[MINOR / PAN-1339 (A)] Fetch local transactions in isolation

[smatthewenglish]

PR description

In an effort to make the change set inevitably necessitated by the acceptance criteria of PAN-1339 less onerous, and consequently the review more palatable, I've decided to serialize it into constituent elements -- each of which constituting a relatively discrete semantic chunk.

Fixed Issue(s)

In order to disseminate local transactions to new peers we'll require a mechanism to fetch local transactions in isolation -- this is that mechanism (along with associated test infrastructure).

[AbdelStark]

LGTM. 2 possible improvements comments.

[AbdelStark]

Maybe we could do it using parallel stream to optimize.

Suggested change

	List<Transaction> getLocalTransactions() {
	List<Transaction> getLocalTransactions() {
	synchronized (pendingTransactions) {
	List<Transaction> localTransactions = new ArrayList<>();
	pendingTransactions
	.entrySet()
	.parallelStream()
	.filter(transaction -> transaction.getValue().isReceivedFromLocalSource())
	.forEach(transaction -> transaction.getValue().getTransaction());
	return localTransactions;
	}
	}

[AbdelStark]

Suggestion tip : cache the filtered list and store a boolean indicating whether the list is still consistent or not. Set it to false when a new transaction is received. We could have a method invalidateCachedLocalTransactions() to set this boolean to false when appropriate.

[AbdelStark]

Class level field to avoid instantiating localTransactions each time localTransactions is called ?

[ajsutton]

I'd avoid any such caching until we know we have a performance issue. We're currently having issues with memory usage so don't want to waste it on extra caches if they aren't necessary.