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 200 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_WAIT_BEFORE_READ,
+    STATE_WAIT_BEFORE_READ_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);
 
   // 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 DoWaitBeforeRead();
+  int DoWaitBeforeReadComplete(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 159 matching lines @@
   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.
+  // This transaction is responsible for writing the response
+  bool write_this_response_;

[jkarlin, 2017/03/07 16:45:42]

This variable seems unnecessary, it's only read in one place which could just as
easily check if it's the entry's writers.

   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 31 matching lines @@
   BeforeHeadersSentCallback before_headers_sent_callback_;
 
   base::WeakPtrFactory<Transaction> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(Transaction);
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_HTTP_CACHE_TRANSACTION_H_