Fixes the cache lock issue.

net/http/http_cache_shared_writers.h

Index: net/http/http_cache_shared_writers.h
diff --git a/net/http/http_cache_shared_writers.h b/net/http/http_cache_shared_writers.h
new file mode 100644
index 0000000000000000000000000000000000000000..eb97f2e16d43dfb659be313dfc98b2b48315925e
--- /dev/null
+++ b/net/http/http_cache_shared_writers.h
@@ -0,0 +1,255 @@
+// Copyright (c) 2016 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.
+
+#ifndef NET_HTTP_HTTP_CACHE_SHARED_WRITERS_H_
+#define NET_HTTP_HTTP_CACHE_SHARED_WRITERS_H_
+
+#include <list>
+#include <memory>
+#include "base/memory/weak_ptr.h"
+#include "net/base/completion_callback.h"
+#include "net/http/http_cache.h"
+
+namespace net {
+
+// SharedWriters represents the set of all HttpCache::Transactions that are
+// reading from the network using the same network transaction and writing to
+// the same cache entry. It is owned by the ActiveEntry.
+class HttpCache::SharedWriters {
+ public:
+  // Creates a new SharedWriters object and transfers the ownership of network
+  // transaction to SharedWriters. Consumer must ensure that |*entry| and
+  // |*cache| outlives |this|. It is ok for cache_transaction to die before this
+  // object.
+  SharedWriters(HttpCache* cache,
+                ActiveEntry* entry,
+                Transaction* cache_transaction,
+                RequestPriority priority,
+                std::unique_ptr<HttpTransaction> network_transaction);
+  ~SharedWriters();
+
+  // Adds a transaction to SharedWriters. Return value is true if it is the
+  // current validating transaction and false if it is waiting.
+  bool AddTransaction(Transaction* transaction);
+
+  // Invokes Read on network transaction if a read is not already in progress.
+  // In case a read is already in progress then this transaction is added to
+  // a waiting queue, read_in_progress is set to true and ERR_IO_PENDING is
+  // returned.
+  int Read(scoped_refptr<IOBuffer> buf,
+           int buf_len,
+           const CompletionCallback& callback,
+           Transaction* transaction,
+           bool* read_in_progress);
+
+  // Invokes WriteData on disk entry.
+  int CacheWrite(scoped_refptr<IOBuffer> buf,
+                 int write_len,
+                 const CompletionCallback& callback,
+                 Transaction* transaction);
+
+  // Invoked when the validating transaction wants to continue with the entry
+  // as the validation successfully matched it.
+  void OnValidationMatch(Transaction* transaction, RequestPriority priority);
+
+  // Invoked when the validating transaction cannot continue with the entry as
+  // the validation did not return a 304. Its fine to continue writing to cache
+  // if this is the only transaction, so network transaction ownership is
+  // transferred to SharedWriters. But if there are other transactions, entry
+  // will be doomed and this transaction will continue reading from the network
+  // so the return value will pass the ownership of the network transaction
+  // back to the transaction.
+  std::unique_ptr<HttpTransaction> OnValidationNoMatch(
+      const std::string& key,
+      Transaction* transaction,
+      std::unique_ptr<HttpTransaction> network_transaction,
+      RequestPriority priority);
+
+  // Invoked when DoneReading is invoked on a shared transaction. The
+  // transaction will be removed from |this|. If another transaction is
+  // currently reading, then other transactions will not be impacted.
+  void DoneReading(Transaction* transaction);
+
+  // Invoked when StopCaching is called for a shared writer transaction.
+  // It stops caching only if there are no other transactions.
+  void StopCaching(Transaction* transaction);
+
+  // All transactions eligible for shared writing from entry's pending queue
+  // will be tracked from SharedWriters after this function.
+  void MoveFromPendingQueue();
+
+  // Posts a task for invoking the io callback of the first transaction waiting
+  // for validation.
+  void ProcessFirstWaitingValidation();
+
+  // Removes a pending transaction.
+  bool RemoveWaitingTransaction(Transaction* transaction);
+
+  // Removes a transaction which is waiting for Read to be invoked by the
+  // consumer.
+  void RemoveIdleTransaction(Transaction* transaction);
+
+  // Removes a transaction waiting on a Read call.
+  void RemoveWaitingForReadTransaction(Transaction* transaction);
+
+  // Removes the currently validating transaction.
+  void RemoveValidatingTransaction(Transaction* transaction);
+
+  // Removes the currently active transaction.
+  void RemoveActiveTransaction(Transaction* transaction);
+
+  // Returns true if this object is empty.
+  bool empty();
+
+  HttpTransaction* network_transaction() { return network_transaction_.get(); }
+
+  // Do not add new transactions if in the process of marking the entry as
+  // truncated.
+  bool CanAddNewTransaction();
+
+  // Invoked when there is a change in a member transaction's priority or a
+  // member transaction is removed.
+  void PriorityChanged();
+
+ private:
+  // Runs the state transition loop. Resets and calls |callback_| on exit,
+  // unless the return value is ERR_IO_PENDING.
+  int DoLoop(int result);
+
+  // IO Completion callback function.
+  void OnIOComplete(int result);
+
+  // State machine functions.
+  int DoNetworkRead();
+  int DoNetworkReadComplete(int result);
+  int DoCacheWriteData(int num_bytes);
+  int DoCacheWriteDataComplete(int result);
+  int DoCacheWriteTruncatedResponse();
+  int DoCacheWriteTruncatedResponseComplete(int result);
+
+  // Helper functions for callback.
+
+  void OnNetworkReadSuccess(int len);
+
+  void OnCacheWriteSuccess(int result);
+
+  void OnCacheWriteFailure();
+
+  void OnNetworkReadFailure(int result);
+
+  void FailureCleanup(int error, bool continue_network_reading);
+
+  // All pending transactions will not be tracked by entry.
+  void MoveToPendingQueue();
+
+  // Notifies the transactions waiting on Read of the result, by posting a task
+  // for each of them.
+  void ProcessWaitingForReadTransactions(int result);
+
+  void OnProcessFirstWaitingValidation();
+
+  // Removes the active transaction from |this|.
+  void ResetActiveTransaction(bool continue_network_reading = false);
+
+  // Sets the state of idle writers so that they can fail any subsequent
+  // Read.
+  void SetIdleWritersFailState(int result);
+
+  // When response is completely written, any idle writers are moved to
+  // entry_->readers.
+  void MoveIdleWritersToReaders();
+
+  // Helper function to let the validating transaction continue being a part of
+  // SharedWriters.
+  void ValidationDoneContinue(Transaction* transaction,
+                              RequestPriority priority);
+
+  // Helper function invoked when response is successfully written to the cache.
+  void ResponseDataComplete();
+
+  bool AttemptTruncation();
+
+  RequestPriority getCurrentHighestPriority();
+
+  enum State {

