HttpCache::Transaction layer allowing parallel validation

net/http/http_cache_transaction.cc

Index: net/http/http_cache_transaction.cc
diff --git a/net/http/http_cache_transaction.cc b/net/http/http_cache_transaction.cc
index 518944650747e6a3dc7f39c58b4b4d7cb1610758..e44e165ea69fdc37e1d478fcaabbe292ae8ce7ac 100644
--- a/net/http/http_cache_transaction.cc
+++ b/net/http/http_cache_transaction.cc
@@ -196,16 +196,7 @@ HttpCache::Transaction::~Transaction() {
 
   if (cache_) {
     if (entry_) {
-      bool cancel_request = reading_ && response_.headers.get();
-      if (cancel_request) {
-        if (partial_) {
-          entry_->disk_entry->CancelSparseIO();
-        } else {
-          cancel_request &= (response_.headers->response_code() == 200);
-        }
-      }
-
-      cache_->DoneWithEntry(entry_, this, cancel_request);
+      cache_->DoneWithEntry(entry_, this, true, partial_ != nullptr);

[jkarlin, 2017/05/30 14:42:38]

Yay for this cleanup!

     } else if (cache_pending_) {
       cache_->RemovePendingTransaction(this);
     }
@@ -451,7 +442,7 @@ void HttpCache::Transaction::DoneReading() {
       // It is necessary to check mode_ & READ because it is possible
       // for mode_ to be NONE and entry_ non-NULL with a write entry
       // if StopCaching was called.
-      cache_->DoneReadingFromEntry(entry_, this);
+      cache_->DoneWithEntry(entry_, this, false, partial_ != nullptr);
       entry_ = NULL;
     }
   }
@@ -565,6 +556,12 @@ void HttpCache::Transaction::GetConnectionAttempts(
               old_connection_attempts_.end());
 }
 
+void HttpCache::Transaction::SetValidatingCannotProceed() {
+  DCHECK(!reading_);
+  next_state_ = STATE_HEADERS_PHASE_CANNOT_PROCEED;
+  entry_ = nullptr;
+}
+
 size_t HttpCache::Transaction::EstimateMemoryUsage() const {
   // TODO(xunjieli): Consider improving the coverage. crbug.com/669108.
   return 0;
@@ -579,7 +576,7 @@ size_t HttpCache::Transaction::EstimateMemoryUsage() const {
 //   GetBackend* -> InitEntry -> OpenEntry* -> CreateEntry* -> AddToEntry* ->
 //   SendRequest* -> SuccessfulSendRequest -> OverwriteCachedResponse ->
 //   CacheWriteResponse* -> TruncateCachedData* -> TruncateCachedMetadata* ->
-//   PartialHeadersReceived
+//   PartialHeadersReceived -> FinishHeaders*
 //
 //   Read():
 //   NetworkRead* -> CacheWriteData*
@@ -588,7 +585,7 @@ size_t HttpCache::Transaction::EstimateMemoryUsage() const {
 //   Start():
 //   GetBackend* -> InitEntry -> OpenEntry* -> AddToEntry* -> CacheReadResponse*
 //   -> CacheDispatchValidation -> BeginPartialCacheValidation() ->
-//   BeginCacheValidation() -> SetupEntryForRead()
+//   BeginCacheValidation() -> SetupEntryForRead() -> FinishHeaders*
 //
 //   Read():
 //   CacheReadData*
@@ -600,7 +597,7 @@ size_t HttpCache::Transaction::EstimateMemoryUsage() const {
 //   BeginCacheValidation() -> SendRequest* -> SuccessfulSendRequest ->
 //   UpdateCachedResponse -> CacheWriteUpdatedResponse* ->
 //   UpdateCachedResponseComplete -> OverwriteCachedResponse ->
-//   PartialHeadersReceived
+//   PartialHeadersReceived -> FinishHeaders*
 //
 //   Read():
 //   CacheReadData*
@@ -611,7 +608,7 @@ size_t HttpCache::Transaction::EstimateMemoryUsage() const {
 //   -> CacheDispatchValidation -> BeginPartialCacheValidation() ->
 //   BeginCacheValidation() -> SendRequest* -> SuccessfulSendRequest ->
 //   OverwriteCachedResponse -> CacheWriteResponse* -> DoTruncateCachedData* ->
-//   TruncateCachedMetadata* -> PartialHeadersReceived
+//   TruncateCachedMetadata* -> PartialHeadersReceived -> FinishHeaders*
 //
 //   Read():
 //   NetworkRead* -> CacheWriteData*
@@ -625,7 +622,7 @@ size_t HttpCache::Transaction::EstimateMemoryUsage() const {
 //   BeginCacheValidation() -> SendRequest* -> SuccessfulSendRequest ->
 //   UpdateCachedResponse -> CacheWriteUpdatedResponse* ->
 //   UpdateCachedResponseComplete -> OverwriteCachedResponse ->
-//   PartialHeadersReceived
+//   PartialHeadersReceived -> FinishHeaders*
 //
 //   Read() 1:
 //   NetworkRead* -> CacheWriteData*
@@ -666,7 +663,7 @@ size_t HttpCache::Transaction::EstimateMemoryUsage() const {
 //   GetBackend* -> InitEntry -> OpenEntry* -> AddToEntry* -> CacheReadResponse*
 //   -> CacheDispatchValidation -> BeginPartialCacheValidation() ->
 //   BeginCacheValidation() -> SendRequest* -> SuccessfulSendRequest ->
-//   OverwriteCachedResponse
+//   OverwriteCachedResponse -> FinishHeaders*
 //
 // 10. HEAD. Sparse entry, partially cached:
 //   Serve the request from the cache, as long as it doesn't require
@@ -691,7 +688,7 @@ size_t HttpCache::Transaction::EstimateMemoryUsage() const {
 //   GetBackend* -> InitEntry -> OpenEntry* -> AddToEntry* -> CacheReadResponse*
 //   -> CacheToggleUnusedSincePrefetch* -> CacheDispatchValidation ->
 //   BeginPartialCacheValidation() -> BeginCacheValidation() ->
-//   SetupEntryForRead()
+//   SetupEntryForRead() -> FinishHeaders*
 //
 //   Read():
 //   CacheReadData*
@@ -705,8 +702,9 @@ int HttpCache::Transaction::DoLoop(int result) {
   DCHECK(!in_do_loop_);
 
