diff --git a/src/clusterfuzz/_internal/base/concurrency.py b/src/clusterfuzz/_internal/base/concurrency.py
index 36fcb39e47..52ce2d4b78 100644
--- a/src/clusterfuzz/_internal/base/concurrency.py
+++ b/src/clusterfuzz/_internal/base/concurrency.py
@@ -21,22 +21,8 @@
 POOL_SIZE = multiprocessing.cpu_count()
 
 
-class SingleThreadPool:
-  """Single thread pool for when it's not worth using Python's thread
-  implementation."""
-
-  def __init__(self, size):
-    del size
-
-  def map(self, f, l):
-    return list(map(f, l))
-
-  def imap_unordered(self, f, l):
-    return list(map(f, l))
-
-
 @contextlib.contextmanager
-def make_pool(pool_size=POOL_SIZE, cpu_bound=False, max_pool_size=None):
+def make_pool(pool_size=POOL_SIZE, max_pool_size=None):
   """Returns a pool that can (usually) execute tasks concurrently."""
   if max_pool_size is not None:
     pool_size = min(pool_size, max_pool_size)
@@ -44,12 +30,9 @@ def make_pool(pool_size=POOL_SIZE, cpu_bound=False, max_pool_size=None):
   # Don't use processes on Windows and unittests to avoid hangs.
   if (environment.get_value('PY_UNITTESTS') or
       environment.platform() == 'WINDOWS'):
-    if cpu_bound:
-      yield SingleThreadPool(pool_size)
-    else:
-      yield futures.ThreadPoolExecutor(pool_size)
+    yield futures.ThreadPoolExecutor(pool_size)
   else:
-    yield multiprocessing.Pool(pool_size)
+    yield futures.ProcessPoolExecutor(pool_size)
 
 
 # TODO(metzman): Find out if batching makes things even faster.
diff --git a/src/clusterfuzz/_internal/base/tasks/__init__.py b/src/clusterfuzz/_internal/base/tasks/__init__.py
index bbf15e57ed..5cd85efd81 100644
--- a/src/clusterfuzz/_internal/base/tasks/__init__.py
+++ b/src/clusterfuzz/_internal/base/tasks/__init__.py
@@ -322,7 +322,7 @@ def get_preprocess_task():
   messages = pubsub_puller.get_messages(max_messages=1)
   if not messages:
     return None
-  task = get_task_from_message(messages[0])
+  task = get_task_from_message(messages[0], task_cls=PubSubTTask)
   if task:
     logs.info('Pulled from preprocess queue.')
   return task
@@ -516,12 +516,45 @@ def dont_retry(self):
     self._pubsub_message.ack()
 
 
-def get_task_from_message(message, can_defer=True) -> Optional[PubSubTask]:
+class PubSubTTask(PubSubTask):
+  """TTask that won't repeat on timeout."""
+  TTASK_TIMEOUT = 30 * 60
+
+  @contextlib.contextmanager
+  def lease(self, _event=None):  # pylint: disable=arguments-differ
+    """Maintain a lease for the task."""
+    task_lease_timeout = TASK_LEASE_SECONDS_BY_COMMAND.get(
+        self.command, get_task_lease_timeout())
+
+    environment.set_value('TASK_LEASE_SECONDS', task_lease_timeout)
+    track_task_start(self, task_lease_timeout)
+    if _event is None:
+      _event = threading.Event()
+    if self.command != 'fuzz':
+      leaser_thread = _PubSubLeaserThread(self._pubsub_message, _event,
+                                          task_lease_timeout)
+    else:
+      leaser_thread = _PubSubLeaserThread(
+          self._pubsub_message, _event, self.TTASK_TIMEOUT, ack_on_timeout=True)
+    leaser_thread.start()
+    try:
+      yield leaser_thread
+    finally:
+      _event.set()
+      leaser_thread.join()
+
+    # If we get here the task succeeded in running. Acknowledge the message.
+    self._pubsub_message.ack()
+    track_task_end()
+
+
+def get_task_from_message(message, can_defer=True,
+                          task_cls=None) -> Optional[PubSubTask]:
   """Returns a task constructed from the first of |messages| if possible."""
   if message is None:
     return None
   try:
-    task = initialize_task(message)
+    task = initialize_task(message, task_cls=task_cls)
   except KeyError:
     logs.error('Received an invalid task, discarding...')
     message.ack()
@@ -560,11 +593,13 @@ def handle_multiple_utask_main_messages(messages) -> List[PubSubTask]:
   return tasks
 
 
-def initialize_task(message) -> PubSubTask:
+def initialize_task(message, task_cls=None) -> PubSubTask:
   """Creates a task from |messages|."""
+  if task_cls is None:
+    task_cls = PubSubTask
 
   if message.attributes.get('eventType') != 'OBJECT_FINALIZE':
-    return PubSubTask(message)
+    return task_cls(message)
 
   # Handle postprocess task.
   # The GCS API for pub/sub notifications uses the data field unlike
@@ -598,13 +633,18 @@ class _PubSubLeaserThread(threading.Thread):
 
   EXTENSION_TIME_SECONDS = 10 * 60  # 10 minutes.
 
