1 files changed, 60 insertions, 0 deletions
diff --git a/comm/mailnews/base/src/nsMsgFolderCache.h b/comm/mailnews/base/src/nsMsgFolderCache.h
new file mode 100644
index 0000000000..480814ad10
--- /dev/null
+++ b/comm/mailnews/base/src/nsMsgFolderCache.h
@@ -0,0 +1,60 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsMsgFolderCache_H
+#define nsMsgFolderCache_H
+
+#include "nsIMsgFolderCache.h"
+#include "nsIFile.h"
+#include "nsITimer.h"
+
+namespace Json {
+class Value;
+};
+
+/**
+ * nsMsgFolderCache implements the folder cache, which stores values which
+ * might be slow for the folder to calculate.
+ * It persists the cache data by dumping it out to a .json file when changes
+ * are made. To avoid huge numbers of writes, this autosaving is deferred -
+ * when a cached value is changed, it'll wait a minute or so before
+ * writing, to collect any other changes that occur during that time.
+ * If any changes are outstanding at destruction time, it'll perform an
+ * immediate save then.
+ */
+class nsMsgFolderCache : public nsIMsgFolderCache {
+ public:
+  friend class nsMsgFolderCacheElement;
+
+  nsMsgFolderCache();
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIMSGFOLDERCACHE
+
+ protected:
+  virtual ~nsMsgFolderCache();
+
+  nsresult LoadFolderCache(nsIFile* jsonFile);
+  nsresult SaveFolderCache(nsIFile* jsonFile);
+  // Flag that a save is required. It'll be deferred by kAutoSaveDelayMs.
+  void SetModified();
+  static constexpr uint32_t kSaveDelayMs = 1000 * 60 * 1;  // 1 minute.
+  static void doSave(nsITimer*, void* closure);
+
+  // Path to the JSON file backing the cache.
+  nsCOMPtr<nsIFile> mCacheFile;
+
+  // This is our data store. Kept as a Json::Value for ease of saving, but
+  // it's actually not a bad format for access (it's basically a std::map).
+  // Using a pointer to allow forward declaration. The json headers aren't
+  // in the include path for other modules, so we don't want to expose them
+  // here.
+  Json::Value* mRoot;
+
+  bool mSavePending;
+  nsCOMPtr<nsITimer> mSaveTimer;
+};
+
+#endif