[jkarlin, 2017/02/03 18:26:19]

The enum declaration should come before the private method declarations. Also,
prefer enum class to enum for type safety, unless you need it to work with
another enum or write it to a histogram.

[shivanisha, 2017/02/06 21:14:10]

done

+    STATE_NONE,
+    STATE_NETWORK_READ,
+    STATE_NETWORK_READ_COMPLETE,
+    STATE_CACHE_WRITE_DATA,
+    STATE_CACHE_WRITE_DATA_COMPLETE,
+    STATE_CACHE_WRITE_TRUNCATED_RESPONSE,
+    STATE_CACHE_WRITE_TRUNCATED_RESPONSE_COMPLETE,
+    STATE_DONE
+  };
+
+  State next_state_ = STATE_NONE;
+
+  // Http Cache.
+  base::WeakPtr<HttpCache> cache_;
+
+  // Owner of this object.
+  ActiveEntry* entry_ = nullptr;
+
+  std::unique_ptr<HttpTransaction> network_transaction_;
+
+  scoped_refptr<IOBuffer> read_buf_;
+  int io_buf_len_ = 0;
+  int write_len_ = 0;
+
+  // The cache transaction that is the current consumer of network_transaction_
+  // ::Read or writing to the entry and is waiting for the operation to be
+  // completed. This is used to ensure there is at most one consumer.
+  // After the network read and cache write is successful and data
+  // written to cache, other waiting transactions will be notified.
+  Transaction* active_transaction_ = nullptr;
+
+  // This will point to the currently validating transaction.
+  Transaction* validating_transaction_ = nullptr;
+
+  // These transactions are waiting for the validating transaction to complete
+  // and then the first of these will begin validation.
+  TransactionList waiting_for_validation_;
+
+  // These transactions are waiting on Read. After the active transaction
+  // completes writing the data to the cache, their buffer would be filled with
+  // the data and their callback will be invoked.
+  struct WaitingForRead {

[jkarlin, 2017/02/03 18:26:20]

struct should be at beginning of private:

[shivanisha, 2017/02/06 21:14:10]

done

+    Transaction* transaction;
+    scoped_refptr<IOBuffer> read_buf;
+    int read_buf_len;
+    int write_len;
+    const CompletionCallback callback;
+    WaitingForRead(Transaction* transaction,
+                   scoped_refptr<IOBuffer> read_buf,
+                   int len,
+                   const CompletionCallback& consumer_callback);
+    ~WaitingForRead();
+    WaitingForRead(const WaitingForRead&);
+  };
+  typedef std::list<WaitingForRead> WaitingForReadList;

[jkarlin, 2017/02/03 18:26:19]

using WaitingForReadList = std::list<WaitingForRead>;

 We avoid typedef in new code.

[shivanisha, 2017/02/06 21:14:10]

done

+  WaitingForReadList waiting_for_read_;
+
+  // Includes a transaction if it is past the validation stage.
+  TransactionSet all_writers_;
+
+  // Current priority of the request. If a higher priority transaction is
+  // added, the priority of network transaction will be increased.
+  RequestPriority priority_ = DEFAULT_PRIORITY;
+
+  CompletionCallback callback_;                 // Consumer's callback.
+  base::Callback<void(bool*)> cache_callback_;  // Cache callback.
+  CompletionCallback io_callback_;
+
+  // Saved so it could be returned to the consumer after marking the entry as
+  // truncated, if needed.
+  int rv_post_truncation_ = 0;
+
+  base::WeakPtrFactory<SharedWriters> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(SharedWriters);
+};
+
+}  // namespace net
+
+#endif  // NET_HTTP_HTTP_CACHE_SHARED_WRITERS_H_