Keep IPC channel referenced once it's needed again

Ensure the IPC channel stays referenced. This is a safe-guard: it's easy
to end up in a situation where the channel needs to be referenced but
it's unreferenced because other code wasn't aware.

Author: novemberborn

lib/process-adapter.js

@@ -24,7 +24,17 @@ exports.send = (name, data) => {
 
 // `process.channel` was added in Node.js 7.1.0, but the channel was available
 // through an undocumented API as `process._channel`.
-exports.ipcChannel = process.channel || process._channel;
+const ipcChannel = process.channel || process._channel;
+let allowUnref = true;
+exports.unrefChannel = () => {
+	if (allowUnref) {
+		ipcChannel.unref();
+	}
+};
+exports.forceRefChannel = () => {
+	allowUnref = false;
+	ipcChannel.ref();
+};
 
 const opts = JSON.parse(process.argv[2]);
 require('./worker-options').set(opts);

lib/test-worker.js

@@ -41,7 +41,7 @@ function exit() {
 	exiting = true;
 
 	// Reference the IPC channel so the exit sequence can be completed.
-	adapter.ipcChannel.ref();
+	adapter.forceRefChannel();
 
 	const stats = runner.buildStats();
 	adapter.send('results', {stats});
@@ -116,7 +116,7 @@ function handleUncaughtException(exception) {
 
 	// Ensure the IPC channel is referenced. The uncaught exception will kick off
 	// the teardown sequence, for which the messages must be received.
-	adapter.ipcChannel.ref();
+	adapter.forceRefChannel();
 
 	adapter.send('uncaughtException', {exception: serialized});
 }
@@ -139,7 +139,7 @@ process.on('ava-teardown', () => {
 	tearingDown = true;
 
 	// Reference the IPC channel so the teardown sequence can be completed.
-	adapter.ipcChannel.ref();
+	adapter.forceRefChannel();
 
 	let rejections = currentlyUnhandled()
 		.filter(rejection => !attributedRejections.has(rejection.promise));
@@ -206,6 +206,6 @@ try {
 		// used to detect when tests stall.
 		// If AVA was not required then the parent process will initiated a teardown
 		// sequence, for which this process ought to stay active.
-		adapter.ipcChannel.unref();
+		adapter.unrefChannel();
 	}
 }