   int rv = result;
+  State state = next_state_;
   do {
-    State state = next_state_;
+    state = next_state_;
     next_state_ = STATE_UNSET;
     base::AutoReset<bool> scoped_in_do_loop(&in_do_loop_, true);
 
@@ -843,6 +841,15 @@ int HttpCache::Transaction::DoLoop(int result) {
       case STATE_CACHE_READ_METADATA_COMPLETE:
         rv = DoCacheReadMetadataComplete(rv);
         break;
+      case STATE_HEADERS_PHASE_CANNOT_PROCEED:
+        rv = DoHeadersPhaseCannotProceed();
+        break;
+      case STATE_FINISH_HEADERS:
+        rv = DoFinishHeaders(rv);
+        break;
+      case STATE_FINISH_HEADERS_COMPLETE:
+        rv = DoFinishHeadersComplete(rv);
+        break;
       case STATE_NETWORK_READ:
         DCHECK_EQ(OK, rv);
         rv = DoNetworkRead();
@@ -879,8 +886,13 @@ int HttpCache::Transaction::DoLoop(int result) {
 
   } while (rv != ERR_IO_PENDING && next_state_ != STATE_NONE);
 
+  // Assert Start() state machine's allowed last state in successful cases when
+  // caching is happening.
+  DCHECK(reading_ || rv != OK || !entry_ ||
+         state == STATE_FINISH_HEADERS_COMPLETE);
+
   if (rv != ERR_IO_PENDING && !callback_.is_null()) {
-    read_buf_ = NULL;  // Release the buffer before invoking the callback.
+    read_buf_ = nullptr;  // Release the buffer before invoking the callback.
     base::ResetAndReturn(&callback_).Run(rv);
   }
 
@@ -907,7 +919,7 @@ int HttpCache::Transaction::DoGetBackendComplete(int result) {
     if (effective_load_flags_ & LOAD_ONLY_FROM_CACHE) {
       if (effective_load_flags_ & LOAD_BYPASS_CACHE) {
         // The client has asked for nonsense.
-        TransitionToState(STATE_NONE);
+        TransitionToState(STATE_FINISH_HEADERS);
         return ERR_CACHE_MISS;
       }
       mode_ = READ;
@@ -930,8 +942,8 @@ int HttpCache::Transaction::DoGetBackendComplete(int result) {
   }
 
   // Use PUT and DELETE only to invalidate existing stored entries.
-  if ((request_->method == "PUT" || request_->method == "DELETE") &&
-      mode_ != READ_WRITE && mode_ != WRITE) {
+  if ((method_ == "PUT" || method_ == "DELETE") && mode_ != READ_WRITE &&
+      mode_ != WRITE) {
     mode_ = NONE;
   }
 
