RelicMonitoring - background or external

// Relic integration point

/**
* Create a transactional scope in which instrumentation that will only add
* trace segments to existing transactions will funciton.
*
* @param Agent agent The agent whose tracer should be used to create the
*                    transaction.
* @param Function callback The function to be run within the transaction.
*/
var runInTransaction = function runInTransaction(agent, callback) {
	return agent.tracer.transactionProxy(function () {
		var transaction = agent.getTransaction();
		callback(transaction);
	})();
}

var Q = require("q");
var agent = require("newrelic");
var coinbase = "litecoin";

runInTransaction(agent, function transactionInScope(transaction) {

	var iTX = agent.getTransaction();
	var trace = transaction.getTrace();

	var measurement = transaction.measure('Blockchain/'+coinbase+'/block');

	// Start a timer
	transaction.timer.begin();
	console.log("transaction", transaction);

	// a work unit
	var delay = function (delay) {
		var d = Q.defer();
		setTimeout(
			function() {
				// stupid timeout to cause a little lag
				console.log("metric", metric);

				var metric = transaction
					.metrics
					.getOrCreateMetric('Blockchain/'+coinbase+'/block');

				console.log("metric",metric);

				var stats = measurement.stats;

				if (stats.callCount < 1) {
					console.log("!OK");
					console.log("stats", stats);
				}

				d.resolve();
			}
			, delay);
		return d.promise;
	};

	// setup some work to track
	// simple promise based approach
	Q.when(delay(1000), function () {
		// stop the timer
		trace.root.timer.end();

		console.log("finalTx", transaction);
		console.log("metrics", transaction.metrics);
		console.log("unscoped", transaction.metrics.unscoped);

		// trace first - it was started inside the tx
		trace.end();
		transaction.end();
	}).then(
		function(){
			agent.stop();
		}
	);
});

On line 27, you should defer the measurement until you have the time elapsed, and pass that time into the measure call, making sure to pass null for the scope. Transaction.prototype.measure isn't inserting a probe so much as generating the metric once there's enough information to capture its metadata.

In general, you should only need line 72 – ending the transaction will also end the trace, which actually recursively closes all its trace segments (this is something of a hack, in that I don't know what would happen inside New Relic's presentation logic if there's a transaction trace with segments that end after the end of the transaction, but I'm reasonably confident it would be nothing good). If you look at https://github.com/newrelic/node-newrelic/blob/master/lib/instrumentation/core/http.js#L24-L32, you can see how we tie a segment's timer to the measurement process.