Caffeinate keeps your computer awake during a long computation by calling caffeinate via an external shell evaluation.
longComputation[t_] := (Pause[t]; {1, 2, 3})
Caffeinate[longComputation[10]]
(* Out: {1, 2, 3} *)
The above calls caffeinate in the system's shell, evaluates longComputation[10] (which takes about 10 seconds to complete and returns {1, 2, 3}), then kills the process.
If the computation is terminated by an abort, e.g. by pressing command., the caffeinate process is still killed due to the use of WithCleanup internally, which protects parts of the computation against aborts. For example,
Caffeinate[longComputation[10]]
$Aborted (* caffeinate process killed nonetheless *)
A maximum time can be specified by either the option MaxTime or, if providing a time specification explicitly, via Caffeinate[t][comp] or comp // Caffeinate[t] syntax.
Caffeinate[longComputation[10], MaxTime -> 60]
The above calls caffeinate -t 60 and caffeinates for at most 60 seconds. It kills the caffeinate process if it's still running once longComputation[10] finishes. (We make sure that the process we're killing is still caffeinate -t 60 in case the caffeinate process ended and the pid got reused for something else.)
longComputation[10] // Caffeinate[5] (* Equivalent to the prior expression *)
longComputation[60] // Caffeinate[{2, 30}] (* Caffeinates for at most 2 minutes and 30 seconds *)
longComputation[60] // Caffeinate[{3, 30, 0}] (* Caffeinates for at most 3 hours and 30 minutes *)
longComputation[60] // Caffeinate[Quantity[1, "Hours"]] (* Caffeinates for at most 1 hour *)
If something unusual happens, you can call Decaffeinate[] to kill all caffeinate processes via shell's killall:
Do[ExternalEvaluate["Shell", "caffeinate &"], {3}]
Decaffeinate[] (* Prints each kill operation performed *)
Decaffeinate[] (* Prints that there are no caffeinate processes running *)
If you need to decaffeinate without printing information for some reason, use DecaffeinateQuietly[].