Which library procedure returns the number of milliseconds elapsed since midnight?

View timers.chpl on GitHub

This primer demonstrates the use of a Timer from the Time module.

Use the Time standard module to bring its symbols into scope.

The quiet configuration constant is set to false when testing (via start_test) so that this test is deterministic.

config const quiet: bool = false;

A Timer can be used like a stopwatch to time portions of code.

To time a procedure, start the timer before calling the procedure and stop it afterwards. Here, we will time the sleep procedure, also defined in the Time module.

t.start();
sleep(1);
t.stop();

To report the time, use the elapsed() method. By default, the elapsed method reports time in seconds.

if !quiet then
  writeln("A. ", t.elapsed(), " seconds");

The elapsed time can also be checked in units other than seconds. The supported units are: microseconds, milliseconds, seconds, minutes, hours.

if !quiet then
  writeln("B. ", t.elapsed(TimeUnits.milliseconds), " milliseconds");

The Timer can be started again to accumulate additional time.

t.start();
sleep(1);
t.stop();
if !quiet then
  writeln("C. ", t.elapsed(TimeUnits.microseconds), " microseconds");

To start the Timer over at zero, call the clear method.

t.clear();
writeln("D. ", t.elapsed(), " seconds");

The timer can be checked while still running. This can be used to time multiple events. Here, the time taken by each iteration of the loop is saved into the iterationTimes array.

config const n = 5;
var iterationTimes: [1..n] real;
t.start();
for i in 1..n {
  var startTime = t.elapsed(TimeUnits.microseconds);
  //
  // This code will be timed n times.
  //
  iterationTimes(i) = t.elapsed(TimeUnits.microseconds) - startTime;
}
t.stop();

Finally, a lighter-weight, but less flexible, way of doing timings is to use the procedure: getCurrentTime(unit: TimeUnits): real

It returns the number of units (seconds by default) that have passed since midnight as a floating-point value. (Note that this makes it not particularly useful for timing things that might run across midnight). As a simple example, we can use the following idiom to time the number of seconds something will take:

const start = getCurrentTime();
sleep(1);
const elapsed = getCurrentTime() - start;

if !quiet then
  writeln("E. ", elapsed, " seconds");

For more information on Chapel’s timing capabilities, refer to the Time section of the Standard Modules online documentation.

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