SessionTime

Status: Stable

documented, exercised by the test suite and/or worked examples, with no known limitations recorded.

Description

SessionTime[]

gives the total number of seconds of wall-clock time elapsed since the beginning of the current Mathilda session.

Examples (4)

Every input below was run against the current Mathilda build and its output recorded.

Basic examples (2)

In[1]:= SessionTime[] >= 0
Out[1]= True

In[2]:= Head[SessionTime[]]
Out[2]= Real

Applications (2)

Always a Real

In[3]:= Head[SessionTime[]]
Out[3]= Real

Grows monotonically from kernel start-up

In[4]:= TrueQ[Positive[SessionTime[]]]
Out[4]= True

Options & behaviour

The elapsed-time value itself grows with every call, so these examples report its sign and head rather than a fixed number.

Implementation notes

Algorithm. builtin_session_time returns dt_wall_seconds() - g_session_start as an EXPR_REAL: the elapsed wall-clock seconds since the kernel started. g_session_start is a file-static captured once in datetime_init (at start-up) from the same monotonic source (clock_gettime(CLOCK_MONOTONIC)) that AbsoluteTiming uses. Because the zero point and the reading share that monotonic clock, time spent inside Pause is counted here, and no NTP step or manual clock change can make the interval go backwards.

Data structures / limits. One double subtraction; struct timespec under dt_wall_seconds. Takes no arguments (returns NULL, leaving it unevaluated, for any other arity). ATTR_PROTECTED. The value is non-deterministic by definition (it grows with elapsed time); it is a session clock, not a numeric kernel, so there is no packed/Compile[] surface.

• Protected.
• Measured from a monotonic clock captured at kernel start-up; includes time spent in Pause.

Attributes: Protected.

References

See also: Pause

• Source: src/datetime.c
• Specification: docs/spec/builtins/time-and-date.md
• Tests: tests/test_datetime.c

Notes & additional examples

Notes

SessionTime[] gives the wall-clock seconds elapsed since the current Mathilda session began. It is measured from a monotonic clock captured at kernel start-up — the same clock source as AbsoluteTiming — so it increases on every call and includes time spent sleeping in Pause.

The exact value is non-deterministic (it depends on how long the session has been running), so useful examples report its structure — its head, or its sign — rather than a fixed number. Contrast TimeUsed, which counts only CPU time and does not advance while the session is idle.