto bidder_worklet = CreateWorklet();
+
+    base::HistogramTester histogram_tester;
+    generate_bid_run_loop_ = std::make_unique<base::RunLoop>();
+    mojo::AssociatedRemote<auction_worklet::mojom::GenerateBidFinalizer>
+        bid_finalizer;
+
+    BeginGenerateBid(bidder_worklet.get(),
+                     bid_finalizer.BindNewEndpointAndPassReceiver());
+
+    if (finalize_before_js_download) {
+      FinishGenerateBid(bid_finalizer);
+      task_environment_.RunUntilIdle();
+      AddJavascriptResponse(&url_loader_factory_, interest_group_bidding_url_,
+                            CreateBasicGenerateBidScript());
+    } else {
+      AddJavascriptResponse(&url_loader_factory_, interest_group_bidding_url_,
+                            CreateBasicGenerateBidScript());
+      task_environment_.RunUntilIdle();
+      FinishGenerateBid(bid_finalizer);
+    }
+
+    task_environment_.RunUntilIdle();
+    EXPECT_FALSE(generate_bid_run_loop_->AnyQuitCalled());
+
+    histogram_tester.ExpectTotalCount(
+        "Ads.InterestGroup.Auction.UsedPremadeContext", 0);
+
+    AddBidderJsonResponse(&url_loader_factory_, kFullSignalsUrl, kJson);
+    task_environment_.RunUntilIdle();
+
+    generate_bid_run_loop_->Run();
+    generate_bid_run_loop_.reset();
+
+    histogram_tester.ExpectUniqueSample(
+        "Ads.InterestGroup.Auction.UsedPremadeContext", true, 1);
+    histogram_tester.ExpectTotalCount(
+        "Ads.InterestGroup.Auction.PremadeContextsScheduledPerThread", 1);
+  }
+}
+
+TEST_P(BidderWorkletMultiThreadingTest,
+       DoesNotPrepareContextsBeforeFinishGenerateBidIfWaitForPromisesEnabled) {
+  interest_group_trusted_bidding_signals_url_ = GURL("https://signals.test/");
+  const GURL kFullSignalsUrl(
+      "https://signals.test/?hostname=top.window.test&interestGroupNames=Fred");
+
+  const char kJson[] = R"({"perInterestGroupData":
+                       {"Fred": {"priorityVector": {"foo": 1.0}}}
+                     })";
+
+  for (bool wait_for_promises : {true, false}) {
+    SCOPED_TRACE(wait_for_promises);
+    url_loader_factory_.ClearResponses();
+    base::test::ScopedFeatureList scoped_feature_list;
+    scoped_feature_list.InitAndEnableFeatureWithParameters(
+        features::kFledgePrepareBidderContextsInAdvance,
+        {{"WaitForPromisesToPrepareContexts",
+          wait_for_promises ? "true" : "false"}});
+    auto bidder_worklet = CreateWorklet();
+    AddJavascriptResponse(&url_loader_factory_, interest_group_bidding_url_,
+                          CreateBasicGenerateBidScript());
+
+    base::HistogramTester histogram_tester;
+    generate_bid_run_loop_ = std::make_unique<base::RunLoop>();
+    mojo::AssociatedRemote<auction_worklet::mojom::GenerateBidFinalizer>
+        bid_finalizer;
+    BeginGenerateBid(bidder_worklet.get(),
+                     bid_finalizer.BindNewEndpointAndPassReceiver());
+    task_environment_.RunUntilIdle();
+    EXPECT_FALSE(generate_bid_run_loop_->AnyQuitCalled());
+
+    histogram_tester.ExpectTotalCount(
+        "Ads.InterestGroup.Auction.UsedPremadeContext", 0);
+
+    AddBidderJsonResponse(&url_loader_factory_, kFullSignalsUrl, kJson);
+    task_environment_.RunUntilIdle();
+
+    // FinishGenerateBid should cause us to generate our bid, but because this
+    // is coming after signals, we never got a chance to prepare contexts.
+    FinishGenerateBid(bid_finalizer);
+
+    generate_bid_run_loop_->Run();
+    generate_bid_run_loop_.reset();
+
+    histogram_tester.ExpectUniqueSample(
+        "Ads.InterestGroup.Auction.UsedPremadeContext", !wait_for_promises, 1);
+    histogram_tester.ExpectTotalCount(
+        "Ads.InterestGroup.Auction.PremadeContextsScheduledPerThread",
+        !wait_for_promises);
+  }
+}
+
 TEST_P(BidderWorkletMultiThreadingTest,
        DoesNotMakeMorePremadeContextsAfterFirstGenerateBid) {
   base::test::ScopedFeatureList scoped_feature_list;

content/services/auction_worklet/public/cpp/auction_worklet_features.cc

@@ -61,6 +61,11 @@ BASE_FEATURE_PARAM(int,
                    &kFledgePrepareBidderContextsInAdvance,
                    "BidderContextsMultiplier",
                    1);
+BASE_FEATURE_PARAM(bool,
+                   kFledgeWaitForPromisesToPrepareContexts,
+                   &kFledgePrepareBidderContextsInAdvance,
+                   "WaitForPromisesToPrepareContexts",
+                   false);
 
 BASE_FEATURE(kFledgeBidderUseBalancingThreadSelector,
              "FledgeBidderUseBalancingThreadSelector",

content/services/auction_worklet/public/cpp/auction_worklet_features.h

@@ -45,6 +45,9 @@ CONTENT_EXPORT BASE_DECLARE_FEATURE_PARAM(
     kFledgeMinBidderContextsPerThreadInAdvance);
 CONTENT_EXPORT BASE_DECLARE_FEATURE_PARAM(int, kFledgeBidderContextsDivisor);
 CONTENT_EXPORT BASE_DECLARE_FEATURE_PARAM(int, kFledgeBidderContextsMultiplier);
+CONTENT_EXPORT BASE_DECLARE_FEATURE_PARAM(
+    bool,
+    kFledgeWaitForPromisesToPrepareContexts);
 
 // Instead of using a hash to assign group-by-origin IGs to threads, use
 // a round robin on joining-origin while ensuring a maximum allowed imbalance