HttpCache::Transaction layer allowing parallel validation

net/http/http_cache_unittest.cc

Index: net/http/http_cache_unittest.cc
diff --git a/net/http/http_cache_unittest.cc b/net/http/http_cache_unittest.cc
index 13182e43f640f9b903d42de3ea9fb53c4c9481f6..62269b7952c8b89bc3d66dc773b42c22f62311fb 100644
--- a/net/http/http_cache_unittest.cc
+++ b/net/http/http_cache_unittest.cc
@@ -147,6 +147,10 @@ void TestLoadTimingCachedResponse(const LoadTimingInfo& load_timing_info) {
   EXPECT_TRUE(load_timing_info.receive_headers_end.is_null());
 }
 
+void DeferNetworkStart(bool* defer) {
+  *defer = true;
+}
+
 class DeleteCacheCompletionCallback : public TestCompletionCallbackBase {
  public:
   explicit DeleteCacheCompletionCallback(MockHttpCache* cache)
@@ -182,6 +186,17 @@ void ReadAndVerifyTransaction(HttpTransaction* trans,
   EXPECT_EQ(expected, content);
 }
 
+void ReadRemainingAndVerifyTransaction(HttpTransaction* trans,
+                                       std::string& already_read,
+                                       const MockTransaction& trans_info) {
+  std::string content;
+  int rv = ReadTransaction(trans, &content);
+  EXPECT_THAT(rv, IsOk());
+
+  std::string expected(trans_info.data);
+  EXPECT_EQ(expected, already_read + content);
+}
+
 void RunTransactionTestBase(HttpCache* cache,
                             const MockTransaction& trans_info,
                             const MockHttpRequest& request,
@@ -1176,180 +1191,1036 @@ TEST(HttpCache, SimpleGET_LoadBypassCache_Implicit) {
   MockTransaction transaction(kSimpleGET_Transaction);
   transaction.request_headers = "pragma: no-cache\r\n";
 
