Pause

Status: Stable

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

Description

Pause[n]

pauses for at least n seconds.

Notes

Pause is accurate only down to a granularity of at least $TimeUnit seconds. The time elapsed during the execution of Pause is counted in SessionTime and AbsoluteTiming, but not in TimeUsed or Timing.

Examples (4)

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

Basic examples (2)

In[1]:= Pause[0] === Null
Out[1]= True

In[2]:= Pause[1/100] === Null
Out[2]= True

Applications (2)

Pause returns Null; zero waits not at all

In[3]:= Pause[0] === Null
Out[3]= True

A rational (or any NumericQ) duration is accepted

In[4]:= Pause[1/100] === Null
Out[4]= True

Implementation notes

Algorithm. builtin_pause blocks for at least n seconds of wall-clock time and returns Null. pause_seconds coerces the argument to a machine double, accepting integers, reals, bignums, rationals, MPFR reals, and any NumericQ symbolic form (Pi, Sqrt[2], …) via numericalize — so Pause[1/4] and Pause[Pi] behave like Mathematica; a genuinely non-numeric argument leaves Pause[x] unevaluated. The double is split into whole seconds and nanoseconds and handed to nanosleep, re-armed with the reported remainder whenever it returns early on a signal (EINTR), so the full duration is always observed. n <= 0 (or non-finite) waits not at all, matching Pause[0].

CPU vs wall clock. nanosleep consumes no CPU, so the elapsed time is counted by the wall clocks (AbsoluteTiming, SessionTime) but is invisible to the CPU clocks (Timing, TimeUsed) — the two clock sources distinguish the cases for free, with no special-casing. Accuracy is bounded by the OS timer granularity ($TimeUnit-scale).

Data structures / limits. struct timespec and a scalar; returns expr_new_symbol(SYM_Null). ATTR_PROTECTED. A blocking wall-clock wait, not a numeric kernel — no packed/Compile[] surface.

• Protected.
• Sleeps on a wall-clock timer (nanosleep) that consumes no CPU, so the elapsed time is counted by AbsoluteTiming and SessionTime but not by Timing or TimeUsed. Timing[Pause[1]] reports ≈ 0; AbsoluteTiming[Pause[1]] reports ≈ 1.
• Accurate down to a granularity of at least $TimeUnit seconds.
• The sleep resumes across signal interruptions, so the full duration is always observed ("at least n seconds").
• n may be any non-negative number: an integer, real, rational (Pause[1/4]), or a NumericQ symbolic form (Pause[Pi]). Zero or negative n returns immediately. A non-numeric argument leaves Pause[x] unevaluated.

Attributes: Protected.

References

See also: AbsoluteTiming, SessionTime, Timing, TimeUsed, $TimeUnit, NumericQ

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

Notes & additional examples

Notes

Pause[n] blocks for at least n seconds of wall-clock time, then returns Null. The argument may be any non-negative number — integer, real, rational (Pause[1/4]), or a NumericQ symbolic form (Pause[Pi]); zero or negative returns immediately, and a non-numeric argument leaves Pause[x] unevaluated.

The wait is a nanosleep, which consumes no CPU. So the elapsed time is counted by AbsoluteTiming and SessionTime but not by Timing or TimeUsed: Timing[Pause[1]] reports about 0, while AbsoluteTiming[Pause[1]] reports about 1. The sleep resumes across signal interruptions, so the full duration is always observed. Accuracy is bounded by the timer granularity $TimeUnit.