@@ -940,13 +952,13 @@ int HttpCache::Transaction::DoGetBackendComplete(int result) {
   // was not modified, the entry is updated and a response is not returned from
   // the cache. If we receive 200, it doesn't matter if there was a validation
   // header or not.
-  if (request_->method == "HEAD" && mode_ == WRITE)
+  if (method_ == "HEAD" && mode_ == WRITE)
     mode_ = NONE;
 
   // If must use cache, then we must fail.  This can happen for back/forward
   // navigations to a page generated via a form post.
   if (!(mode_ & READ) && effective_load_flags_ & LOAD_ONLY_FROM_CACHE) {
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return ERR_CACHE_MISS;
   }
 
@@ -963,6 +975,9 @@ int HttpCache::Transaction::DoGetBackendComplete(int result) {
   // This is only set if we have something to do with the response.
   range_requested_ = (partial_.get() != NULL);
 
+  // mode_ may change later, save the initial mode in case we need to restart
+  // this request.
+  restart_info_.mode = mode_;
   return OK;
 }
 
@@ -971,7 +986,7 @@ int HttpCache::Transaction::DoInitEntry() {
   DCHECK(!new_entry_);
 
   if (!cache_.get()) {
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return ERR_UNEXPECTED;
   }
 
@@ -1008,13 +1023,13 @@ int HttpCache::Transaction::DoOpenEntryComplete(int result) {
   }
 
   if (result == ERR_CACHE_RACE) {
-    TransitionToState(STATE_INIT_ENTRY);
+    TransitionToState(STATE_HEADERS_PHASE_CANNOT_PROCEED);
     return OK;
   }
 
-  if (request_->method == "PUT" || request_->method == "DELETE" ||
-      (request_->method == "HEAD" && mode_ == READ_WRITE)) {
-    DCHECK(mode_ == READ_WRITE || mode_ == WRITE || request_->method == "HEAD");
+  if (method_ == "PUT" || method_ == "DELETE" ||
+      (method_ == "HEAD" && mode_ == READ_WRITE)) {
+    DCHECK(mode_ == READ_WRITE || mode_ == WRITE || method_ == "HEAD");
     mode_ = NONE;
     TransitionToState(STATE_SEND_REQUEST);
     return OK;
@@ -1034,7 +1049,7 @@ int HttpCache::Transaction::DoOpenEntryComplete(int result) {
 
   // The entry does not exist, and we are not permitted to create a new entry,
   // so we must fail.
-  TransitionToState(STATE_NONE);
+  TransitionToState(STATE_FINISH_HEADERS);
   return ERR_CACHE_MISS;
 }
 
@@ -1053,8 +1068,9 @@ int HttpCache::Transaction::DoDoomEntryComplete(int result) {
   net_log_.EndEventWithNetErrorCode(NetLogEventType::HTTP_CACHE_DOOM_ENTRY,
                                     result);
   cache_pending_ = false;
-  TransitionToState(result == ERR_CACHE_RACE ? STATE_INIT_ENTRY
-                                             : STATE_CREATE_ENTRY);
+  TransitionToState(result == ERR_CACHE_RACE
+                        ? STATE_HEADERS_PHASE_CANNOT_PROCEED
+                        : STATE_CREATE_ENTRY);
   return OK;
 }
 
@@ -1081,7 +1097,7 @@ int HttpCache::Transaction::DoCreateEntryComplete(int result) {
       break;
 
     case ERR_CACHE_RACE:
-      TransitionToState(STATE_INIT_ENTRY);
+      TransitionToState(STATE_HEADERS_PHASE_CANNOT_PROCEED);
       break;
 
     default:
@@ -1162,13 +1178,13 @@ int HttpCache::Transaction::DoAddToEntryComplete(int result) {
   new_entry_ = NULL;
 
   if (result == ERR_CACHE_RACE) {
-    TransitionToState(STATE_INIT_ENTRY);
+    TransitionToState(STATE_HEADERS_PHASE_CANNOT_PROCEED);
     return OK;
   }
 
   if (result == ERR_CACHE_LOCK_TIMEOUT) {
     if (mode_ == READ) {
-      TransitionToState(STATE_NONE);
+      TransitionToState(STATE_FINISH_HEADERS);
       return ERR_CACHE_MISS;
     }
 
@@ -1182,12 +1198,16 @@ int HttpCache::Transaction::DoAddToEntryComplete(int result) {
     return OK;
   }
 
-  open_entry_last_used_ = entry_->disk_entry->GetLastUsed();
+  // TODO(crbug.com/713354) Access timestamp for histograms only if entry is
+  // already written, to avoid data race since cache thread can also access
+  // this.
+  if (!cache_->IsWritingInProgress(entry_))
+    open_entry_last_used_ = entry_->disk_entry->GetLastUsed();
 
