WorkQueueExecutor: remove atexit handler (#3407)

This PR removes the atexit handler of WorkQueueExecutor as discussed in #3334.

Co-authored-by: Ben Clifford <[email protected]>

parsl/executors/workqueue/executor.py

@@ -3,7 +3,6 @@
 high-throughput system for delegating Parsl tasks to thousands of remote machines
 """
 
-import atexit
 import threading
 import multiprocessing
 import logging
@@ -298,24 +297,6 @@ def __init__(self,
         if self.init_command != "":
             self.launch_cmd = self.init_command + "; " + self.launch_cmd
 
-        # register atexit handler to cleanup when Python shuts down
-        atexit.register(self.atexit_cleanup)
-
-        # Attribute indicating whether this executor was started to shut it down properly.
-        # This safeguards cases where an object of this executor is created but
-        # the executor never starts, so it shouldn't be shutdowned.
-        self.is_started = False
-
-        # Attribute indicating whether this executor was shutdown before.
-        # This safeguards cases where this object is automatically shut down (e.g.,
-        # via atexit) and the user also explicitly calls shut down. While this is
-        # permitted, the effect of an executor shutdown should happen only once.
-        self.is_shutdown = False
-
-    def atexit_cleanup(self):
-        # Calls this executor's shutdown method upon Python exiting the process.
-        self.shutdown()
-
     def _get_launch_command(self, block_id):
         # this executor uses different terminology for worker/launch
         # commands than in htex
@@ -325,8 +306,6 @@ def start(self):
         """Create submit process and collector thread to create, send, and
         retrieve Parsl tasks within the Work Queue system.
         """
-        # Mark this executor object as started
-        self.is_started = True
         self.tasks_lock = threading.Lock()
 
         # Create directories for data and results
@@ -713,14 +692,6 @@ def shutdown(self, *args, **kwargs):
         """Shutdown the executor. Sets flag to cancel the submit process and
         collector thread, which shuts down the Work Queue system submission.
         """
-        if not self.is_started:
-            # Don't shutdown if the executor never starts.
-            return
-
-        if self.is_shutdown:
-            # Don't shutdown this executor again.
-            return
-
         logger.debug("Work Queue shutdown started")
         self.should_stop.value = True
 
@@ -741,7 +712,6 @@ def shutdown(self, *args, **kwargs):
         self.collector_queue.close()
         self.collector_queue.join_thread()
 
-        self.is_shutdown = True
         logger.debug("Work Queue shutdown completed")
 
     @wrap_with_logs