Fixes the cache lock issue.

net/http/http_cache_shared_writers.h

+// 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"
+
+// Shared reading from the network and writing to the cache enables multiple
+// HttpCache::Transactions to drive reading the response body from the network.
+// This ensures that a slow consumer does not starve other consumers of the
+// same resource. Shared reading/writing starts after the first transaction has
+// read the response headers. Subsequent transactions are then able to join
+// reading the response. A shared transaction will either read the already
+// written part of the response from the cache or invoke read on the network
+// and write to the cache, depending on its read offset.
+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.
+  static void Create(Transaction* cacheTransaction,
+                     std::unique_ptr<HttpTransaction> network_transaction,
+                     base::WeakPtr<HttpCache> cache,
+                     RequestPriority priority);
+  SharedWriters(base::WeakPtr<HttpCache> cache,
+                ActiveEntry* entry,
+                Transaction* cache_transaction,
+                RequestPriority priority,
+                std::unique_ptr<HttpTransaction> network_transaction);
+  ~SharedWriters();
+
+  // Adds a transaction to SharedWriters. Return value is OK if it is the
+  // current validating transaction and ERR_IO_PENDING if it is waiting.
+  int 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, the
+  // entry is 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);
+
+  // 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 a pending transaction.
+  bool RemoveWaitingForValidationTransaction(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:
+  enum class State {
+    NONE,
+    NETWORK_READ,
+    NETWORK_READ_COMPLETE,
+    CACHE_WRITE_DATA,
+    CACHE_WRITE_DATA_COMPLETE,
+    CACHE_WRITE_TRUNCATED_RESPONSE,
+    CACHE_WRITE_TRUNCATED_RESPONSE_COMPLETE,
+    DONE
+  };
+
+  // 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 {
+    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&);
+  };
+
+  using WaitingForReadList = std::list<WaitingForRead>;
+  // Runs the state transition loop. Resets and calls |callback_| on exit,
+  // unless the return value is ERR_IO_PENDING.
+  int DoLoop(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 OnNetworkReadFailure(int result);
+
+  bool AttemptTruncation();
+
+  void OnCacheWriteSuccess(int result);
+
+  // Helper function invoked when response is successfully written to the cache.
+  void ResponseDataComplete();
+
+  void OnCacheWriteFailure();
+
+  void FailureCleanup(int error, bool continue_network_reading);
+
+  // All pending transactions will not be tracked by entry.
+  void MoveToPendingQueue();
+
+  // All transactions eligible for shared writing from entry's pending queue
+  // will be tracked from SharedWriters after this function.
+  void MoveFromPendingQueue();
+
+  // When response is completely written, any idle writers are moved to
+  // entry_->readers.
+  void MoveIdleWritersToReaders();
+
+  // Posts a task for invoking the io callback of the first transaction waiting
+  // for validation.
+  void ProcessFirstWaitingValidation();
+
+  void OnProcessFirstWaitingValidation();
+
+  // Notifies the transactions waiting on Read of the result, by posting a task
+  // for each of them.
+  void ProcessWaitingForReadTransactions(int result);
+
+  // 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);
+
+  // Helper function to let the validating transaction continue being a part of
+  // SharedWriters.
+  void ValidationDoneContinue(Transaction* transaction,
+                              RequestPriority priority);
+
+  RequestPriority getCurrentHighestPriority();
+
+  // IO Completion callback function.
+  void OnIOComplete(int result);
+
+  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_;
+
+  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_