-  RunTransactionTest(cache.http_cache(), transaction);
+  RunTransactionTest(cache.http_cache(), transaction);
+
+  EXPECT_EQ(2, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(2, cache.disk_cache()->create_count());
+}
+
+TEST(HttpCache, SimpleGET_LoadBypassCache_Implicit2) {
+  MockHttpCache cache;
+
+  // write to the cache
+  RunTransactionTest(cache.http_cache(), kSimpleGET_Transaction);
+
+  // force this transaction to write to the cache again
+  MockTransaction transaction(kSimpleGET_Transaction);
+  transaction.request_headers = "cache-control: no-cache\r\n";
+
+  RunTransactionTest(cache.http_cache(), transaction);
+
+  EXPECT_EQ(2, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(2, cache.disk_cache()->create_count());
+}
+
+TEST(HttpCache, SimpleGET_LoadValidateCache) {
+  MockHttpCache cache;
+
+  // Write to the cache.
+  RunTransactionTest(cache.http_cache(), kSimpleGET_Transaction);
+
+  // Read from the cache.
+  RunTransactionTest(cache.http_cache(), kSimpleGET_Transaction);
+
+  // Force this transaction to validate the cache.
+  MockTransaction transaction(kSimpleGET_Transaction);
+  transaction.load_flags |= LOAD_VALIDATE_CACHE;
+
+  HttpResponseInfo response_info;
+  BoundTestNetLog log;
+  LoadTimingInfo load_timing_info;
+  RunTransactionTestWithResponseInfoAndGetTiming(
+      cache.http_cache(), transaction, &response_info, log.bound(),
+      &load_timing_info);
+
+  EXPECT_EQ(2, cache.network_layer()->transaction_count());
+  EXPECT_EQ(1, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+  EXPECT_TRUE(response_info.network_accessed);
+  TestLoadTimingNetworkRequest(load_timing_info);
+}
+
+TEST(HttpCache, SimpleGET_LoadValidateCache_Implicit) {
+  MockHttpCache cache;
+
+  // write to the cache
+  RunTransactionTest(cache.http_cache(), kSimpleGET_Transaction);
+
+  // read from the cache
+  RunTransactionTest(cache.http_cache(), kSimpleGET_Transaction);
+
+  // force this transaction to validate the cache
+  MockTransaction transaction(kSimpleGET_Transaction);
+  transaction.request_headers = "cache-control: max-age=0\r\n";
+
+  RunTransactionTest(cache.http_cache(), transaction);
+
+  EXPECT_EQ(2, cache.network_layer()->transaction_count());
+  EXPECT_EQ(1, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+}
+
+// Tests that |unused_since_prefetch| is updated accordingly (e.g. it is set to
+// true after a prefetch and set back to false when the prefetch is used).
+TEST(HttpCache, SimpleGET_UnusedSincePrefetch) {
+  MockHttpCache cache;
+  HttpResponseInfo response_info;
+
+  // A normal load does not have |unused_since_prefetch| set.
+  RunTransactionTestWithResponseInfoAndGetTiming(
+      cache.http_cache(), kSimpleGET_Transaction, &response_info,
+      BoundTestNetLog().bound(), nullptr);
+  EXPECT_FALSE(response_info.unused_since_prefetch);
+  EXPECT_FALSE(response_info.was_cached);
+
+  // The prefetch itself does not have |unused_since_prefetch| set.
+  MockTransaction prefetch_transaction(kSimpleGET_Transaction);
+  prefetch_transaction.load_flags |= LOAD_PREFETCH;
+  RunTransactionTestWithResponseInfoAndGetTiming(
+      cache.http_cache(), prefetch_transaction, &response_info,
+      BoundTestNetLog().bound(), nullptr);
+  EXPECT_FALSE(response_info.unused_since_prefetch);
+  EXPECT_TRUE(response_info.was_cached);
+
+  // A duplicated prefetch has |unused_since_prefetch| set.
+  RunTransactionTestWithResponseInfoAndGetTiming(
+      cache.http_cache(), prefetch_transaction, &response_info,
+      BoundTestNetLog().bound(), nullptr);
+  EXPECT_TRUE(response_info.unused_since_prefetch);
+  EXPECT_TRUE(response_info.was_cached);
+
+  // |unused_since_prefetch| is still true after two prefetches in a row.
+  RunTransactionTestWithResponseInfoAndGetTiming(
+      cache.http_cache(), kSimpleGET_Transaction, &response_info,
+      BoundTestNetLog().bound(), nullptr);
+  EXPECT_TRUE(response_info.unused_since_prefetch);
+  EXPECT_TRUE(response_info.was_cached);
+
+  // The resource has now been used, back to normal behavior.
+  RunTransactionTestWithResponseInfoAndGetTiming(
+      cache.http_cache(), kSimpleGET_Transaction, &response_info,
+      BoundTestNetLog().bound(), nullptr);
+  EXPECT_FALSE(response_info.unused_since_prefetch);
+  EXPECT_TRUE(response_info.was_cached);
+}
+
+static void PreserveRequestHeaders_Handler(const HttpRequestInfo* request,
+                                           std::string* response_status,
+                                           std::string* response_headers,
+                                           std::string* response_data) {
+  EXPECT_TRUE(request->extra_headers.HasHeader(kExtraHeaderKey));
+}
+
+// Tests that we don't remove extra headers for simple requests.
+TEST(HttpCache, SimpleGET_PreserveRequestHeaders) {
+  MockHttpCache cache;
+
+  MockTransaction transaction(kSimpleGET_Transaction);
+  transaction.handler = PreserveRequestHeaders_Handler;
+  transaction.request_headers = EXTRA_HEADER;
+  transaction.response_headers = "Cache-Control: max-age=0\n";
+  AddMockTransaction(&transaction);
+
+  // Write, then revalidate the entry.
+  RunTransactionTest(cache.http_cache(), transaction);
+  RunTransactionTest(cache.http_cache(), transaction);
+
+  EXPECT_EQ(2, cache.network_layer()->transaction_count());
+  EXPECT_EQ(1, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+  RemoveMockTransaction(&transaction);
+}
+
+// Tests that we don't remove extra headers for conditionalized requests.
+TEST(HttpCache, ConditionalizedGET_PreserveRequestHeaders) {
+  MockHttpCache cache;
+
+  // Write to the cache.
+  RunTransactionTest(cache.http_cache(), kETagGET_Transaction);
+
+  MockTransaction transaction(kETagGET_Transaction);
+  transaction.handler = PreserveRequestHeaders_Handler;
+  transaction.request_headers = "If-None-Match: \"foopy\"\r\n" EXTRA_HEADER;
+  AddMockTransaction(&transaction);
+
+  RunTransactionTest(cache.http_cache(), transaction);
+
+  EXPECT_EQ(2, cache.network_layer()->transaction_count());
+  EXPECT_EQ(1, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+  RemoveMockTransaction(&transaction);
+}
+
+TEST(HttpCache, SimpleGET_ManyReaders) {
+  MockHttpCache cache;
+
+  MockHttpRequest request(kSimpleGET_Transaction);
+
+  std::vector<std::unique_ptr<Context>> context_list;
+  const int kNumTransactions = 5;
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(base::MakeUnique<Context>());
+    auto& c = context_list[i];
+
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+
+    c->result =
+        c->trans->Start(&request, c->callback.callback(), NetLogWithSource());
+  }
+
+  // All requests are waiting for the active entry.
+  for (auto& context : context_list) {
+    EXPECT_EQ(LOAD_STATE_WAITING_FOR_CACHE, context->trans->GetLoadState());
+  }
+
+  // Allow all requests to move from the Create queue to the active entry.
+  base::RunLoop().RunUntilIdle();
+
+  // The first request should be a writer at this point, and the subsequent
+  // requests should have passed the validation phase and waiting for the
+  // response to be written to the cache before they can read.
+  EXPECT_TRUE(cache.IsWriterPresent(kSimpleGET_Transaction.url));
+  EXPECT_EQ(kNumTransactions - 1,
+            cache.GetCountDoneHeadersQueue(kSimpleGET_Transaction.url));
+
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  // All requests depend on the writer, and the writer is between Start and
+  // Read, i.e. idle.
+  for (auto& context : context_list) {
+    EXPECT_EQ(LOAD_STATE_IDLE, context->trans->GetLoadState());
+  }
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    auto& c = context_list[i];
+    if (c->result == ERR_IO_PENDING)
+      c->result = c->callback.WaitForResult();
+
+    if (i > 0) {
+      EXPECT_FALSE(cache.IsWriterPresent(kSimpleGET_Transaction.url));
+      EXPECT_EQ(kNumTransactions - i,
+                cache.GetCountReaders(kSimpleGET_Transaction.url));
+    }
+
+    ReadAndVerifyTransaction(c->trans.get(), kSimpleGET_Transaction);
+  }
+
+  // We should not have had to re-open the disk entry
+
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+}
+
+// Tests that we can have parallel validation on range requests.
+TEST(HttpCache, RangeGET_ParallelValidationNoMatch) {
+  MockHttpCache cache;
+
+  ScopedMockTransaction transaction(kRangeGET_TransactionOK);
+  MockHttpRequest request(transaction);
+
+  std::vector<std::unique_ptr<Context>> context_list;
+  const int kNumTransactions = 5;
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(base::MakeUnique<Context>());
+    auto& c = context_list[i];
+
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+
+    c->result =
+        c->trans->Start(&request, c->callback.callback(), NetLogWithSource());
+  }
+
+  // All requests are waiting for the active entry.
+  for (auto& context : context_list) {
+    EXPECT_EQ(LOAD_STATE_WAITING_FOR_CACHE, context->trans->GetLoadState());
+  }
+
+  // Allow all requests to move from the Create queue to the active entry.
+  base::RunLoop().RunUntilIdle();
+
+  // The first entry should have been doomed. Since the 1st transaction has not
+  // started writing to the cache, MockDiskEntry::CouldBeSparse() returns false
+  // leading to restarting the dooming the entry and restarting the second
+  // transaction.
+  EXPECT_TRUE(cache.IsWriterPresent(kRangeGET_TransactionOK.url));
+  EXPECT_EQ(0, cache.GetCountDoneHeadersQueue(kRangeGET_TransactionOK.url));
+
+  EXPECT_EQ(5, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(5, cache.disk_cache()->create_count());
+
+  for (auto& context : context_list) {
+    EXPECT_EQ(LOAD_STATE_IDLE, context->trans->GetLoadState());
+  }
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    auto& c = context_list[i];
+    if (c->result == ERR_IO_PENDING)
