patroni.async_executor module

Implement facilities for executing asynchronous tasks.

class patroni.async_executor.AsyncExecutor(cancellable: CancellableSubprocess, ha_wakeup: Callable[[...], None])View on GitHub

Bases: object

Asynchronous executor of (long) tasks.

Variables:

critical_task – a CriticalTask instance to handle execution of critical background tasks.

__init__(cancellable: CancellableSubprocess, ha_wakeup: Callable[[...], None]) → NoneView on GitHub

Create a new instance of AsyncExecutor.

Configure the given cancellable and ha_wakeup, initializes the control attributes, and instantiate the lock and event objects that are used to access attributes and manage communication between threads.

Parameters:

  • cancellable – a subprocess that supports being cancelled.

  • ha_wakeup – function to wake up the HA loop.

property busy: bool

True if there is an action scheduled to occur, else False.

cancel() → NoneView on GitHub

Request cancellation of a scheduled async task, if any.

Note

Wait until task is cancelled before returning control to caller.

reset_scheduled_action() → NoneView on GitHub

Unschedule a previously scheduled action, if any.

Note

Must be called once the scheduled task finishes or is cancelled.

run(func: Callable[[...], Any], args: Tuple[Any, ...] = ()) → Any | NoneView on GitHub

Run func with args.

Note

Expected to be executed through a thread.

Parameters:

  • func – function to be run. If it returns anything other than None, HA loop will be woken up at the end of run() execution.

  • args – arguments to be passed to func.

Returns:

None if func execution has been cancelled or faced any exception, otherwise the result of func.

run_async(func: Callable[[...], Any], args: Tuple[Any, ...] = ()) → NoneView on GitHub

Start an async thread that runs func with args.

Parameters:

  • func – function to be run. Will be passed through args to Thread with a target of run().

  • args – arguments to be passed along to Thread with func.

schedule(action: str) → str | NoneView on GitHub

Schedule action to be executed.

Note

Must be called before executing a task.

Note

action can only be scheduled if there is no other action currently scheduled.

Parameters:

action – action to be executed.

Returns:

None if action has been successfully scheduled, or the previously scheduled action, if any.

property scheduled_action: str | None

The currently scheduled action, if any, else None.

try_run_async(action: str, func: Callable[[...], Any], args: Tuple[Any, ...] = ()) → str | NoneView on GitHub

Try to run an async task, if none is currently being executed.

Parameters:

  • action – name of the task to be executed.

  • func – actual function that performs the task action.

  • args – arguments to be passed to func.

Returns:

None if func was scheduled successfully, otherwise an error message informing of an already ongoing task.

class patroni.async_executor.CriticalTaskView on GitHub

Bases: object

Represents a critical task in a background process that we either need to cancel or get the result of.

Fields of this object may be accessed only when holding a lock on it. To perform the critical task the background thread must, while holding lock on this object, check is_cancelled flag, run the task and mark the task as complete using complete().

The main thread must hold async lock to prevent the task from completing, hold lock on critical task object, call cancel(). If the task has completed cancel() will return False and result field will contain the result of the task. When cancel() returns True it is guaranteed that the background task will notice the is_cancelled flag.

Variables:

  • is_cancelled – if the critical task has been cancelled.

  • result – contains the result of the task, if it has already been completed.

__init__() → NoneView on GitHub

Create a new instance of CriticalTask.

Instantiate the lock and the task control attributes.

cancel() → boolView on GitHub

Tries to cancel the task.

Note

Caller must hold lock on async executor and the task when calling.

Returns:

False if the task has already run, or True it has been cancelled.

complete(result: Any) → NoneView on GitHub

Mark task as completed along with a result.

Note

Must be called from async thread. Caller must hold lock on task when calling.

reset() → NoneView on GitHub

Must be called every time the background task is finished.

Note

Must be called from async thread. Caller must hold lock on async executor when calling.