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]) → None View 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

+

property _busy: bool_

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

cancel() → None View 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() → None View 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 | None View on GitHub

Run func with args. + Note

  Expected to be executed through a thread.
  +
  Parameters:::
  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, …​] = ()) → None View on GitHub

Start an async thread that runs func with args. +

Parameters

+

schedule(action: str) → str | None View 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 | None View on GitHub

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

Parameters
Returns

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

_class _patroni.async_executor.CriticalTask View 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:

+

__init\\__() → None View on GitHub

Create a new instance of CriticalTask.
Instantiate the lock and the task control attributes. +

cancel() → bool View 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) → None View 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() → None View 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.

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