+      c->result = c->callback.WaitForResult();
+
+    ReadAndVerifyTransaction(c->trans.get(), kRangeGET_TransactionOK);
+  }
+
+  EXPECT_EQ(5, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(5, cache.disk_cache()->create_count());
+}
+
+// Tests parallel validation on range requests with non-overlapping ranges.
+TEST(HttpCache, RangeGET_ParallelValidationDifferentRanges) {
+  MockHttpCache cache;
+
+  ScopedMockTransaction transaction(kRangeGET_TransactionOK);
+
+  std::vector<std::unique_ptr<Context>> context_list;
+  const int kNumTransactions = 2;
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(base::MakeUnique<Context>());
+  }
+
+  // Let 1st transaction complete headers phase for ranges 40-49.
+  std::string first_read;
+  {
+    MockHttpRequest request(transaction);
+    auto& c = context_list[0];
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+
+    c->result =
+        c->trans->Start(&request, c->callback.callback(), NetLogWithSource());
+    base::RunLoop().RunUntilIdle();
+
+    // Start writing to the cache so that MockDiskEntry::CouldBeSparse() returns
+    // true.
+    const int kBufferSize = 5;
+    scoped_refptr<IOBuffer> buffer(new IOBuffer(kBufferSize));
+    ReleaseBufferCompletionCallback cb(buffer.get());
+    c->result = c->trans->Read(buffer.get(), kBufferSize, cb.callback());
+    EXPECT_EQ(kBufferSize, cb.GetResult(c->result));
+
+    std::string data_read(buffer->data(), kBufferSize);
+    first_read = data_read;
+
+    EXPECT_EQ(LOAD_STATE_READING_RESPONSE, c->trans->GetLoadState());
+  }
+
+  // 2nd transaction requests ranges 30-39.
+  {
+    transaction.request_headers = "Range: bytes = 30-39\r\n" EXTRA_HEADER;
+    MockHttpRequest request(transaction);
+    auto& c = context_list[1];
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+
+    c->result =
+        c->trans->Start(&request, c->callback.callback(), NetLogWithSource());
+    base::RunLoop().RunUntilIdle();
+
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+  }
+
+  EXPECT_TRUE(cache.IsWriterPresent(kRangeGET_TransactionOK.url));
+  EXPECT_EQ(1, cache.GetCountDoneHeadersQueue(kRangeGET_TransactionOK.url));
+
+  EXPECT_EQ(2, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    auto& c = context_list[i];
+    if (c->result == ERR_IO_PENDING)
+      c->result = c->callback.WaitForResult();
+
+    if (i == 0) {
+      ReadRemainingAndVerifyTransaction(c->trans.get(), first_read,
+                                        transaction);
+      continue;
+    }
+
+    transaction.data = "rg: 30-39 ";
+    ReadAndVerifyTransaction(c->trans.get(), transaction);
+  }
+
+  EXPECT_EQ(2, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  // Fetch from the cache to check that ranges 30-49 have been successfully
+  // cached.
+  {
+    MockTransaction transaction(kRangeGET_TransactionOK);
+    transaction.request_headers = "Range: bytes = 30-49\r\n" EXTRA_HEADER;
+    transaction.data = "rg: 30-39 rg: 40-49 ";
+    std::string headers;
+    RunTransactionTestWithResponse(cache.http_cache(), transaction, &headers);
+    Verify206Response(headers, 30, 49);
+  }
+
+  EXPECT_EQ(2, cache.network_layer()->transaction_count());
+  EXPECT_EQ(1, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+}
+
+// Tests parallel validation on range requests with overlapping ranges.
+TEST(HttpCache, RangeGET_ParallelValidationOverlappingRanges) {
+  MockHttpCache cache;
+
+  ScopedMockTransaction transaction(kRangeGET_TransactionOK);
+
+  std::vector<std::unique_ptr<Context>> context_list;
+  const int kNumTransactions = 2;
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(base::MakeUnique<Context>());
+  }
+
+  // Let 1st transaction complete headers phase for ranges 40-49.
+  std::string first_read;
+  {
+    MockHttpRequest request(transaction);
+    auto& c = context_list[0];
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+
+    c->result =
+        c->trans->Start(&request, c->callback.callback(), NetLogWithSource());
+    base::RunLoop().RunUntilIdle();
+
+    // Start writing to the cache so that MockDiskEntry::CouldBeSparse() returns
+    // true.
+    const int kBufferSize = 5;
+    scoped_refptr<IOBuffer> buffer(new IOBuffer(kBufferSize));
+    ReleaseBufferCompletionCallback cb(buffer.get());
+    c->result = c->trans->Read(buffer.get(), kBufferSize, cb.callback());
+    EXPECT_EQ(kBufferSize, cb.GetResult(c->result));
+
+    std::string data_read(buffer->data(), kBufferSize);
+    first_read = data_read;
+
+    EXPECT_EQ(LOAD_STATE_READING_RESPONSE, c->trans->GetLoadState());
+  }
+
+  // 2nd transaction requests ranges 30-49.
+  {
+    transaction.request_headers = "Range: bytes = 30-49\r\n" EXTRA_HEADER;
+    MockHttpRequest request(transaction);
+    auto& c = context_list[1];
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+
+    c->result =
+        c->trans->Start(&request, c->callback.callback(), NetLogWithSource());
+    base::RunLoop().RunUntilIdle();
+
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+  }
+
+  EXPECT_TRUE(cache.IsWriterPresent(kRangeGET_TransactionOK.url));
+  EXPECT_EQ(1, cache.GetCountDoneHeadersQueue(kRangeGET_TransactionOK.url));
+
+  // Should have created another transaction for the uncached range.
+  EXPECT_EQ(2, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    auto& c = context_list[i];
+    if (c->result == ERR_IO_PENDING)
+      c->result = c->callback.WaitForResult();
+
+    if (i == 0) {
+      ReadRemainingAndVerifyTransaction(c->trans.get(), first_read,
+                                        transaction);
+      continue;
+    }
+
+    transaction.data = "rg: 30-39 rg: 40-49 ";
+    ReadAndVerifyTransaction(c->trans.get(), transaction);
+  }
+
+  EXPECT_EQ(2, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  // Fetch from the cache to check that ranges 30-49 have been successfully
+  // cached.
+  {
+    MockTransaction transaction(kRangeGET_TransactionOK);
+    transaction.request_headers = "Range: bytes = 30-49\r\n" EXTRA_HEADER;
+    transaction.data = "rg: 30-39 rg: 40-49 ";
+    std::string headers;
+    RunTransactionTestWithResponse(cache.http_cache(), transaction, &headers);
+    Verify206Response(headers, 30, 49);
+  }
+
+  EXPECT_EQ(2, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+}
+
+// Parallel validation results in 200.
+TEST(HttpCache, SimpleGET_ParallelValidationNoMatch) {
+  MockHttpCache cache;
+  MockHttpRequest request(kSimpleGET_Transaction);
+  request.load_flags |= LOAD_VALIDATE_CACHE;
+  std::vector<std::unique_ptr<Context>> context_list;
+  const int kNumTransactions = 5;
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(base::MakeUnique<Context>());
+    auto& c = context_list[i];
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+    c->result =
+        c->trans->Start(&request, c->callback.callback(), NetLogWithSource());
+  }
+
+  // All requests are waiting for the active entry.
+  for (auto& context : context_list) {
+    EXPECT_EQ(LOAD_STATE_WAITING_FOR_CACHE, context->trans->GetLoadState());
+  }
+
+  // Allow all requests to move from the Create queue to the active entry.
+  base::RunLoop().RunUntilIdle();
+
+  // The first request should be a writer at this point, and the subsequent
+  // requests should have passed the validation phase and created their own
+  // entries since none of them matched the headers of the earlier one.
+  EXPECT_TRUE(cache.IsWriterPresent(kSimpleGET_Transaction.url));
+
+  // Note that there are only 3 entries created and not 5 since every other
+  // transaction would have gone to the network.
+  EXPECT_EQ(5, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(3, cache.disk_cache()->create_count());
+
+  // All requests depend on the writer, and the writer is between Start and
+  // Read, i.e. idle.
+  for (auto& context : context_list) {
+    EXPECT_EQ(LOAD_STATE_IDLE, context->trans->GetLoadState());
+  }
+
+  for (auto& context : context_list) {
+    if (context->result == ERR_IO_PENDING)
+      context->result = context->callback.WaitForResult();
+    ReadAndVerifyTransaction(context->trans.get(), kSimpleGET_Transaction);
+  }
+
+  EXPECT_EQ(5, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(3, cache.disk_cache()->create_count());
+}
+
+// Tests that a GET followed by a DELETE results in DELETE immediately starting
+// the headers phase and the entry is doomed.
+TEST(HttpCache, SimpleGET_ParallelValidationDelete) {
+  MockHttpCache cache;
+
+  MockHttpRequest request(kSimpleGET_Transaction);
+  request.load_flags |= LOAD_VALIDATE_CACHE;
+
+  MockHttpRequest delete_request(kSimpleGET_Transaction);
+  delete_request.method = "DELETE";
+
+  std::vector<std::unique_ptr<Context>> context_list;
+  const int kNumTransactions = 2;
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(base::MakeUnique<Context>());
+    auto& c = context_list[i];
+
+    MockHttpRequest* this_request = &request;
+    if (i == 1)
+      this_request = &delete_request;
+
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+
+    c->result = c->trans->Start(this_request, c->callback.callback(),
+                                NetLogWithSource());
+  }
+
+  // All requests are waiting for the active entry.
+  for (auto& context : context_list) {
+    EXPECT_EQ(LOAD_STATE_WAITING_FOR_CACHE, context->trans->GetLoadState());
+  }
+
+  // Allow all requests to move from the Create queue to the active entry.
+  base::RunLoop().RunUntilIdle();
+
+  // The first request should be a writer at this point, and the subsequent
+  // request should have passed the validation phase and doomed the existing
+  // entry.
+  EXPECT_TRUE(
+      cache.disk_cache()->IsDiskEntryDoomed(kSimpleGET_Transaction.url));
+
+  EXPECT_EQ(2, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  // All requests depend on the writer, and the writer is between Start and
