What is the purpose of the change

• Refactor getSharedClient
• fix What is the advantage of this lock? #5987

Brief changelog

• The current lock mode

        locks.putIfAbsent(key, new Object());
        synchronized (locks.get(key)) {
                //do some thing
                //remove lock
                locks.remove(key);
        }

• The situation which there is a problem:
  When thread A finishes executing locks.putIfAbsent(key, new Object()),
  another thread B which holding the lock executes locks.remove(key),
  and then thread A executes synchronized (locks.get(key)).

• Attempt get lock by computeIfAbsent like this:

        synchronized (locks.computeIfAbsent(key, (k) -> new Object())) {
                try{
                        //do some thing
                } finally {
                        //remove lock
                        locks.remove(key);
            }
        }

• The situation which there is a problem:
  1.When thread A finishes executing synchronized (locks.computeIfAbsent(key, (k) -> new Object())) create the lock LockA And synchronized ,
  2.Another thread B synchronized with LockA,
  3.Thread A executes locks.remove(key).
  4.Thread B hold the LockA And synchronized.
  5.Thread C executing synchronized (locks.computeIfAbsent(key, (k) -> new Object())) create the lock LockC And synchronized .
  -It seems difficult to remove a lock without any threads waiting for it exactly.

Verifying this change

Run test cases.

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