   // TODO(jkarlin): We should either handle the case or DCHECK.
   if (result != OK) {
     NOTREACHED();
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return result;
   }
 
@@ -1226,29 +1246,37 @@ int HttpCache::Transaction::DoCacheReadResponseComplete(int result) {
     return OnCacheReadError(result, true);
   }
 
-  int current_size = entry_->disk_entry->GetDataSize(kResponseContentIndex);
-  int64_t full_response_length = response_.headers->GetContentLength();
-
-  // Some resources may have slipped in as truncated when they're not.
-  if (full_response_length == current_size)
-    truncated_ = false;
-
-  // The state machine's handling of StopCaching unfortunately doesn't deal well
-  // with resources that are larger than 2GB when there is a truncated or sparse
-  // cache entry. While the state machine is reworked to resolve this, the
-  // following logic is put in place to defer such requests to the network. The
-  // cache should not be storing multi gigabyte resources. See
-  // http://crbug.com/89567.
-  if ((truncated_ || response_.headers->response_code() == 206) &&
-      !range_requested_ &&
-      full_response_length > std::numeric_limits<int32_t>::max()) {
-    // Does not release the cache entry. If another transaction wants to use
-    // this cache entry while this transaction is active, the second transaction
-    // will fall back to the network after the timeout.
-    DCHECK(!partial_);
-    mode_ = NONE;
-    TransitionToState(STATE_SEND_REQUEST);
-    return OK;
+  // TODO(crbug.com/713354) Only get data size if there is no other transaction
+  // currently writing the response body due to the data race mentioned in the
+  // associated bug.
+  if (!cache_->IsWritingInProgress(entry_)) {
+    int current_size = entry_->disk_entry->GetDataSize(kResponseContentIndex);
+    int64_t full_response_length = response_.headers->GetContentLength();
+
+    // Some resources may have slipped in as truncated when they're not.
+    if (full_response_length == current_size)
+      truncated_ = false;
+
+    // The state machine's handling of StopCaching unfortunately doesn't deal
+    // well with resources that are larger than 2GB when there is a truncated or
+    // sparse cache entry. While the state machine is reworked to resolve this,
+    // the following logic is put in place to defer such requests to the
+    // network. The cache should not be storing multi gigabyte resources. See
+    // http://crbug.com/89567.
+    if ((truncated_ || response_.headers->response_code() == 206) &&
+        !range_requested_ &&
+        full_response_length > std::numeric_limits<int32_t>::max()) {
+      DCHECK(!partial_);
+
+      // Doom the entry so that no other transaction gets added to this entry
+      // and avoid a race of not being able to check this condition because
+      // writing is in progress.
+      cache_->DoneWritingToEntry(entry_, false, this);
+      entry_ = nullptr;
+      mode_ = NONE;
+      TransitionToState(STATE_SEND_REQUEST);
+      return OK;
+    }
   }
 
   if (response_.unused_since_prefetch !=
@@ -1330,7 +1358,7 @@ int HttpCache::Transaction::DoCacheQueryData() {
 int HttpCache::Transaction::DoCacheQueryDataComplete(int result) {
   DCHECK_EQ(OK, result);
   if (!cache_.get()) {
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return ERR_UNEXPECTED;
   }
 
@@ -1340,7 +1368,7 @@ int HttpCache::Transaction::DoCacheQueryDataComplete(int result) {
 // We may end up here multiple times for a given request.
 int HttpCache::Transaction::DoStartPartialCacheValidation() {
   if (mode_ == NONE) {
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return OK;
   }
 
@@ -1354,15 +1382,15 @@ int HttpCache::Transaction::DoCompletePartialCacheValidation(int result) {
     if (mode_ & WRITE) {
       DoneWritingToEntry(true);
     } else {
-      cache_->DoneReadingFromEntry(entry_, this);
+      cache_->DoneWithEntry(entry_, this, false, partial_ != nullptr);
       entry_ = NULL;
     }
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return result;
   }
 
   if (result < 0) {
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return result;
   }
 
@@ -1388,7 +1416,7 @@ int HttpCache::Transaction::DoSendRequest() {
   int rv =
       cache_->network_layer_->CreateTransaction(priority_, &network_trans_);
   if (rv != OK) {
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return rv;
   }
   network_trans_->SetBeforeNetworkStartCallback(before_network_start_callback_);
@@ -1410,7 +1438,7 @@ int HttpCache::Transaction::DoSendRequest() {
 int HttpCache::Transaction::DoSendRequestComplete(int result) {
   TRACE_EVENT0("io", "HttpCacheTransaction::DoSendRequestComplete");
   if (!cache_.get()) {
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return ERR_UNEXPECTED;
   }
 
