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 5f870c6cdd56503b606817e410f4c0b9205bbb2c..224496f44d013e1180f222bf6220de6539571e60 100644
--- a/net/http/http_cache_transaction.cc
+++ b/net/http/http_cache_transaction.cc
@@ -170,6 +170,7 @@ HttpCache::Transaction::Transaction(RequestPriority priority, HttpCache* cache)
       new_entry_(NULL),
       new_response_(NULL),
       mode_(NONE),
+      original_mode_(NONE),
       reading_(false),
       invalid_range_(false),
       truncated_(false),
@@ -182,6 +183,7 @@ HttpCache::Transaction::Transaction(RequestPriority priority, HttpCache* cache)
       couldnt_conditionalize_request_(false),
       bypass_lock_for_test_(false),
       fail_conditionalization_for_test_(false),
+      validating_cannot_proceed_(false),
       io_buf_len_(0),
       read_offset_(0),
       effective_load_flags_(0),
@@ -210,16 +212,12 @@ 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);
-        }
-      }
+      bool cancel_response = cache_->IsTransactionCurrentOrFutureWriter(
+          entry_, this, request_->method);
+      if (cancel_response && partial_)
+        entry_->disk_entry->CancelSparseIO();
 
-      cache_->DoneWithEntry(entry_, this, cancel_request);
+      cache_->DoneWithEntry(entry_, this, cancel_response);
     } else if (cache_pending_) {
       cache_->RemovePendingTransaction(this);
     }
@@ -374,6 +372,8 @@ bool HttpCache::Transaction::IsReadyToRestartForAuth() {
 
 int HttpCache::Transaction::Read(IOBuffer* buf, int buf_len,
                                  const CompletionCallback& callback) {
+  // TODO(shivanisha): A lot of tests invoke Read on a HEAD request which
+  // should not be allowed in the Read() method. Fix those tests.

[jkarlin, 2017/04/03 14:32:48]

I assume that the tests are defensive due to the high likelihood that a customer
would call READ() on a HEAD requestion.

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

That might be the case, removing the todo from here.

   DCHECK_EQ(next_state_, STATE_NONE);
   DCHECK(buf);
   DCHECK_GT(buf_len, 0);
@@ -579,6 +579,11 @@ void HttpCache::Transaction::GetConnectionAttempts(
               old_connection_attempts_.end());
 }
 
+void HttpCache::Transaction::SetValidatingCannotProceed() {

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

Suggestion: As I understand it, this is only expected to be called while we're
in header validation.  Should we DCHECK that?  

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

Done. Added DCHECK(!reading_)

+  validating_cannot_proceed_ = true;
+  entry_ = nullptr;
+}
+
 size_t HttpCache::Transaction::EstimateMemoryUsage() const {
   // TODO(xunjieli): Consider improving the coverage. crbug.com/669108.
   return 0;
@@ -593,7 +598,7 @@ size_t HttpCache::Transaction::EstimateMemoryUsage() const {
 //   GetBackend* -> InitEntry -> OpenEntry* -> CreateEntry* -> AddToEntry* ->
 //   SendRequest* -> SuccessfulSendRequest -> OverwriteCachedResponse ->
 //   CacheWriteResponse* -> TruncateCachedData* -> TruncateCachedMetadata* ->
-//   PartialHeadersReceived
+//   PartialHeadersReceived -> FinishHeaders*
 //
 //   Read():
 //   NetworkRead* -> CacheWriteData*
@@ -602,7 +607,7 @@ size_t HttpCache::Transaction::EstimateMemoryUsage() const {
 //   Start():
 //   GetBackend* -> InitEntry -> OpenEntry* -> AddToEntry* -> CacheReadResponse*
 //   -> CacheDispatchValidation -> BeginPartialCacheValidation() ->
-//   BeginCacheValidation() -> SetupEntryForRead()
+//   BeginCacheValidation() -> SetupEntryForRead() -> FinishHeaders*
 //
 //   Read():
 //   CacheReadData*
@@ -614,7 +619,7 @@ size_t HttpCache::Transaction::EstimateMemoryUsage() const {
 //   BeginCacheValidation() -> SendRequest* -> SuccessfulSendRequest ->
 //   UpdateCachedResponse -> CacheWriteUpdatedResponse* ->
 //   UpdateCachedResponseComplete -> OverwriteCachedResponse ->
-//   PartialHeadersReceived
+//   PartialHeadersReceived -> FinishHeaders*
 //
 //   Read():
 //   CacheReadData*
@@ -625,7 +630,7 @@ size_t HttpCache::Transaction::EstimateMemoryUsage() const {
 //   -> CacheDispatchValidation -> BeginPartialCacheValidation() ->
 //   BeginCacheValidation() -> SendRequest* -> SuccessfulSendRequest ->
 //   OverwriteCachedResponse -> CacheWriteResponse* -> DoTruncateCachedData* ->
-//   TruncateCachedMetadata* -> PartialHeadersReceived
+//   TruncateCachedMetadata* -> PartialHeadersReceived -> FinishHeaders*
 //
 //   Read():
 //   NetworkRead* -> CacheWriteData*
@@ -639,7 +644,7 @@ size_t HttpCache::Transaction::EstimateMemoryUsage() const {
 //   BeginCacheValidation() -> SendRequest* -> SuccessfulSendRequest ->
 //   UpdateCachedResponse -> CacheWriteUpdatedResponse* ->
 //   UpdateCachedResponseComplete -> OverwriteCachedResponse ->
-//   PartialHeadersReceived
+//   PartialHeadersReceived -> FinishHeaders*
 //
 //   Read() 1:
 //   NetworkRead* -> CacheWriteData*
@@ -680,7 +685,7 @@ 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
@@ -705,7 +710,7 @@ size_t HttpCache::Transaction::EstimateMemoryUsage() const {
 //   GetBackend* -> InitEntry -> OpenEntry* -> AddToEntry* -> CacheReadResponse*
 //   -> CacheToggleUnusedSincePrefetch* -> CacheDispatchValidation ->
 //   BeginPartialCacheValidation() -> BeginCacheValidation() ->
-//   SetupEntryForRead()
+//   SetupEntryForRead() -> FinishHeaders*
 //
 //   Read():
 //   CacheReadData*
@@ -719,8 +724,9 @@ 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);
 
