Disk cache: Reference CL for the implementation of file format version 3.

net/disk_cache/v3/backend_impl_v3.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.
+
+// See net/disk_cache/disk_cache.h for the public interface of the cache.
+
+#ifndef NET_DISK_CACHE_V3_BACKEND_IMPL_V3_H_
+#define NET_DISK_CACHE_V3_BACKEND_IMPL_V3_H_
+
+#include "base/files/file_path.h"
+#include "base/hash_tables.h"
+#include "base/synchronization/waitable_event.h"
+#include "base/timer.h"
+#include "net/disk_cache/block_files.h"
+#include "net/disk_cache/disk_cache.h"
+#include "net/disk_cache/stats.h"
+#include "net/disk_cache/stress_support.h"
+#include "net/disk_cache/trace.h"
+#include "net/disk_cache/v3/block_bitmaps.h"
+#include "net/disk_cache/v3/eviction_v3.h"
+#include "net/disk_cache/v3/index_table.h"
+
+namespace net {
+class NetLog;
+}  // namespace net
+
+namespace disk_cache {
+
+class IndexTable;
+class EntryImplV3;
+
+// This class implements the Backend interface. An object of this
+// class handles the operations of the cache for a particular profile.
+class NET_EXPORT_PRIVATE BackendImplV3 : public Backend {
+  friend class EvictionV3;
+ public:
+  enum BackendFlags {
+    MAX_SIZE = 1 << 1,            // A maximum size was provided.
+    UNIT_TEST_MODE = 1 << 2,      // We are modifying the behavior for testing.
+    UPGRADE_MODE = 1 << 3,        // This is the upgrade tool (dump).
+    EVICTION_V2 = 1 << 4,         // Use of new eviction was specified.
+    BASIC_UNIT_TEST = 1 << 5,     // Identifies almost all unit tests.
+    NO_LOAD_PROTECTION = 1 << 6,  // Don't act conservatively under load.
+    NO_BUFFERING = 1 << 7,        // Disable extended IO buffering.
+    NO_CLEAN_ON_EXIT              // Avoid saving data at exit time.
+  };
+
+  BackendImplV3(const base::FilePath& path, base::MessageLoopProxy* cache_thread,
+              net::NetLog* net_log);
+  virtual ~BackendImplV3();
+
+  // Performs general initialization for this current instance of the cache.
+  int Init(const CompletionCallback& callback);
+
+  // Same behavior as OpenNextEntry but walks the list from back to front.
+  int OpenPrevEntry(void** iter, Entry** prev_entry,
+                    const CompletionCallback& callback);
+
+  // Sets the maximum size for the total amount of data stored by this instance.
+  bool SetMaxSize(int max_bytes);
+
+  // Sets the cache type for this backend.
+  void SetType(net::CacheType type);
+
+  // Creates a new storage block of size block_count.
+  bool CreateBlock(FileType block_type, int block_count,
+                   Addr* block_address);
+
+  // Updates the ranking information for an entry.
+  void UpdateRank(EntryImplV3* entry, bool modified);
+
+  // Permanently deletes an entry, but still keeps track of it.
+  void InternalDoomEntry(EntryImplV3* entry);
+
+  // This method must be called when an entry is released for the last time, so
+  // the entry should not be used anymore. |address| is the cache address of the
+  // entry.
+  void OnEntryDestroyBegin(Addr address);
+
+  // This method must be called after all resources for an entry have been
+  // released.
+  void OnEntryDestroyEnd();
+
+  // Methods that perform file IO. Each method result in a task posted to the
+  // cache thread, with the |callback| invoked when the operation completes.
+  // Any error would result in the |entry| being automatically deleted. Note
+  // that these methods do not operate directly on entries, but rather on the
+  // |address| provided. For example, Delete() deletes the data pointed by
+  // |address|, it doesn't delete |entry|.