@@ -1441,7 +1469,7 @@ int HttpCache::Transaction::DoSendRequestComplete(int result) {
     DoneWritingToEntry(true);
   }
 
-  TransitionToState(STATE_NONE);
+  TransitionToState(STATE_FINISH_HEADERS);
   return result;
 }
 
@@ -1455,7 +1483,7 @@ int HttpCache::Transaction::DoSuccessfulSendRequest() {
       new_response->headers->response_code() == 407) {
     SetAuthResponse(*new_response);
     if (!reading_) {
-      TransitionToState(STATE_NONE);
+      TransitionToState(STATE_FINISH_HEADERS);
       return OK;
     }
 
@@ -1480,7 +1508,7 @@ int HttpCache::Transaction::DoSuccessfulSendRequest() {
     mode_ = NONE;
     partial_.reset();
     ResetNetworkTransaction();
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return ERR_CACHE_AUTH_FAILURE_AFTER_READ;
   }
 
@@ -1512,20 +1540,18 @@ int HttpCache::Transaction::DoSuccessfulSendRequest() {
   }
 
   // Invalidate any cached GET with a successful PUT or DELETE.
-  if (mode_ == WRITE &&
-      (request_->method == "PUT" || request_->method == "DELETE")) {
+  if (mode_ == WRITE && (method_ == "PUT" || method_ == "DELETE")) {
     if (NonErrorResponse(new_response->headers->response_code())) {
       int ret = cache_->DoomEntry(cache_key_, NULL);
       DCHECK_EQ(OK, ret);
     }
-    cache_->DoneWritingToEntry(entry_, true);
+    cache_->DoneWritingToEntry(entry_, true, this);
     entry_ = NULL;
     mode_ = NONE;
   }
 
   // Invalidate any cached GET with a successful POST.
-  if (!(effective_load_flags_ & LOAD_DISABLE_CACHE) &&
-      request_->method == "POST" &&
+  if (!(effective_load_flags_ & LOAD_DISABLE_CACHE) && method_ == "POST" &&
       NonErrorResponse(new_response->headers->response_code())) {
     cache_->DoomMainEntryForUrl(request_->url);
   }
@@ -1533,10 +1559,10 @@ int HttpCache::Transaction::DoSuccessfulSendRequest() {
   RecordNoStoreHeaderHistogram(request_->load_flags, new_response);
 
   if (new_response_->headers->response_code() == 416 &&
-      (request_->method == "GET" || request_->method == "POST")) {
+      (method_ == "GET" || method_ == "POST")) {
     // If there is an active entry it may be destroyed with this transaction.
     SetResponse(*new_response_);
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return OK;
   }
 
@@ -1624,7 +1650,6 @@ int HttpCache::Transaction::DoUpdateCachedResponseComplete(int result) {
   } else if (entry_ && !handling_206_) {
     DCHECK_EQ(READ_WRITE, mode_);
     if (!partial_ || partial_->IsLastRange()) {
-      cache_->ConvertWriterToReader(entry_);
       mode_ = READ;
     }
     // We no longer need the network transaction, so destroy it.
@@ -1657,12 +1682,12 @@ int HttpCache::Transaction::DoOverwriteCachedResponse() {
 
   SetResponse(*new_response_);
 
-  if (request_->method == "HEAD") {
+  if (method_ == "HEAD") {
     // This response is replacing the cached one.
     DoneWritingToEntry(false);
     mode_ = NONE;
     new_response_ = NULL;
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return OK;
   }
 
@@ -1683,6 +1708,19 @@ int HttpCache::Transaction::DoOverwriteCachedResponse() {
 int HttpCache::Transaction::DoCacheWriteResponse() {
   TRACE_EVENT0("io", "HttpCacheTransaction::DoCacheWriteResponse");
   TransitionToState(STATE_CACHE_WRITE_RESPONSE_COMPLETE);
+
+  // Invalidate any current entry with a successful response if this transaction
+  // cannot write to this entry. This transaction then continues to read from
+  // the network without writing to the backend.
+  bool is_match = response_.headers->response_code() == 304;
+  if (entry_ && response_.headers &&
+      !cache_->CanTransactionWriteResponseHeaders(entry_, this, is_match)) {
+    cache_->DoneWritingToEntry(entry_, false, this);
+    entry_ = nullptr;
+    mode_ = NONE;
+    return OK;
+  }
+
   return WriteResponseInfoToEntry(truncated_);
 }
 
