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      1 /*
      2  * libjingle
      3  * Copyright 2004--2005, Google Inc.
      4  *
      5  * Redistribution and use in source and binary forms, with or without
      6  * modification, are permitted provided that the following conditions are met:
      7  *
      8  *  1. Redistributions of source code must retain the above copyright notice,
      9  *     this list of conditions and the following disclaimer.
     10  *  2. Redistributions in binary form must reproduce the above copyright notice,
     11  *     this list of conditions and the following disclaimer in the documentation
     12  *     and/or other materials provided with the distribution.
     13  *  3. The name of the author may not be used to endorse or promote products
     14  *     derived from this software without specific prior written permission.
     15  *
     16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
     17  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
     18  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
     19  * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
     20  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
     21  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
     22  * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
     23  * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
     24  * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
     25  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     26  */
     27 
     28 #ifndef TALK_BASE_DISKCACHE_H__
     29 #define TALK_BASE_DISKCACHE_H__
     30 
     31 #include <map>
     32 #include <string>
     33 
     34 #ifdef WIN32
     35 #undef UnlockResource
     36 #endif  // WIN32
     37 
     38 namespace talk_base {
     39 
     40 class StreamInterface;
     41 
     42 ///////////////////////////////////////////////////////////////////////////////
     43 // DiskCache - An LRU cache of streams, stored on disk.
     44 //
     45 // Streams are identified by a unique resource id.  Multiple streams can be
     46 // associated with each resource id, distinguished by an index.  When old
     47 // resources are flushed from the cache, all streams associated with those
     48 // resources are removed together.
     49 // DiskCache is designed to persist across executions of the program.  It is
     50 // safe for use from an arbitrary number of users on a single thread, but not
     51 // from multiple threads or other processes.
     52 ///////////////////////////////////////////////////////////////////////////////
     53 
     54 class DiskCache {
     55 public:
     56   DiskCache();
     57   virtual ~DiskCache();
     58 
     59   bool Initialize(const std::string& folder, size_t size);
     60   bool Purge();
     61 
     62   bool LockResource(const std::string& id);
     63   StreamInterface* WriteResource(const std::string& id, size_t index);
     64   bool UnlockResource(const std::string& id);
     65 
     66   StreamInterface* ReadResource(const std::string& id, size_t index) const;
     67 
     68   bool HasResource(const std::string& id) const;
     69   bool HasResourceStream(const std::string& id, size_t index) const;
     70   bool DeleteResource(const std::string& id);
     71 
     72  protected:
     73   virtual bool InitializeEntries() = 0;
     74   virtual bool PurgeFiles() = 0;
     75 
     76   virtual bool FileExists(const std::string& filename) const = 0;
     77   virtual bool DeleteFile(const std::string& filename) const = 0;
     78 
     79   enum LockState { LS_UNLOCKED, LS_LOCKED, LS_UNLOCKING };
     80   struct Entry {
     81     LockState lock_state;
     82     mutable size_t accessors;
     83     size_t size;
     84     size_t streams;
     85     time_t last_modified;
     86   };
     87   typedef std::map<std::string, Entry> EntryMap;
     88   friend class DiskCacheAdapter;
     89 
     90   bool CheckLimit();
     91 
     92   std::string IdToFilename(const std::string& id, size_t index) const;
     93   bool FilenameToId(const std::string& filename, std::string* id,
     94                     size_t* index) const;
     95 
     96   const Entry* GetEntry(const std::string& id) const {
     97     return const_cast<DiskCache*>(this)->GetOrCreateEntry(id, false);
     98   }
     99   Entry* GetOrCreateEntry(const std::string& id, bool create);
    100 
    101   void ReleaseResource(const std::string& id, size_t index) const;
    102 
    103   std::string folder_;
    104   size_t max_cache_, total_size_;
    105   EntryMap map_;
    106   mutable size_t total_accessors_;
    107 };
    108 
    109 ///////////////////////////////////////////////////////////////////////////////
    110 // CacheLock - Automatically manage locking and unlocking, with optional
    111 // rollback semantics
    112 ///////////////////////////////////////////////////////////////////////////////
    113 
    114 class CacheLock {
    115 public:
    116   CacheLock(DiskCache* cache, const std::string& id, bool rollback = false)
    117   : cache_(cache), id_(id), rollback_(rollback)
    118   {
    119     locked_ = cache_->LockResource(id_);
    120   }
    121   ~CacheLock() {
    122     if (locked_) {
    123       cache_->UnlockResource(id_);
    124       if (rollback_) {
    125         cache_->DeleteResource(id_);
    126       }
    127     }
    128   }
    129   bool IsLocked() const { return locked_; }
    130   void Commit() { rollback_ = false; }
    131 
    132 private:
    133   DiskCache* cache_;
    134   std::string id_;
    135   bool rollback_, locked_;
    136 };
    137 
    138 ///////////////////////////////////////////////////////////////////////////////
    139 
    140 }  // namespace talk_base
    141 
    142 #endif // TALK_BASE_DISKCACHE_H__
    143