Callbacks¶

The optional on_start and on_end callbacks are invoked once per measurement. Both receive the same Measurement instance that the Timer yields or appends for that run.

When they are invoked and what they receive¶

Callback	When	State of the Measurement
`on_start(measurement)`	When timing is about to start (on enter of the block or start of the decorated call).	`metadata` is set (a deep copy of the Timer’s initial metadata). `wall_time` and `cpu_time` are `None`.
`on_end(measurement)`	When timing has just ended (on block exit or end of the decorated call).	`wall_time` and `cpu_time` are set. `metadata` may have been mutated in the block or in `on_start`.

Use on_start to add to metadata (e.g. from context variables). Use on_end to read durations and metadata and send them to logging, OpenTelemetry, or a metrics pipeline.

Synchronous only¶

Callbacks are synchronous only. They are invoked on the same thread and must return before the Timer continues. To integrate with asynchronous exporters (e.g. OpenTelemetry), schedule work from the callback (e.g. asyncio.create_task(export(m)) in an async context, or use a thread or queue).

Example¶

from timerun import Timer

with Timer(on_end=lambda m: print(m.wall_time.timedelta)):
    pass  # code block to be measured

For applied patterns (logging, files, OpenTelemetry), see Share results.

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