+  // Read, i.e. idle.
+  for (auto& context : context_list) {
+    EXPECT_EQ(LOAD_STATE_IDLE, context->trans->GetLoadState());
+  }
+
+  for (auto& context : context_list) {
+    if (context->result == ERR_IO_PENDING)
+      context->result = context->callback.WaitForResult();
+    ReadAndVerifyTransaction(context->trans.get(), kSimpleGET_Transaction);
+  }
+
+  EXPECT_EQ(2, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+}
+
+// Tests that a transaction which is in validated queue can be destroyed without
+// any impact to other transactions.
+TEST(HttpCache, SimpleGET_ParallelValidationCancelValidated) {
+  MockHttpCache cache;
+
+  MockHttpRequest request(kSimpleGET_Transaction);
+
+  std::vector<std::unique_ptr<Context>> context_list;
+  const int kNumTransactions = 2;
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(base::MakeUnique<Context>());
+    auto& c = context_list[i];
+
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+
+    c->result =
+        c->trans->Start(&request, c->callback.callback(), NetLogWithSource());
+  }
+
+  // Allow all requests to move from the Create queue to the active entry.
+  base::RunLoop().RunUntilIdle();
+
+  // The first request should be a writer at this point, and the subsequent
+  // requests should have completed validation.
+
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  EXPECT_TRUE(cache.IsWriterPresent(kSimpleGET_Transaction.url));
+  EXPECT_EQ(1, cache.GetCountDoneHeadersQueue(kSimpleGET_Transaction.url));
+
+  context_list[1].reset();
+
+  EXPECT_EQ(0, cache.GetCountDoneHeadersQueue(kSimpleGET_Transaction.url));
+
+  // Complete the rest of the transactions.
+  for (auto& context : context_list) {
+    if (!context)
+      continue;
+    ReadAndVerifyTransaction(context->trans.get(), kSimpleGET_Transaction);
+  }
+
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+}
+
+// Tests that a transaction which is in readers can be destroyed without
+// any impact to other transactions.
+TEST(HttpCache, SimpleGET_ParallelValidationCancelReader) {
+  MockHttpCache cache;
+
+  MockHttpRequest request(kSimpleGET_Transaction);
+
+  MockTransaction transaction(kSimpleGET_Transaction);
+  transaction.load_flags |= LOAD_VALIDATE_CACHE;
+  MockHttpRequest validate_request(transaction);
+
+  int kNumTransactions = 4;
+  std::vector<std::unique_ptr<Context>> context_list;
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(base::MakeUnique<Context>());
+    auto& c = context_list[i];
+
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+
+    MockHttpRequest* this_request = &request;
+    if (i == 3) {
+      this_request = &validate_request;
+      c->trans->SetBeforeNetworkStartCallback(base::Bind(&DeferNetworkStart));
+    }
+
+    c->result = c->trans->Start(this_request, c->callback.callback(),
+                                NetLogWithSource());
+  }
+
+  // Allow all requests to move from the Create queue to the active entry.
+  base::RunLoop().RunUntilIdle();
+
+  EXPECT_EQ(2, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  EXPECT_TRUE(cache.IsWriterPresent(kSimpleGET_Transaction.url));
+  EXPECT_EQ(2, cache.GetCountDoneHeadersQueue(kSimpleGET_Transaction.url));
+  EXPECT_TRUE(cache.IsHeadersTransactionPresent(kSimpleGET_Transaction.url));
+
+  // Complete the response body.
+  auto& c = context_list[0];
+  ReadAndVerifyTransaction(c->trans.get(), kSimpleGET_Transaction);
+
+  // Rest of the transactions should move to readers.
+  EXPECT_FALSE(cache.IsWriterPresent(kSimpleGET_Transaction.url));
+  EXPECT_EQ(2, cache.GetCountReaders(kSimpleGET_Transaction.url));
+  EXPECT_EQ(0, cache.GetCountDoneHeadersQueue(kSimpleGET_Transaction.url));
+  EXPECT_TRUE(cache.IsHeadersTransactionPresent(kSimpleGET_Transaction.url));
+
+  // Add 2 new transactions.
+  kNumTransactions = 6;
+
+  for (int i = 4; i < kNumTransactions; ++i) {
+    context_list.push_back(base::MakeUnique<Context>());
+    auto& c = context_list[i];
+
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+
+    c->result =
+        c->trans->Start(&request, c->callback.callback(), NetLogWithSource());
+  }
+
+  EXPECT_EQ(2, cache.GetCountAddToEntryQueue(kSimpleGET_Transaction.url));
+
+  // Delete a reader.
+  context_list[1].reset();
+
+  // Deleting the reader did not impact any other transaction.
+  EXPECT_EQ(1, cache.GetCountReaders(kSimpleGET_Transaction.url));
+  EXPECT_EQ(2, cache.GetCountAddToEntryQueue(kSimpleGET_Transaction.url));
+  EXPECT_TRUE(cache.IsHeadersTransactionPresent(kSimpleGET_Transaction.url));
+
+  // Resume network start for headers_transaction. It will doom the entry as it
+  // will be a 200 and will go to network for the response body.
+  auto& context = context_list[3];
+  context->trans->ResumeNetworkStart();
+
+  // The pending transactions will be added to a new entry.
+  base::RunLoop().RunUntilIdle();
+
+  EXPECT_EQ(1, cache.GetCountDoneHeadersQueue(kSimpleGET_Transaction.url));
+  EXPECT_TRUE(cache.IsWriterPresent(kSimpleGET_Transaction.url));
+
+  // Complete the rest of the transactions.
+  for (int i = 2; i < kNumTransactions; ++i) {
+    auto& c = context_list[i];
+    ReadAndVerifyTransaction(c->trans.get(), kSimpleGET_Transaction);
+  }
+
+  EXPECT_EQ(3, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(2, cache.disk_cache()->create_count());
+}
+
+// Tests that a transaction is in validated queue and writer is destroyed
+// leading to restarting the validated transaction.
+TEST(HttpCache, SimpleGET_ParallelValidationCancelWriter) {
+  MockHttpCache cache;
+
+  MockHttpRequest request(kSimpleGET_Transaction);
+
+  MockTransaction transaction(kSimpleGET_Transaction);
+  transaction.load_flags |= LOAD_VALIDATE_CACHE;
+  MockHttpRequest validate_request(transaction);
+
+  const int kNumTransactions = 3;
+  std::vector<std::unique_ptr<Context>> context_list;
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(base::MakeUnique<Context>());
+    auto& c = context_list[i];
+
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+
+    MockHttpRequest* this_request = &request;
+    if (i == 2) {
+      this_request = &validate_request;
+      c->trans->SetBeforeNetworkStartCallback(base::Bind(&DeferNetworkStart));
+    }
+
+    c->result = c->trans->Start(this_request, c->callback.callback(),
+                                NetLogWithSource());
+  }
+
+  // Allow all requests to move from the Create queue to the active entry.
+  base::RunLoop().RunUntilIdle();
+
+  EXPECT_EQ(2, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  EXPECT_TRUE(cache.IsWriterPresent(kSimpleGET_Transaction.url));
+  EXPECT_TRUE(cache.IsHeadersTransactionPresent(kSimpleGET_Transaction.url));
+  EXPECT_EQ(1, cache.GetCountDoneHeadersQueue(kSimpleGET_Transaction.url));
+
+  // Deleting the writer at this point will lead to destroying the entry and
+  // restarting the remaining transactions which will then create a new entry.
+  context_list[0].reset();
+
+  // Resume network start for headers_transaction. It should be restarted due to
+  // writer cancellation.
+  auto& c = context_list[2];
+  c->trans->ResumeNetworkStart();
+
+  base::RunLoop().RunUntilIdle();
+
+  EXPECT_TRUE(cache.IsWriterPresent(kSimpleGET_Transaction.url));
+  EXPECT_TRUE(cache.IsHeadersTransactionPresent(kSimpleGET_Transaction.url));
+
+  // Resume network start for the transaction the second time.
+  c->trans->ResumeNetworkStart();
+  base::RunLoop().RunUntilIdle();
+
+  // Headers transaction would have doomed the new entry created.
+  EXPECT_TRUE(
+      cache.disk_cache()->IsDiskEntryDoomed(kSimpleGET_Transaction.url));
+
+  // Complete the rest of the transactions.
+  for (auto& context : context_list) {
+    if (!context)
+      continue;
+    ReadAndVerifyTransaction(context->trans.get(), kSimpleGET_Transaction);
+  }
+
+  EXPECT_EQ(4, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(2, cache.disk_cache()->create_count());
+}
+
+// Tests when a writer is destroyed mid-read and entry is marked as truncated,
+// it should lead to restarting the dependent transactions.
+TEST(HttpCache, SimpleGET_ParallelValidationCancelWriterTruncateEntry) {
+  MockHttpCache cache;
+
+  ScopedMockTransaction transaction(kSimpleGET_Transaction);
+  transaction.response_headers =
+      "Last-Modified: Wed, 28 Nov 2007 00:40:09 GMT\n"
+      "Content-Length: 22\n"
+      "Etag: \"foopy\"\n";
+  MockHttpRequest request(transaction);
+
+  const int kNumTransactions = 3;
+  std::vector<std::unique_ptr<Context>> context_list;
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(base::MakeUnique<Context>());
+    auto& c = context_list[i];
+
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+
+    c->result =
+        c->trans->Start(&request, c->callback.callback(), NetLogWithSource());
+  }
+
+  // Allow all requests to move from the Create queue to the active entry.
+  base::RunLoop().RunUntilIdle();
+
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  EXPECT_TRUE(cache.IsWriterPresent(kSimpleGET_Transaction.url));
+  EXPECT_EQ(2, cache.GetCountDoneHeadersQueue(kSimpleGET_Transaction.url));
+
+  // Let first transaction read some bytes, so that entry can be marked as
+  // truncated.
+  {
+    auto& c = context_list[0];
+    const int kBufferSize = 5;
+    scoped_refptr<IOBuffer> buffer(new IOBuffer(kBufferSize));
+    ReleaseBufferCompletionCallback cb(buffer.get());
+    c->result = c->trans->Read(buffer.get(), kBufferSize, cb.callback());
+    EXPECT_EQ(kBufferSize, cb.GetResult(c->result));
+  }
+
+  // Deleting the writer at this point will lead to restarting the remaining
+  // transactions which will then be able to read the truncated status of the
+  // entry.
+  context_list[0].reset();
+
+  base::RunLoop().RunUntilIdle();
 
