Executor Modules

This module contains the classes Executor and Task. The class Executor can be used to subprocess an application locally. For MPI programs, or any program using non-local compute resources, one of the inherited classes should be used. Inherited classes include MPI and Balsam variants. An executor can create and manage multiple tasks. The user function can issue and manage tasks using the submit, poll, wait, and kill functions. Task attributes are queried to determine status. Functions are also provided to access and interrogate files in the task’s working directory. A manager_poll function can be used to poll for STOP signals from the manager.

See this example for usage.

See the Executor APIs for optional arguments.

Alternative Executors:

Executor Class

Only create an object of this class for running local serial-launched applications. To run MPI applications and use detected resources, use an alternative Executor class, as shown above.

class executor.Executor

The executor can create, poll and kill runnable tasks

Class Attributes:


Executor – executor: The executor object is stored here and can be retrieved in user functions.

Object Attributes:


list_of_tasks (list) – A list of tasks created in this executor


Instantiate a new Executor instance.

A new Executor object is created. This is typically created in the user calling script.

register_calc(full_path, app_name=None, calc_type=None, desc=None)

Registers a user application to libEnsemble.

The full_path of the application must be supplied. Either app_name or calc_type can be used to identify the application in user scripts (in the submit function). app_name is recommended.

  • full_path (String) – The full path of the user application to be registered

  • app_name (String, optional) – Name to identify this application.

  • calc_type (String, optional) – Calculation type: Set this application as the default ‘sim’ or ‘gen’ function.

  • desc (String, optional) – Description of this application

submit(calc_type=None, app_name=None, app_args=None, stdout=None, stderr=None, dry_run=False, wait_on_run=False)

Create a new task and run as a local serial subprocess.

The created task object is returned.

  • calc_type (String, optional) – The calculation type: ‘sim’ or ‘gen’ Only used if app_name is not supplied. Uses default sim or gen application.

  • app_name (String, optional) – The application name. Must be supplied if calc_type is not.

  • app_args (string, optional) – A string of the application arguments to be added to task submit command line

  • stdout (string, optional) – A standard output filename

  • stderr (string, optional) – A standard error filename

  • dry_run (boolean, optional) – Whether this is a dry_run - no task will be launched; instead runline is printed to logger (at INFO level)

  • wait_on_run (boolean, optional) – Whether to wait for task to be polled as RUNNING (or other active/end state) before continuing


task – The lauched task object

Return type

obj: Task

Task Class

Tasks are created and returned through the Executor submit() function. Tasks can be polled and killed with the respective poll and kill functions. Task information can be queried through the task attributes below and the query functions. Note that the task attributes are updated only when they are polled/killed (or through other task or Executor functions).

class executor.Task(app=None, app_args=None, workdir=None, stdout=None, stderr=None, workerid=None, dry_run=False)

Manages the creation, configuration and status of a launchable task


Returns true if the named file exists in the task’s workdir


Kills or cancels the supplied task

Sends SIGTERM, waits for a period of <wait_time> for graceful termination, then sends a hard kill with SIGKILL. If <wait_time> is 0, we go immediately to SIGKILL; if <wait_time> is none, we never do a SIGKILL.


Polls and updates the status attributes of the task


Opens and reads the named file in the task’s workdir


Opens and reads the task’s stderr file in the task’s workdir


Opens and reads the task’s stdout file in the task’s workdir


Returns true if the task’s stderr file exists in the workdir


Returns true if the task’s stdout file exists in the workdir


Waits on completion of the task or raises TimeoutExpired exception

Status attributes of task are updated on completion.


timeout – Time in seconds after which a TimeoutExpired exception is raised


Returns true if the task’s workdir exists

Task Attributes

Following is a list of task status and configuration attributes that can be retrieved from a task.


These should not be set directly. Tasks are launched by the Executor, and task information can be queried through the task attributes below and the query functions.

Task status attributes include the following:


(string) The task status. One of (‘UNKNOWN’|’CREATED’|’WAITING’|’RUNNING’|’FINISHED’|’USER_KILLED’|’FAILED’)


(process obj) The process object used by the underlying process manager (e.g., return value of subprocess.Popen).


(int) The errorcode/return code used by the underlying process manager.


(Boolean) True means task has finished running - not whether it was successful.


(Boolean) Did task complete successfully (e.g., the returncode is zero)?


(int) Time in seconds that task has been running.


(int) Total time from task submission to completion (only available when task is finished).

Run configuration attributes - some will be autogenerated:


(string) Work directory for the task


(string) Name of task - autogenerated


(app obj) Use application/executable, registered using exctr.register_calc


(string) Application arguments as a string


(string) Name of file where the standard output of the task is written (in task.workdir)


(string) Name of file where the standard error of the task is written (in task.workdir)