Adds a modified copy of talk/base to webrtc/base. It is the first step in migrating talk/base to webrtc/base.

BUG=N/A
R=andrew@webrtc.org, wu@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/12199004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6107 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/base/diskcache.h

@@ -0,0 +1,125 @@
+/*
+ *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_BASE_DISKCACHE_H__
+#define WEBRTC_BASE_DISKCACHE_H__
+
+#include <map>
+#include <string>
+
+#if defined(WEBRTC_WIN)
+#undef UnlockResource
+#endif  // WEBRTC_WIN 
+
+namespace rtc {
+
+class StreamInterface;
+
+///////////////////////////////////////////////////////////////////////////////
+// DiskCache - An LRU cache of streams, stored on disk.
+//
+// Streams are identified by a unique resource id.  Multiple streams can be
+// associated with each resource id, distinguished by an index.  When old
+// resources are flushed from the cache, all streams associated with those
+// resources are removed together.
+// DiskCache is designed to persist across executions of the program.  It is
+// safe for use from an arbitrary number of users on a single thread, but not
+// from multiple threads or other processes.
+///////////////////////////////////////////////////////////////////////////////
+
+class DiskCache {
+public:
+  DiskCache();
+  virtual ~DiskCache();
+
+  bool Initialize(const std::string& folder, size_t size);
+  bool Purge();
+
+  bool LockResource(const std::string& id);
+  StreamInterface* WriteResource(const std::string& id, size_t index);
+  bool UnlockResource(const std::string& id);
+
+  StreamInterface* ReadResource(const std::string& id, size_t index) const;
+
+  bool HasResource(const std::string& id) const;
+  bool HasResourceStream(const std::string& id, size_t index) const;
+  bool DeleteResource(const std::string& id);
+
+ protected:
+  virtual bool InitializeEntries() = 0;
+  virtual bool PurgeFiles() = 0;
+
+  virtual bool FileExists(const std::string& filename) const = 0;
+  virtual bool DeleteFile(const std::string& filename) const = 0;
+
+  enum LockState { LS_UNLOCKED, LS_LOCKED, LS_UNLOCKING };
+  struct Entry {
+    LockState lock_state;
+    mutable size_t accessors;
+    size_t size;
+    size_t streams;
+    time_t last_modified;
+  };
+  typedef std::map<std::string, Entry> EntryMap;
+  friend class DiskCacheAdapter;
+
+  bool CheckLimit();
+
+  std::string IdToFilename(const std::string& id, size_t index) const;
+  bool FilenameToId(const std::string& filename, std::string* id,
+                    size_t* index) const;
+
+  const Entry* GetEntry(const std::string& id) const {
+    return const_cast<DiskCache*>(this)->GetOrCreateEntry(id, false);
+  }
+  Entry* GetOrCreateEntry(const std::string& id, bool create);
+
+  void ReleaseResource(const std::string& id, size_t index) const;
+
+  std::string folder_;
+  size_t max_cache_, total_size_;
+  EntryMap map_;
+  mutable size_t total_accessors_;
+};
+
+///////////////////////////////////////////////////////////////////////////////
+// CacheLock - Automatically manage locking and unlocking, with optional
+// rollback semantics
+///////////////////////////////////////////////////////////////////////////////
+
+class CacheLock {
+public:
+  CacheLock(DiskCache* cache, const std::string& id, bool rollback = false)
+  : cache_(cache), id_(id), rollback_(rollback)
+  {
+    locked_ = cache_->LockResource(id_);
+  }
+  ~CacheLock() {
+    if (locked_) {
+      cache_->UnlockResource(id_);
+      if (rollback_) {
+        cache_->DeleteResource(id_);
+      }
+    }
+  }
+  bool IsLocked() const { return locked_; }
+  void Commit() { rollback_ = false; }
+
+private:
+  DiskCache* cache_;
+  std::string id_;
+  bool rollback_, locked_;
+};
+
+///////////////////////////////////////////////////////////////////////////////
+
+}  // namespace rtc
+
+#endif // WEBRTC_BASE_DISKCACHE_H__