   EXPECT_EQ(2, cache.network_layer()->transaction_count());
   EXPECT_EQ(0, cache.disk_cache()->open_count());
-  EXPECT_EQ(2, cache.disk_cache()->create_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  // Complete the rest of the transactions.
+  for (auto& context : context_list) {
+    if (!context)
+      continue;
+    ReadAndVerifyTransaction(context->trans.get(), kSimpleGET_Transaction);
+  }
 }
 
-TEST(HttpCache, SimpleGET_LoadBypassCache_Implicit2) {
+// Tests that when StopCaching is invoked on a writer, dependent transactions
+// are restarted.
+TEST(HttpCache, SimpleGET_ParallelValidationStopCaching) {
   MockHttpCache cache;
 
-  // write to the cache
-  RunTransactionTest(cache.http_cache(), kSimpleGET_Transaction);
+  MockHttpRequest request(kSimpleGET_Transaction);
 
-  // force this transaction to write to the cache again
   MockTransaction transaction(kSimpleGET_Transaction);
-  transaction.request_headers = "cache-control: no-cache\r\n";
-
-  RunTransactionTest(cache.http_cache(), transaction);
+  transaction.load_flags |= LOAD_VALIDATE_CACHE;
+  MockHttpRequest validate_request(transaction);
 
-  EXPECT_EQ(2, cache.network_layer()->transaction_count());
-  EXPECT_EQ(0, cache.disk_cache()->open_count());
-  EXPECT_EQ(2, cache.disk_cache()->create_count());
-}
+  const int kNumTransactions = 3;
+  std::vector<std::unique_ptr<Context>> context_list;
 
-TEST(HttpCache, SimpleGET_LoadValidateCache) {
-  MockHttpCache cache;
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(base::MakeUnique<Context>());
+    auto& c = context_list[i];
 
-  // Write to the cache.
-  RunTransactionTest(cache.http_cache(), kSimpleGET_Transaction);
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
 