@@ -857,6 +863,12 @@ int HttpCache::Transaction::DoLoop(int result) {
       case STATE_CACHE_READ_METADATA_COMPLETE:
         rv = DoCacheReadMetadataComplete(rv);
         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();
@@ -893,8 +905,13 @@ 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);
   }
 
@@ -921,7 +938,7 @@ 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;
@@ -960,7 +977,7 @@ int HttpCache::Transaction::DoGetBackendComplete(int result) {
   // 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;
   }
 
@@ -977,6 +994,9 @@ 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.
+  original_mode_ = mode_;
   return OK;
 }
 
@@ -985,7 +1005,7 @@ int HttpCache::Transaction::DoInitEntry() {
   DCHECK(!new_entry_);
 
   if (!cache_.get()) {
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return ERR_UNEXPECTED;
   }
 
@@ -1048,7 +1068,7 @@ 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;
 }
 
@@ -1182,7 +1202,7 @@ int HttpCache::Transaction::DoAddToEntryComplete(int result) {
 
   if (result == ERR_CACHE_LOCK_TIMEOUT) {
     if (mode_ == READ) {
-      TransitionToState(STATE_NONE);
+      TransitionToState(STATE_FINISH_HEADERS);
       return ERR_CACHE_MISS;
     }
 
@@ -1201,7 +1221,7 @@ int HttpCache::Transaction::DoAddToEntryComplete(int result) {
   // TODO(jkarlin): We should either handle the case or DCHECK.
   if (result != OK) {
     NOTREACHED();
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return result;
   }
 
@@ -1344,7 +1364,7 @@ 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;
   }
 
@@ -1354,7 +1374,7 @@ 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;
   }
 
@@ -1371,12 +1391,12 @@ int HttpCache::Transaction::DoCompletePartialCacheValidation(int result) {
       cache_->DoneReadingFromEntry(entry_, this);
       entry_ = NULL;
     }
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return result;
   }
 
   if (result < 0) {
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return result;
   }
 
@@ -1402,7 +1422,7 @@ 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_);
@@ -1424,7 +1444,7 @@ 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;
   }
 
@@ -1455,7 +1475,7 @@ int HttpCache::Transaction::DoSendRequestComplete(int result) {
     DoneWritingToEntry(true);
   }
 
-  TransitionToState(STATE_NONE);
+  TransitionToState(STATE_FINISH_HEADERS);
   return result;
 }
 
@@ -1469,7 +1489,7 @@ int HttpCache::Transaction::DoSuccessfulSendRequest() {
       new_response->headers->response_code() == 407) {
     SetAuthResponse(*new_response);
     if (!reading_) {
-      TransitionToState(STATE_NONE);
+      TransitionToState(STATE_FINISH_HEADERS);
       return OK;
     }
 
@@ -1494,7 +1514,7 @@ int HttpCache::Transaction::DoSuccessfulSendRequest() {
     mode_ = NONE;
     partial_.reset();
     ResetNetworkTransaction();
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return ERR_CACHE_AUTH_FAILURE_AFTER_READ;
   }
 
@@ -1532,7 +1552,7 @@ int HttpCache::Transaction::DoSuccessfulSendRequest() {
       int ret = cache_->DoomEntry(cache_key_, NULL);
       DCHECK_EQ(OK, ret);
     }
-    cache_->DoneWritingToEntry(entry_, true);
+    cache_->DoneWritingToEntry(entry_, true, this);
     entry_ = NULL;
     mode_ = NONE;
   }
@@ -1550,7 +1570,7 @@ int HttpCache::Transaction::DoSuccessfulSendRequest() {
       (request_->method == "GET" || request_->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;
   }
 
