[improve][broker]Use cursor.isActive instead to judge if cursor is active

[gaozhangmin]

Motivation

When a cursor is activated, use cursor.isActive instead of activeCursors.get(cursor.getName()) == null to judge cursor's status. more readable.

Modifications

Use cursor.isActive instead to judge if cursor is active

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Matching PR in forked repository

gaozhangmin#7

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[Technoboy-]

If change like this, I think it's better like

if (!cursor.isActive()) {
   Position positionForOrdering = config.isCacheEvictionByMarkDeletedPosition()
                        ? cursor.getMarkDeletedPosition()
                        : cursor.getReadPosition();
     if (positionForOrdering == null) {
             positionForOrdering = PositionImpl.EARLIEST;
     }
     synchronized (activeCursors) {
          activeCursors.add(cursor, positionForOrdering);
     }
}          

[michaeljmarshall]

Just for reference, this change ultimately relies on a call to this method:

pulsar/managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/ManagedLedgerImpl.java

Lines 3695 to 3697 in 3bb93cb

	public boolean isCursorActive(ManagedCursor cursor) {
	return activeCursors.get(cursor.getName()) != null;
	}

We don't want to change the scope of the synchronized block, as far as I can tell.

[michaeljmarshall]

I do not think we should have made this change. The ManagedCursor can have alternate implementations, and I think the meaning of activating a cursor in the ledger is not necessarily the same as the whether the cursor views itself as active. For example, if the cursor had its own view of activity that diverges, we could get into odd conditions.

[michaeljmarshall]

If any refactoring were to be made, I think we should have switched to use the ManagedLedgerImpl#isCursorActive method.

[michaeljmarshall]

I didn't see any follow up on my comments, so I propose a fix here: #19322