-  // Read from the cache.
-  RunTransactionTest(cache.http_cache(), kSimpleGET_Transaction);
+    MockHttpRequest* this_request = &request;
+    if (i == 2) {
+      this_request = &validate_request;
+      c->trans->SetBeforeNetworkStartCallback(base::Bind(&DeferNetworkStart));
+    }
 
-  // Force this transaction to validate the cache.
-  MockTransaction transaction(kSimpleGET_Transaction);
-  transaction.load_flags |= LOAD_VALIDATE_CACHE;
+    c->result = c->trans->Start(this_request, c->callback.callback(),
+                                NetLogWithSource());
+  }
 
-  HttpResponseInfo response_info;
-  BoundTestNetLog log;
-  LoadTimingInfo load_timing_info;
-  RunTransactionTestWithResponseInfoAndGetTiming(
-      cache.http_cache(), transaction, &response_info, log.bound(),
-      &load_timing_info);
+  // Allow all requests to move from the Create queue to the active entry.
+  base::RunLoop().RunUntilIdle();
 
   EXPECT_EQ(2, cache.network_layer()->transaction_count());
-  EXPECT_EQ(1, cache.disk_cache()->open_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
   EXPECT_EQ(1, cache.disk_cache()->create_count());
-  EXPECT_TRUE(response_info.network_accessed);
-  TestLoadTimingNetworkRequest(load_timing_info);
-}
 
-TEST(HttpCache, SimpleGET_LoadValidateCache_Implicit) {
-  MockHttpCache cache;
+  EXPECT_TRUE(cache.IsWriterPresent(kSimpleGET_Transaction.url));
+  EXPECT_TRUE(cache.IsHeadersTransactionPresent(kSimpleGET_Transaction.url));
+  EXPECT_EQ(1, cache.GetCountDoneHeadersQueue(kSimpleGET_Transaction.url));
 
-  // write to the cache
-  RunTransactionTest(cache.http_cache(), kSimpleGET_Transaction);
+  // Invoking StopCaching on the writer will lead to dooming the entry and
+  // restarting the remaining transactions which will then create a new entry.
+  context_list[0]->trans->StopCaching();
 
-  // read from the cache
-  RunTransactionTest(cache.http_cache(), kSimpleGET_Transaction);
+  // Resume network start for headers_transaction. It should be restarted due to
+  // writer cancellation.
+  auto& c = context_list[2];
+  c->trans->ResumeNetworkStart();
 
-  // force this transaction to validate the cache
-  MockTransaction transaction(kSimpleGET_Transaction);
-  transaction.request_headers = "cache-control: max-age=0\r\n";
+  base::RunLoop().RunUntilIdle();
 
-  RunTransactionTest(cache.http_cache(), transaction);
+  EXPECT_TRUE(cache.IsWriterPresent(kSimpleGET_Transaction.url));
+  EXPECT_TRUE(cache.IsHeadersTransactionPresent(kSimpleGET_Transaction.url));
 
-  EXPECT_EQ(2, cache.network_layer()->transaction_count());
-  EXPECT_EQ(1, cache.disk_cache()->open_count());
-  EXPECT_EQ(1, cache.disk_cache()->create_count());
+  // Resume network start for the transaction the second time.
+  c->trans->ResumeNetworkStart();
+  base::RunLoop().RunUntilIdle();
+
+  // Headers transaction would have doomed the new entry created.
+  EXPECT_TRUE(
+      cache.disk_cache()->IsDiskEntryDoomed(kSimpleGET_Transaction.url));
+
+  // Complete the rest of the transactions.
+  for (auto& context : context_list) {
+    if (!context)
+      continue;
+    ReadAndVerifyTransaction(context->trans.get(), kSimpleGET_Transaction);
+  }
+
+  EXPECT_EQ(4, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(2, cache.disk_cache()->create_count());
 }
 
-// Tests that |unused_since_prefetch| is updated accordingly (e.g. it is set to
-// true after a prefetch and set back to false when the prefetch is used).
-TEST(HttpCache, SimpleGET_UnusedSincePrefetch) {
+// Tests that a transaction is currently in headers phase and is destroyed
+// leading to destroying the entry.
+TEST(HttpCache, SimpleGET_ParallelValidationCancelHeaders) {
   MockHttpCache cache;
-  HttpResponseInfo response_info;
-
-  // A normal load does not have |unused_since_prefetch| set.
-  RunTransactionTestWithResponseInfoAndGetTiming(
-      cache.http_cache(), kSimpleGET_Transaction, &response_info,
-      BoundTestNetLog().bound(), nullptr);
-  EXPECT_FALSE(response_info.unused_since_prefetch);
-  EXPECT_FALSE(response_info.was_cached);
 
-  // The prefetch itself does not have |unused_since_prefetch| set.
-  MockTransaction prefetch_transaction(kSimpleGET_Transaction);
-  prefetch_transaction.load_flags |= LOAD_PREFETCH;
-  RunTransactionTestWithResponseInfoAndGetTiming(
-      cache.http_cache(), prefetch_transaction, &response_info,
-      BoundTestNetLog().bound(), nullptr);
-  EXPECT_FALSE(response_info.unused_since_prefetch);
-  EXPECT_TRUE(response_info.was_cached);
+  MockHttpRequest request(kSimpleGET_Transaction);
 
-  // A duplicated prefetch has |unused_since_prefetch| set.
-  RunTransactionTestWithResponseInfoAndGetTiming(
-      cache.http_cache(), prefetch_transaction, &response_info,
-      BoundTestNetLog().bound(), nullptr);
-  EXPECT_TRUE(response_info.unused_since_prefetch);
-  EXPECT_TRUE(response_info.was_cached);
+  const int kNumTransactions = 2;
+  std::vector<std::unique_ptr<Context>> context_list;
 
-  // |unused_since_prefetch| is still true after two prefetches in a row.
-  RunTransactionTestWithResponseInfoAndGetTiming(
-      cache.http_cache(), kSimpleGET_Transaction, &response_info,
-      BoundTestNetLog().bound(), nullptr);
-  EXPECT_TRUE(response_info.unused_since_prefetch);
-  EXPECT_TRUE(response_info.was_cached);
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(base::MakeUnique<Context>());
+    auto& c = context_list[i];
 
-  // The resource has now been used, back to normal behavior.
-  RunTransactionTestWithResponseInfoAndGetTiming(
-      cache.http_cache(), kSimpleGET_Transaction, &response_info,
-      BoundTestNetLog().bound(), nullptr);
-  EXPECT_FALSE(response_info.unused_since_prefetch);
-  EXPECT_TRUE(response_info.was_cached);
-}
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
 
-static void PreserveRequestHeaders_Handler(const HttpRequestInfo* request,
-                                           std::string* response_status,
-                                           std::string* response_headers,
-                                           std::string* response_data) {
-  EXPECT_TRUE(request->extra_headers.HasHeader(kExtraHeaderKey));
-}
+    if (i == 0)
+      c->trans->SetBeforeNetworkStartCallback(base::Bind(&DeferNetworkStart));
 