@@ -1744,10 +1782,12 @@ int HttpCache::Transaction::DoPartialHeadersReceived() {
   new_response_ = NULL;
 
   if (!partial_) {
-    if (entry_ && entry_->disk_entry->GetDataSize(kMetadataIndex))
+    if (entry_ && entry_->disk_entry->GetDataSize(kMetadataIndex)) {
       TransitionToState(STATE_CACHE_READ_METADATA);
-    else
-      TransitionToState(STATE_NONE);
+    } else {
+      DCHECK(!reading_);
+      TransitionToState(STATE_FINISH_HEADERS);
+    }
     return OK;
   }
 
@@ -1761,13 +1801,59 @@ int HttpCache::Transaction::DoPartialHeadersReceived() {
     // We are about to return the headers for a byte-range request to the user,
     // so let's fix them.
     partial_->FixResponseHeaders(response_.headers.get(), true);
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
   } else {
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
   }
   return OK;
 }
 
+int HttpCache::Transaction::DoHeadersPhaseCannotProceed() {
+  // If its the Start state machine and it cannot proceed due to a cache
+  // failure, restart this transaction.
+  DCHECK(!reading_);
+  TransitionToState(STATE_INIT_ENTRY);
+  cache_entry_status_ = restart_info_.cache_entry_status;
+  entry_ = nullptr;
+  mode_ = restart_info_.mode;
+  if (network_trans_)
+    network_trans_.reset();
+
+  return OK;
+}
+
+int HttpCache::Transaction::DoFinishHeaders(int result) {
+  if (!entry_ || result != OK) {
+    TransitionToState(STATE_NONE);
+    return result;
+  }
+
+  TransitionToState(STATE_FINISH_HEADERS_COMPLETE);
+
+  // If it was an auth failure or 416, this transaction should continue to be
+  // headers_transaction till consumer takes an action, so no need to do
+  // anything now.
+  if (auth_response_.headers.get() ||
+      (new_response_ && new_response_->headers &&
+       new_response_->headers->response_code() == 416))
+    return OK;
+
+  // If the transaction needs to wait because another transaction is still
+  // writing the response body, it will return ERR_IO_PENDING now and the
+  // io_callback_ will be invoked when the wait is done.
+  return cache_->DoneWithResponseHeaders(entry_, this, partial_ != nullptr);
+}
+
+int HttpCache::Transaction::DoFinishHeadersComplete(int rv) {
+  if (rv == ERR_CACHE_RACE) {
+    TransitionToState(STATE_HEADERS_PHASE_CANNOT_PROCEED);
+    return OK;
+  }
+
+  TransitionToState(STATE_NONE);
+  return rv;
+}
+
 int HttpCache::Transaction::DoCacheReadMetadata() {
   TRACE_EVENT0("io", "HttpCacheTransaction::DoCacheReadMetadata");
   DCHECK(entry_);
@@ -1790,7 +1876,8 @@ int HttpCache::Transaction::DoCacheReadMetadataComplete(int result) {
                                     result);
   if (result != response_.metadata->size())
     return OnCacheReadError(result, false);
-  TransitionToState(STATE_NONE);
+
+  TransitionToState(STATE_FINISH_HEADERS);
   return OK;
 }
 
@@ -1823,7 +1910,7 @@ int HttpCache::Transaction::DoNetworkReadComplete(int result) {
 int HttpCache::Transaction::DoCacheReadData() {
   TRACE_EVENT0("io", "HttpCacheTransaction::DoCacheReadData");
 
-  if (request_->method == "HEAD") {
+  if (method_ == "HEAD") {
     TransitionToState(STATE_NONE);
     return 0;
   }
@@ -1961,6 +2048,7 @@ void HttpCache::Transaction::SetRequest(const NetLogWithSource& net_log,
   net_log_ = net_log;
   request_ = request;
   effective_load_flags_ = request_->load_flags;
+  method_ = request_->method;
 
   if (cache_->mode() == DISABLE)
     effective_load_flags_ |= LOAD_DISABLE_CACHE;
@@ -2040,7 +2128,7 @@ void HttpCache::Transaction::SetRequest(const NetLogWithSource& net_log,
   if (range_found && !(effective_load_flags_ & LOAD_DISABLE_CACHE)) {
     UpdateCacheEntryStatus(CacheEntryStatus::ENTRY_OTHER);
     partial_.reset(new PartialData);
-    if (request_->method == "GET" && partial_->Init(request_->extra_headers)) {
+    if (method_ == "GET" && partial_->Init(request_->extra_headers)) {
       // We will be modifying the actual range requested to the server, so
       // let's remove the header here.
       custom_request_.reset(new HttpRequestInfo(*request_));
@@ -2054,6 +2142,7 @@ void HttpCache::Transaction::SetRequest(const NetLogWithSource& net_log,
       partial_.reset(NULL);
     }
   }
+  restart_info_.cache_entry_status = cache_entry_status_;
 }
 
 bool HttpCache::Transaction::ShouldPassThrough() {
@@ -2065,18 +2154,18 @@ bool HttpCache::Transaction::ShouldPassThrough() {
   if (effective_load_flags_ & LOAD_DISABLE_CACHE)
     return true;
 