-  def __init__(self, message, done_event, max_lease_seconds):
+  def __init__(self,
+               message,
+               done_event,
+               max_lease_seconds,
+               ack_on_timeout=False):
     super().__init__()
 
     self.daemon = True
     self._message = message
     self._done_event = done_event
     self._max_lease_seconds = max_lease_seconds
+    self._ack_on_timeout = ack_on_timeout
 
   def run(self):
     """Run the leaser thread."""
@@ -616,6 +656,9 @@ def run(self):
         if time_left <= 0:
           logs.info('Lease reached maximum lease time of {} seconds, '
                     'stopping renewal.'.format(self._max_lease_seconds))
+          if self._ack_on_timeout:
+            logs.info('Acking on timeout')
+            self._message.ack()
           break
 
         extension_seconds = min(self.EXTENSION_TIME_SECONDS, time_left)
diff --git a/src/clusterfuzz/_internal/google_cloud_utils/storage.py b/src/clusterfuzz/_internal/google_cloud_utils/storage.py
index 11107d956c..7a7bee5211 100644
--- a/src/clusterfuzz/_internal/google_cloud_utils/storage.py
+++ b/src/clusterfuzz/_internal/google_cloud_utils/storage.py
@@ -14,6 +14,7 @@
 """Functions for managing Google Cloud Storage."""
 
 import collections
+from concurrent import futures
 import copy
 import datetime
 import json
@@ -1367,7 +1368,7 @@ def _mappable_sign_urls_for_existing_file(url_and_include_delete_urls):
 def sign_urls_for_existing_files(urls, include_delete_urls):
   logs.info('Signing URLs for existing files.')
   args = ((url, include_delete_urls) for url in urls)
-  result = maybe_parallel_map(_sign_urls_for_existing_file, args)
+  result = parallel_map(_sign_urls_for_existing_file, args)
   logs.info('Done signing URLs for existing files.')
   return result
 
@@ -1377,17 +1378,24 @@ def get_arbitrary_signed_upload_url(remote_directory):
       get_arbitrary_signed_upload_urls(remote_directory, num_uploads=1))[0]
 
 
-def maybe_parallel_map(func, arguments):
+def parallel_map(func, argument_list):
   """Wrapper around pool.map so we don't do it on OSS-Fuzz hosts which
   will OOM."""
-  if not environment.is_tworker():
-    # TODO(b/metzman): When the rearch is done, internal google CF won't have
-    # tworkers, but maybe should be using parallel.
-    return map(func, arguments)
-
   max_size = 2
-  with concurrency.make_pool(cpu_bound=True, max_pool_size=max_size) as pool:
-    return pool.imap_unordered(func, arguments)
+  timeout = 120
+  with concurrency.make_pool(max_pool_size=max_size) as pool:
+    calls = {pool.submit(func, argument) for argument in argument_list}
+    while calls:
+      finished_calls, _ = futures.wait(
+          calls, timeout=timeout, return_when=futures.FIRST_COMPLETED)
+      if not finished_calls:
+        logs.error('No call completed.')
+        for call in calls:
+          call.cancel()
+        raise TimeoutError(f'Nothing completed within {timeout} seconds')
+      for call in finished_calls:
+        calls.remove(call)
+        yield call.result(timeout=timeout)
 
 
 def get_arbitrary_signed_upload_urls(remote_directory: str, num_uploads: int):
@@ -1406,6 +1414,6 @@ def get_arbitrary_signed_upload_urls(remote_directory: str, num_uploads: int):
 
   urls = (f'{base_path}-{idx}' for idx in range(num_uploads))
   logs.info('Signing URLs for arbitrary uploads.')
-  result = maybe_parallel_map(get_signed_upload_url, urls)
+  result = parallel_map(get_signed_upload_url, urls)
   logs.info('Done signing URLs for arbitrary uploads.')
   return result