Datastores are preloaded only for content principals. The preloading is triggered as soon as possible to lower the chance of blocking the main thread in content process. If there is no physical database on disk for given origin, datastore is not created. Preloaded datastores are kept alive for 20 seconds.
An attribute for checking if the next gen local storage implementation is enabled is exposed via a new interface nsILocalStorageManager which should be used for any other local storage specific stuff.
The implementation is based on a cache (datastore) living in the parent process and sync IPC calls initiated from content processes.
IPC communication is done using per principal/origin database actors which connect to the datastore.
The synchronous blocking of the main thread is done by creating a nested event target and spinning the event loop.
This patch adds a new IPDL protocol PBackgroundLocalStorageCache. It is used by LocalStorageCache object to broadcast changes in local storage cache to other content processes. Each origin has its own PBackgroundLocalStorageCache, so now we can notify content processes that actually have a local storage cache for given origin. This greatly improves performance and reduces memory footprint especialy when local storage changes carry big strings and/or happen very quickly (before this patch all child processes were blindly notified).
- stop inheriting StorageDBBridge in StorageDBThread and StorageDBChild
- move StorageDBThread and StorageDBChild initialization out of LocalStorageCache
- use IPC even for the intra-process communication in main process
- rationalize a bit storage observer code
- make StorageDBParent to always be created and destroyed on the background thread