@@ -1566,6 +1586,21 @@ int HttpCache::Transaction::DoSuccessfulSendRequest() {
   }
 
   TransitionToState(STATE_OVERWRITE_CACHED_RESPONSE);
+
+  if (!entry_)
+    return OK;
+
+  // Invalidate any current entry with a successful response if this transaction
+  // cannot write to this entry.
+  if (new_response->headers->response_code() != 304 &&
+      (entry_->writer || !entry_->readers.empty())) {

[jkarlin, 2017/04/03 14:32:48]

In regards to: entry_->writer || !entry_->readers.empty()

Perhaps instead, cache_->CanOverwriteActiveEntry()? 

That way the HCT isn't aware of the ActiveEntry's states.

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

Good call, invoked IsCurrentOrFutureWriter for this case as well.

+    DCHECK_EQ(entry_->headers_transaction, this);

[jkarlin, 2017/04/03 14:32:48]

Why not call DoneWritingToEntry(false); here like on line 1540 instead of
calling cache_->DoneWithResponseHeaders?

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

Done and removed is_match argument from DoneWithResponseHeaders

+    cache_->DoneWithResponseHeaders(entry_, this, false);
+    entry_ = nullptr;
+    mode_ = NONE;
+    return OK;
+  }
+
   return OK;
 }
 
@@ -1638,7 +1673,6 @@ 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.
@@ -1676,7 +1710,7 @@ int HttpCache::Transaction::DoOverwriteCachedResponse() {
     DoneWritingToEntry(false);
     mode_ = NONE;
     new_response_ = NULL;
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return OK;
   }
 
@@ -1758,10 +1792,12 @@ 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;
   }
 
@@ -1775,13 +1811,64 @@ 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::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 there is no response body to be written or read, it does not need to
+  // wait.
+  if (request_->method == "HEAD")
+    return OK;
+
+  return cache_->DoneWithResponseHeaders(entry_, this, true);
+}
+
+int HttpCache::Transaction::DoFinishHeadersComplete(int rv) {
+  if (rv == ERR_CACHE_RACE) {
+    RestartAfterValidationStarted();
+    return OK;
+  }
+
+  TransitionToState(STATE_NONE);
+  return rv;
+}
+
+void HttpCache::Transaction::RestartAfterValidationStarted() {
+  DCHECK(!reading_);
+  next_state_ = STATE_INIT_ENTRY;
+  cache_entry_status_ = CacheEntryStatus::ENTRY_UNDEFINED;
+  entry_ = nullptr;
+  mode_ = original_mode_;
+  if (network_trans_)
+    network_trans_.reset();
+}
+
+void HttpCache::Transaction::ConvertToReadMode() {
+  DCHECK(!reading_);
+  mode_ = READ;
+  if (network_trans_)
+    ResetNetworkTransaction();
+}
+
 int HttpCache::Transaction::DoCacheReadMetadata() {
   TRACE_EVENT0("io", "HttpCacheTransaction::DoCacheReadMetadata");
   DCHECK(entry_);
@@ -1804,7 +1891,8 @@ 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;
 }
 
@@ -2101,18 +2189,18 @@ 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() != VALIDATION_NONE) {
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
     return ERR_CACHE_MISS;
   }
 
@@ -2122,7 +2210,7 @@ int HttpCache::Transaction::BeginCacheRead() {
   if (entry_->disk_entry->GetDataSize(kMetadataIndex))
     TransitionToState(STATE_CACHE_READ_METADATA);
   else
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
 
   return OK;
 }
@@ -2635,7 +2723,7 @@ int HttpCache::Transaction::SetupEntryForRead() {
       partial_.reset();
     }
   }
-  cache_->ConvertWriterToReader(entry_);
+
   mode_ = READ;
 
   if (request_->method == "HEAD")
@@ -2644,7 +2732,7 @@ int HttpCache::Transaction::SetupEntryForRead() {
   if (entry_->disk_entry->GetDataSize(kMetadataIndex))
     TransitionToState(STATE_CACHE_READ_METADATA);
   else
-    TransitionToState(STATE_NONE);
+    TransitionToState(STATE_FINISH_HEADERS);
   return OK;
 }
 
@@ -2723,7 +2811,7 @@ 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
 }
@@ -3080,6 +3168,14 @@ void HttpCache::Transaction::RecordHistograms() {
 }
 
 void HttpCache::Transaction::OnIOComplete(int result) {
+  // If its the Start state machine and it cannot proceed due to failure by
+  // another transaction in writing the response, restart this transaction.
+  if (validating_cannot_proceed_) {
+    DCHECK(!reading_);
+    validating_cannot_proceed_ = false;
+    RestartAfterValidationStarted();
+  }
+
   DoLoop(result);
 }