-// Tests that we don't remove extra headers for simple requests.
-TEST(HttpCache, SimpleGET_PreserveRequestHeaders) {
-  MockHttpCache cache;
+    c->result =
+        c->trans->Start(&request, c->callback.callback(), NetLogWithSource());
+  }
 
-  MockTransaction transaction(kSimpleGET_Transaction);
-  transaction.handler = PreserveRequestHeaders_Handler;
-  transaction.request_headers = EXTRA_HEADER;
-  transaction.response_headers = "Cache-Control: max-age=0\n";
-  AddMockTransaction(&transaction);
+  base::RunLoop().RunUntilIdle();
 
-  // Write, then revalidate the entry.
-  RunTransactionTest(cache.http_cache(), transaction);
-  RunTransactionTest(cache.http_cache(), transaction);
+  EXPECT_TRUE(cache.IsHeadersTransactionPresent(kSimpleGET_Transaction.url));
+  EXPECT_EQ(1, cache.GetCountAddToEntryQueue(kSimpleGET_Transaction.url));
 
-  EXPECT_EQ(2, cache.network_layer()->transaction_count());
-  EXPECT_EQ(1, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
   EXPECT_EQ(1, cache.disk_cache()->create_count());
-  RemoveMockTransaction(&transaction);
-}
-
-// Tests that we don't remove extra headers for conditionalized requests.
-TEST(HttpCache, ConditionalizedGET_PreserveRequestHeaders) {
-  MockHttpCache cache;
 
-  // Write to the cache.
-  RunTransactionTest(cache.http_cache(), kETagGET_Transaction);
+  // Delete the headers transaction.
+  context_list[0].reset();
 
-  MockTransaction transaction(kETagGET_Transaction);
-  transaction.handler = PreserveRequestHeaders_Handler;
-  transaction.request_headers = "If-None-Match: \"foopy\"\r\n"
-                                EXTRA_HEADER;
-  AddMockTransaction(&transaction);
+  base::RunLoop().RunUntilIdle();
 
-  RunTransactionTest(cache.http_cache(), transaction);
+  // Complete the rest of the transactions.
+  for (auto& context : context_list) {
+    if (!context)
+      continue;
+    ReadAndVerifyTransaction(context->trans.get(), kSimpleGET_Transaction);
+  }
 
   EXPECT_EQ(2, cache.network_layer()->transaction_count());
-  EXPECT_EQ(1, cache.disk_cache()->open_count());
-  EXPECT_EQ(1, cache.disk_cache()->create_count());
-  RemoveMockTransaction(&transaction);
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(2, cache.disk_cache()->create_count());
 }
 
-TEST(HttpCache, SimpleGET_ManyReaders) {
+// Similar to the above test, except here cache write fails and the
+// validated transactions should be restarted.
+TEST(HttpCache, SimpleGET_ParallelValidationFailWrite) {
   MockHttpCache cache;
 
   MockHttpRequest request(kSimpleGET_Transaction);
 
-  std::vector<std::unique_ptr<Context>> context_list;
   const int kNumTransactions = 5;
+  std::vector<std::unique_ptr<Context>> context_list;
 
   for (int i = 0; i < kNumTransactions; ++i) {
     context_list.push_back(base::MakeUnique<Context>());
-    Context* c = context_list[i].get();
+    auto& c = context_list[i];
 
     c->result = cache.CreateTransaction(&c->trans);
     ASSERT_THAT(c->result, IsOk());
@@ -1360,40 +2231,57 @@ TEST(HttpCache, SimpleGET_ManyReaders) {
   }
 
   // All requests are waiting for the active entry.
-  for (int i = 0; i < kNumTransactions; ++i) {
-    Context* c = context_list[i].get();
-    EXPECT_EQ(LOAD_STATE_WAITING_FOR_CACHE, c->trans->GetLoadState());
+  for (auto& context : context_list) {
+    EXPECT_EQ(LOAD_STATE_WAITING_FOR_CACHE, context->trans->GetLoadState());
   }
 
   // Allow all requests to move from the Create queue to the active entry.
   base::RunLoop().RunUntilIdle();
 
   // The first request should be a writer at this point, and the subsequent
-  // requests should be pending.
+  // requests should have passed the validation phase and waiting for the
+  // response to be written to the cache before they can read.
+  EXPECT_TRUE(cache.IsWriterPresent(kSimpleGET_Transaction.url));
+  EXPECT_EQ(4, cache.GetCountDoneHeadersQueue(kSimpleGET_Transaction.url));
+
+  // All requests depend on the writer, and the writer is between Start and
+  // Read, i.e. idle.
+  for (auto& context : context_list) {
+    EXPECT_EQ(LOAD_STATE_IDLE, context->trans->GetLoadState());
+  }
+
+  // The first request should be a writer at this point, and the subsequent
+  // requests should have passed the validation phase and waiting for the
+  // response to be written to the cache before they can read.
 
   EXPECT_EQ(1, cache.network_layer()->transaction_count());
   EXPECT_EQ(0, cache.disk_cache()->open_count());
   EXPECT_EQ(1, cache.disk_cache()->create_count());
 
-  // All requests depend on the writer, and the writer is between Start and
-  // Read, i.e. idle.
-  for (int i = 0; i < kNumTransactions; ++i) {
-    Context* c = context_list[i].get();
-    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
-  }
+  // Fail the request.
+  cache.disk_cache()->set_soft_failures(true);
+  // We have to open the entry again to propagate the failure flag.
+  disk_cache::Entry* en;
+  cache.OpenBackendEntry(kSimpleGET_Transaction.url, &en);
+  en->Close();
 
   for (int i = 0; i < kNumTransactions; ++i) {
-    Context* c = context_list[i].get();
+    auto& c = context_list[i];
     if (c->result == ERR_IO_PENDING)
       c->result = c->callback.WaitForResult();
+    if (i == 1) {
+      // The earlier entry must be destroyed and its disk entry doomed.
+      EXPECT_TRUE(
+          cache.disk_cache()->IsDiskEntryDoomed(kSimpleGET_Transaction.url));
+    }
     ReadAndVerifyTransaction(c->trans.get(), kSimpleGET_Transaction);
   }
 
-  // We should not have had to re-open the disk entry
-
-  EXPECT_EQ(1, cache.network_layer()->transaction_count());
-  EXPECT_EQ(0, cache.disk_cache()->open_count());
-  EXPECT_EQ(1, cache.disk_cache()->create_count());
+  // Since validated transactions were restarted and new entry read/write
+  // operations would also fail, all requests would have gone to the network.
+  EXPECT_EQ(5, cache.network_layer()->transaction_count());
+  EXPECT_EQ(1, cache.disk_cache()->open_count());
+  EXPECT_EQ(5, cache.disk_cache()->create_count());
 }
 
 // This is a test for http://code.google.com/p/chromium/issues/detail?id=4769.
@@ -1440,11 +2328,12 @@ TEST(HttpCache, SimpleGET_RacingReaders) {
   c->result = c->callback.WaitForResult();
   ReadAndVerifyTransaction(c->trans.get(), kSimpleGET_Transaction);
 
