HttpCache::Transaction layer allowing parallel validation

net/http/http_cache_transaction.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file declares HttpCache::Transaction, a private class of HttpCache so
 // it should only be included by http_cache.cc
 
 #ifndef NET_HTTP_HTTP_CACHE_TRANSACTION_H_
 #define NET_HTTP_HTTP_CACHE_TRANSACTION_H_
 
@@ skipping 97 matching lines @@
   bool AddTruncatedFlag();
 
   HttpCache::ActiveEntry* entry() { return entry_; }
 
   // Returns the LoadState of the writer transaction of a given ActiveEntry. In
   // other words, returns the LoadState of this transaction without asking the
   // http cache, because this transaction should be the one currently writing
   // to the cache entry.
   LoadState GetWriterLoadState() const;
 
   const CompletionCallback& io_callback() { return io_callback_; }

[Randy Smith (Not in Mondays), 2017/03/31 19:26:12]

Would you be willing to put a documentation comment here as we discussed a bit
in person?  The key thing I'd like called out is that, at least for HC<->HC::T
communciation, this *isn't* the usual IO Callback (which generally means
"Whatever you (the consumer class) requested is done and I have no further
knowledge of you".  The first part is true ("Operation requested is done") and
part of the second is true ("Nothing further will happen until you get back to
me") but the HC::T is still tied to the HC and needs to take that into account.

Possibly the right place for this is near OnIOComplete(), and should also
acknowledge that this callback is used for disk writes and network reads as well
(which I think do behave like the regular io completions).

[shivanisha, 2017/04/03 20:16:49]

Done.

 
   const NetLogWithSource& net_log() const;
 
   // Bypasses the cache lock whenever there is lock contention.
   void BypassLockForTest() {
     bypass_lock_for_test_ = true;
   }
 
   // Generates a failure when attempting to conditionalize a network request.
   void FailConditionalizationForTest() {
@@ skipping 28 matching lines @@
   void SetPriority(RequestPriority priority) override;
   void SetWebSocketHandshakeStreamCreateHelper(
       WebSocketHandshakeStreamBase::CreateHelper* create_helper) override;
   void SetBeforeNetworkStartCallback(
       const BeforeNetworkStartCallback& callback) override;
   void SetBeforeHeadersSentCallback(
       const BeforeHeadersSentCallback& callback) override;
   int ResumeNetworkStart() override;
   void GetConnectionAttempts(ConnectionAttempts* out) const override;
 
+  // Invoked when parallel validation cannot proceed due to response failure
+  // and this transaction needs to be restarted.
+  void SetValidatingCannotProceed();

[Randy Smith (Not in Mondays), 2017/03/31 19:26:12]

So conceptually this seems like the same thing as ERR_CACHE_RACE, except that
ERR_CACHE_RACE is sent synchronously and this can happen asynchronously.  Is
there any way to combine both signals into one?

If not, I'd at least like to make the connection (and difference) clear in the
comments.  

[shivanisha, 2017/04/03 20:16:49]

Combined the 2 in the following manner:
- Created a separate state STATE_HEADERS_PHASE_CANNOT_PROCEED which will be set
in this function instead of a boolean so no extra code will be needed in
OnIOComplete().
- In all ERR_CACHE_RACE scenarios also, the same state will be set.
- The new state's Do function will be responsible for restarting the state
machine to STATE_INIT_ENTRY and other variables' resetting.

[Randy Smith (Not in Mondays), 2017/04/04 21:21:16]

Awesome!  Thank you.

+
+  // Converts mode_ to read-only and resets if there is a network transaction.
+  void ConvertToReadMode();
+
   // Returns the estimate of dynamically allocated memory in bytes.
   size_t EstimateMemoryUsage() const;
 
  private:
   static const size_t kNumValidationHeaders = 2;
   // Helper struct to pair a header name with its value, for
   // headers used to validate cache entries.
   struct ValidationHeaders {
     ValidationHeaders() : initialized(false) {}
 
@@ skipping 36 matching lines @@
     STATE_OVERWRITE_CACHED_RESPONSE,
     STATE_CACHE_WRITE_RESPONSE,
     STATE_CACHE_WRITE_RESPONSE_COMPLETE,
     STATE_TRUNCATE_CACHED_DATA,
     STATE_TRUNCATE_CACHED_DATA_COMPLETE,
     STATE_TRUNCATE_CACHED_METADATA,
     STATE_TRUNCATE_CACHED_METADATA_COMPLETE,
     STATE_PARTIAL_HEADERS_RECEIVED,
     STATE_CACHE_READ_METADATA,
     STATE_CACHE_READ_METADATA_COMPLETE,
+    STATE_FINISH_HEADERS,
+    STATE_FINISH_HEADERS_COMPLETE,
 
     // These states are entered from Read/AddTruncatedFlag.
     STATE_NETWORK_READ,
     STATE_NETWORK_READ_COMPLETE,
     STATE_CACHE_READ_DATA,
     STATE_CACHE_READ_DATA_COMPLETE,
     STATE_CACHE_WRITE_DATA,
     STATE_CACHE_WRITE_DATA_COMPLETE,
     STATE_CACHE_WRITE_TRUNCATED_RESPONSE,
     STATE_CACHE_WRITE_TRUNCATED_RESPONSE_COMPLETE
   };
 
   // Used for categorizing validation triggers in histograms.
   // NOTE: This enumeration is used in histograms, so please do not add entries
   // in the middle.
   enum ValidationCause {
     VALIDATION_CAUSE_UNDEFINED,
     VALIDATION_CAUSE_VARY_MISMATCH,
     VALIDATION_CAUSE_VALIDATE_FLAG,
     VALIDATION_CAUSE_STALE,
     VALIDATION_CAUSE_ZERO_FRESHNESS,
     VALIDATION_CAUSE_MAX
   };
 
   // Runs the state transition loop. Resets and calls |callback_| on exit,
   // unless the return value is ERR_IO_PENDING.
   int DoLoop(int result);
+  int DoLoopImpl(int result);

[Randy Smith (Not in Mondays), 2017/03/31 19:26:12]

I don't think this exists anymore?

