DefaultSimpUserRegistry Use ReentrantLock to Prevent Pinning

[csh0034]

modified the part where pinning occurs in DefaultSimpUserRegistry due to the use of synchronized when using VT
I would appreciate any feedback 😃

[pankratz76]

nicely done

[pankratz76]

Suggested change

	this.sessionLock.lock();
	sessionLock.lock();

There is no overloaded field that makes the this. access required, right? Both are correct, but if there is no ambiguity, it's more concise to leave it out.

[csh0034]

Thank you for your valuable feedback.
I actually considered this when making the code changes.

Looking at other classes that use ReentrantLock, I noticed that they all include this.
so I decided to keep it for consistency.
(e.g., SubProtocolWebSocketHandler, InMemoryWebSessionStore.ExpiredSessionChecker)

[jhoeller]

Are you experiencing any actual pinning there? The code within those synchronized blocks is not performing any blocking operations as far as I can see. From that perspective, it should be fine as-is.

[csh0034]

@jhoeller
I modified the code based on an article suggesting replacing synchronized with ReentrantLock to prevent VT pinning in Spring Blog. If there are no blocking operations and it doesn't cause any issues, feel free to close the PR.

[jhoeller]

Alright, let's keep it as-is then since we keep using such synchronization around local data structure operations in other places as well.

Thanks for your efforts, in any case!