-  if (request_->method == "GET" || request_->method == "HEAD")
+  if (method_ == "GET" || method_ == "HEAD")
     return false;
 
-  if (request_->method == "POST" && request_->upload_data_stream &&
+  if (method_ == "POST" && request_->upload_data_stream &&
       request_->upload_data_stream->identifier()) {
     return false;
   }
 
-  if (request_->method == "PUT" && request_->upload_data_stream)
+  if (method_ == "PUT" && request_->upload_data_stream)
     return false;
 
-  if (request_->method == "DELETE")
+  if (method_ == "DELETE")
     return false;
 
   return true;
@@ -2087,28 +2176,28 @@ int HttpCache::Transaction::BeginCacheRead() {
   // TODO(jkarlin): Either handle this case or DCHECK.
   if (response_.headers->response_code() == 206 || partial_) {
     NOTREACHED();
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return ERR_CACHE_MISS;
   }
 
   // We don't have the whole resource.
   if (truncated_) {
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return ERR_CACHE_MISS;
   }
 
   if (RequiresValidation()) {
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return ERR_CACHE_MISS;
   }
 
-  if (request_->method == "HEAD")
+  if (method_ == "HEAD")
     FixHeadersForHead();
 
   if (entry_->disk_entry->GetDataSize(kMetadataIndex))
     TransitionToState(STATE_CACHE_READ_METADATA);
   else
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
 
   return OK;
 }
@@ -2118,7 +2207,7 @@ int HttpCache::Transaction::BeginCacheValidation() {
 
   bool skip_validation = !RequiresValidation();
 
-  if (request_->method == "HEAD" &&
+  if (method_ == "HEAD" &&
       (truncated_ || response_.headers->response_code() == 206)) {
     DCHECK(!partial_);
     if (skip_validation)
@@ -2176,7 +2265,7 @@ int HttpCache::Transaction::BeginPartialCacheValidation() {
 
   // Partial requests should not be recorded in histograms.
   UpdateCacheEntryStatus(CacheEntryStatus::ENTRY_OTHER);
-  if (request_->method == "HEAD")
+  if (method_ == "HEAD")
     return BeginCacheValidation();
 
   if (!range_requested_) {
@@ -2314,7 +2403,7 @@ bool HttpCache::Transaction::RequiresValidation() {
     return true;
   }
 
-  if (request_->method == "PUT" || request_->method == "DELETE")
+  if (method_ == "PUT" || method_ == "DELETE")
     return true;
 
   bool validation_required_by_headers = response_.headers->RequiresValidation(
@@ -2340,7 +2429,7 @@ bool HttpCache::Transaction::RequiresValidation() {
 bool HttpCache::Transaction::ConditionalizeRequest() {
   DCHECK(response_.headers.get());
 
-  if (request_->method == "PUT" || request_->method == "DELETE")
+  if (method_ == "PUT" || method_ == "DELETE")
     return false;
 
   // This only makes sense for cached 200 or 206 responses.
@@ -2434,7 +2523,7 @@ bool HttpCache::Transaction::ValidatePartialResponse() {
   bool partial_response = (response_code == 206);
   handling_206_ = false;
 
-  if (!entry_ || request_->method != "GET")
+  if (!entry_ || method_ != "GET")
     return true;
 
   if (invalid_range_) {
@@ -2541,7 +2630,7 @@ void HttpCache::Transaction::IgnoreRangeRequest() {
   if (mode_ & WRITE)
     DoneWritingToEntry(mode_ != WRITE);
   else if (mode_ & READ && entry_)
-    cache_->DoneReadingFromEntry(entry_, this);
+    cache_->DoneWithEntry(entry_, this, false, partial_ != nullptr);
 
   partial_.reset(NULL);
   entry_ = NULL;
@@ -2568,16 +2657,16 @@ int HttpCache::Transaction::SetupEntryForRead() {
       partial_.reset();
     }
   }
-  cache_->ConvertWriterToReader(entry_);
+
   mode_ = READ;
 
