The new infrastructure consists of a separate bridge between the content and the
parent process and a separate local storage database in the parent process.
The new infrastructure can be used for storing and sharing of private browsing
data across content processes.
This patch only creates necessary infrastructure, actual enabling of storing and
sharing of data across content processes will be done in a follow-up patch.
Differential Revision: https://phabricator.services.mozilla.com/D96562
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.
Everything that goes in a PLDHashtable (and its derivatives, like
nsTHashtable) needs to inherit from PLDHashEntryHdr. But through a lack
of enforcement, copy constructors for these derived classes didn't
explicitly invoke the copy constructor for PLDHashEntryHdr (and the
compiler didn't invoke the copy constructor for us). Instead,
PLDHashTable explicitly copied around the bits that the copy constructor
would have.
The current setup has two problems:
1) Derived classes should be using move construction, not copy
construction, since anything that's shuffling hash table keys/entries
around will be using move construction.
2) Derived classes should take responsibility for transferring bits of
superclass state around, and not rely on something else to handle that.
The second point is not a huge problem for PLDHashTable (PLDHashTable
only has to copy PLDHashEntryHdr's bits in a single place), but future
hash table implementations that might move entries around more
aggressively would have to insert compensation code all over the
place. Additionally, if moving entries is implemented via memcpy (which
is quite common), PLDHashTable copying around bits *again* is
inefficient.
Let's fix all these problems in one go, by:
1) Explicitly declaring the set of constructors that PLDHashEntryHdr
implements (and does not implement). In particular, the copy
constructor is deleted, so any derived classes that attempt to make
themselves copyable will be detected at compile time: the compiler
will complain that the superclass type is not copyable.
This change on its own will result in many compiler errors, so...
2) Change any derived classes to implement move constructors instead of
copy constructors. Note that some of these move constructors are,
strictly speaking, unnecessary, since the relevant classes are moved
via memcpy in nsTHashtable and its derivatives.
- 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
Jan Varga
Andrea Marchesini
Ciure Andrei
Sylvestre Ledru
Jan Varga
Nathan Froyd
Gabriele Svelto
Daniel Holbert
Boris Zbarsky