+  void ReadData(EntryImplV3* entry, Addr address, int offset,
+                net::IOBuffer* buffer, int buffer_len,
+                const CompletionCallback& callback);
+  void WriteData(EntryImplV3* entry, Addr address, int offset,
+                 net::IOBuffer* buffer, int buffer_len,
+                 const CompletionCallback& callback);
+  void MoveData(EntryImplV3* entry, Addr source, Addr destination, int len,
+                const CompletionCallback& callback);
+  void Truncate(EntryImplV3* entry, Addr address, int offset);
+  void Delete(EntryImplV3* entry, Addr address);
+  void Close(EntryImplV3* entry, Addr address);
+
+  // Delete or fix a given |cell| from the index table.
+  void DeleteCell(IndexCell* cell, int32 cell_id);
+  void FixCell(IndexCell* cell, int32 cell_id);
+
+  // Evicts the entry located at |address|, with the given |hash|. Returns true
+  // if the entry can be evicted and the caller should expect a completion
+  // notification, false otherwise.
+  // This method is used by the eviction module, and OnEvictEntryComplete() will
+  // be called to notify the end of the operation.
+  bool EvictEntry(uint32 hash, Addr address);
+
+  // If the |address| corresponds to an open entry, returns a pointer to that
+  // entry, otherwise returns NULL. Note that this method increases the ref
+  // counter for the entry.
+  EntryImplV3* GetOpenEntry(Addr address) const;
+
+  // Returns the maximum size for a file to reside on the cache.
+  int MaxFileSize() const;
+
+  // A user data block is being created, extended or truncated.
+  void ModifyStorageSize(int32 old_size, int32 new_size);
+
+  // Logs requests that are denied due to being too big.
+  void TooMuchStorageRequested(int32 size);
+
+  // Returns true if a temporary buffer is allowed to be extended.
+  bool IsAllocAllowed(int current_size, int new_size, bool force);
+
+  // Tracks the release of |size| bytes by an entry buffer.
+  void BufferDeleted(int size);
+
+  // Only intended for testing the two previous methods.
+  int GetTotalBuffersSize() const {
+    return buffer_bytes_;
+  }
+
+  // Returns true if this instance seems to be under heavy load.
+  bool IsLoaded() const;
+
+  // Returns the current time. For tests to run properly, use this method
+  // instead of calling base::Time::Now() directly.
+  base::Time GetCurrentTime() const;
+
+  // Returns the full histogram name, for the given base |name| and experiment,
+  // and the current cache type. The name will be "DiskCache.t.name_e" where n
+  // is the cache type and e the provided |experiment|.
+  std::string HistogramName(const char* name, int experiment) const;
+
+  net::CacheType cache_type() const {
+    return cache_type_;
+  }
+
+  bool read_only() const {
+    return read_only_;
+  }
+
+  // Returns a weak pointer to this object.
+  base::WeakPtr<BackendImplV3> GetWeakPtr();
+
+  // Returns true if we should send histograms for this user again. The caller
+  // must call this function only once per run (because it returns always the
+  // same thing on a given run).
+  bool ShouldReportAgain();
+
+  // Reports some data when we filled up the cache.
+  void FirstEviction();
+
+  // Called when an interesting event should be logged (counted).
+  void OnEvent(Stats::Counters an_event);
+
+  // Keeps track of payload access (doesn't include metadata).
+  void OnRead(int bytes);
+  void OnWrite(int bytes);
+
+  // Increases the size of the index file.
+  void GrowIndex();
+
+  // Increases the size of the block files.
+  void GrowBlockFiles();
+
+  // Saved the index to the backup file.
+  void SaveIndex(net::IOBuffer* buffer, int buffer_len);
+
+  // Timer callback to calculate usage statistics and perform backups.
+  void OnTimerTick();
+
+  // Sets internal parameters to enable unit testing mode.
+  void SetUnitTestMode();
+
+  // Sets internal parameters to enable upgrade mode (for internal tools).
+  void SetUpgradeMode();
+
+  // Sets the eviction algorithm to version 2.
+  void SetNewEviction();
+
+  // Sets an explicit set of BackendFlags.
