diff --git a/aos/build/build.py b/aos/build/build.py
index 5d7011d..27e11d5 100755
--- a/aos/build/build.py
+++ b/aos/build/build.py
@@ -9,6 +9,53 @@
 import string
 import shutil
 import errno
+import queue
+import threading
+
+class TestThread(threading.Thread):
+  def __init__(self, executable, env, done_queue, start_semaphore):
+    super(TestThread, self).__init__(
+        name=os.path.split(executable)[1])
+
+    self.executable = executable
+    self.env = env
+    self.done_queue = done_queue
+    self.start_semaphore = start_semaphore
+
+    self.process_lock = threading.Lock()
+    self.process = None
+    self.stopped = False
+
+  def run(self):
+    with self.start_semaphore:
+      if self.stopped: return
+      test_output('Starting test %s...' % self.name)
+      self.output, subprocess_output = os.pipe()
+      with self.process_lock:
+        self.process = subprocess.Popen((self.executable,
+                                         '--gtest_color=yes'),
+                                        env=self.env,
+                                        stderr=subprocess.STDOUT,
+                                        stdout=subprocess_output,
+                                        stdin=open(os.devnull, 'r'))
+      os.close(subprocess_output)
+      self.process.wait()
+      with self.process_lock:
+        self.returncode = self.process.returncode
+        self.process = None
+        if not self.stopped:
+          self.done_queue.put(self)
+
+  def terminate_process(self):
+    with self.process_lock:
+      self.stopped = True
+      if not self.process: return
+      self.process.terminate()
+  def kill_process(self):
+    with self.process_lock:
+      self.stopped = True
+      if not self.process: return
+      self.process.kill()
 
 def aos_path():
   return os.path.join(os.path.dirname(__file__), '..')
@@ -31,6 +78,11 @@
 def user_output(message):
   print('build.py: ' + message, file=sys.stderr)
 
+test_output_lock = threading.RLock()
+def test_output(message):
+  with test_output_lock:
+    print('build.py: ' + message, file=sys.stdout)
+
 class Processor(object):
   class UnknownPlatform(Exception):
     def __init__(self, message):
@@ -217,11 +269,11 @@
   SANITIZER_TEST_WARNINGS = {
       'memory': (True,
 """We don't have all of the libraries instrumented which leads to lots of false
-errors with msan (especially stdlibc++).
-TODO(brians): Figure out a way to deal with it."""),
+  errors with msan (especially stdlibc++).
+  TODO(brians): Figure out a way to deal with it."""),
       'undefined': (False,
 """There are several warnings in other people's code that ubsan catches.
-The following have been verified non-interesting:
+  The following have been verified non-interesting:
     include/c++/4.8.2/array:*: runtime error: reference binding to null pointer of type 'int'
       This happens with ::std::array<T, 0> and it doesn't seem to cause any issues.
     output/downloaded/eigen-3.2.1/Eigen/src/Core/util/Memory.h:782:*: runtime error: load of misaligned address 0x* for type 'const int', which requires 4 byte alignment
@@ -256,8 +308,9 @@
     if is_test:
       self.default_platforms = self.select_platforms(architecture='amd64',
                                                      debug=True)
-      for sanitizer in PrimeProcessor.SANITIZER_TEST_WARNINGS:
-        self.default_platforms -= self.select_platforms(sanitizer=sanitizer)
+      for sanitizer, warning in PrimeProcessor.SANITIZER_TEST_WARNINGS.items():
+        if warning[0]:
+          self.default_platforms -= self.select_platforms(sanitizer=sanitizer)
     elif is_deploy:
       # TODO(brians): Switch to deploying the code built with clang.
       self.default_platforms = self.select_platforms(architecture='arm',
@@ -342,6 +395,10 @@
           'target',
           help='target to build',
           nargs='*')
+      parser.add_argument(
+          '--jobs', '-j',
+          help='number of things to do at once',
+          type=int)
     def AddCommonArgs(parser):
       parser.add_argument(
           'platforms',
@@ -548,9 +605,11 @@
         user_output("Not running gyp")
 
       try:
-        subprocess.check_call(
-            (tools_config['NINJA'],
-             '-C', platform.outdir()) + tuple(targets),
+        call = (tools_config['NINJA'],
+                '-C', platform.outdir()) + tuple(targets)
+        if args.jobs:
+          call += ('-j', str(args.jobs))
+        subprocess.check_call(call,
             stdin=open(os.devnull, 'r'),
             env=env(platform))
       except subprocess.CalledProcessError as e:
@@ -562,12 +621,59 @@
       platform.deploy(args.dry_run)
     elif args.action_name == 'tests':
       dirname = os.path.join(platform.outdir(), 'tests')
-      for f in targets or os.listdir(dirname):
-        user_output('Running test %s...' % f)
-        subprocess.check_call(
-            os.path.join(dirname, f),
-            env=env(platform))
-        user_output('Test %s succeeded' % f)
+      done_queue = queue.Queue()
+      running = []
+      if args.jobs:
+        number_jobs = args.jobs
+      else:
+        number_jobs = os.sysconf('SC_NPROCESSORS_ONLN') + 2
+      test_start_semaphore = threading.Semaphore(number_jobs)
+      if targets:
+        to_run = []
+        for target in targets:
+          if target.endswith('_test'):
+            to_run.append(target)
+      else:
+        to_run = os.listdir(dirname)
+      for f in to_run:
+        thread = TestThread(os.path.join(dirname, f), env(platform), done_queue,
+                            test_start_semaphore)
+        running.append(thread)
+        thread.start()
+      try:
+        while running:
+          done = done_queue.get()
+          running.remove(done)
+          with test_output_lock:
+            test_output('Output from test %s:' % done.name)
+            for line in os.fdopen(done.output):
+              if not sys.stdout.isatty():
+                # Remove color escape codes.
+                line = re.sub(r'\x1B\[[0-9;]*[a-zA-Z]', '', line)
+              sys.stdout.write(line)
+            if done.returncode == 0:
+              test_output('Test %s succeeded' % done.name)
+            else:
+              test_output('Test %s failed' % done.name)
+              user_output('Aborting because of test failure.')
+              exit(1)
+      finally:
+        if running:
+          test_output('Killing other tests...')
+          for thread in running:
+            thread.terminate_process()
+          to_remove = []
+          for thread in running:
+            thread.join(5)
+            if not thread.is_alive():
+              to_remove.append(thread);
+          for thread in to_remove: running.remove(thread)
+          for thread in running:
+            test_output(
+                'Test %s did not terminate. Killing it.' % thread.name)
+            thread.kill_process()
+            thread.join()
+          test_output('Done killing other tests')
 
     user_output('Done building %s (%d/%d)' % (platform, num, len(platforms)))
     num += 1