Plugin driver should be lock free

[h-a-n-a]

Problem

Given the example above, currently, the plugin_driver locks itself completely, if it requires write(a.k.a mutable reference), which would lead to potential deadlock if developers want to asset the plugin_driver in the hook body.

More detailed info would be added later.

Status quo

Modifying plugin data is not that common, but locking plugin_driver would definitely add conflicts when using different hooks recursively. It would be better to even use RwLock in plugin to reduce lock contention.

Suggestion

Remove RwLock for plugin_driver and use interior mutability in plugins.

[h-a-n-a]

Conclusion: follow the suggestion