Manage IsolatedContext with reference counts

webkit/fileapi/isolated_context.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.
 
 #ifndef WEBKIT_FILEAPI_ISOLATED_CONTEXT_H_
 #define WEBKIT_FILEAPI_ISOLATED_CONTEXT_H_
 
 #include <map>
 #include <set>
 #include <string>
@@ skipping 36 matching lines @@
   // it can properly return the original path '/a/b/foo' by looking up the
   // internal mapping.  Similarly if a dropped entry is a directory and its
   // path is like '/a/b/dir' a virtual path like '/<fsid>/dir/foo' can be
   // cracked into '/a/b/dir/foo'.
   //
   // This may return an empty string (thus invalid as an ID) if the given
   // file set contains non absolute paths.
   std::string RegisterIsolatedFileSystem(const std::set<FilePath>& fileset);
 
   // Revokes filesystem specified by the given filesystem_id.
+  // Note that this revokes the filesystem no matter how many references it has.
+  // It is ok to call this on the filesystem that has been already deleted
+  // (if its reference count had reached 0).
   void RevokeIsolatedFileSystem(const std::string& filesystem_id);
 
+  // Adds a reference to a filesystem specified by the given filesystem_id.
+  void AddReference(const std::string& filesystem_id);
+
+  // Removes a reference to a filesystem specified by the given filesystem_id.
+  // If the reference count reaches 0 the isolated context gets destroyed.
+  // It is ok to call this on the filesystem that has been already deleted
+  // (e.g. by RevokeIsolatedFileSystem).
+  void RemoveReference(const std::string& filesystem_id);
+
   // Cracks the given |virtual_path| (which should look like
   // "/<filesystem_id>/<relative_path>") and populates the |filesystem_id|
   // and |platform_path| if the embedded <filesystem_id> is registerred
   // to this context.  |root_path| is also populated to have the platform
   // root (toplevel) path for the |virtual_path|
   // (i.e. |platform_path| = |root_path| + <relative_path>).
   //
   // Returns false if the given virtual_path or the cracked filesystem_id
   // is not valid.
   //
@@ skipping 26 matching lines @@
   friend struct base::DefaultLazyInstanceTraits<IsolatedContext>;
 
   // Maps from filesystem id to a path conversion map for top-level entries.
   typedef std::map<FilePath, FilePath> PathMap;
   typedef std::map<std::string, PathMap> IDToPathMap;
 
   // Obtain an instance of this class via GetInstance().
   IsolatedContext();
   ~IsolatedContext();
 
+  // Removes the given filesystem without locking.
+  // (The caller must hold a lock)
+  void RevokeWithoutLocking(const std::string& filesystem_id);
+
   // Returns a new filesystem_id.  Called with lock.
   std::string GetNewFileSystemId() const;
 
   // This lock needs to be obtained when accessing the toplevel_map_.
   mutable base::Lock lock_;
 
   // Maps the toplevel entries to the filesystem id.
   IDToPathMap toplevel_map_;
 
   // Holds a set of writable ids.
   // Isolated file systems are created read-only by default, and this set
   // holds a list of exceptions.
   // Detailed filesystem permission may be provided by an external
   // security policy manager, e.g. ChildProcessSecurityPolicy.
   std::set<std::string> writable_ids_;
 
+  // Reference counts. Note that an isolated filesystem is created with ref==0.
+  // and will get deleted when the ref count reaches <=0.
+  std::map<std::string, int> ref_counts_;
+
   DISALLOW_COPY_AND_ASSIGN(IsolatedContext);
 };
 
 }  // namespace fileapi
 
 #endif  // WEBKIT_FILEAPI_ISOLATED_CONTEXT_H_