Before this patch, it was only possible to initialize a snapshot to the Partial state or AllOrderedItems state. Now there's a third state AllOrderedKeys.
This improves performance by eliminating sync calls to parent process when we know nothing about a key in content process (in that case we have to use a sync call to the parent process to see if there's a value for it).
With this patch we always try to send all keys to content when a snapshot is being initialized. For this to work efficiently, we cache the size of all keys.
Having cached size of all keys also allows us to just iterate the mValues hashtable when the size of keys is bigger than snapshot prefill threshold (instead of iterating over the mKeys array and joining with mValues for each particular key).
There's some additional cleanup in snapshot info construction and Datastore::SetItem/RemoveItem/Clear methods.
This improves performance a lot in cases when multiple operations are invoked by a single JS function (number of sync IPC calls is reduced to a minimum). It also improves correctness since changes are not visible to other content processes until a JS function finishes.
The patch implements core infrastructure, all items are sent to content when a snapshot is initialized and everything is fully working. However, sending of all items at once is not optimal for bigger databases. Support for lazy loading of items is implemented in a following patch.
If a database actor already exists for given origin, reuse it instead of creating a new one. This improves memory footprint a bit and also eliminates some round trips to the parent process.
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.
Storage events are fired either directly after getting response from synchronous SetItem call or through observers. When a new onstorage event listener is added, we sycnhronously register an observer in the parent process. There's always only one observer actor per content process.
PBackgroundLSDatabase is now managed by a new PBackgroundLSObject protocol. PBackgroundLSObject is needed to eliminate the need to pass the principal info and document URI everytime a write operation occurs.
Preparation of an observer shares some states with preparation of a datastore, so common stuff now lives in LSRequestBase and preparation of a datastore now implements a nested state machine.
This patch was enhanced by asuth to drop observers only when the last storage listener is removed.
EventListenerRemoved is invoked on any removal, not just the final removal, so we need to make sure it's the final removal before dropping observer.
Preparation of datastores now creates real database files on disk. The LocalStorage directory is protected by a directory lock.
Infrastructure for database schema upgrades is in place too.
Database actors are now explicitely tracked by the datastore. When the last actor finishes the directory lock is released.
Added also implementation for QuotaClient::GetUsageForOrigin() and QuotaClient::AbortOperations().
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.
Jan Varga