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System Time & Scheduling

Jobify is designed for performance and precision by completely avoiding polling. This architectural choice provides significant advantages but requires an understanding of how Jobify interacts with the system clock.

  • Zero Idle CPU

    No background loops checking for tasks. Resources are consumed only during execution.

  • High Precision

    Triggered by low-level OS event notification mechanisms (epoll, kqueue).

  • High Scalability

    Efficiently handles thousands of concurrent timers via the asyncio event loop.

  • Native Performance

    Directly leverages the speed and efficiency of the underlying OS event loop.

Polling vs. Native Timers

Most Python schedulers (like APScheduler v3 or Celery) rely on a polling loop that repeatedly checks the current time against a task list.

Jobify uses asyncio.loop.call_at. When you schedule a task, Jobify calculates the exact moment it should run and registers a timer directly in the event loop.

The Trade-off: Clock Adjustments

Because Jobify registers a specific delay once, it is sensitive to significant system clock shifts (manual changes or NTP jumps).

Wall-Clock vs. Monotonic Time

Type Name Behavior
Wall-Clock (datetime.now()) Current calendar time. Can jump forward/backward.
Monotonic (time.monotonic()) Steadily increasing. Unaffected by system time changes.

Internal Flow

  1. Read Wall-Clock: Get current time (e.g., 14:50).
  2. Calculate Delay: Scheduled for 15:00 → 10 minute (600s) delay.
  3. Register Timer: Tell the event loop: "Run this in 600s of Monotonic time".

Clock Shift Impact

If the system clock is manually changed to 15:00 immediately after scheduling, the Monotonic clock does not change. The task will still run after 600s of real time (when the system clock shows 15:10).

Handling Time Changes

If your system clock changes significantly (e.g., after a long sleep or NTP correction), simply restart the application.

On startup, Jobify will:

  1. Read the updated wall-clock time.
  2. Recalculate delays for all stored tasks.
  3. Register fresh timers with the event loop.

This ensures all tasks align correctly with the new system time.