-  // Now we have 2 active readers and two queued transactions.
-
+  // Now all transactions should be waiting for read to be invoked. Two readers
+  // are because of the load flags and remaining two transactions were converted
+  // to readers after skipping validation. Note that the remaining two went on
+  // to process the headers in parallel with readers present on the entry.
   EXPECT_EQ(LOAD_STATE_IDLE, context_list[2]->trans->GetLoadState());
-  EXPECT_EQ(LOAD_STATE_WAITING_FOR_CACHE,
-            context_list[3]->trans->GetLoadState());
+  EXPECT_EQ(LOAD_STATE_IDLE, context_list[3]->trans->GetLoadState());
 
   c = context_list[1].get();
   ASSERT_THAT(c->result, IsError(ERR_IO_PENDING));
@@ -1504,12 +2393,16 @@ TEST(HttpCache, SimpleGET_DoomWithPending) {
                                 NetLogWithSource());
   }
 
+  base::RunLoop().RunUntilIdle();
+
   // The first request should be a writer at this point, and the two subsequent
   // requests should be pending. The last request doomed the first entry.
 
   EXPECT_EQ(2, cache.network_layer()->transaction_count());
 
-  // Cancel the first queued transaction.
+  // Cancel the second transaction. Note that this and the 3rd transactions
+  // would have completed their headers phase and would be waiting in the
+  // done_headers_queue when the 2nd transaction is cancelled.
   context_list[1].reset();
 
   for (int i = 0; i < kNumTransactions; ++i) {
@@ -1551,11 +2444,12 @@ TEST(HttpCache, FastNoStoreGET_DoneWithPending) {
   base::RunLoop().RunUntilIdle();
 
   // The first request should be a writer at this point, and the subsequent
-  // requests should be pending.
+  // requests should have completed validation. Since the validation does not
+  // result in a match, a new entry would be created.
 
-  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(3, cache.network_layer()->transaction_count());
   EXPECT_EQ(0, cache.disk_cache()->open_count());
-  EXPECT_EQ(1, cache.disk_cache()->create_count());
+  EXPECT_EQ(2, cache.disk_cache()->create_count());
 
   // Now, make sure that the second request asks for the entry not to be stored.
   request_handler.set_no_store(true);
@@ -1609,6 +2503,9 @@ TEST(HttpCache, SimpleGET_ManyWriters_CancelFirst) {
     if (c->result == ERR_IO_PENDING)
       c->result = c->callback.WaitForResult();
     // Destroy only the first transaction.
+    // This should lead to all transactions to restart, even those that have
+    // validated themselves and were waiting for the writer transaction to
+    // complete writing to the cache.
     if (i == 0) {
       context_list[i].reset();
     }
@@ -2497,6 +3394,8 @@ TEST(HttpCache, ETagGET_ConditionalRequest_304_NoStore) {
 //     be returned.
 // (4) loads |kUrl| from cache only -- expects |cached_response_2| to be
 //     returned.
+// The entry will be created once and will be opened for the 3 subsequent
+// requests.
 static void ConditionalizedRequestUpdatesCacheHelper(
     const Response& net_response_1,
     const Response& net_response_2,
@@ -6069,13 +6968,14 @@ TEST(HttpCache, GET_IncompleteResource_Cancel) {
   rv = c->trans->Read(buf.get(), buf->size(), c->callback.callback());
   EXPECT_EQ(5, c->callback.GetResult(rv));
 
-  // Cancel the requests.
+  // Since |pending| is currently validating the already written headers
+  // it will be restarted as well.
   c.reset();
   pending.reset();
 
   EXPECT_EQ(1, cache.network_layer()->transaction_count());
   EXPECT_EQ(1, cache.disk_cache()->open_count());
-  EXPECT_EQ(2, cache.disk_cache()->create_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
 
   base::RunLoop().RunUntilIdle();
   RemoveMockTransaction(&transaction);
@@ -6800,46 +7700,6 @@ TEST(HttpCache, WriteMetadata_Fail) {
   EXPECT_EQ(1, cache.disk_cache()->create_count());
 }
 
-// Tests that if a metadata writer transaction hits cache lock timeout, it will
-// error out.
-TEST(HttpCache, WriteMetadata_CacheLockTimeout) {
-  MockHttpCache cache;
-
-  // Write to the cache
-  HttpResponseInfo response;
-  RunTransactionTestWithResponseInfo(cache.http_cache(), kSimpleGET_Transaction,
-                                     &response);
-  EXPECT_FALSE(response.metadata.get());
-
-  MockHttpRequest request(kSimpleGET_Transaction);
-  Context c1;
-  ASSERT_THAT(cache.CreateTransaction(&c1.trans), IsOk());
-  ASSERT_EQ(ERR_IO_PENDING, c1.trans->Start(&request, c1.callback.callback(),
-                                            NetLogWithSource()));
-
-  cache.SimulateCacheLockTimeout();
-
-  // Write meta data to the same entry.
-  scoped_refptr<IOBufferWithSize> buf(new IOBufferWithSize(50));
-  memset(buf->data(), 0, buf->size());
-  base::strlcpy(buf->data(), "Hi there", buf->size());
-  cache.http_cache()->WriteMetadata(GURL(kSimpleGET_Transaction.url),
-                                    DEFAULT_PRIORITY, response.response_time,
-                                    buf.get(), buf->size());
-
-  // Release the buffer before the operation takes place.
-  buf = NULL;
-
-  // Makes sure we finish pending operations.
-  base::RunLoop().RunUntilIdle();
-
-  RunTransactionTestWithResponseInfo(cache.http_cache(), kSimpleGET_Transaction,
-                                     &response);
-
-  // The writer transaction should fail due to cache lock timeout.
-  ASSERT_FALSE(response.metadata.get());
-}
-
 // Tests that we ignore VARY checks when writing metadata since the request
 // headers for the WriteMetadata transaction are made up.
 TEST(HttpCache, WriteMetadata_IgnoreVary) {
@@ -7167,10 +8027,6 @@ TEST(HttpCache, StopCachingWithAuthDeletesEntry) {
     EXPECT_THAT(callback.GetResult(rv), IsOk());
 
     trans->StopCaching();
-
-    scoped_refptr<IOBuffer> buf(new IOBuffer(256));
-    rv = trans->Read(buf.get(), 10, callback.callback());
-    EXPECT_EQ(callback.GetResult(rv), 10);
   }
   RemoveMockTransaction(&mock_transaction);
 
@@ -7219,7 +8075,9 @@ TEST(HttpCache, StopCachingSavesEntry) {
   }
 
   // Verify that the entry is marked as incomplete.
-  VerifyTruncatedFlag(&cache, kSimpleGET_Transaction.url, true, 0);
+  // VerifyTruncatedFlag(&cache, kSimpleGET_Transaction.url, true, 0);
+  // Verify that the entry is doomed.
+  cache.disk_cache()->IsDiskEntryDoomed(kSimpleGET_Transaction.url);
 }
 
 // Tests that we handle truncated enries when StopCaching is called.