-  if (request_->method == "HEAD")
+  if (method_ == "HEAD")
     FixHeadersForHead();
 
   if (entry_->disk_entry->GetDataSize(kMetadataIndex))
     TransitionToState(STATE_CACHE_READ_METADATA);
   else
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
   return OK;
 }
 
@@ -2656,7 +2745,7 @@ void HttpCache::Transaction::DoneWritingToEntry(bool success) {
 
   RecordHistograms();
 
-  cache_->DoneWritingToEntry(entry_, success);
+  cache_->DoneWritingToEntry(entry_, success, this);
   entry_ = NULL;
   mode_ = NONE;  // switch to 'pass through' mode
 }
@@ -2679,7 +2768,7 @@ int HttpCache::Transaction::OnCacheReadError(int result, bool restart) {
   if (restart) {
     DCHECK(!reading_);
     DCHECK(!network_trans_.get());
-    cache_->DoneWithEntry(entry_, this, false);
+    cache_->DoneWithEntry(entry_, this, false, partial_ != nullptr);
     entry_ = NULL;
     is_sparse_ = false;
     partial_.reset();
@@ -2708,7 +2797,7 @@ void HttpCache::Transaction::DoomPartialEntry(bool delete_object) {
   DVLOG(2) << "DoomPartialEntry";
   int rv = cache_->DoomEntry(cache_key_, NULL);
   DCHECK_EQ(OK, rv);
-  cache_->DoneWithEntry(entry_, this, false);
+  cache_->DoneWithEntry(entry_, this, false, partial_ != nullptr);
   entry_ = NULL;
   is_sparse_ = false;
   truncated_ = false;
@@ -2804,7 +2893,7 @@ bool HttpCache::Transaction::CanResume(bool has_data) {
   if (has_data && !entry_->disk_entry->GetDataSize(kResponseContentIndex))
     return false;
 
-  if (request_->method != "GET")
+  if (method_ != "GET")
     return false;
 
   // Note that if this is a 206, content-length was already fixed after calling
@@ -2853,7 +2942,7 @@ void HttpCache::Transaction::RecordHistograms() {
   DCHECK_NE(CacheEntryStatus::ENTRY_UNDEFINED, cache_entry_status_);
   if (!cache_.get() || !cache_->GetCurrentBackend() ||
       cache_->GetCurrentBackend()->GetCacheType() != DISK_CACHE ||
-      cache_->mode() != NORMAL || request_->method != "GET") {
+      cache_->mode() != NORMAL || method_ != "GET") {
     return;
   }
 
@@ -2867,10 +2956,14 @@ void HttpCache::Transaction::RecordHistograms() {
        cache_entry_status_ == CacheEntryStatus::ENTRY_CANT_CONDITIONALIZE);
   int64_t freshness_periods_since_last_used = 0;
 
-  if (stale_request) {
+  if (stale_request && !open_entry_last_used_.is_null()) {
+    // Note that we are not able to capture those transactions' histograms which
+    // when added to entry, the response was being written by another
+    // transaction because getting the last used timestamp might lead to a data
+    // race in that case. TODO(crbug.com/713354).
+
     // For stale entries, record how many freshness periods have elapsed since
     // the entry was last used.
-    DCHECK(!open_entry_last_used_.is_null());
     DCHECK(!stale_entry_freshness_.is_zero());
     base::TimeDelta time_since_use = base::Time::Now() - open_entry_last_used_;
     freshness_periods_since_last_used =
@@ -2903,7 +2996,7 @@ void HttpCache::Transaction::RecordHistograms() {
     // response header mime type, which could be incorrect, so this is just an
     // estimate.
     if (mime_type == "text/html" &&
-        (request_->load_flags & LOAD_MAIN_FRAME_DEPRECATED)) {
+        (effective_load_flags_ & LOAD_MAIN_FRAME_DEPRECATED)) {
       CACHE_STATUS_HISTOGRAMS(".MainFrameHTML");
     } else if (mime_type == "text/html") {
       CACHE_STATUS_HISTOGRAMS(".NonMainFrameHTML");
@@ -2943,7 +3036,8 @@ void HttpCache::Transaction::RecordHistograms() {
 
   if (cache_entry_status_ == CacheEntryStatus::ENTRY_OTHER)
     return;
-  DCHECK(!range_requested_);
+
+  DCHECK(!range_requested_) << "Cache entry status " << cache_entry_status_;
   DCHECK(!first_cache_access_since_.is_null());
 
   TimeDelta total_time = base::TimeTicks::Now() - first_cache_access_since_;