+  void SetFlags(uint32 flags);
+
+  // Sends a dummy operation through the operation queue, for unit tests.
+  int FlushQueueForTest(const CompletionCallback& callback);
+
+  // Performs final cleanup, for unit tests.
+  int CleanupForTest(const CompletionCallback& callback);
+
+  // Trims an entry (all if |empty| is true) from the list of deleted
+  // entries. This method should be called directly on the cache thread.
+  void TrimForTest(bool empty);
+
+  // Trims an entry (all if |empty| is true) from the list of deleted
+  // entries. This method should be called directly on the cache thread.
+  void TrimDeletedListForTest(bool empty);
+
+  // Simulates that aditional |seconds| have elapsed, for testing purposes.
+  void AddDelayForTest(int seconds);
+
+  // Returns a net error code to inform the caller when the entry with the
+  // desired |key| is completely closed.
+  int WaitForEntryToCloseForTest(const std::string& key,
+                                 const CompletionCallback& callback);
+
+  // Performs a simple self-check, and returns the number of dirty items
+  // or an error code (negative value).
+  int SelfCheck();
+
+  // Backend implementation.
+  virtual net::CacheType GetCacheType() const OVERRIDE;
+  virtual int32 GetEntryCount() const OVERRIDE;
+  virtual int OpenEntry(const std::string& key, Entry** entry,
+                        const CompletionCallback& callback) OVERRIDE;
+  virtual int CreateEntry(const std::string& key, Entry** entry,
+                          const CompletionCallback& callback) OVERRIDE;
+  virtual int DoomEntry(const std::string& key,
+                        const CompletionCallback& callback) OVERRIDE;
+  virtual int DoomAllEntries(const CompletionCallback& callback) OVERRIDE;
+  virtual int DoomEntriesBetween(base::Time initial_time,
+                                 base::Time end_time,
+                                 const CompletionCallback& callback) OVERRIDE;
+  virtual int DoomEntriesSince(base::Time initial_time,
+                               const CompletionCallback& callback) OVERRIDE;
+  virtual int OpenNextEntry(void** iter, Entry** next_entry,
+                            const CompletionCallback& callback) OVERRIDE;
+  virtual void EndEnumeration(void** iter) OVERRIDE;
+  virtual void GetStats(StatsItems* stats) OVERRIDE;
+  virtual void OnExternalCacheHit(const std::string& key) OVERRIDE;
+
+ private:
+  typedef base::hash_map<CacheAddr, EntryImplV3*> EntriesMap;
+  class IOCallback;
+  class Worker;
+  class WorkItem;
+
+  void AdjustMaxCacheSize();
+  bool InitStats(void* stats_data);
+  void StoreStats();
+
+  // Deletes the cache and starts again.
+  void RestartCache(const CompletionCallback& callback);
+  void PrepareForRestart();
+
+  // Performs final cleanup.
+  void CleanupCache();
+
+  // Creates a new entry object. Returns zero on success, or a disk_cache error
+  // on failure.
+  int NewEntry(WorkItem* work_item, EntryImplV3** entry);
+
+  // Scans |entries| and the list of open entries looking for a match. Returns
+  // NULL if no match is fouond.
+  EntryImplV3* LookupOpenEntry(const EntrySet& entries, const std::string key);
+
+  // Opens the next or previous entry on a cache iteration.
+  int OpenFollowingEntry(bool forward, void** iter, Entry** next_entry,
+                         const CompletionCallback& callback);
+
+  // Continue an enumeration by getting more cells or the next entry to open.
+  bool GetMoreCells(WorkItem* work_item);
+  bool OpenNext(WorkItem* work_item);
+
+  // Doom |entry| if directed by the work_item.
+  void Doom(EntryImplV3* entry, WorkItem* work_item);
+
+  // Update the user visible iterator an tell the user about it.
+  void UpdateIterator(EntryImplV3* entry, WorkItem* work_item);
+
+  // Handles the used storage count.
