IGNITE-9410 Thin client transactions support

[alex-plekhanov]

No description provided.

[pavlukhin]

It looks like we have a possible memory leak here. TcpClientTransaction has a reference to TcpClientTransactions which has a reference to ThreadLocal<TcpClientTransaction> tx. If some TcpClientTransactions are not in use anymore but left a value in thread-local that value and TcpClientTransactions instance will never be garbage-collected. Making TcpClientTransaction class static should protect from it.

[alex-plekhanov]

We can't make TcpClientTransaction static, because we need TcpClientTransactions context here.
I don't quite understand how we can get possible leak here. If nobody holds the reference to TcpClientTransactions instance and nobody holds the reference to TcpClientTransaction instances, which were created by this TcpClientTransactions, the only references left outside of garbage objects it's a WeakReference to ThreadLocal from threads which have used this TcpClientTransactions instance. These weak references don't prevent to collect garbage objects.
Did I miss something?

[alex-plekhanov]

Sorry, I got it. There is a weak reference only to ThreadLocal instance, but regular reference to TcpClientTransaction from the thread-local table, so memory leak is possible.
I will try to fix it tomorrow.

[alex-plekhanov]

I've fixed the implementation. Also, I've found and fixed server-side transactions leak (transaction has left in active set after an attempt to end it when it's impossible to resume the transaction).

[pavlukhin]

👍

[isapego]

Please see several minor comments.

[isapego]

Here and in other places, imports should not be re-ordered. See this page for details: https://cwiki.apache.org/confluence/display/IGNITE/Coding+Guidelines#CodingGuidelines-PackageImporting

[alex-plekhanov]

It was wrong formated before this patch: Import should be ordered alphabetically, but packages starting with 'java.' should be declared prior to others.
Now it exactly matches coding guidelines.