Add worker support to DDK

Change-Id: I0ae333f1bd6776840b1377579377695a582c46ef
Reviewed-on: https://dart-review.googlesource.com/30623
Reviewed-by: Jens Johansen <jensj@google.com>
Reviewed-by: Jake Macdonald <jakemac@google.com>
Commit-Queue: Sigmund Cherem <sigmund@google.com>

pkg/dev_compiler/bin/dartdevk.dart

@@ -9,14 +9,18 @@ import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
+import 'package:bazel_worker/bazel_worker.dart';
 import 'package:dev_compiler/src/kernel/command.dart';
 import 'package:front_end/src/api_unstable/ddc.dart' as fe;
 
 Future main(List<String> args) async {
-  if (args.isNotEmpty && args.last == "--batch") {
-    await runBatch(args.sublist(0, args.length - 1));
+  var parsedArgs = _preprocessArgs(args);
+  if (parsedArgs.isBatch) {
+    await runBatch(parsedArgs.args);
+  } else if (parsedArgs.isWorker) {
+    await new _CompilerWorker(parsedArgs.args).run();
   } else {
-    var result = await compile(args);
+    var result = await compile(parsedArgs.args);
     var succeeded = result.result;
     exitCode = succeeded ? 0 : 1;
   }
@@ -60,3 +64,80 @@ Future runBatch(List<String> batchArgs) async {
   var time = watch.elapsedMilliseconds;
   print('>>> BATCH END (${tests - failed})/$tests ${time}ms');
 }
+
+/// Runs the compiler worker loop.
+class _CompilerWorker extends AsyncWorkerLoop {
+  /// The original args supplied to the executable.
+  final List<String> _startupArgs;
+
+  _CompilerWorker(this._startupArgs) : super();
+
+  /// Performs each individual work request.
+  Future<WorkResponse> performRequest(WorkRequest request) async {
+    var args = _startupArgs.toList()..addAll(request.arguments);
+
+    var output = new StringBuffer();
+    var result = await runZoned(() => compile(args), zoneSpecification:
+        new ZoneSpecification(print: (self, parent, zone, message) {
+      output.writeln(message.toString());
+    }));
+    return new WorkResponse()
+      ..exitCode = result.result ? 0 : 1
+      ..output = output.toString();
+  }
+}
+
+/// Preprocess arguments to determine whether DDK is used in batch mode or as a
+/// persistent worker.
+///
+/// When used in batch mode, we expect a `--batch` parameter last.
+///
+/// When used as a persistent bazel worker, the `--persistent_worker` might be
+/// present, and an argument of the form `@path/to/file` might be provided. The
+/// latter needs to be replaced by reading all the contents of the
+/// file and expanding them into the resulting argument list.
+_ParsedArgs _preprocessArgs(List<String> args) {
+  if (args.isEmpty) return new _ParsedArgs(false, false, args);
+
+  String lastArg = args.last;
+  if (lastArg == '--batch') {
+    return new _ParsedArgs(true, false, args.sublist(0, args.length - 1));
+  }
+
+  var newArgs = [];
+  bool isWorker = false;
+  var len = args.length;
+  for (int i = 0; i < len; i++) {
+    var arg = args[i];
+    if (i == len - 1 && arg.startsWith('@')) {
+      newArgs.addAll(_readLines(arg.substring(1)));
+    } else if (arg == '--persistent_worker') {
+      isWorker = true;
+    } else {
+      newArgs.add(arg);
+    }
+  }
+  return new _ParsedArgs(false, isWorker, newArgs);
+}
+
+/// Return all lines in a file found at [path].
+Iterable<String> _readLines(String path) {
+  try {
+    return new File(path)
+        .readAsStringSync()
+        .replaceAll('\r\n', '\n')
+        .replaceAll('\r', '\n')
+        .split('\n')
+        .where((String line) => line.isNotEmpty);
+  } on FileSystemException catch (e) {
+    throw new Exception('Failed to read $path: $e');
+  }
+}
+
+class _ParsedArgs {
+  final bool isBatch;
+  final bool isWorker;
+  final List<String> args;
+
+  _ParsedArgs(this.isBatch, this.isWorker, this.args);
+}