+  void AddStorageSize(int32 bytes);
+  void SubstractStorageSize(int32 bytes);
+
+  // Update the number of referenced cache entries.
+  void IncreaseNumRefs();
+  void DecreaseNumRefs();
+  void IncreaseNumEntries();
+  void DecreaseNumEntries();
+
+  // Methods to post and receive notifications about tasks executed on the
+  // cache thread.
+  void PostWorkItem(WorkItem* work_item);
+  void OnWorkDone(WorkItem* work_item);
+  void OnInitComplete(WorkItem* work_item);
+  void OnGrowIndexComplete(WorkItem* work_item);
+  void OnGrowFilesComplete(WorkItem* work_item);
+  void OnOperationComplete(WorkItem* work_item);
+  void OnOpenEntryComplete(WorkItem* work_item);
+  void OnOpenForResurrectComplete(WorkItem* work_item);
+  void OnEvictEntryComplete(WorkItem* work_item);
+  void OnOpenNextComplete(WorkItem* work_item);
+
+  // Last part of CreateEntry(). |short_record| may point to stored data about
+  // a previously evicted entry matching this |key|.
+  int OnCreateEntryComplete(const std::string& key, uint32 hash, 
+                            ShortEntryRecord* short_record, Entry** entry,
+                            const CompletionCallback& callback);
+
+  // Dumps current cache statistics to the log.
+  void LogStats();
+
+  // Send UMA stats.
+  void ReportStats();
+
+  // Reports an uncommon, recoverable error.
+  void ReportError(int error);
+
+  // Performs basic checks on the index file. Returns false on failure.
+  bool CheckIndex();
+
+  // Part of the self test. Returns the number or dirty entries, or an error.
+  int CheckAllEntries();
+
+  // Part of the self test. Returns false if the entry is corrupt.
+  bool CheckEntry(EntryImplV3* cache_entry);
+
+  // Returns the maximum total memory for the memory buffers.
+  int MaxBuffersSize();
+
+  IndexTable index_;
+  base::FilePath path_;  // Path to the folder used as backing storage.
+  BlockBitmaps block_files_;
+  int32 max_size_;  // Maximum data size for this instance.
+  EvictionV3 eviction_;  // Handler of the eviction algorithm.
+  EntriesMap open_entries_;  // Map of open entries.
+  int num_refs_;  // Number of referenced cache entries.
+  int max_refs_;  // Max number of referenced cache entries.
+  int entry_count_;  // Number of entries accessed lately.
+  int byte_count_;  // Number of bytes read/written lately.
+  int buffer_bytes_;  // Total size of the temporary entries' buffers.
+  int up_ticks_;  // The number of timer ticks received (OnTimerTick).
+  int test_seconds_;  // The "current time" for tests.
+  net::CacheType cache_type_;
+  int uma_report_;  // Controls transmission of UMA data.
+  uint32 user_flags_;  // Flags set by the user.
+  bool init_;  // controls the initialization of the system.
+  bool restarted_;
+  bool read_only_;  // Prevents updates of the rankings data (used by tools).
+  bool disabled_;
+  bool lru_eviction_;  // What eviction algorithm should be used.
+  bool first_timer_;  // True if the timer has not been called.
+  bool user_load_;  // True if we see a high load coming from the caller.
+  bool growing_index_;
+  bool growing_files_;
+
+  net::NetLog* net_log_;
+
+  Stats stats_;  // Usage statistics.
+  scoped_ptr<base::RepeatingTimer<BackendImplV3> > timer_;  // Usage timer.
+  scoped_refptr<TraceObject> trace_object_;  // Initializes internal tracing.
+  scoped_refptr<base::MessageLoopProxy> cache_thread_;
+  scoped_refptr<Worker> worker_;
+  base::WeakPtrFactory<BackendImplV3> ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(BackendImplV3);
+};
+
+}  // namespace disk_cache
+
+#endif  // NET_DISK_CACHE_V3_BACKEND_IMPL_V3_H_