michael@0: // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
michael@0: // Use of this source code is governed by a BSD-style license that can be
michael@0: // found in the LICENSE file.
michael@0: 
michael@0: #ifndef BASE_REVOCABLE_STORE_H_
michael@0: #define BASE_REVOCABLE_STORE_H_
michael@0: 
michael@0: #include "base/ref_counted.h"
michael@0: 
michael@0: // |RevocableStore| is a container of items that can be removed from the store.
michael@0: class RevocableStore {
michael@0:  public:
michael@0:   // A |StoreRef| is used to link the |RevocableStore| to its items.  There is
michael@0:   // one StoreRef per store, and each item holds a reference to it.  If the
michael@0:   // store wishes to revoke its items, it sets |store_| to null.  Items are
michael@0:   // permitted to release their reference to the |StoreRef| when they no longer
michael@0:   // require the store.
michael@0:   class StoreRef : public base::RefCounted<StoreRef> {
michael@0:    public:
michael@0:     StoreRef(RevocableStore* store) : store_(store) { }
michael@0: 
michael@0:     void set_store(RevocableStore* store) { store_ = store; }
michael@0:     RevocableStore* store() const { return store_; }
michael@0: 
michael@0:    private:
michael@0:     RevocableStore* store_;
michael@0: 
michael@0:     DISALLOW_EVIL_CONSTRUCTORS(StoreRef);
michael@0:   };
michael@0: 
michael@0:   // An item in the store.  On construction, the object adds itself to the
michael@0:   // store.
michael@0:   class Revocable {
michael@0:    public:
michael@0:     Revocable(RevocableStore* store);
michael@0:     ~Revocable();
michael@0: 
michael@0:     // This item has been revoked if it no longer has a pointer to the store.
michael@0:     bool revoked() const { return !store_reference_->store(); }
michael@0: 
michael@0:   private:
michael@0:     // We hold a reference to the store through this ref pointer.  We release
michael@0:     // this reference on destruction.
michael@0:     scoped_refptr<StoreRef> store_reference_;
michael@0: 
michael@0:     DISALLOW_EVIL_CONSTRUCTORS(Revocable);
michael@0:   };
michael@0: 
michael@0:   RevocableStore();
michael@0:   ~RevocableStore();
michael@0: 
michael@0:   // Revokes all the items in the store.
michael@0:   void RevokeAll();
michael@0: 
michael@0:   // Returns true if there are no items in the store.
michael@0:   bool empty() const { return count_ == 0; }
michael@0: 
michael@0:  private:
michael@0:   friend class Revocable;
michael@0: 
michael@0:   // Adds an item to the store.  To add an item to the store, construct it
michael@0:   // with a pointer to the store.
michael@0:   void Add(Revocable* item);
michael@0: 
michael@0:   // This is the reference the unrevoked items in the store hold.
michael@0:   scoped_refptr<StoreRef> owning_reference_;
michael@0: 
michael@0:   // The number of unrevoked items in the store.
michael@0:   int count_;
michael@0: 
michael@0:   DISALLOW_EVIL_CONSTRUCTORS(RevocableStore);
michael@0: };
michael@0: 
michael@0: #endif  // BASE_REVOCABLE_STORE_H_