{governor} is a governor (or
speed limiter) which limits the rate at which a
for-loop or while-loop will run.
The total execution speed is limited by inserting short pauses based upon the time to run through the loop. The waiting time is adjusted continuously to meet the target duration.
A common use for {governor} will be timing animation at,
say, 30 frames per second.
library(governor)
# Limit loop to 30 frames-per-second i.e. 1/30th of a second per frame.
gov <- gov_init(1/30);
# Running the loop 30 times at 30 frames-per-second should take ~1 second
# The actual work in this loop only takes 0.3seconds (30 * 0.01)
# So `gov_wait()` will pause every loop to maintain the interval
system.time({
for (i in 1:30) {
Sys.sleep(0.01) # Work done in loop
gov_wait(gov) # Compensate to keep interval loop time
}
})
#> user system elapsed
#> 0.001 0.002 1.030When the actual work in the loop is fast, {governor} can
compensate by waiting a longer amount of time.
When the work in the loop is slow, then {governor} can
advise that the work for the next frame be skipped.
In this example, we want the loop to run at 30 frames per second
(i.e. an interval of 0.033 seconds), but the work itself takes 0.04
seconds. The return value of gov_wait() is a logical value
indicating whether it is recommended that the next frame is skipped in
order to achieve the desired loop interval.
In the output from this code, the skip variable is
printed to show that gov_wait() is advising that many
frames should be skipped.
library(governor)
# Run loop at 30fps if possible
# Set a high learning rate so it will converge quickly
gov <- gov_init(1/30);
# Running the loop 30 times at 30 frames-per-second should take ~1 second
# The actual work should take a total of 0.1 * 30 = 3 seconds!
system.time({
skip <- FALSE
for (i in 1:30) {
if (!skip) {
Sys.sleep(0.1) # Work done in loop
}
skip <- gov_wait(gov) # Compensate to keep interval loop time
cat(skip, "\n")
}
})
#> FALSE
#> FALSE
#> TRUE
#> FALSE
#> TRUE
#> TRUE
#> TRUE
#> TRUE
#> FALSE
#> FALSE
#> TRUE
#> TRUE
#> TRUE
#> FALSE
#> TRUE
#> TRUE
#> FALSE
#> TRUE
#> TRUE
#> FALSE
#> TRUE
#> TRUE
#> FALSE
#> TRUE
#> TRUE
#> FALSE
#> TRUE
#> TRUE
#> FALSE
#> TRUE
#> user system elapsed
#> 0.004 0.000 1.239Timers are like alarm clocks that will return TRUE when
the given duration has elapsed.
After returning TRUE, the timer will reset internally
such that they will trigger again after another period has elapsed.
long_timer <- timer_init(1)
short_timer <- timer_init(0.1)
counter <- 0L
while(TRUE) {
if (timer_check(long_timer)) {
cat("\nLong timer fired at count: ", counter, "\n")
break;
}
if (timer_check(short_timer)) {
cat("Short timer fired at count: ", counter, "\n")
}
counter <- counter + 1L
}
#> Short timer fired at count: 102346
#> Short timer fired at count: 208481
#> Short timer fired at count: 315420
#> Short timer fired at count: 421936
#> Short timer fired at count: 529771
#> Short timer fired at count: 637659
#> Short timer fired at count: 745152
#> Short timer fired at count: 853236
#> Short timer fired at count: 959092
#>
#> Long timer fired at count: 1050692