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.. _timestamps:
==============================================================================
Timestamps
==============================================================================
.. _event_timestamps:
------------------------------------------------------------------------------
Event timestamps
------------------------------------------------------------------------------
Most libinput events provide a timestamp in millisecond and/or microsecond
resolution. These timestamp usually increase monotonically, but libinput
does not guarantee that this always the case. In other words, it is possible
to receive an event with a timestamp earlier than the previous event.
For example, if a touchpad has :ref:`tapping` enabled, a button event may have a
lower timestamp than an event from a different device. Tapping requires the
use of timeouts to detect multi-finger taps and/or :ref:`tapndrag`.
Consider the following event sequences from a touchpad and a mouse:
::
Time Touchpad Mouse
---------------------------------
t1 finger down
t2 finger up
t3 movement
t4 tap timeout
For this event sequence, the first event to be sent to a caller is in
response to the mouse movement: an event of type
**LIBINPUT_EVENT_POINTER_MOTION** with the timestamp t3.
Once the timeout expires at t4, libinput generates an event of
**LIBINPUT_EVENT_POINTER_BUTTON** (press) with a timestamp t1 and an event
**LIBINPUT_EVENT_POINTER_BUTTON** (release) with a timestamp t2.
Thus, the caller gets events with timestamps in the order t3, t1, t2,
despite t3 > t2 > t1.
libinput timestamps use **CLOCK_MONOTONIC**.
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