[shivanisha, 2017/04/03 20:16:49]

Removed

 
   // Each of these methods corresponds to a State value.  If there is an
   // argument, the value corresponds to the return of the previous state or
   // corresponding callback.
   int DoGetBackend();
   int DoGetBackendComplete(int result);
   int DoInitEntry();
   int DoOpenEntry();
   int DoOpenEntryComplete(int result);
   int DoDoomEntry();
@@ skipping 19 matching lines @@
   int DoCacheWriteUpdatedResponseComplete(int result);
   int DoUpdateCachedResponseComplete(int result);
   int DoOverwriteCachedResponse();
   int DoCacheWriteResponse();
   int DoCacheWriteResponseComplete(int result);
   int DoTruncateCachedData();
   int DoTruncateCachedDataComplete(int result);
   int DoTruncateCachedMetadata();
   int DoTruncateCachedMetadataComplete(int result);
   int DoPartialHeadersReceived();
+  int DoFinishHeaders(int result);
+  int DoFinishHeadersComplete(int result);
   int DoCacheReadMetadata();
   int DoCacheReadMetadataComplete(int result);
   int DoNetworkRead();
   int DoNetworkReadComplete(int result);
   int DoCacheReadData();
   int DoCacheReadDataComplete(int result);
   int DoCacheWriteData(int num_bytes);
   int DoCacheWriteDataComplete(int result);
   int DoCacheWriteTruncatedResponse();
   int DoCacheWriteTruncatedResponseComplete(int result);
@@ skipping 108 matching lines @@
   int DoRestartPartialRequest();
 
   // Resets the relavant internal state to remove traces of internal processing
   // related to range requests. Deletes |partial_| if |delete_object| is true.
   void ResetPartialState(bool delete_object);
 
   // Resets |network_trans_|, which must be non-NULL.  Also updates
   // |old_network_trans_load_timing_|, which must be NULL when this is called.
   void ResetNetworkTransaction();
 
+  // Since a transaction could be doing validation of request headers in
+  // parallel with another request writing response data to the entry, failure
+  // to write the data might lead to restarting this request. This function
+  // resets all the required variables to be able to restart the transaction's
+  // state machine.
+  void RestartAfterValidationStarted();
+
   // Returns true if we should bother attempting to resume this request if it is
   // aborted while in progress. If |has_data| is true, the size of the stored
   // data is considered for the result.
   bool CanResume(bool has_data);
 
   // Setter for response_ and auth_response_. It updates its cache entry status,
   // if needed.
   void SetResponse(const HttpResponseInfo& new_response);
   void SetAuthResponse(const HttpResponseInfo& new_response);
 
@@ skipping 23 matching lines @@
   base::WeakPtr<HttpCache> cache_;
   HttpCache::ActiveEntry* entry_;
   HttpCache::ActiveEntry* new_entry_;
   std::unique_ptr<HttpTransaction> network_trans_;
   CompletionCallback callback_;  // Consumer's callback.
   HttpResponseInfo response_;
   HttpResponseInfo auth_response_;
   const HttpResponseInfo* new_response_;
   std::string cache_key_;
   Mode mode_;
+  Mode original_mode_;  // Used when restarting the transaction.
   bool reading_;  // We are already reading. Never reverts to false once set.
   bool invalid_range_;  // We may bypass the cache for this request.
   bool truncated_;  // We don't have all the response data.
   bool is_sparse_;  // The data is stored in sparse byte ranges.
   bool range_requested_;  // The user requested a byte range.
   bool handling_206_;  // We must deal with this 206 response.
   bool cache_pending_;  // We are waiting for the HttpCache.
   bool done_reading_;  // All available data was read.
   bool vary_mismatch_;  // The request doesn't match the stored vary data.
   bool couldnt_conditionalize_request_;
   bool bypass_lock_for_test_;  // A test is exercising the cache lock.
   bool fail_conditionalization_for_test_;  // Fail ConditionalizeRequest.
+  // Parallel validation cannot proceed due to response failure, restart the
+  // transaction.
+  bool validating_cannot_proceed_;
   scoped_refptr<IOBuffer> read_buf_;
   int io_buf_len_;
   int read_offset_;
   int effective_load_flags_;
   int write_len_;
   std::unique_ptr<PartialData> partial_;  // We are dealing with range requests.
   CompletionCallback io_callback_;
 
   // Members used to track data for histograms.
   // This cache_entry_status_ takes precedence over
@@ skipping 34 matching lines @@
   bool in_do_loop_;
 
   base::WeakPtrFactory<Transaction> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(Transaction);
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_HTTP_CACHE_TRANSACTION_H_